Final Report Summary - SHOPERA (Energy Efficient Safe SHip OPERAtion)
Executive Summary:
The 2012 guidelines on the method of calculation of the attained Energy Efficiency Design Index (EEDI) for new ships (MEPC.212(63)) represent a major step forward in implementing the REGULATIONS ON ENERGY EFFICIENCY OF SHIPS (resolution MEPC.203(62)). There are, however, serious concerns regarding the sufficiency of propulsion power and of steering devices to maintain the manoeuvrability of ships in adverse conditions, assuming that the ship marginally passes the relevant EEDI criterion. This gave reason for additional considerations and studies at IMO (MEPC 64/4/13 and MEPC 64/INF7). Furthermore, whereas present EEDI regulations concern the limitation of gas emissions by ship operation, what may be understood as a new constraint in ship design and operation, it is urgent to look holistically into integrated ship design and operational environments and implement multi-objective optimization procedures, looking for the right balance between ship’s efficiency and economy, safety and greenness.
To this end, the SHOPERA consortium was put together representing the whole spectrum of stakeholders in the maritime industry and with superior expertise and scientific know-how in hydrodynamic tools development, validation of software tools, experimental techniques and expertise in ship design and international maritime rule making. Project SHOPERA addressed the above raised, urgent regulatory issues by:
• Further development and refinement of existing high fidelity, hydrodynamic simulation software tools for the efficient analysis of the seakeeping and manoeuvring performance and safety of ships in complex environmental and/or adverse sea/weather conditions (including the consideration of winds and extreme sea events). The efficiency of steering devices and the effect of restricted waterways in port areas have been considered. Extensive use has been made of state-of-the-art numerical simulation tools available to the consortium, which have been adapted to the needs of the project and have been supported by a comprehensive model testing programme.
• Performing seakeeping/manoeuvring model tests in combined seaway/wind environment by use of a series of prototypes of different ship types (tanker, containership, RoRo ferry), to provide the required basis for the validation of employed software tools and the results obtained by numerical simulations.
• Integrating validated software tools for the hydrodynamic/manoeuvrability assessment of ships in adverse seaway/weather conditions into ship design software platforms and set-up of optimization procedures in which ship’s performance is assessed holistically, thus, looking for the minimum powering requirement to ensure safe ship operation in adverse seaway/weather conditions, while keeping the right balance between ship economy, efficiency and safety of the ship and the marine/air environment.
• Putting together design teams that comprise designers, shipyards, owners and class societies to conduct investigations on the impact of the proposed new guidelines for the assessment of the minimum propulsion power to maintain manoeuvrability in adverse conditions (MEPC 64/4/13) on the design and operational characteristics of various ship types.
• Developing new guidelines for the required minimum propulsion power and steering performance to maintain manoeuvrability of ships in adverse environmental conditions.
• Establishing minimum propulsion power ensuring safe operation for various types of ships.
• Preparing and submitting to IMO a summary of results and recommendations for further consideration.
Project Context and Objectives:
The 2012 Guidelines on the method of calculation of the attained Energy Efficiency Design Index (EEDI) for new ships, resolution MEPC.212(63) represent a major step forward in implementing the regulations on energy efficiency of ships, resolution MEPC. 203(62). However, concerns had been expressed regarding sufficiency of propulsion and steering abilities of ships to maintain their manoeuvrability in adverse conditions if the EEDI requirements are achieved by simple reduction of the installed engine power. This gave a reason for additional considerations and studies by IACS, which served as a basis for the Interim Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions, MSC-MEPC.2/Circ.11 (2012), which were updated in annex 1 to document MEPC 65/4/3 and subsequently adopted by resolution MEPC.232(65) and was further updated by resolutions MEPC.255(67) and MEPC.262(68).
To address these challenges, several research projects were initiated at international level, among them the 3 years research project SHOPERA (Energy Efficient Safe SHip OPERAtion, www.shopera.org 2013-2016), funded by the European Commission in the frame of FP7 and representing the whole spectrum of the European maritime industry, including classification societies, universities, research organisations, model basins, ship designers, shipyards and ship operators.
Scenarios of adverse conditions and manoeuvrability criteria
In SHOPERA, a review of existing regulations, interviews of ship masters and analysis of accident statistics and detailed accident investigations were conducted to identify relevant scenarios, criteria and corresponding standards (environmental conditions) which should be employed to assess the sufficiency of propulsion and steering systems of ships for manoeuvrability in adverse conditions. Three scenarios of adverse conditions were identified, in which manoeuvrability characteristics of ships are challenged in different way:
1. Weather-vaning in the open sea, which imposes less strict requirements on the manoeuvring, albeit in more severe weather conditions. Arguably, the inability to manoeuvre in the open sea should not lead to a loss of the ship anyway, because safety of ships, which are unable to manoeuvre and are drifting in beam sea, should be ensured by the Severe Wind and Rolling Criterion (Weather Criterion), MSC.267(85).
2. Manoeuvring in coastal waters imposes strong functional requirements on ship’s manoeuvrability: in principle, any manoeuvre may be required, perhaps in a complex navigational situation and in a seaway from a direction unfavourable for manoeuvring. However, the relevant weather conditions are rather moderate, because in an increasing storm, ship masters timely search for shelter or leave to the open sea. Therefore, this scenario requires both a sufficient steering ability, to avoid grounding, collision or contact, in seaway headings not always favourable for steering, and a sufficient propulsion ability, to enable timely leaving coastal area.
3. Manoeuvring at limited speed in restricted areas, typically during approaching to or entering ports, where the ship’s speed is restricted due to navigational requirements. Because this scenario does not lead to any restriction on the installed minimum power, it is not considered here.
Correspondingly, three criteria are proposed to assess the sufficiency of propulsion and steering systems of ships for manoeuvrability in adverse conditions: Weather-vaning ability, i.e. the ability of the ship to change and keep heading in head to bow-quartering waves; Steering ability, i.e. the ship’s ability to perform any manoeuvre in seaway from any direction; and Propulsion ability, understood as the ship’s ability to maintain some speed (proposal: 6 knots) in seaway from any direction.
Assessment framework and evaluation methods
Compliance with the IMO Manoeuvrability Standards, MSC.137(76) is demonstrated in full-scale calm water sea trials; full-scale trials are, however, impossible to conduct for the evaluation of manoeuvrability in adverse conditions. Evaluation of the proposed criteria in transient model experiments with self-propelled models in simulated irregular waves and wind, or with corresponding numerical simulations, is presently unfeasible for regulatory purposes. The assessment procedures proposed by SHOPERA are based on a combination of freely chosen evaluation methods (experimental, numerical or empirical) for different components of the assessment procedure, and a combination of these components in a simple assessment procedure. The assessment procedure itself can also be freely chosen between three complexity levels:
1. Comprehensive Assessment, allows the best accuracy. Still, the designer can choose between numerical, experimental or empirical methods, which should, however, all ensure satisfactory accuracy of results.
2. A less complex, Simplified Assessment, which still takes into account the physics of the problem, but uses a reduced number of assessment scenarios and reduced complexity of equations; this assessment also allows the choice between experimental, numerical or empirical methods to evaluate different elements of the procedure and has the complexity of a spreadsheet calculation.
3. The simplest assessment procedure, a Sufficient Propulsion and Steering Ability Check, is based on pure empirical / statistical formulae, which define the required installed power as a function of main ship parameters and require few simple pocket computer calculations.
Both the Comprehensive and Simplified Assessments require the definition of time-average forces due to waves including added resistance, wind forces, calm-water reactions, rudder-induced forces and propeller characteristics. According to the SHOPERA approach, these contributions can be defined separately, with different methods (experimental, numerical or empirical) as necessary. According to the performed sensitivity analysis, the most important contributions for the propulsion and steering in adverse conditions are the time-averaged surge and sway forces due to waves, the surge and sway force and yaw moment due to calm-water reactions and the lateral rudder force. Especially important for practical approval is the availability of suitable empirical methods for all elements of the assessment procedure. SHOPERA has undertaken a thorough validation of empirical methods for calm-water reactions, wind forces and rudder forces, including bi-lateral benchmarking with the JASNOE project and concluded that such methods are in principle available for practical use, if used within their applicability limits, with the exception of the time-average wave forces.
The development and validation of numerical and empirical methods for the time-average wave forces, including added resistance, was one of the most important research issues of SHOPERA and was addressed as following:
1. Extensive model tests were performed for three ship types (a 14,000 TEU container ship, a standard VLCC tanker and a small RoPax) in over 1,300 conditions, including various draughts, water depths, forward speeds and wave directions, lengths and heights to generate a validation database for numerical and empirical methods.
2. Several evaluation methods were developed and validated, ranging from high-fidelity CFD methods to 3D panel codes and simple empirical formulae.
3. To evaluate the availability of methods that can be used in practical assessment, SHOPERA conducted an international benchmark study of numerical and empirical methods. The results showed a notable progress in the development of both numerical and empirical methods in the last years and availability, in principle, of numerical methods for practical regulatory purposes, if their application is properly verified.
A critical aspect of manoeuvrability of ships in adverse conditions is the correct modelling of the main engine and the propulsion system under high load in adverse conditions. Frequently used assumptions of constant torque, constant power or constant rotation speed may lead to misleadingly optimistic predictions. In SHOPERA, output limits of diesel engines under high load were investigated, and recommendations for the practical assessment were provided.
Case studies of existing fleet and optimization exercises
The aim of the case studies and optimization exercises carried out by SHOPERA was, first, to systematically compare the proposed criteria with each other and to identify possible redundancies or loopholes. The studies concerned bulk carriers, tankers, general cargo vessels, container ships, LNG and gas carriers, reefers, RoRo cargo vessels, RoPax vessels and cruise vessels, chosen within the whole range of representative sizes and installed power.
The systematic comparison between the three proposed criteria shows that the marginal wave height (i.e. maximum wave height, up to which the vessel can fulfil the respective criterion) according to the weather-vaning criterion is very well correlated with the marginal wave height according to the propulsion criterion, which means that one of these criteria may be redundant. The marginal wave heights according to the propulsion and steering criteria also correlate with each other to some degree.
Results from the conducted case studied show that the marginal wave heights are ship size-dependent for all three criteria: larger vessels are able to satisfy the proposed criteria at greater wave heights than smaller vessels. Whether the standard wave height should also be ship size-dependent, however, may be a subject of discussion with all interested stakeholders. The arguments for ship size-dependent standard wave height are:
1. The dependency of the marginal wave heights on the ship size was revealed from the application of manoeuvrability criteria to existing vessels, thus it reflects existing design and operational practices.
2. Consequences of accidents are generally greater for larger vessels, thus the frequency of accidents implied by the standard wave heights should be for them lower.
3. The impact of seaway on ship’s motions and manoeuvrability in waves diminishes with increasing ship size.
Results show also that the marginal wave heights differ substantially, between ship types. Bulk carriers and tankers show very similar marginal wave heights, which are lower to significantly lower than the marginal wave heights of other vessel types; this is mostly due to their lower specific installed power compared to other vessel types, like container ships, and due to advanced propulsion and steering concepts typical for other vessel types, like twin screw, diesel-electric propulsion, controllable pitch propellers or pods.
Concerning possible conflicts between the requirements to safe manoeuvring in adverse conditions and the strengthening of EEDI requirements, especially at the later Phases of EEDI implementation, the following results were obtained:
1. If existing vessels, satisfying requirements of a certain Phase of EEDI implementation, are compared across all ship types, bulk carriers and tankers show remarkably similar marginal wave heights, which are also lowest among all ship types.
2. If vessels are selected that satisfy the proposed by SHOPERA criteria for manoeuvrability in adverse conditions at the standard wave heights according to the 2013 Interim Guidelines, bulk carriers and tankers seem to marginally fulfil the requirements of Phase 2 EEDI implementation, but not of Phase 3, whereas vessels of other types are able to satisfy or even over-satisfy the requirements of Phase 3.
3. For EEDI Phase 3-compliant bulk carriers and tankers to pass the proposed manoeuvrability requirements, the standard wave heights need to be lowered compared to those in the 2013 Interim Guidelines.
4. The conducted parametric optimisation studies for RoPax ships revealed ample manoeuvrability margins in adverse conditions, but problems of compliance with the EEDI Phase 3 requirements, whereas the Phase 2 requirements appear marginally fulfilled. This finding is also confirmed by other studies of the European passenger shipping industry and should be an additional subject of discussion among all interested stakeholders.
Dissemination of results
A large number of papers and conference presentations were produced by the SHOPERA consortium; a list of selected papers is given in the Annex. Additionally, four public workshops were organized by the project for open discussion or results and exchange of opinions with the maritime industry, other projects and maritime safety stakeholders.
Submissions to IMO
SHOPERA had a close collaboration with a research project of the Japanese maritime industry, coordinated by the Japan Society of Naval Architects and Ocean Engineers (JASNOE) with the aim to exchange information about the progress of work of both projects and ultimately to prepare and submit a joint proposal for the draft revised Guidelines to MEPC 70/71. The joint proposal of the two projects has being submitted with the document MEPC 70/5/20, with supplementary information submitted in a series of INF documents.
Independently of the above joint submission with Japan, which refers to tankers, bulk carriers and combination carriers, an additional document (MEPC 70-INF.33) was submitted, aiming to inform all interested stakeholders about the whole range of results of the project SHOPERA, which covered all types of ships affected by the EEDI framework.
Project Results:
1 Introduction to project SHOPERA – Objectives
The introduction of the Energy Efficiency Design Index (EEDI) was a major step towards improving energy efficiency and reducing greenhouse gas (GHG) emissions of shipping. It has also raised concerns that some ship designers might choose to lower the installed power to achieve EEDI requirements instead of introducing innovative propulsion concepts. This can lead to insufficient propulsion and steering abilities of ships to maintain manoeuvrability under adverse weather conditions, thus to a serious ship safety problem. Work carried out by IACS highlighted this issue and led to the development of first draft guidelines for consideration by IMO in 2011, IMO MEPC 62/5/19 and MEPC 62/INF.21 which resulted later in 2012 Interim Guidelines, see IMO MEPC 64/4/13, MEPC 64/INF.7 updated in 2013 in Res. MEPC.232 (65). Even though the 2013 Interim Guidelines prevent irrational reduction of installed power, their sufficiency was disputed, especially concerning the definition of the minimum power lines, adversity of the weather conditions to be considered in the assessment and removal of comprehensive assessment. Several research initiatives in various European countries as well as Japan and the Republic of Korea, aiming at updating these guidelines (see, e.g. IMO submissions MSC 93/21/5 and MSC 93/INF.13 by Greece, MEPC 67/INF.22 by Japan, MEPC 67/4/16 by Denmark, Japan and the Republic of Korea, and MEPC 67/INF.14 by Germany, Norway and the United Kingdom) were started and are expected to lead to the rationalization of the interim guidelines.
To address the above challenges by in-depth research, the EU funded project SHOPERA (Energy Efficient Safe SHip OPERAtion) (2013-2016) was launched in October 2013, aiming to develop suitable numerical methods and software tools and to conduct systematic case studies, which will enable the development of improved guidelines and their submission for consideration to IMO. A strong European RTD consortium was formed, representing the whole spectrum of the European maritime industry, including classification societies, universities, research organisations and model basins, ship designers, shipyards and ship operators. The project's objectives were to:
• Develop criteria and corresponding environmental conditions for the assessment of the sufficiency of propulsion and steering systems of ships for manoeuvrability in adverse conditions, including open sea, coastal waters and restricted areas.
• Develop and adapt existing high fidelity hydrodynamic simulation software tools for the efficient analysis of the seakeeping and manoeuvring performance of ships in complex environmental and adverse weather conditions.
• Perform seakeeping and manoeuvring model tests in seaway by using a series of prototypes of different ship types to provide the required basis for the validation of employed software tools.
• Develop simplified assessment procedures, to the extent feasible, which should enable a quick assessment of the safety margins of ship designs with respect to the minimum propulsion and steering requirements for manoeuvrability in adverse weather conditions.
• Integrate validated methods and software tools for manoeuvrability assessment of ships in adverse weather conditions into a ship design software platform and combine it with a multi-objective optimization procedure, targeting sufficient propulsion and steering requirements for safe ship operation in adverse weather conditions while keeping the right balance between ship economy, efficiency and safety.
• Conduct investigations of the impact of the proposed requirements on the propulsion and steering abilities of ships for manoeuvrability in adverse conditions on the design and operational characteristics of various ship types by design teams comprising designers, shipyards, ship owners, classification societies, research institutes and universities. The impact on EEDI was also investigated by implementation of the developed holistic optimisation procedure in a series of case studies.
2 Scenarios and Criteria
2.1 Existing Regulations
Manoeuvrability of ships is presently normed by IMO Standards for Ship Manoeuvrability, IMO (2002), which address turning, initial turning, yaw checking, course keeping and emergency stopping abilities, evaluated in simple standard manoeuvres in calm water. These Standards have been often criticized for not addressing ship manoeuvring characteristics at low speed, in restricted areas and in adverse weather conditions; the importance of the latter increased after the introduction of EEDI. In EE-WG 1/4 (2010), IACS put together the requirements of classification societies related to the redundancy or duplication of the propulsion system to indicate relevant criteria and environmental conditions for steering and propulsion in adverse weather conditions. Studies by IACS on minimum power requirements for manoeuvrability in adverse weather conditions started with analysis of functional requirements to manoeuvrability in the open sea and coastal areas, MEPC 62/5/19 (2011) and 62/INF.21 (2011), concluding that manoeuvring in coastal waters is more challenging than in the open sea; the resulting criteria for ship propulsion and steering abilities were formulated in MEPC 64/4/13 (2012) and 64/INF.7 (2012): the ship should be able, in seaway from any direction, to (1) keep course and (2) keep advance speed of at least 4.0 knots. The corresponding weather conditions are not too severe, because ship masters do not stay near the coast in an increasing storm and either search for a shelter or leave to the open sea and take a position with enough room for drifting. The standard environmental conditions defined by IACS (wind speed 15.7 m/s at significant wave height 4.0 m for ships with Lpp=200 m to 19.0 m/s and 5.5 m, respectively, for Lpp=250 m and greater) were derived by benchmarking of tankers, bulk carriers and container ships in the EEDI database against these two criteria.
2.2 Accidents
In SHOPERA, available detailed investigations of accidents related to insufficient manoeuvrability in adverse weather conditions were studied. Summarising, as the most frequent cause of heavy weather-related grounding accidents is waiting at anchor in heavy weather and too late starting of the engine. In several accidents, vessels were not able to move away from the coast or turn into seaway despite full engine power applied. Regarding adverse weather conditions related to accidents, we may recall the well-known statistics of the HARDER project indicating that more than 80% of the collisions happened at significant wave height below 2 m, whereas significant wave heights exceeding 4 m were practically not recorded. Similar results were obtained from a comprehensive statistical analysis of ship accidents in adverse sea conditions, conducted in SHOPERA. From these statistics it is evident that:
1. The most vulnerable ship types with respect to navigational accidents in adverse conditions are general cargo ships, followed by Ro-Ro ferries, bulk carriers and tankers.
2. For these ship types, the accident location varies between port areas (almost exclusively for Ro-Ro ferries) and generally limited waters, such as port and restricted waters (for general cargo vessels and bulkers); for tankers, we observe some increased sensitivity in route (open seas) conditions.
3. Inclusion in the statistical analysis of very rare abnormal weather events (hurricanes, typhoons etc.) does not significantly alter the statistics.
4. Observed mean wind speeds of about 10 m/s and significant wave heights of 1.49 m are remarkably low; this also applies to the statistical quartiles, with lower values observed for collisions and groundings and the highest recorded values related to contacts.
5. There is a statistically significant difference in mean wave height between ship types, which means that some ship types are more affected by wave height than the others.
6. The calculated accident rates, related to the Fleet at Risk, are in the range of 10-5 to 10-3 accidents per ship per year, i.e. by one order of magnitude lower than accident rates calculated in Formal Safety Assessments, which do not consider the prevailing weather conditions.
7. Among the three navigational accident types, groundings exhibit the highest rates for cargo carrying ships in general, whereas for Ro-Ro ships contacts are associated with the highest rates.
8. Based on the available information, hull damage was selected as a main consequence variable for the risk analysis. The collected data were organized in categories of increasing level of severity, considering their qualitative nature.
9. The risk analysis implemented the concept of risk triplets defined by Scenario, Frequency, and Consequence, and enabled the generation of three distinct types of risk-related curves, based on accident frequencies per ship type, per ship type and size class, and per ship and accident type.
10. Overall, groundings and contacts in heavy weather conditions are the accident types with the highest risk across all ship types.
11. Comparison of risk levels between ship types shows that Ro-Ro Ferries and RoRo Cargo ships exhibit high risk values due to high accident frequency and medium level of consequences, whereas Gas Carriers, Tankers and Bulk Carriers exhibit high risk values due to the observed high level of accident consequences.
2.3 Interviews of Ship Masters
Interviews of masters of about 50 container ships, bulk carriers and tankers conducted in the projects PerSee and SHOPERA indicate that in the open sea, the captain usually has more freedom and can decide what severity of weather conditions is acceptable for his ship, depending on the freeboard, cargo, stability and propulsion and steering characteristics of the vessel. On the other hand, when caught in most violent storms, steering against seaway may be impossible for any vessel; in such circumstances, drifting with seaway was considered as an acceptable option for a limited time if there is enough room for drifting. However, the available power is important for escaping the storm and bringing the ship into safe weather conditions. Manoeuvring in coastal areas was reported as more challenging than manoeuvring in the open sea, because, in principle, any manoeuvre, sometimes in unfavourable seaway direction with respect to the ship, may be required. Environmental conditions are, however, less severe than in the open sea, because ship masters do not remain near the coast in a growing storm, but either search for shelter or leave to the open sea. As relevant manoeuvring problems, steering problems were mentioned in the interviews insignificantly more often than propulsion problems (83% vs. 60% of cases, respectively); insufficient engine power was mentioned more frequently for bulk carriers and tankers, whereas insufficient rudder capability more frequently for container vessels. As a very specific manoeuvring problem in restricted waters, manoeuvrability at limited speed (due to navigational restrictions, e.g. during approaching ports) was mentioned, in strong wind and, sometimes, strong current, but usually without large waves because of protected areas.
2.4 Proposal for Scenarios and Criteria
Based on the above results, Shigunov and Papanikolaou (2014) proposed three scenarios, in which steering and propulsion abilities of ships are challenged in a different way and which require, therefore, specific criteria: open sea, coastal areas and restricted areas at limited speed. For the open sea, the ability of ship to weather-vane, i.e. keep heading in head to bow-quartering seaway, was proposed as a criterion. Regarding corresponding environmental conditions, it was noted that none of the existing ships can steer against waves and wind in most severe possible storms, therefore, benchmarking of the existing world fleet with respect to the weather-vaning criterion was proposed to define the standard wave height. For the coastal areas, two criteria were proposed: the ability of the ship to perform any manoeuvre and the ability to maintain some speed over ground to enable leaving the coastal area before the storm escalates; due to navigational restrictions, both criteria should be possible to fulfil in seaway from any direction. The corresponding environmental conditions are less severe than in the open sea and should also be defined by benchmarking of existing ships against these criteria. Manoeuvrability at limited speed in restricted areas refers to situations where the ship master has to reduce the applied engine power (and thus forward speed) significantly below available power because of navigational restrictions, e.g. during approaching to or entering ports, navigation in channels and rivers etc. Because full available power cannot be applied in this scenario, the corresponding manoeuvrability criteria will not impose any restrictions on minimum propulsion power, thus this scenario is not considered here. Based on this, SHOPERA proposed the following criteria for manoeuvrability in adverse weather conditions: weather vaning ability in heavy weather in the open sea and steering and propulsion abilities in increasing storm in coastal areas.
In the practical assessment, weather-vaning ability was treated in a simplified way, as the ability of the ship to keep position in bow to bow-quartering seaway; this simplification follows from the observation, confirmed by model tests, that the ship will not be able to keep heading under the action of environmental forces if the forward speed is not sufficiently large, because of significantly reduced manoeuvring reactions on the hull and steering force on the rudder.
The steering ability in increasing storm in coastal areas is understood as the ability of the ship to perform any manoeuvre in seaway from any direction. An equivalent, but easier to verify in practice criterion is proposed, that the ship should be able to start or continue course change in seaway from any direction. This formulation should be distinguished from the traditional course-keeping problem: the steering ability is understood here as the ability of the steering system to overcome environmental forces and start (or continue) course change during an arbitrary manoeuvre (i.e. capability of the steering system); for this ability, it does not matter whether each intermediate state during manoeuvre is stable or not, thus the stability of the ship on each particular course is not addressed, whereas the traditional definition of course-keeping addresses stability of straightforward motion. Note that the proposed criterion does not exclude the ship’s ability to perform also straightforward motion (which is one of “all” required manoeuvres): even if a ship is directionally unstable on some course, it will still be able to follow this course using rudder for continuous course corrections.
The propulsion ability in increasing storm in coastal areas ensures that the ship is able to leave coastal area in a sufficient time before the storm escalates. As the minimum required advance speed, 6.0 knots was chosen by SHOPERA, instead of 4.0 knots used in 2013 Interim Guidelines, to take into account possibly strong currents in coastal areas. The corresponding environmental conditions for these three criteria need to be defined by benchmarking of existing vessels.
2.5 Environmental Conditions
Wave Height
The existing 2013 Interim Guidelines do not consider manoeuvring criteria for the open sea. SHOPERA has introduced the weather-vaning criterion for the open sea, which requires corresponding standard environmental conditions. A straightforward choice of the North Atlantic scatter table, IACS (2001), is not fully suitable to define the weather conditions to be used with the weather-vaning criterion as although this scatter table is based on visual onboard observations, BMT (1986), it is unknown whether ships were able to manoeuvre in the reported sea states and what manoeuvres they were able to perform; in particular, it is unknown whether existing ships can or cannot weather-vane in such sea states. Finally, safety of a ship that is not able to weather-vane in a certain sea state in the open sea and thus has to drift in beam seaway will still be ensured due to the IMO Severe Wind and Rolling Criterion (Weather Criterion), IMO (2008). Therefore, benchmarking of the existing fleet with respect to the weather-vaning criterion appears as the most rational way to define the standard wave height: the standard wave heights should be defined in such a way that the majority of the existing vessels fulfil the related requirements, taking into account that the present safety level with respect to manoeuvrability-related accidents in heavy weather is satisfactory, Ventikos et al. (2014).
For increasing storm in coastal waters, the 2013 Interim Guidelines use two criteria, course keeping and advance speed. The corresponding standard wave heights were defined by benchmarking of tankers, bulk carriers and container ships in the EEDI database against these two criteria, which led to the significant wave height of 4.0 m and wind speed of 15.7 m/s for ships with Lpp=200 m and significant wave height of 5.5 m, and wind speed of 19.0 m/s for Lpp=250 m and greater, with a linear interpolation of wave height and wind speed for Lpp between 200 m and 250 m. SHOPERA aimed at validation of the proposed weather conditions with respect to available measurements and other data sources. The problem is, on the one hand, that there are no fully unified recommendations for the seaway parameters for coastal areas. Second, met-ocean climate of coastal areas strongly depends on the region and local bathymetry, which maybe difficult to fully account for in regulations.
The coastal areas considered by SHOPERA included: access channel to the port of Antwerp, Scottish waters and the port of Leixões, Bitner-Gregersen et al. (2016). The 40 nautical mile long access channel to the port of Antwerp is dredged in a rather protected sand banks area, whereas both the Scottish coastal waters and the port of Leixões are not as protected. Correspondingly, the former area indicates milder wave heights than the latter two. Note also that the observations for these three areas were not uniformed, they had different duration. The maximum observed significant wave heights occurred with different probabilities in these areas and had different values; for the access channel to the port of Antwerp, Scottish waters and the port of Leixões of about 4.5 m, 5.5 m and 6.0 m, respectively.
Noting that the available data refer to fixed locations, whereas ship masters do not remain on the same position near the coast in a growing storm, but either search for shelter or leave to the open sea, SHOPERA has used also several other sources to estimate rationally the required standard wave heights. Statistics of the weather conditions during manoeuvring-related accidents in adverse weather conditions, Ventikos et al. (2014), shows remarkably mild environmental conditions during accidents (mean wind speed of about 10 m/s and mean significant wave height about 1.5 m), which agrees with the earlier statistics from the HARDER project, indicating significant wave height below 2.0 m in 80% of collisions and absence of collisions at significant wave heights greater than 4.0 m. The study by IACS, EE-WG 1/4 (2010), also identifies rather mild standard wave heights for weather-vaning (wind speed up to 21 m/s and significant wave height up to 5.4 m) and advance speed (wind force up to Bft 8 at 6.0 knots advance speed) requirements. On the other hand, maximum significant wave heights and wind speeds during manoeuvrability-related accidents achieve, according to SHOPERA statistics, in rare cases 7.0 m and 20 m/s, respectively. Detailed accident reports indicate wind force up to Bft 10 (in excess of 23 m/s) and significant wave heights above 6.0 m during few accidents in coastal areas. However, the well-documented case ATSB (2008), where the significant wave height exceeded 6.0 m, clearly indicates unacceptably long waiting of the vessel at anchor in an increasing storm as the reason of the accident. Similar conclusions follow from the interviews of ship masters: 50% of the ship masters prefer to leave coastal areas before wind increases to Bft 8 and significant wave height achieves 5.0 m.
The scatter between the wave heights relevant for manoeuvrability in coastal areas from different sources is not really surprising if we take into account that manoeuvrability performance depends, to a large extent, on characteristics of the vessel and on the operational experience and practices of the ship master. Therefore, benchmarking of the existing fleet with respect to the new criteria appears as the most rational way to define the standard wave height, for several reasons. In SHOPERA, dedicated case studies were undertaken concerning all ship types considered in the EEDI regulations.
Wind Speed
The influence of wind forces on propulsion and steering ability in seaway is comparable to the influence of the time-average wave forces for ships with a large windage area, such as container vessels and pure car and truck carriers, and is less important, but not negligible, for vessels with moderate windage area, such as bulk carriers and tankers, Shigunov (2015). For practical assessment, it is convenient to use a unified wind speed-wave height relationship (perhaps different for the open sea and coastal areas) rather than use wind speed as an additional standard. The problem in the derivation of such a unified relation is that the relation between wind speed and wave height strongly depends on the fetch, wind duration and presence of wind sea and swell. Because these factors depend on location, the relation between the wind speed and wave height is location dependent, even when considered in a statistical sense. In SHOPERA, various alternative formulae, expressing the relationship between the wind speed and the significant wave height have been reviewed and proposals have been made both for open sea and for coastal areas.
Other Sea State Parameters
In severe to very extreme sea states, the influence of swell maybe less significant compared to the wind sea, whereas in small to moderate seaways, the influence of swell may be significant. For the open sea, it is feasible to assume a situation of a ship weather-vaning for a prolonged time until the storm finishes, i.e. a developed storm situation is relevant for the assessment of the weather-vaning ability in the open sea. For a fully developed sea state, the Bretschneider spectrum (also referred to as a two-parameter ITTC spectrum) is generally recommended by ITTC while the Pierson-Moskowitz spectrum is widely used by the marine industry.
For coastal waters, the assumed scenario, confirmed by the interviews of ship masters undertaken by SHOPERA, is that ship masters do not remain near the coast in a growing storm until it escalates, but either search for shelter or leave to the open sea. Therefore, the feasible scenario to be applied with the steering and propulsion criteria is a developing storm. For a developing storm a general recommendation is to use the JONSWAP spectrum with the peak parameter of 3.3 i.e. as used in the 2013 Interim Guidelines for the evaluation of ship manoeuvrability in coastal areas. As a realistic assumption, directional spreading of wave energy with respect to mean wave direction is recommended; as the spreading function, cos^2-spreading was used in SHOPERA.
The range of characteristic wave periods (for clarity, the peak wave period will be used) used in the assessment has a significant influence on the assessment results. For the propulsion ability criterion, as well as for the weather-vaning criterion, the upper (long waves) boundary of the used peak wave periods defines whether and how much of the added resistance peak is taken into account, whereas the lower boundary (short waves) is important for larger, especially blunt, vessels for which a significant part of added resistance comes from short wave components. For the steering ability criterion, external excitation increases with increasing wave frequency, therefore, it is important how the lower boundary (short waves) of the peak wave periods is defined. The lower boundary of peak wave periods used in the 2013 Interim Guidelines, 7.0 s, is slightly conservative, because it crosses the theoretical maximum storm steepness boundary in the relevant range of significant wave heights. The upper boundary, 15.0 s, although theoretically possible, is unnecessary large, because such large wave periods are not critical for propulsion or steering ability. SHOPERA proposed suitable formulae for the lower and upper boundaries of peak wave periods as functions of significant wave height.
3 Assessment Procedures
The general assessment concept proposed by SHOPERA is to allow free choice of assessment procedures of different complexity (similarly to 2012 Interim Guidelines), ranging from simple empirical formulae to advanced assessment procedures, so that the designer can select the most suitable procedure depending on the particular design needs. Simple assessment procedures are sufficient for the majority of conventional vessels, whereas more accurate assessment procedures and evaluation methods are required for cases with large uncertainties, such as innovative propulsion and steering solutions, which are intended to be promoted by the EEDI regulations. SHOPERA proposes three alternative assessment procedures:
• Comprehensive Assessment allows the best accuracy, solving coupled nonlinear motion equations. Still, the designer does not have to use tedious/expensive evaluation methods for different components, but can choose between numerical, experimental or empirical methods for different elements. This type of assessment is anyway necessary for ships with innovative propulsion and steering arrangements.
• Simplified Assessment, a first-principle assessment with reduced number of considered situations and reduced complexity of motion equations, also allowing choosing between experimental, numerical or empirical methods to evaluate force components, and having complexity of a spreadsheet calculation.
• Sufficient Propulsion and Steering Ability Check is based on pure empirical formulae to define the required installed power as a function of main ship parameters (deadweight, block coefficient, windage area, rudder area, engine and propulsion type), of a complexity of a pocket calculator.
3.1 Comprehensive Assessment
Compliance with the IMO Manoeuvrability Standards, IMO (2002), is demonstrated in full-scale trials, which is impossible for ship manoeuvrability assessment in adverse weather conditions. Alternatively, the proposed criteria (weather vaning, steering and propulsion abilities) can be evaluated, in principle, directly in transient model experiments with self-propelled ship models in simulated irregular waves and wind, for all required combinations of wave directions and periods. This is, however, presently unfeasible for practical purposes for several reasons: First, providing reliable statistical predictions in irregular seaway requires repeating tests in multiple long realisations of each seaway, which is too expensive. Besides, few facilities exist worldwide, able to perform such tests, making such tests impractical for routine design and approval. Third, verification of such tests by the Administration is impossible (unless the test program is repeated), which makes this approach impractical for approval. Finally, results of such tests depend heavily on the time history of steering, causing too large variability and uncertainty of test results, which therefore cannot be reliably verified especially in marginal cases (i.e. cases near the failure boundary, which are the actual cases of interest in approval). Alternative to such model tests, direct numerical simulations of transient manoeuvres in irregular seaway, are not mature enough yet for routine design and approval, ITTC Manoeuvring Committee (2008). The approach proposed by SHOPERA is based on separate evaluation of different acting forces (waves, wind, propeller, rudder etc.) using simple model tests, numerical simulations or empirical formulae, and combination of the defined forces in a simple numerical model. Whereas the resulting procedure is based on first principles and takes into account all relevant physics, it is at the same time
• verifiable by Administrations or Recognised Organisations,
• based on technology presently available in the industry,
• inexpensive and as accurate as presently practicable,
• flexible, since designers and administrations are free to choose alternative methods (experimental, numerical or empirical) depending on designer needs,
• open for updates when new numerical or experimental methods are developed, without the need to revise the Guidelines.
The Comprehensive Assessment procedure proposed by SHOPERA is based on neglecting oscillatory forces and moments due to waves and thus considering only time average forces and moments, assuming that the time scale of such oscillations is shorter than the time scale of manoeuvring motions. This effectively reduces the evaluation of manoeuvrability criteria to a solution of coupled motion equations in the horizontal plane under the action of time-average wave-induced forces, as well as wind forces, calm-water forces, rudder forces and propeller thrust. Adequate procedures for the evaluation of steering ability and propulsion ability criteria have been developed and proposed. The advantage of the proposed Comprehensive Assessment, and the main difference from the Comprehensive Assessment in the 2012 Interim Guidelines is that the different effects (wind, waves, calm water, rudder, propeller and engine) can be measured or computed separately, if necessary with different methods (experimental, numerical or empirical). Note that even if model tests or complex numerical computations are used for some of contributions, they are done in stationary setups under well-controlled conditions and combined in a simple mathematical model.
3.2 Evaluation Methods for Components of Forces and Moments
Opposite to the transient manoeuvring tests in simulated wind and irregular waves, the proposed procedure relies on measurements of separate forces in well-controlled steady conditions. For calm-water, wind, rudder and propeller forces, such experiments are well established and can be done in many facilities world-wide (note that calm-water resistance and propulsion characteristics, including open-water propeller characteristics and hull-propeller interaction coefficients can be taken from the model tests that are required for EEDI verification anyway). However, measurement of the time-average wave forces requires advanced measurements in a seakeeping basin, therefore, cannot be used routinely.
Numerical methods are presently available, in principle, for the same forces (calm-water, wind, rudder and propeller) as well; however, their use in regulatory assessment requires a significant effort by administrations and recognised organisations. Availability of numerical methods for time-average wave forces is one of the most critical issues: the absence of suitable numerical methods for added resistance led to the removal of numerical methods from the 2013 Interim Guidelines. Development and validation of numerical methods for time-average wave forces and moments was one of the major tasks of SHOPERA. Model test measurements of such forces were done for three ship models (a 14000 TEU container vessel, a VLCC tanker and a RoRo) for various ship speeds and wave directions and periods (with particular emphasis on short waves); results of these measurements were used for an international benchmarking of the available numerical methods for time-average wave forces. The results of this benchmarking show a significant progress of numerical methods in the last years and indicate the principal availability of numerical methods for regulatory purposes, if applied correctly.
Especially important for the practical implementation of any practical procedure is the availability of empirical methods for different force components. In addition to the well-established empirical methods for wind forces, Blendermann (1993), Fujiwara et al. (2006), extensive validation studies were carried out together with the project from Japan for calm-water reactions and rudder forces in propeller race, which indicate availability of such empirical methods for the practical use; however, designers and Administrations should ensure that empirical methods are used within their applicability limits.
An important aspect of propulsion and steering in adverse conditions is a correct description of the engine under high load. In SHOPERA, air/surge limits of diesel engines (two- and four-stroke) were verified and recommendations were provided for practical assessment procedures.
3.3 Simplified Assessment
The aim of the development of the Simplified Assessment was to have a simple enough procedure for routine use by Administrations by reducing the number of calculations (solution cases) as well as the number of terms in motion equations, while keeping all relevant physics. In particular, the Simplified Assessment addresses the same criteria as those enforced in the Comprehensive Assessment (weather-vaning, steering and propulsion). The simplified procedures for steering ability (ability to start or continue course change in any seaway direction) and propulsion ability (ability to keep a minimum advance speed in all seaway directions) were proposed in Shigunov et al. (2014).
Simplified Steering Ability Assessment
The starting point is the system of coupled motion equations in the horizontal plane, solved for all relevant forward speeds and all seaway directions to check that the ship is able to start or continue course change in seaway from any direction. Note that for the steering ability, both the steering system and propulsion (which influences steering ability) are required and should be integral parts of the assessment: e.g. ships with powerful propulsion may have a smaller rudder, whereas ships with weaker propulsion may compensate this with larger or more effective steering devices. Results of Comprehensive Assessment for many ships show that the dimensioning condition for the installed power, i.e. the condition at which the ratio of the required to available delivered power is maximised along the line of maximum steering effort (further referred to for brevity as critical condition for steering) is close to beam seaway. Note that from experience, as well as from the results of Comprehensive Assessment for many ships, critical conditions for steering occur most frequently in stern quartering waves; however, in such situations the required power is less than the required power defined by the Propulsion Ability. When the Steering Ability is dominating for the definition of the installed power, the critical conditions are always close to beam seaway situations. This allows reducing the evaluation of the time-average wave and wind forces to beam seaways. The second simplification stems from the observation that the levers of time-average wave and wind yaw moment are negligible compared to the lever of the calm-water yaw moment in critical conditions for steering.
As a result, the system of coupled motion equations in the horizontal plane is significantly simplified. To define the components of forces and moments in the Simplified Assessment of Steering Ability, any of the methods used in the Comprehensive Assessment can be applied; in addition, application of simplified empirical formulae seems suitable for this assessment level. Such formulae and their validation are proposed.
Simplified Propulsion Ability Assessment
The starting point is the system of coupled motion equations in the horizontal plane, which has to be solved for all possible seaway directions to demonstrate that the ship is able to keep forward speed of at least 6.0 knots in seaway from any direction. Noting that bow seaways are most critical for required power at a given speed, it is enough to consider only seaways from 0 to about 60 degrees off-bow in the assessment. Further, neglecting the influence of drift on the required thrust and required power allows omitting equations for the lateral forces and yaw moments. Thus only the equation for the longitudinal forces needs to be considered, and only in head waves. However, it is important to keep in mind that the time-average longitudinal force due to waves should be taken as the maximum force in mean wave directions between 0 and 60 degrees off-bow. The various force components can be found using any method from the Comprehensive Assessment (empirical, numerical or experimental). However, it seems logical to allow using also simpler approximations for these terms in the Simplified Assessment.
3.4 Sufficient Propulsion and Steering Ability Check
The simplest assessment procedure, Sufficient Propulsion and Steering Ability Check, is based on pure empirical formulae to define the required installed power as a function of main ship parameters. Three different groups of formulas have been developed in SHOPERA. The formulae proposed by SHOPERA are based on the application of the comprehensive propulsion and steering assessment procedures to over 400 bulk carriers, tankers, container ships and general cargo vessels equipped with two-stroke low-speed diesel engines, a fixed-pitch propeller and a conventional rudder. For each ship, the maximum significant wave height was found, at which the required brake power is equal to the available brake power, separately for steering and propulsion criteria. Based on these results, MCR was approximated as empirical formulae of significant wave height, for each combination of main ship parameters, and then, the required installed power was found that satisfies the standard significant wave heights for propulsion and steering. The resulting empirical formula, for propulsion ability requirement is:
MCT=0.21*SQRT(CB)*LPP^2
where MCR, kW, is the required installed power in terms of the maximum continuous rating of the engine, CB the block coefficient and LPP the length between perpendiculars. The corresponding empirical formula for the steering ability requirement is:
MCR=0.15*CR*LPP^2
Where CR is an appropriate coefficient depending on the ship characteristics. Testing of the proposed formulae by all interested stakeholders and its validation are required to approve / improve them; it should be noted that these formulae are suitable only for vessels equipped with two-stroke low-speed diesel engines, a fixed-pitch propeller and a conventional rudder; for other types of engine, propulsion and steering the simplified or comprehensive assessment should be used.
3.5 Engine and Propulsion
Within the comprehensive and simplified assessment procedures, a steady engine model can be used to define available brake power as a function of the engine rotation rate, defined by the engine diagram: Several propeller curves are superimposed on the engine diagram among which a light propeller curve, corresponding to clean hull in calm water; along this curve, engine’s power is nearly proportional to the cubic power of the engine’s rotational speed. Heavy propeller curves are assumed for fouled hull in seaway and are obtained by increasing the light propeller curve power by an appropriate sea margin. In the assessment of the sufficiency of the installed diesel engine for manoeuvrability in adverse conditions, it is necessary to take into account that the maximum continuous output of a diesel engine is bounded, depending on its rotation speed, by several limits:
• Power limit, at the maximum rotation rates. At the power limit, maximum power continuously provided by the engine is constant and equal to MCR.
• Maximum torque limit, defined by the shafting system bearing strength, at the moderately reduced rotation rates. At the maximum torque limit, torque is constant and thus the maximum engine output is proportional to rotation speed.
• Surge limit, at low rotation rates. To the left of the surge limit, the engine will lack air from the turbocharger for the combustion process.
Due to increased resistance in adverse conditions or during manoeuvres, the propeller curve shifts upwards, and the maximum engine output is defined by the intersection point of this curve with one of the engine limit curves (either the Maximum torque limit or the Surge limit). At low added resistance, e.g. in normal operation in low to moderate sea states, maximum torque is relevant, whereas for propulsion and manoeuvring in heavy weather, surge limit becomes the limiting curve. At this point, the available delivered power is reduced compared to MCR. This available delivered power is compared with the required delivered power defined from the propeller model.
SHOPERA has performed case studies for vessels with various types of engine and propulsion besides the low-speed two-stroke diesel engine working directly on a fixed-pitch propeller. Although in the practical approval, verified manufacturer data describing engine limit curves and propeller characteristics should be used, a summary of approaches used to consider other types of the engine and propulsion in the SHOPERA case studies is given below:
• For 4-stroke diesel, the air-surge limit curve is much more restrictive than the air-surge limit curve for 2-stroke engines. In SHOPERA, measurement data were used for 4-stroke diesels.
• For a diesel-electric propulsion, it was assumed that the power output of an electric motor is independent from the rotation speed, i.e. the output of the engine was assumed constant at all rotation speeds. In emergency situation, 100% of MCR can be considered as the maximum available power.
• For a vessel equipped with a controlled-pitch propeller, it was assumed that the propeller operates at a constant rotation rate, and the pitch of propeller blades was varied to adjust the propeller to the actual forward speed and required thrust.
The propeller thrust is found from the equilibrium of forces in the x-direction. Using the known thrust, the advance ratio J is found using known open-water propeller characteristic KT(J) along with the propeller advance speed. From the advance ratio J, the torque coefficient KQ(J) is found using the open-water propeller characteristics. After that, the propeller rotation speed and the required delivered power to the propeller are readily obtained.
3.6 Development and Refinement of Numerical Tools
Numerical hydrodynamic tools are essential to predict the dynamics of ships in various conditions of interest and an abundant choice of tools is available, each one with its specific characteristics as to the problems addressed and the formulation adopted for the solution. Consequently each tool has its level of accuracy and its limits of application. During this project, different types of hydrodynamic codes have been further extended in order to better deal with the specific problems considered in the project. One type is potential flow seakeeping codes used for predicting added resistance in waves and for loss of stability in waves; other potential flow codes deal with methods for manoeuvring prediction both in waves and in confined waters, which represent two extreme situations to which the usual deep water manoeuvring codes need to be further developed. Another type of codes is based on field methods, which include different types of CFD codes. Many applications of these codes have the objective of determining off-line databases for describing second-order wave forces, approximations of manoeuvring hull forces in shallow water, rudder forces behind the propeller in waves, simplified unsteady model for a screw propeller and peculiarities of hull-propeller interaction coefficients in waves. These databases are meant to augment the manoeuvring potential codes with those features, improving their prediction ability while keeping the speed of computation in acceptable limits. Other applications aim at direct predictions of ship motions by coupling with the 6DOF ship motion simulator other features such as of engine dynamics and automatic controllers and coupling with a propeller model. Several developments have being made in parallel by various SHOPERA partners and thus only some typical results are herein presented.
Potential Flow Methods
The calculation of the added resistance of ships in waves is a very important scientific and practical aspect of the project, as it directly addresses the required minimum powering for the ship to advance at certain speed in waves, while it leads to the estimation of the fuel consumption during ship voyages; three different project teams are working on this subject on the basis of potential theory and associated software tools. An existing numerical model of added resistance calculation and speed loss estimation developed by Prpić-Oršić and Faltinsen (2012) has been improved by accounting for the effect of air resistance. The total wind velocity is a combination of a steady-state or mean velocity and a turbulent (gust) velocity. The mean speed is calculated as a function of significant wave height according to the one-parameter Pierson-Moskowitz spectrum. The gust component is a random process with zero mean represented by a gust spectrum. The wind direction is assumed to be the same as wave direction. The numerical model has been extended for the effect of various dynamic effects (slamming, deck wetness, bow acceleration and propeller emergence) on voluntary ship speed reduction and so arranged to allow the prediction of ship’s behaviour for the whole range of ship speeds and heading angles, which is an essential part of weather routing systems (Vettor and Guedes Soares, 2015).
The 3D seakeeping code HYBRID of NTUA has being further developed for simulating the 6 DoF nonlinear ship motions in adverse sea states and for studying the parametric rolling problem. The HYBRID code has been applied to the study of parametric rolling problem of the ITTC-A1 ship and the calculation of drift forces and added resistance of RoPAX, KVLCC2, and DTC ships. The HYBRID code is essentially a nonlinear time domain method based on the impulse response function concept and incorporates the nonlinear Froude-Krylov force and hydrostatic force to simulate the six DoF ship motions, Liu et al (2014). For the calculation of drift forces and added resistance, a far-field method and a proper semi-empirical formula for short wave region correction are used.
The OceanWave3D software of DTU solves the linearized, forward-speed potential flow problem to predict seakeeping and added resistance in waves. The tool is based on an arbitrarily high-order finite difference method, and two gridding approaches are under development: 1) overlapping boundary fitted structured grids; and 2) an immersed boundary technique based on the method of weighted least-squares. The overlapping grid approach has been validated for linear seakeeping and added resistance both with Neuman-Kelvin and double-body flow linearization (Amini Afshar et al. 2015) and is currently being tested with real ship geometries. The immersed boundary technique has been validated for wave-less problems, and is being extended to solve the linear seakeeping problem. In order to extend both of these methods to treat fully nonlinear wave structure interaction, a new automated derivation procedure has been developed for implementing arbitrarily high-order Weighted Essentially Non-Oscillatory (WENO) schemes on uniform and non-uniform finite difference grids. Such a WENO treatment of the convective terms in the nonlinear, forward-speed free surface boundary conditions is shown to be robust and stable for all combinations of ship speed and wave celerity. This paves the way to extending the code to nonlinear wave-ship interaction. Future developments include parallel implementation and extensions to nonlinearities
A time domain code ‘Waqum2’ has been developed to simulate ship manoeuvring in waves. Based on the state of the art of maneuvering models and sea-keeping theory, a unified theory is used herein to develop this code, which can simulate ship responses in a sea state in time domain. The fluid memory effect is included in this code through a convolution function. The considered environment loads include wind and wave loads. The actuator force is composed of propeller force and rudder force. All the loads and actuator forces are given in individual force module, and they can be enabled or disabled based on the analysis requirement for a particular case. An engine model is also available in the code, which enable us to study ship responses in adverse sea more accurately and systematically. A PID controller is implemented in this code to control rudder angle and rpm of propeller or power output from engine. The verification of this code is performed (Guo, et al., 2016).
Field Methods
Several simulations were performed for different ships in waves using the RANS solver OpenFOAM. Drift forces were computed for different heading angles and compared with available experimental data. Ships under investigation were the Wigley hull III, the Duisburg Test Case (DTC) containership, described by el Moctar et al. (2012) and a Cruise-Vessel. During these first studies, influencing parameters such as discretization, numerical setups and modes of motion were investigated. Achievements have been obtained with respect to the following aspects: Grid and convergence study, preliminary validation study for the calculation of second order wave forces and comparison between fixed and spring constrained surge motions on added resistance (Ley et al 2014). The final objective is to develop off-line databases for second order wave forces, approximations of manoeuvring forces in shallow water, rudder forces behind the propeller in waves, a simplified unsteady model for a screw propeller and peculiarities of hull-propeller interaction coefficients in waves, obtained by a RANS solver.
The RANS code Neptuno (Cura Hochbaum & Voigt, 2002) has been enhanced with a new body force propeller model, allowing a better approximation of the rudder inflow and propeller torque. The code can be used to calculate forces on the hull due to waves, current and wind to derive a coefficient set including these environmental effects. The new body force model is based on a large set of RANS calculations for the isolated propeller rotating in homogenous inflow. The present calculations were made for a stock propeller with six blades. The advance coefficient J and the angle of incidence α were varied in a range of 0.1 to 0.9 and 0° to 30°, respectively. For each time step of the calculated case – which corresponds to a specific rotation angle of a considered propeller blade – the resulting pressure and shear stresses in each cell of a triangular grid on both the suction and pressure side of the blade are saved. The propeller disk is then discretized with a polar grid and for each cell of this grid the three components of the mean force per unit area caused by all propeller blades over a complete revolution are calculated and stored in a database for each considered pair J and α. In addition, the corresponding induced velocities of the propeller in an upstream reference plane are saved as well. When setting up the RANS calculation of a forced motion test, each cell of the polar grid on the propeller disk gets mapped to a cell in the computational domain and vice versa. The individual inflow condition at this cell is then evaluated from the total local wake field. There are three inflow parameters considered – the inflow speed and two angles, the first angle corresponding to the angle α mentioned above and the second one, which allows for turning back the current situation at the considered cell to the general situation assumed when generating the database, where the oblique propeller inflow was always horizontal. This makes it possible to take into account any inflow condition to the propeller as occurring for instance during sway and yaw motions of the ship. The body forces for each cell within the propeller region foreseen in the computational grid for the RANS simulation of virtual captive model tests are obtained from the database depending on the current inflow condition using a two-dimensional interpolation on J and α.
Another approach that is being pursued is the simulation of ships in manoeuvring conditions by coupling a potential flow method for the representation of the propeller with a RANS solver, which simulates the bulk flow around the hull. The objective is to find a correction factor for the propeller wake in varying inflow conditions, in order to have the real wake field and propeller forces during manoeuvres. In the present research the propeller suction is modelled as the suction of an equivalent actuator disk with angular varying loads. Only a one-cell layer of body forces is used in the propeller axial direction, even though more layers could be used if needed. The RANS code FINFLO was coupled with a propeller lifting line method for the prediction of the effective wake. The correction factors were calculated for a relatively light loaded propeller condition using circumferentially averaged values. Future work will consist of applying the correction factor approach to ship flow in manoeuvring conditions.
3.7 Validation of Evaluation Methods
One of the most important gaps in the state of the art of ship hydrodynamics before the project was the absence of validated numerical and empirical methods for the computation of time-average wave forces and moments, including the added resistance in waves. Although some measurements were available for the longitudinal component of such forces, both at zero and non-zero speeds, most data were available for head waves only; virtually no systematic measurements were freely available for the added resistance in oblique waves, as well as for the side drift force and yaw drift moment on ships, especially for non-zero forward speed. Providing experimental data for the validation of advanced methods or simplified models for rudder forces in propeller race, not sufficiently available yet in the open literature, was an additional objective of the experimental studies. Finally, validation of the proposed criteria for manoeuvring in waves (weather-vaning, steering and propulsion) can be done using direct transient simulations of manoeuvres in waves in time domain. However, such simulation methods themselves require validation by comparison with experiments; in the open literature, only limited amount of such experimental results is available. To close this gap a test matrix was defined, which specifies test conditions and values to be measured; summarizing, the following model tests were performed in deep and shallow water to provide validation data for the developed numerical models:
• Time-average wave forces including added resistance in regular waves;
• Added resistance in irregular waves;
• Propulsion and speed loss in regular waves;
• Rudder forces in regular waves;
• Rudder forces in propeller race at high propeller loading;
• Turning circle in regular waves;
• Zig-zag manoeuvres in regular waves.
Three vessel types of significantly different hydrodynamic characteristics were selected to provide a sufficiently broad variety of hull geometries for the validation of numerical tools: a VLCC tanker (the KVLCC2 tanker designed by MOERI), a post-panamax container ship (the Duisburg Test Case (DTC) container vessel designed by the Institute of Ship Technology) and a RoPax ferry. For these three hullforms, a comprehensive test program consisting of more than 1,300 different model tests has been carried out by four SHOPERA partners:
• At Norsk Marinteknisk Forskningsinstitutt (MARINTEK), 390 model tests for deep water conditions were performed in the large Towing Tank and the Ocean Basin.
• At the Canal de Experiencias Hidrodinámicas de el Pardo (CEHIPAR) 220 model tests were performed for deep water conditions in the Ship Dynamics Laboratory.
• In the Seakeeping Basin of the Technische Universität Berlin (TUB), a facility of the former VWS Berlin, another 180 model tests were conducted in shallow and intermediate water depth.
• Finally, Flanders Hydraulics Research (EVFH) unique towing carriage facility was exploited, which allows to run a significant number of tests in fully automated mode. Due to this unique feature, the major share of the test program – 560 experiments (added resistance, drift force, propulsion and manoeuvring tests in waves) – were conducted in shallow water conditions at the EVFH towing tank.
Model Test Specification
While the RoPax vessel was exclusively tested in deep water conditions at MARINTEK, both deep and shallow water tests were conducted for the KVLCC2 and DTC at all four participating partner institutions. The SHOPERA test campaign focused on the following test types:
• Added Resistance and Drift Force Measurements: For the added resistance and drift force tests at forward speed, the models were towed at predefined forward speed without propeller by a carriage with a spring frame, which had also integrated force transducers. For the zero-speed drift force tests, the models were moored by a spring system with integrated force transducers. Heave, pitch and roll motions were unrestrained, while surge, sway and yaw were restrained by springs. An exception was the drift force/added resistance tests at forward speed performed at TUB, in which the model was self-propelled and held captive by a measuring device consisting of spring held sleds. This newly developed measuring device consists of a frame with a pair of y-sleds, which carry an x-sled each, so that the model can surge, sway and yaw within certain limits determined by the stiffness of the attached springs. The sleds allow for motions both alongside and perpendicular to the direction of the towing carriage, as well as yaw motions. Parameters of variation for the added resistance and drift force tests were the under keel clearance, the ship forward speed, the loading condition and the heading over a relevant range of wave periods.
• Propulsion Tests in Waves: For the propulsion tests in waves the models were self-propelled and free running. Course was kept by an autopilot controlling the rudders. The purpose was to determine propulsive coefficients and speed loss in regular waves over a range of periods as well as in selected irregular sea states. By variation of the propeller revolution a constant mean forward speed in waves was achieved.
• Rudder Force Tests: For rudder force tests in calm water, the models were self-propelled and captive. The rudders were equipped with sensors for forces and shaft moments. For different propeller revolutions, the rudder angle was slowly varied from zero to 35°.
• Manoeuvring Test in Waves: The experimental determination of manoeuvring characteristics in selected wave scenarios was a further focal point of SHOPERA. The setup for the manoeuvring tests was similar to the one for the propulsion tests in waves - the models were self-propelled and free running with predefined constant propeller revolutions set. Parameters of variation for turning circles encompass the initial heading and the regular wave period. For zig-zag tests, only the wave period was varied. During PMM and Circular Motion tests, the models were being kept captive.
The effects of various characteristics of ship’s hull form on the added resistance in waves were investigated to derive new empirical formulae for the time-average wave forces, including added resistance, based on best fitting of available experimental data for different types of hull forms. Extensive validations of the proposed empirical formulae were carried out for different types of ships and in comparison with other empirical methods as well as more advanced approaches. An extensive study on second order forces in regular waves was also performed by field methods. Quadratic response amplitude operators (RAOs) for the forces were compared with experimental results for two different ship types. The ratio between wave and ship length was varied from 0.2 to 2.5. Thus, both, relatively short waves and long waves were considered.
Several semi-empirical methods for the forces on full-spade and semi-spade rudders in propeller race were developed and tested, based on the approach described in Brix (1993). In addition, a model was developed for the forces acting on podded drives during manoeuvring.
Validation of the proposed criteria for manoeuvring in waves (weather-vaning, steering and propulsion) can be done using direct transient simulations of manoeuvres in waves in time domain. To do this, such simulation methods themselves require validation by comparison with experiments. In the open literature, few such experimental results are available. For the comparison with the conducted manoeuvring experiments for the DTC container ship, a complete set of calm water manoeuvring coefficients was computed using RANS-CFD simulations. Numerical predictions agreed fairly well with the free running experiment to the starboard side. Differences of the free running test to port and to starboard side, have still to be clarified and may be related to the fitting of the twisted rudder. Turning circle manoeuvring tests were performed at different ship speeds in regular waves of different heights and headings. The nonlinear equations of motion for six degrees of freedom or, alternatively, four degrees of freedom, were solved in time domain. The hydrodynamic coefficients for calm water reactions were computed using virtual PMM tests with viscous field methods. Turning circle tests were performed in regular waves of height 2 m, period 12.5 s with the initial heading from head. The computed and measured trajectories for the DTC and S175 container ships agree fairly well with the experiments.
4 Benchmarking of Time-Average Wave Forces & Moments
An open blind international benchmark study has been organized by SHOPERA using for validation selected tank test results, which were obtained within the SHOPERA project, while some benchmark test data were made available from experimental studies in Japan. The aim of this benchmark study was to assess the accuracy/reliability of current numerical simulation methods on calculating the mean second order forces/moment and simulating the manoeuvrability of a ship in waves of varying complexity; simplified formulas, potential flow methods, motion simulators and viscous field methods, were compared with each other and with model tests for selected cases. The comparative experimental data were not known to the study participants, hence it can be concluded that the present benchmark assessment was based on a solid foundation and allowed an assessment of the genuine capabilities of benchmarked codes. The submitted simulation results were analysed and compared with corresponding model experimental data to conclude on the accuracy and efficiency of the methods. The outcomes of the study were presented at a public workshop on April 15, 2016, Lloyds Register, London (see http://www.shopera.org/benchmark-study/eedings/presentations of the workshop). Two well-known hullforms were used for the study:
The Duisburg Test Case (DTC) containership design is a modern post Panamax 14,000 TEU container vessel. It was developed by the Institute of Ship Technology, Ocean Engineering and Transport Systems (ISMT) of the University of Duisburg-Essen in collaboration with Germanischer Lloyd for benchmarking and validation of numerical methods; its lines and other characteristics are available to the public.
The KVLCC2 is a VLCC type tanker vessel, representing the second variant of a modern tanker design developed by the Korean Institute of Ship & Ocean Engineering (KRISO) with bulb bow and U-shaped stern lines. The hull lines have been exclusively developed for testing and benchmarking and this ship has been widely used benchmarks of international scientific committees, like ITTC and SIMMAN.
4.1 Added Resistance in Waves
For the added resistance of the DTC ship, 13 participants made 15 submissions; for the added resistance of KVLCC2 ship, 10 participants made 11 submissions. At higher speed in head waves, the spreading of results among the various methods and in comparison to the experimental data is moderate, while most methods seem to deliver results with good agreement with the experimental data. It should be herein noted that the test range of frequencies/wave lengths, extending to very short waves of λ/L ≈ 0.2 is quite demanding introducing uncertainties both to the experiments and computations. At lower speeds in head waves, the spreading among the numerical results gets larger, and the deviation from experimental results is also significant. The quality of the numerical predictions by some methods is poor, but several others are satisfactory. It should be noted that the range of tested scenarios refers to a great extent to the short waves region, where the physics of the problem become very complicated for both the numerical and experimental methods (breaking waves, viscous effects, etc.). For oblique waves, tank tests have been conducted only for low speeds and 60 deg heading. In general, a relatively good agreement has been observed for the DTC ship, whereas for the KVLCC2 ship the performance is similar.
4.2 Drift Forces and Moments
For the mean side force and yaw moment of the DTC ship, 10 participants made 13 submissions. For the KVLCC2 ship, 8 participants made 9 submissions. The convergence of results on the drift force in the transverse direction is general good, while the results for the mean yaw moment are less satisfactory. This may have been expected, as the yaw moment is the combined effect of forces both in the longitudinal and the transverse direction, and any discrepancy in the mean force in the longitudinal direction trivially leads to unsatisfactory results in the mean yaw moment. The performance of the various methods is similar to that observed in the previous tests.
4.3 Benchmarking Conclusions
The benchmark study concerned two large ships, the DTC containership and the KVLCC2 tanker, which are both well over 300m in terms of length. For such large ships, the encountered waves in actual sea conditions are mostly ‘short’, namely λ/L < 0.5 where the benchmark study focused on. The study delivered a good insight into the predictability of complicated hydrodynamic phenomena on the basis of experimental and numerical studies. It provided also valuable benchmark data to the international scientific community for future research on a subject with strong scientific and engineering background linked to international maritime regulations. Some essential aspects of the subject were noticed and should be further studied in the future. In particular, examining the numerical simulation results in comparison to model experimental data, the following may be concluded:
1. The predictability of the added resistance is generally decent to good. The performance of the tested methods is better for moderate speeds and worsens with decreasing speed. Also, the agreement is better for the tested full type ship (KVLCC2) than for the DTC containership hull form.
2. The predictability of the second order forces/moments (drift forces and yaw moment), is generally worse than for the added resistance and again worse for the DTC ship than the KVLCC2 ship.
3. For the manoeuvrability simulations, the behaviour of various employed numerical methods is not consistent. Despite the large spreading among the numerical methods and deviation from experimental results, some methods, performing well in one case, were not good for another case, thus conclusions could not be drawn, except for some qualitative effects of the impact of incoming waves.
4. The overall impression of the submitted results based on strip theories was not satisfactory. This is mainly due to its insufficiency in accounting the 3D and end effects (bow and stern) of the hull form, which are significant in the present study subject.
5. BEM methods implementing various theories performed as category of methods best in the present benchmark due to their essential merits: comparatively easy to use, when the code is properly programmed and validated and with decent results for non-extreme designs and loading/environmental conditions.
6. A reliable assessment of CFD/RANS methods was not possible due to limited participation and some delivered odd results. This may be attributed to improper use of codes (meshing etc.), allowing the conclusion that CFD codes are highly dependent on their usage, rather than on the physics of the studied problem or the code itself.
7. There was also one empirical method participating in the benchmark study by submitting results on the prediction of added resistance. For the studied cases, the empirical method delivered good results, showing a promising performance.
Some additional general comments may be concluded:
a. Limitations of the numerical methods: CFD tools are highly dependent on the end-users’ skills (background, experience with the type of problem, etc). In general, however, the quality of predictions is solely dependent on the code developer’s know-how and the code user’s experience.
b. The particularity of hull form: The scattering of the numerical results is more serious for the DTC ship than for the KVLCC2 ship. This can be credited to the effect of their hull form. The DTC ship disposes a relatively small draft (in comparison with other main particulars), an extended bulbous bow close to the free surface and a transom stern with long overhang near the calm water free surface. It is well known that these are two critical issues, namely, an emerging bulbous bow and immersing transom stern, with the associated complex wave phenomena and rapid change of the wetted part of the ship. Potential flow, panelling methods are not performing well in these conditions due to their essential limitations. However, even RANS methods are challenged under similar conditions and may fail, if not properly used.
c. The tested waves: As the size of the tested ships is large (>300m), representative sea states fall into the relatively short waves. In order to measure the small absolute values during model tests, quite steep waves were generated and tested. This may have created additional uncertainty in the benchmarked results, independently of the specific hull form. This uncertainty can only be partially controlled by using larger ship models for testing or applying full scale CFD simulations in future work.
d. Uncertainty of experimental data: The studied complex hydrodynamic phenomena put great challenges not only to numerical methods, but also to model experiments. This is obvious, when observing the spread of comparative model experimental data for similar conditions. This may be attributed to limitations of the used hardware, which is sometimes tested to its limits (e.g. measurement of very small force values of few Newtons), the inherent limitations of the size of tested ship models and generated scaled waves, the lack of repeatability of test measurements, etc.
5 Case Studies
It is not realistic and not necessary to design ships for operation in the worst possible storms that can be theoretically encountered, given that ships can nowadays timely avoid such stormy conditions by improved weather forecasts and satellite information systems. The standard operational wave heights of ships should be defined in such a way that the majority of the existing vessels fulfils the related requirements, because, first, present design and operational practices cannot be changed abruptly, for example, because of the introduction of EEDI and, second, the present safety level with respect to manoeuvrability-related accidents in heavy weather is satisfactory, Ventikos et al. (2014). Notably, to similar conclusions comes a study by IACS, EE-WG 1/4 (2010), which identifies rather mild standard wave heights for weather-vaning (wind speed up to 21 m/s and significant wave height up to 5.4 m) and advance speed (up to Bft 8 at 6.0 knots advance speed) requirements. Therefore, benchmarking of the existing fleet with respect to the herein proposed new criteria appears as the most rational way to define standard wave heights. Such an approach was also used in the IACS studies on minimum power requirements and led to the environmental conditions in the 2013 Interim Guidelines: wind speed 15.7 m/s at significant wave height 4.0 m for ships with length BP up to 200 m to 19.0 m/s and 5.5 m, respectively, for length BP of 250 m and greater. Therefore, case studies were undertaken in SHOPERA concerning all ship types considered in the EEDI regulations.
5.1 Comparison between Criteria
The weather-vaning ability was treated using a simplified criterion, as the ability of the ship to keep position in bow to bow-quartering seaway; this simplification follows from the observation that the ship will not be able to keep heading under the action of environmental forces if the forward speed is not sufficiently large, because of significantly reduced manoeuvring reactions on the hull and steering force on the rudder. Comparisons of marginal significant wave heights according to comprehensive propulsion assessment using 4.0 knots advance speed with marginal significant wave heights according to the comprehensive position keeping assessments for bulk carriers, tankers and container vessels have been performed verifying that marginal wave heights for position-keeping are consistently greater than those for 4.0 knots propulsion; the deviation between results decreases with increasing ship size, according to Froude law. Note, however, that the marginal wave heights according to these assessments are very well correlated, which means that for norming, one of the criteria is redundant. Before making the final choice, a comparison with assessment based on other weather-vaning criteria would be useful, e.g. with the more comprehensive “heading recovery” criterion proposed by the project conducted in The Netherlands.
Comparisons have been also performed between the marginal wave heights according to comprehensive propulsion assessment (here, 6.0 knots advance speed was used) with marginal wave heights according to steering assessment for bulk carriers, tankers, general cargo vessels and container ships. The marginal wave heights according to these two criteria are also correlated to some degree, however, with significantly more spreading than for the position keeping vs. propulsion. It can be concluded that fulfilment of the propulsion ability requirement at a certain marginal significant wave height guarantees fulfilment also of the steering ability requirement at a marginal significant wave height of about 1.0 m smaller. The difference becomes slightly greater than 1.0 m at the propulsion marginal significant wave heights above about 5.5 m, which are, perhaps, not relevant anyway. Note, however, that this correlation between the propulsion and steering abilities stems from the fact that the steering systems of the considered ships are properly dimensioned according to other requirements, e.g. IMO Manoeuvrability Standards (2002).
5.2 Definition of Standard Wave Heights Using Comprehensive Assessment
One of the aims of the Case Studies was to provide recommendations for the standard wave heights using Comprehensive Assessment. This study was done as follows: first, a sample of representative vessels was selected; after that, the Comprehensive Assessment of Propulsion and Steering Abilities was applied to find the marginal wave height (separately for Propulsion and Steering and for different ship types and sizes); finally, a fit of the determined marginal wave heights vs. length BP was done to define the standard wave height per ship type and overall for all ship types; note that the marginal wave heights were considered separately for the Propulsion and Steering Abilities.
To select representative vessels, several series of designs were generated:
1. Series of bulk carriers and tankers along the defined boundary lines MCR=f(Lpp), which exclude a certain percentage of vessels with lower power. As the “bottom line”, a line corresponding to the limit of 5% of the low-powered vessels was used; besides, 10%-, 20%- and 30%-lines were defined and series of ships were generated. For comparison, low-power series were generated also for container ships and general cargo vessels. These series were generated using the IHS-FairPlay data for each vessel type.
2. Series of bulk carriers and tankers along the lines MCR=f(Lpp) corresponding to vessels marginally fulfilling the requirements of EEDI Phase 1, 2 and 3.
3. Series of bulk carriers and tankers along the Minimum Power Lines according to the 2013 Interim Guidelines, Res. MEPC.232(65) as amended by Res. MEPC.255(67) and MEPC.262(68).
The marginal significant wave heights obtained with Comprehensive Propulsion and Steering assessment were plotted vs. the Length BP, for the bulk carriers and tankers (in some cases results for low-power container ships and general cargo vessels were included for comparison) with the installed power corresponding to the 5% and 20% of low power vessels of the FairPlay database. Bulk carriers and tankers look very similar with respect to the marginal wave heights and are significantly below container ships. The results indicate that, if only the propulsion ability is taken into account, bulk carriers and tankers with a power at about the 20% MCR line of the FairPlay database are slightly above the current standard (hs=5.5 m at Lpp=250 m); Steering Ability appears to be more critical, i.e. it corresponds to lower marginal wave heights than Propulsion Ability. Similar plots have been produced for bulk carriers and tankers marginally satisfying the requirements of EEDI implementation Phase 3, 2 and 1, respectively. The results show that if only propulsion ability is taken into account, the current standard hs=5.5 m at Lpp=250 m is fulfilled by Phase 1-compliant tankers and bulk carriers and, marginally, by Phase 2 compliant tankers and bulk carriers. In addition to the above, plots have been produced for the marginal significant wave heights according to comprehensive propulsion and steering abilities assessments for bulk carriers and tankers, which marginally satisfy the Minimum Power Lines of 2013 Interim Guidelines. Based on the obtained marginal wave heights for bulk carriers and tankers, and requiring that the standard wave height for the propulsion ability assessment is equal to the standard wave height according to the 2013 Interim Guidelines of 5.5 m for vessels with Lpp=250 m, the following can be proposed:
hs=min(2.2+Lpp/75 5.5)
or alternatively the standard wave heights can be set equal to those (slightly less conservative for vessels of Lpp < 250 m) in the 2013 Interim Guidelines.
To define standard wave heights for the steering ability assessment, it was assumed that, on the average, the same percentage of vessels from the total number of vessels used should fail the steering ability assessment as the propulsion ability assessment (for the individual vessels, one or the other requirement can be dominating). This led to the following proposal:
hs=2.0+Lpp/100
One observation from these results is that the marginal wave heights are ship size-dependent: larger vessels are able to fulfil both propulsion and steering requirements at greater significant wave heights than smaller vessels. This is understandable physically; in principle, ship size dependent standard wave heights may be acceptable from the pragmatic point of view: because consequences of accidents are greater for larger vessels, acceptable probability of accidents should be lower for larger vessels. Besides, ship size-dependent standard wave height would reflect existing design and operational practices: smaller vessels, obviously, do not operate in storms of the same severity as larger vessels. Note that standard wave heights in the 2013 Interim Guidelines are also ship-size dependent, however, this is a subject of ongoing discussion. Another conclusion is that the marginal wave heights differ, partly substantially, between different ship types. A final note concerns the possibility of contradiction between fulfilling the proposed requirements to manoeuvrability in adverse weather conditions and the possibility to fulfil EEDI requirements, which are progressively strengthening from Phase 1 to Phase 3. It is interesting to note that whereas the selected low-power general cargo vessels and container carriers satisfy the standard wave heights corresponding to the 2013 Interim Guidelines and, at the same time, easily fulfil the requirements to Phase 3 of EEDI implementation (as presently formulated), the selected bulk carriers and tankers, marginally satisfying standard wave heights of the 2013 Interim Guidelines, are able to marginally fulfil requirements of Phase 2 of EEDI implementation, but not the requirements of Phase 3. Note, however, that standard wave heights can be adjusted to the marginal wave heights of Phase 3-compliant bulk carriers and tankers, i.e. effectively, slow-steaming designs; whether such vessels can be considered as representative vessels of fleet in service requires a prolonged discussion with all interested stakeholders.
5.3 Comparison between Ship Types using Simplified Assessment
The simplified assessment of propulsion and steering ability is more conservative than the comprehensive assessment, therefore, it was not applied to define the standard wave heights. On the other hand, it can be used to compare performance of vessels of different types with respect to EEDI requirements, when selected vessels of different types have comparable performance with respect to manoeuvrability in adverse conditions. In this study, vessels of different types were selected, which have the same marginal wave heights (computed using simplified assessment procedure) as bulk carriers and tankers, marginally compliant with the requirements of either Phase 1, 2 or 3 of EEDI implementation. The analysis identified EEDI phase that these selected vessels were able to satisfy. The analysis showed that the general cargo vessels satisfy either the same EEDI phase as the bulk carriers and tankers with the same marginal wave heights (this concerns old designs of general cargo vessels), to “higher” Phases; all other vessel types (Cruise Vessels, LNG and Gas Carriers, RoRo Cargo and RoPax) achieve significantly “higher” phases of EEDI implementation than bulk carriers and tankers if they have comparable marginal wave heights with respect to manoeuvrability in heavy weather. Plots have been elaborated showing marginal significant wave heights according to simplified propulsion and simplified steering abilities assessment for bulk carriers, tankers, container vessels, general cargo vessels, LNG and gas carriers, RoRo cargo vessels, reefers and RoPax vessels. In each of these plots, only vessels satisfying requirements of a certain EEDI implementation phase are shown. The plots show that for each EEDI phase, bulk carriers and tankers show remarkably similar marginal significant wave heights, which are lowest over all ship types. Container vessels demonstrate high marginal wave heights due to high installed power; passenger vessels (RoPax and cruise vessels) show significantly higher marginal wave heights than other vessel types due to advanced propulsion and steering systems (twin screw, diesel-electric main propulsion, controlled pitch propeller, pods).
A final note concerns the question whether the standard wave heights should depend on ship type. On the one hand consequences of accidents, as well as operational practices, differ between different ship types, especially between passenger and cargo vessels. Besides, the revealed differences in the marginal wave heights between different ship types reflect established design and operational practices, which should not be drastically changed by new regulations, assuming that the present level of safety is satisfactory. Both these arguments are in favour of correspondingly different standard wave heights per ship type. On the other hand, the revealed difference in the manoeuvring characteristics in heavy weather reflects, obviously, different requirements to the operational performance of the propulsion and steering systems of ships of different types, not related to safety. Obviously, reaching a conclusion regarding ship type-dependency of standard wave heights requires a prolonged discussion with all interested stakeholders.
5.4 Study of redundancy of proposed criteria with respect to existing standards
The criteria proposed by SHOPERA have been evaluated regarding their redundancy with respect to existing regulations, as a function of ship type and size.
First, the redundancy of weather-vaning criteria with respect to Intact Stability code (IS code) is investigated. The results of numerical simulations of motions in waves were combined with the assessment of steering and propulsion ability in seaway for a 8400 TEU post-panamax container ship. Bases on the analysis, it could be concluded that ship can drift in open sea without capsizing, if there is enough room; thus, the IS code seems to ensure that at least the investigated ship types will not capsize. The large roll motions could lead to a shift of the center of gravity of some ship types, such as, bulk carriers, general cargo ships and RoRo vessels, which are not considered in the existing IS code. In such cases, the ships may capsize, but this is not an issue of the minimum powering in waves, EEDI regulatory provisions. To make sure the safety of these ships in open sea, the IS code should be improved to take care of this, or ship’s ability to change heading in open sea needs to be required.
Regarding the steering criteria, it has been verified whether Vck- solution in the simplified assessment of 2013 Interim Guidelines, class requirement on minimum rudder areas and the IMO Manoeuvrability Standards ensure good correlation of steering and propulsion criteria to render the steering criterion redundant. The investigations show that:
• The Vck – solution used in the Simplified Assessment of 2013 Interim Guidelines seem not to lead to a redundancy of the steering criteria.
• The marginal wave heights of propulsion and steering criteria are still correlated to some degree with minimum rudder area required by DNV Rule (2005). The spreading of the results with minimum required rudder areas is larger than that with installed rudder areas. With the minimum required rudder areas, the fulfilment of propulsion ability at certain wave height ensures the fulfilment of the steering ability at a wave height of about 2.0 m smaller. In the joint SHOPERA-Japan submission to IMO for bulkcarriers, tankers and combinations carriers over 20,000 t DWT, the resulting wave heights for the propulsion ability were maximum 1.5m larger than for the steering ability. Thus, the results show that the minimum rudder areas given by DNV Rule (2005) lead to a slightly less wave heights for the steering criterion.
• IMO Manoeuvrability Standards have been developed to evaluate the manoeuvring performance of ships with traditional propulsion and steering systems (e.g. driven ships with conventional rudders). The results of the investigations show that the IMO Manoeuvrability Standards ensure good correlation of steering and propulsion criteria for the investigated case study ship. Further case studies are needed to verify this for other ship types and sizes.
Regarding the propulsion criterion, the analysis shows that IMO Manoeuvrability Standards cannot make the propulsion criterion proposed by SHOPERA redundant.
5.5 Sensitivity studies
The sensitivity studies were performed using a comprehensive assessment to provide recommendations for allowed tolerances for numerical, empirical and experimental methods concerning the propeller curves (KT, KQ curves), propulsion coefficients (wake fraction and thrust deduction), time-average wave-induced forces, wind forces and calm water forces.
The effect of the minimum required forward speeds (4 knot vs. 6 knot) on the results is studied with the comprehensive method. The results show that an effect of the forward speed on the marginal wave heights of different ship types is very similar. The change of the marginal wave heights is about 0.5m. The change of the required power for bulk carriers, tankers and container ships is about 26% - 33% of the required power compared to a ship speed of 4 knots. However, the change is larger for general cargo ships, namely about 27%- 37% of the required power compared to a ship speed of 4 knots.
6 Optimisation
The challenge of identifying a suitable and efficient path between the conflicting requirements of reducing greenhouse emissions and at the same time maintaining adequate safety of ships in adverse sea conditions is the main objective of the SHOPERA project. To this end, a specific work package is foreseen in SHOPERA for the development of a multi-objective optimization procedure, in which a ship’s performance is assessed holistically, thus, looking for the minimum powering requirement to ensure safe ship operation in adverse seaway/weather conditions, while keeping the right balance between ship economy, efficiency and safety of the ship and the marine/air environment. The planned optimization studies were implemented in two phases: The first phase consists of a Global Optimization, aiming to identify most favourable combinations of main dimensions, form parameters and other integrated characteristics of the ship. The second phase consists of a Detailed Optimization, including hullform details. These studies should be carried out applying refined and more accurate methods than those used for the global optimization.
6.1 Parametric Model for the Global Optimization
Parametric models for RoPax ships, tankers and bulk carriers were developed within the NAPA software. Additional parametric models for cruise ships, container ships, general cargo carriers and LNG carriers were developed within the CAESES software. These parametric models are able to perform in a fully automatic way and without the need of any user intervention a series of basic tasks:
1. Hullform development
2. Resistance and propulsion estimations
3. Development of internal layout
4. Weights estimation - Definition of Loading Conditions
5. Evaluation of transport capacity (e.g. payload and, depending on ship type, lanes length, number of cars/trucks, cargo holds or cargo tanks volume, number of TEUs)
6. Evaluation of Stability Criteria and other Regulatory Requirements (e.g. oil outflow index for tankers etc.)
7. Assessment of Building and Operational Cost, Annual Income and Selected Economic Indices (e.g. NPV, RFR based on a specified operational scenario)
8. Evaluation of Energy Efficiency Design Index (EEDI)
9. Evaluation of hydrodynamic/manoeuvring performance in adverse seaway/weather conditions based on the criteria and procedures developed by SHOPERA.
6.2 Global Optimization studies
The developed parametric model has been applied for the design and optimization of two RoPax ships. The objective of these studies was to maximise the Net Present Value of the investment, while ensuring compliance with safety regulations, EEDI Phase I or Phase II requirements and the SHOPERA criteria for manoeuvrability in adverse weather conditions, as well as various operational constraints such as draught and trim constraints for the various loading conditions, upper limit on building cost, lower limits on DWT and lanes length requirements, constraints on the average truck weight etc. The smaller of the two RoPax ships is designed for a roundtrip length of 320 sm, with a transport capacity of 1,200 passengers, 200 private cars and 21 trucks and a service speed of 23.8 kn. The second ROPAX ship is designed for a roundtrip length of 514sm, with a transport capacity of 1,800 passengers, 640 private cars and 130 trucks and a service speed of 27kn. The results from the optimization of the two ROPAX ships indicate that compliance with the EEDI Phase II requirement was quite demanding, as most of the unfeasible designs failed to satisfy this criterion. However, in the case of the small ROPAX ship, a number of 161 designs were identified, capable of complying with Phase II requirement while at the same time, only two of them were identified, marginally fulfilling Phase III requirement. For the larger ROPAX ship, a number of 293 designs were identified, capable of complying with Phase II requirement while no design was found complying with Phase III. In contrast to what was observed in the case of tankers and bulk carriers, compliance with the SHOPERA propulsion criterion in adverse weather conditions was easily achieved, even by the designs with reduced propulsion power, complying with EEDI phase III. This of course was not an unexpected result, since RoPax ships are highly powered in comparison with other types of ships of equal displacement.
Two Crude Oil Carriers have been optimized using the developed optimization platforms. The smaller of the two Oil Carriers is a SUEZMAX tanker, fitted with a main engine delivering 18,660 kW MCR at 91 RPM. The larger Oil Carrier is a VLCC (actually, the larger designs obtained had a size at or above the limits of existing VLCCs), fitted with a Wärtsilä 7RT-flex84T-D main engine delivering 29439 kW MCR at 76 RPM. For both ships, a significant number of designs was identified complying with the EEDI Phase I requirement and with the SHOPERA propulsion criterion. No design was found complying with Phase II. To investigate the possibility of achieving compliance with EEDI Phase II requirement, calculations have been repeated with smaller engines, resulting in a reduction of service speed of approximately 0.44 kn in the case of the Suezmax tanker and 0.8kn in case of the VLCC. With the smaller engines, both the EEDI Phase II requirements and the SHOPERA propulsion criterion are fulfilled.
Two Bulk Carriers have been optimized. The smaller of the two Bulk Carriers had a DWT in the area of 37,000t and was fitted with a main engine delivering 6,900 kW MCR at 129 RPM. The second Bulk Carriers had a DWT in the area of 58,600t DWT and was fitted with a main engine delivering 9,020 kW MCR at 125 RPM. For the smaller bulk carrier, EEDI Phase I requirement and the SHOPERA propulsion criterion was easily fulfilled, while a number of designs was found complying with EEDI Phase II. To investigate the possibility of achieving compliance with EEDI Phase III requirement, calculations have been repeated with a smaller engine, resulting in a reduction of service speed of approximately 1.2 kn. With this new engine, both the EEDI Phase III requirements and the SHOPERA propulsion criterion are fulfilled. For the larger bulk carrier, it was also possible to find a series of designs complying with the EEDI Phase I requirement, although by a relatively small margin, and at the same time fulfilling the SHOPERA propulsion criterion. No design was found fulfilling Phase II requirement. A smaller engine has been selected and calculations for the obtained feasible designs were repeated, resulting in a service speed reduction of approximately 0.7 kn. With this new engine, both the EEDI Phase II requirements and the SHOPERA propulsion criterion are fulfilled.
Two containership case studies have been examined: a 5,000 TEU and a 10,000 TEU containership. The optimization studies resulted in a series of designs complying with EEDI Phase II requirements, as well as with the SHOERA propulsion and steering criteria. In contrast to what was observed for tankers and bulk carriers, for the smaller Container ship the steering criterion was easier to comply with than the propulsion criterion. In the case of the larger Container ship optimization, some ships (particularly those with DWT around 90 kt) are also exhibiting a larger margin with respect to the steering criterion, while for those with a DWT above 110 kt the opposite seems to be true.
The optimization of a 46,000 ton DWT General Cargo ship has been also carried out, resulting in a series of design alternatives complying with EEDI Phase II requirements, as well as with the SHOERA propulsion and steering criteria. Also in this case, the steering criterion was easier to comply with than the propulsion criterion.
The Cruise Ship global optimization study was carried out for a ship designed for worldwide and year-round operation following the summer season in Europe and Caribbean areas, thus assuming a constant number of passengers and revenue. Initially 50 feasible designs were found. However after careful screening of the candidates the number of feasible designs has decreased to 37. Some designs have been rejected due to poor resulting geometry. The obtained results indicate that compliance with EEDI Phase II & III was easily achieved. Compliance with the SHOPERA criteria for manoeuvrability in adverse weather conditions was also achieved. The results were obtained with Level 2 criteria as developed for Cruise Ships with CPP propulsion.
The LNG global optimization study was carried out for a ship designed for worldwide and year-round operation. Initially 60 feasible designs were found. However after careful screening of the candidates the number of feasible designs has decreased to 34. Some designs have been rejected due to poor resulting geometry. The obtained results indicate that compliance with EEDI Phase II & III was not easily achieved, many designs passed Phase II but almost all failed to pass Phase III. Compliance with the SHOPERA criteria for manoeuvrability in adverse weather conditions was achieved, with no particular problems observed to pass the 6 knots propulsion threshold. The results were obtained with Level 2 criteria as developed for Single Screw FPP propulsion.
6.3 Local hullform optimizations
Five ship types were selected for detailed hullform optimization. Three of them have been extensively studied in the other WPs of SHOPERA; the Calmac RoPax, the DTC container ship and the KVLCC2 tanker. A Cruise Ship, derived by the global optimization was the 4th ship selected for detailed hullform optimization studies and finally the D-Bulker of NAPA was also used by courtesy of NAPA Ltd. The Calmac RoPax represents a small Roro Passenger ferry, which is operating in area where both confined waterways and adverse open sea weather conditions prevail. Two versions were analysed: with and w/o a bulbous bow. For the KVLCC2 tanker and the D-Bulker, along with the original version, featuring a bulbous bow, two alternatives were tested, one with a bulbous bow of increased size and one w/o a bulbous bow.
The hydrodynamic performance analysis both for the tanker and the bulk carrier revealed that the larger bulbous bow section seemed to decrease the resistance both in shallow and deep water. The difference of resistance in shallow and deep water was significant. The versions without the bulbous bow provided the largest resistance in all conditions.
The added resistance in waves of the tanker ship was minimized with the non-bulbous bow version. This version, however, produced clearly the highest resistance values in calm water. Quite the converse trend was observed with the bulkers, as the version with no bulbous bow, had clearly the highest value for the added resistance in waves.
The bow form optimization of the Cruise ship and the Container ship has been conducted to ascertain the performance of their hull in terms of the added resistance in waves. The step-wise modifications were done on the hull and the added resistance in waves of different frequencies were calculated. An in-house code was used based on the pressure integration method. In the first stage of the work for the cruise ship optimization, a sensitivity analysis of 15 parameters was made by changing by ±10% the original values. Next the most influent parameters were identified and a response surface was fit to the results, using a linear polynomial approximation. Finally by determining the minimum value of the added resistance, the optimum combination of the parameters was obtained. In the bow form optimization of a Container ship hull, all the form parameters were used. Next a response surface was fit to the results of a systematic variation conducted by altering the hull parameters by a factor of ±10%. Finally, by determining the minimum value of the added resistance, the optimum combination of the form parameters was obtained.
References
• Papanikolaou, A., Zaraphonitis, G., Bitner-Gregersen, E., Shigunov, V., El Moctar, O., Guedes Soares, C., Reddy, D.N. Sprenger, F., “Energy Efficient Safe Ship Operation (SHOPERA)”, 2015 World Maritime Technology Conference (WMTC150), 3-7 Nov. 2015, Rhode Island (USA).
• Papanikolaou, A., Zaraphonitis, G., Bitner-Gregersen, E., Shigunov, V., El Moctar, O., Guedes Soares, C., Reddy, D.N. Sprenger, F., “Energy Efficient Safe Ship Operation (SHOPERA)”, Proc. 12th Int. Marine Design Conference (IMDC2015 ), 11-14 May 2015, Tokyo (Japan)
• Papanikolaou, A., Zaraphonitis, G., Bitner-Gregersen, E., Shigunov, V., El Moctar, O., Guedes Soares, C., Reddy, D. N., Sprenger, F., “Minimum Propulsion and Steering Requirements for Efficient and Safe Operation (SHOPERA)”, Invited paper, 37th Motorship Propulsion and Emissions Conference, 4-5 March 2015, Hamburg (Germany).
• Shigunov, V., Papanikolaou, A., “Criteria for Minimum Powering and Maneuverability in Adverse Weather Conditions”, 14th Int. Ship Stability Workshop (ISSW), 29th Sept.- 1st Oct. 2014, Kuala Lumpur, Malaysia.
• V. Shigunov (2015), “Manoeuvrability in adverse conditions”, Proc. 34th Int. Conf. on Ocean, Offshore and Arctic Engineering OMAE2015, St. John's, Newfoundland, Canada; Paper Nr. OMAE2015-41628.
• Bitner-Gregersen, E.M Guedes Soares, C. and Vantorre, M., “Adverse weather conditions for ship manoeuvrability”, Transportation Research Procedia 14 (2016) 1631–1640. (Presented also at the 6th EC Transport Research Arena April 18-21, Warsaw, Poland 2016).
• Bingjie Guo, Eivind Ruth, Håvard Austefjord, Elzbieta M. Bitner-Gregersen, Olav Rognebakke, “Time domain Analysis on Ship Maneuvering in Adverse Sea State”, OMAE2016 – 54589, Proceedings of the ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering OMAE2016, 19 – 24 June, 2016, Busan,South Korea.
• N . P . Ventikos , A . Koimtzoglou , K . Louzis , and E . Eliopoulou, “Statistics for marine accidents in adverse weather conditions”, Maritime Technology and Engineering (MARTECH) 2014.
• Prpić-Oršić and Faltinsen (2012) Estimation of ship speed loss and associated CO2 emissions in a seaway, Ocean Engineering, 44, 1, 1-10 .
• R. Vettor & C. Guedes Soares, “Multi-objective Route Optimization for Onboard Decision Support System”, 11th International Conference TRANSNAV 2015 on Marine Navigation and Safety of Sea Transportation - Gdynia (17th - 19th June, 2015).
• Papanikolaou, A., Liu, S. Zaraphonitis, G. (2014), “Time Domain Simulation of Nonlinear Ship Motions Using an Impulsive Responsive Function Method”, 2nd International Conference on Maritime Technology ICMT2014, Glasgow.
• Amini Afshar, H.B. Bingham and R. Read. (2015), “A high-order finite-difference linear seakeeping solver tool for calculation of added resistance in waves”, 29th International Workshop on Water Waves and Floating Bodies, Bristol, UK. Available from: http://www.iwwwfb.org.
• el Moctar, O., V. Shigunov and T. Zorn, “Duisburg Test Case: Post-Panamax Container Ship for Benchmarking”, Journal of Ship Technology Research, Vol.59 No.3 pp. 50-65, 2012.
• Ley, J., S. Sigmund and O. el Moctar, “Numerical Prediction of the Added Resistance of Ships in Waves”, Proc. 33rd ASME Int. Conf. on Ocean, Offshore and Arctic Engineering, San Francisco, USA. - Paper Nr. OMAE2014-24216, 2014.
• Cura Hochbaum, A. and M. Voigt, “Towards the Simulation of Seakeeping and Manoeuvring based on the Computation of the Free Surface Viscous Ship Flow”, Fukuoka, Japan, 24th ONR Symposium on Naval Hydrodynamics, 2002.
• Brix, J. E. (1993),” Manoeuvring Technical Manual” – Seehafen Verlag, Hamburg.
• Blendermann, W. (1993), “Parameter identification of wind loads on ships”, Journal of Wind Engineering and Industrial Aerodynamics, 51 (1993), p. 339.
• Fujiwara, T., Ueno, M. and Ikeda, Y. (2006), “Cruising performance of a large passenger ship in heavy sea”, Proc. 16-th Int. Offshore and Polar Engineering Conf., Vol. III, pp. 304-311
Potential Impact:
1 Potential Impact
The ultimate aim of the project is to develop revised guidelines for various types of ships to evaluate the ability of ships to maintain manoeuvrability under adverse conditions. The proposal for the guidelines has been prepared and submitted to IMO-MEPC 70 with the aim of their finalisation and adoption at MEPC 71. The key results and conclusions of the project have been submitted as an accompanying information paper. The submission was done through the flag state delegation of Norway and supported by the member states Denmark, Germany and Spain.
The revised guidelines for definition of the minimum required power and steering performance to maintain manoeuvrability under adverse conditions, submitted to IMO-MEPC 70 for consideration and possible adoption at MEPC 71, will, if adopted, shape ship designs in the post-EEDI era, will have significant contribution towards the preservation of the current levels of safety of ships operating in adverse weather condition and will ensure widest possible exploitation of the project results. Besides, the new numerical methods, software tools and testing techniques developed in the project would be urgently required in the industry upon adoption of the updated guidelines, which will ensure their world-wide exploitation. In addition, the developed optimisation techniques, which allow combining safety in adverse conditions with EEDI requirements, would also be demanded by the industry.
Existing software tools, already developed by a project partner before the project start, that were validated, refined, adapted or extended during the project, remain at the disposal of this partner. New software tools that have been developed during the elaboration of the project will remain for their exploitation at the disposal of the partners that were involved in their development with a positive impact on the competitiveness of the corresponding partners as well as on the design of safer and more efficient ships. In both cases, the software tools will be exploited after the end of the project by providing services to the industry and by using them in research, development and education.
Innovative experimental techniques and procedures developed in the project will be further exploited by the partners that were responsible for their development.
The optimized ship designs will be exploited by the partners involved in their development, whereas the new knowledge and understanding of the behaviour of various types of ships at low speed under adverse sea conditions will be openly available to the scientific community.
2 SHOPERA - Exploitation Plan
Activities and measures for the exploitation of the research output were coordinated by the Exploitation Committee, consisting of the Project Coordinator, the WP1, WP6 and WP7 leaders (DNV, LR and GL, respectively) and, additionally, RINA as a representative of classification societies and also DAN and FSG as representatives of the participating ship operators and yards. A preliminary Exploitation Plan has been issued with the Mid-Term Assessment Report. In this deliverable, the Exploitation Plan is finalised.
2.1 Exploitable Results
2.1.1 Revised Guidelines
The ultimate aim of the project is to develop revised guidelines for various types of ships to evaluate the ability of ships to maintain manoeuvrability under adverse conditions. The proposal for the guidelines has been prepared and submitted to IMO-MEPC 70 with the aim of their finalisation and adoption at MEPC 71. The key results and conclusions of the project have been submitted as an accompanying information paper. To ensure awareness of the key stakeholders at IMO about the project’s objectives, methods and results and to facilitate acceptance of the results by IMO, the following activities have been conducted:
1. During the project, five papers have been submitted to IMO-MEPC sessions from MEPC 67 to MEPC 70 regarding objectives and the time plan of SHOPERA, its aims, deliverables and results to ensure awareness of the key stakeholders at IMO about the project and facilitate acceptance of the results by the IMO at the end of the project. Moreover, two presentations were done at IMO MEPC to support the submissions with personal explanations and feedback. As a result, IMO-MEPC 67 decided to wait up the completion of the project SHOPERA before updating the 2013 Interim Guidelines. Several IMO delegations referred to the project and its anticipated contribution.
2. The project SHOPERA has closely collaborated with the parallel RTD project conducted in Japan, funded by the Japan Government, NKK class and Japan Shipyard Research Association, and coordinated by the Japan Society of Naval Architects and Ocean Engineers. The two projects have been able to submit a common proposal to IMO-MEPC 70 with agreed contents of the revised guidelines.
3. Four public workshops were organised by SHOPERA and two international workshops were organised by Japan, which included presentations of the project plans, contemporary results and outlined the final guidelines.
2.1.2 Assessment Procedures
The proposal for the revised guidelines developed by the project allows free choice between three assessment procedures: Comprehensive Assessment, Simplified Assessment, and the Sufficient Propulsion and Steering Ability Check.
The Comprehensive Assessment allows for the best accuracy by solving coupled nonlinear motion equations in the time domain, and can be implemented in a dedicated software tool. Several partners have developed such software tools during the project; these tools will remain at the disposal of the partners that were involved in their development and will be exploited by providing services to the industry and by using them in research, development and education.
The Simplified Assessment, a first-principle assessment with reduced number of considered situations and reduced complexity of motion equations, can be implemented as a spreadsheet calculation. The MS Excel spreadsheets developed by Germanischer Lloyd were distributed to the ship yards, design offices, classification societies and universities to be used in case studies and optimisation exercises during the project and will be freely available after the end of the project.
The Sufficient Propulsion and Steering Ability Check is based on pure empirical formulae, defining the required installed power as a function of main ship parameters and having a complexity of a pocket calculator, thus this assessment level can be easily used by anybody once adopted.
Project results will also be used for the development of classification rules by the classification societies.
2.1.3 Evaluation Methods
Both Comprehensive and Simplified Assessments are based on a modular principle, so that the designers and administrations can choose between numerical, experimental or empirical methods for different input elements to the procedure. From the required input elements (time-averaged surge and sway forces due to waves, wind forces, calm-water manoeuvring reactions, rudder forces, propeller forces and engine characteristics), the time-average surge and sway forces due to waves and the rudder forces were found to be the most uncertain among the most important contributions.
Therefore, significant effort was dedicated in the project to the development, validation and exploitation of the numerical and empirical methods for the time-average wave forces (including added resistance) and rudder forces. For the time-average wave forces (including added resistance), extensive model tests were performed for three ship types (a modern 14,000 TEU container ship design, a standard VLCC tanker and a small European RoPax) in over 1,300 conditions, including various draughts, water depths, forward speeds and wave directions, lengths and heights to generate a unique validation database for numerical and empirical methods. The results are available to all project partners for the validation of numerical tools. Several numerical methods were developed and validated, which will remain at the disposal of the partners that were involved in their development and will be exploited after the end of the project by providing services to the industry. In addition, several empirical formulae were developed of various degree of complexity, which are simple enough to be used by any designer or administration.
Moreover, to evaluate the world-wide availability of methods that can be used in the practical assessment, SHOPERA conducted an international benchmark study of numerical and empirical methods for the time-average wave-induced forces and moments and simulation of ship manoeuvres in waves. Sixteen organizations (six SHOPERA partners and ten external participants) from all over the world participated in the study, including industry, research institution and academia, therefore, this exercise represents an important exploitation activity. The results of this benchmarking exercise have been published at the joint SHOPERA-ITTC workshop in London and will be described in a detailed public report soon.
Another open benchmarking exercise dedicated to ship motions and time-average wave-induced forces in shallow water will be carried out shortly after the end of SHOPERA, using measurement data from captive and free-running model tests in waves in medium deep and shallow water obtained in SHOPERA. The results of this benchmarking should be presented at the 5th MASHCON Conference which will be held in 2019 in Ostend.
The experimental results used within these benchmarking exercises will be publicly available; other experimental results remain available only to SHOPERA partners, but will become publicly available once SHOPERA partners publish them in the open literature.
2.1.4 Optimisation Results
In the project, optimisation techniques, software tools and software have been developed, which allow combining sufficient safety in adverse conditions with EEDI requirements. These techniques and tools will remain at the disposal of the partners that were involved in their development and will be exploited after the end of the project by providing services to the industry and by using them in research, development and education.
The optimized ship designs will be exploited by the partners involved in their development, whereas the new knowledge and understanding of the behaviour of various types of ships at low speed under adverse conditions are openly available to the scientific community for further exploitation through publications.
2.2 Exploitation Plan
The key project outcomes, their exploitation area, exploitation timeline and responsible partners are listed below.
Exploitable product(s) or measure(s): D1.1.1 Environmental data sets
Sector(s) of application: Ship design, Rule development, Education
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: DNV, IST, GL, EVFH
Exploitable product(s) or measure(s): D1.2.1 Accident data
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: NTUA, GL
Exploitable product(s) or measure(s): D1.3.1 Safety criteria
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: GL
Exploitable product(s) or measure(s): D2.1.1 Potential flow methods for seakeeping and stability in waves
Sector(s) of application: Ship design, Ship operation (routing, SEEMP), Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: IST, GL, NTUA, SU
Exploitable product(s) or measure(s): D2.2.1 Potential flow methods for manoeuvring in waves
Sector(s) of application: Ship design, Ship operation (routing, SEEMP), Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: DNV, GL, IST, NTUA, RINA, DTU
Exploitable product(s) or measure(s): D2.3.1 Potential flow methods for manoeuvring in confined waters
Sector(s) of application: Ship design, Ship operation (routing, SEEMP), Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: IST, SU
Exploitable product(s) or measure(s): D2.4.1 Field methods to determine ship hydrodynamic characteristics
Sector(s) of application: Ship design
Timetable for commercial use: In use
Owner and other partner(s) involved: TUB, VTT, IST, SU, UDE, GL
Exploitable product(s) or measure(s): D2.5.1 Field methods to determine ship hydrodynamic characteristics
Sector(s) of application: Ship design
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: UDE, IST, LR, NTUA
Exploitable product(s) or measure(s): D3.1.1 Innovative experimental techniques
Sector(s) of application: Ship design
Timetable for commercial use: In use
Owner and other partner(s) involved: MARINTEK, CEHIPAR, EVFH, TUB
Exploitable product(s) or measure(s): D3.1.2 Model test data
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: In use
Owner and other partner(s) involved: MARINTEK, CEHIPAR, EVFH, TUB
Exploitable product(s) or measure(s): D4.5.1 Comprehensive Assessment software tools
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: Finalisation of guidelines (April 2017)
Owner and other partner(s) involved: GL, UDE, DNV, NTUA, RINA
Exploitable product(s) or measure(s): D4.5.2 Simplified Assessment tools
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: Finalisation of guidelines (April 2017)
Owner and other partner(s) involved: GL
Exploitable product(s) or measure(s): D5.1.1 Integrated optimization platform
Sector(s) of application: Ship design
Timetable for commercial use: In use
Owner and other partner(s) involved: NTUA, IST, UDE, FSG, ULJ, VTT, DUT, NAP
Exploitable product(s) or measure(s): D5.3.1 Optimisation know-how to combine safety with EEDI requirements
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: In use
Owner and other partner(s) involved: NTUA
Exploitable product(s) or measure(s): D7.7.1 Revised guidelines for sufficient manoeuvrability in adverse conditions
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: October 2016 (submission to IMO) – April 2017 (finalisation)
Owner and other partner(s) involved: GL, LR, NTUA
3 SHOPERA-Dissemination Activities
Dissemination of the research output has been facilitated mainly through technical publications in international scientific journals, conferences and workshops. The consortium also facilitated the dissemination of the research output to a wider audience through a series of articles and presentations in public mass media. A project-specific web site has been created and is constantly updated and maintained by the coordinator during the elaboration of the project and for at least 3 years after the project’s end. A public area is maintained on the project’s web site, allowing free access to selected deliverables, reports and publications resulting from the elaboration of the project. To exchange views with external experts in ship design, hydrodynamics, safety and operation, shipowners, regulators and other stakeholders on hydrodynamic, design and regulatory aspects of norming manoeuvrability in adverse conditions, fine-tune the objectives of the project and the way ahead and, at the same time, facilitate acceptance of the project outcomes by the key stakeholders, four public workshops have been organised within the project.
3.1 Peer Reviewed Journal Papers
20 Papers, full list in D.7.6
3.2 Peer Reviewed Conference Papers
58 Papers, full list in D.7.6
3.3 Submissions to IMO
1. IMO MEPC (2014) EU Project “Energy Efficient Safe SHip OPERAtion” (SHOPERA), Paper MEPC 67/INF.14 submitted by Germany, Norway and United Kingdom
2. IMO (2016) Progress report of SHOPERA and JASNAOE projects for development of the revised minimum propulsion power Guidelines, Paper MEPC 69/INF.23 submitted by Denmark, Germany, Japan and Norway 12 February 2016
3. IMO (2016) Progress report of SHOPERA and Japan's projects and outline of draft revised Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions, Paper MEPC 70/5/20 submitted by Denmark, Germany and Japan
4. IMO (2016) Supplementary information on the draft revised Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions, Paper MEPC 70/INF.30 submitted by Denmark, Germany and Japan
5. IMO (2016) Results of research project "Energy Efficient Safe Ship Operation" (SHOPERA), Paper MEPC 70/INF.33 submitted by Denmark, Germany, Norway and Spain 19 August 2016
3.4 SHOPERA Presentations
5 submissions, full list in D.7.6
3.5 Mass media
The SHOPERA project was selected among EU funded projects for presentation at the EURONEWS channel. The video was produced by EURONEWS Science with films/interviews at ULJANIK shipyards, Croatia and CEHIPAR, Spain. The video was first transmitted by EURONEWS on Monday 26/09/2016 and broadcasted the whole week after. The program is now available in all the 13 languages on EURONEWS' website: http://www.euronews.com/programs/futuris/ and, on the EURONEWS' YouTube channels (http://eurone.ws/MMZbq and https://www.youtube.com/user/euronewsknowledge/videos).
3.6 First Public SHOPERA Workshop
The first workshop “Introduction of the Project to Key Stakeholders” was organised by GL with the assistance of NTUA on October 30, 2014, in Hamburg, to communicate the objectives of the project to the wider scientific and technical community and to the various stakeholders.
The first part of the workshop included presentations by external speakers, representing the majority of views of industry and experts at IMO (BIMCO, Greek and Danish Shipowners Associations, IACS, ITTC), industry research groups in the subject area (Common Research Ships), as well as overseas research views from Japan and India. Industry representatives underlined very high expectations about the outcome of the project regarding the future regulatory work on EEDI at IMO.
In the second part, SHOPERA partners presented challenges addressed by SHOPERA along with the state of work and the proposed way ahead. Discussions were lively and most valuable in the substance. The common feeling was that the workshop greatly contributed to the understanding of some controversial matters and clarified the view of how to proceed in the next few years, even if the subject is politically very tricky and scientifically very demanding.
The main output from this workshop was the awareness of the key stakeholders of the project and facilitation of the acceptance of the expected results. The feedback from the external participants has been used to refine the objectives of the project and shape the way ahead.
List of Presentations:
1. Jeppe Skovbakke Juhl (BIMCO) EEDI – Minimum power to ensure safe maneuvering in adverse conditions
2. George A. Gratsos (Hellenic Chamber of Shipping) Minimum power requirements for safe navigation
3. Hans Otto Kristensen (Danish Shipowners’ Association) Some thoughts about minimum power for safe manoeuvring in adverse weather conditions
4. Torsten Mundt (DNV GL) IACS contribution on the minimum required power issue: A retrospection
5. Frans Quadvlieg (Cooperative Research Ships, Group on Manoeuvrability in Waves) Manoeuvring in adverse weather
6. Reint Dallinga, Olav Rognebakke (Cooperative Research Ships, Added Resistance in Waves Group) Added resistance - physical insights. Cooperative Research Ships JIP results
7. Masaru Tsujimoto (National Maritime Research Institute) Japan's research activities on minimum propulsion power requirement - Hydrodynamic approach
8. Apurba Ranjan Kar (Indian Register of Shipping) Ship Manoeuvrability: An overview of ongoing studies by Indian Register of Shipping
9. Anton Minchev (FORCE Technology) Manoeuvring aspects at ultra-slow speeds
10. Apostolos Papanikolaou (SHOPERA, NTUA) Introduction: Overview SHOPERA
11. Elzbieta M. Bitner-Gregersen (SHOPERA, DNVGL) Met-ocean description
12. Koimtzoglou A., Louzis K., Eliopoulou E., Ventikos N.P. (SHOPERA, NTUA) Identification of ships and risk analysis of relevant marine accidents
13. Vladimir Shigunov (SHOPERA, DNVGL) Manoeuvrability criteria
14. Carlos Guedes Soares (SHOPERA, IST): Development and Refinement of Numerical Hydrodynamic Tools
15. Ould El Moctar (SHOPERA, UDE): Numerical Investigation of Added Resistance in Waves
16. Florian Sprenger (SHOPERA, MRTK) Experimental Studies
3.7 Second Public SHOPERA Workshop
The second public SHOPERA workshop was organized by IST with the assistance of NTUA on October 15, 2015 in Lisbon. The aim of this workshop was to communicate the findings of the first two years of the elaboration of the project to the wider scientific and technical community as well as to the various stakeholders and to obtain valuable feedback from the external participants regarding the set objectives and the procedures adopted in order to meet these objectives. Besides representatives of the SHOPERA consortium, there were also presenters and participants form outside the consortium and members of the SHOPERA Advisory committee, such as the International Maritime Organisation (IMO), the European Maritime Safety Agency (EMSA), the Ministry of Land, Infrastructure, Transport and Tourism of Japan, flag administrations (Netherlands) and the Association of the Netherlands Shipbuilders.
During the morning session of the workshop, external experts and SHOPERA partners addressed topics related with the general SHOPERA objectives, such us regulatory work in IMO related to the minimum powering requirements of ships in relation with the EEDI requirements, and prediction of added resistance of ships in waves. In addition, the project coordinator, Apostolos Papanikolaou presented an overview of the objectives and rational of the SHOPERA project, its workpackages and current status of work.
During the afternoon session, the progress of work of workpackages 1, 2, 3 and 4 was presented. WP1 was presented by Dr. E. Bitner-Gregersen (Task 1.1 Environmental Conditions) and Dr. Vladimir Shigunov (Criteria and Assessment Framework, Task 1.3). Then Prof. Carlos Guedes Soares and Prof. Ould el Moctar provided an overview of the software tools for the assessment of the hydrodynamic performance of ships with respect to their manoeuvring characteristics and added resistance in waves that are refined and extended in WP2 and their validation, carried out in WP4, using experimental results derived in WP3. Finally, the large program of tank tests, carried out in WP3 by MARINTEK, CEHIPAR, EVFH and TUB was presented by Dr. Florian Sprenger and Messrs. Adolfo Maron, Thibaut Van Zwijnsvoorde and Antonio Lengwinat respectively.
List of presentations
1. Masao Yamasaki, International Maritime Organisation (IMO) Marine Environment Division, Interim Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions.
2. Takahiro Kijima, Director for Environment Policy, Ministry of Land, Infrastructure, Transport and Tourism, JAPAN, Revision of the Interim Minimum Power Guidelines, based on the project results such as SHOPERA and JASNAOE.
3. Torsten Mundt, DNVGL, The “min. req. Power issue” and the desire to manoeuvre out.
4. Reint Dallinga, MARIN & CRS, Netherlands, Added resistance from a linear theory.
5. Masaru Tsujimoto, NMRI, Japan, Progress of Japan's Research Activities on Minimum Propulsion Power Requirement.
6. Apostolos Papanikolaou (NTUA), Introduction-Overview SHOPERA
7. Elzbieta Bitner-Gregersen (DNVGL), Environmental Conditions
8. Vladimir Shigunov (DNVGL), Criteria and Assessment Framework
9. Carlos Guedes Soares (IST), O. El Moctar (UDE), Development and Refinement of Numerical Hydrodynamic Tools
10. Florian. Sprenger (MRTK) and other Exp. Tanks representatives, Experimental Studies
3.8 Third Public SHOPERA Workshop
The third public SHOPERA workshop was hosted by LR and jointly organised by LR, NTUA and ITTC Manoeuvring Committee on April 14, 2016 in London with representatives from the ITTC Seakeeping, Stability and Performance Committees. The aim of this workshop was to communicate the findings from the elaboration of the project to the wider scientific and technical community, to enhance collaboration of the SHOPERA partners with other research teams working on the same or similar research topics in Japan, Korea, The Netherlands as well as with the ITTC Manoeuvring Committee and Seakeeping Committee and to obtain valuable feedback from the external participants regarding the set objectives and the procedures adopted in order to meet these objectives.
Along with representatives of the SHOPERA consortium, there were also presenters and participants from the ITTC Committees for Manoeuvring, Seakeeping, Stability and Performance, members of the SHOPERA Advisory committee and other external experts. The objectives of the workshop were presented by Apostolos Papanikolaou, NTUA.
List of presentations
1. Vladimir Shigunov (DNVGL), SHOPERA: Criteria, Assessment Framework, Methods
2. Hironori Yasukawa, (Hiroshima University), Japanese R & D Project on Manoeuvring in Adverse Condition and Minimum Power Requirement of Ships.
3. Yeon Gyu Kim, Dong Jin Yeo (KRISO), Sang Hyun Kim (Inha Univ.) Research Activities on Manoeuvring in Waves in Korea.
4. Pierre-Emmanuel Guillerm (Ecole Centrale de Nantes), How to develop manoeuvring in waves standard for model tests and numerical simulation methods.
5. Yonghwan Kim (Seoul National University), Seakeeping Analysis Coupled with Manoeuvring Problem.
6. Gregory Grigoropoulos (NTUA), Towards more rational guidelines to determine minimum propulsion power for Safe Operation under adverse Weather Conditions
3.9 Fourth Public SHOPERA Workshop
The fourth public SHOPERA workshop was hosted and organised by NTUA on September 28, 2016 in Athens. The aim of this workshop was to provide the overall presentation of the elaboration of the project, with emphasis on the set objectives, adopted procedures towards the objectives, major achievements, key results, collaboration with similar studies in Japan and the Netherlands, conclusions and recommendations. In particular, the developed new guidelines for the required minimum propulsion power and steering performance of various types of ships to maintain manoeuvrability under adverse conditions were presented and discussed with the scientific community and key stakeholders. The main output from this workshop was the wide awareness of the key stakeholders, particularly IMO members, of the proposed updated guideline, and better acceptance of the project results, on the one hand, and the feedback received at the workshop on the other hand.
The first part of the workshop was devoted to presentations by SHOPERA partners presenting the major achievements of the last 12 months of the elaboration of the project, while the second part included presentations by representatives of the SHOPERA Advisory Committee and other invited external speakers, representing views of the industry. The workshop was closed by Prof. Apostolos Papanikolaou (NTUA) who discussed the submissions to IMO that resulted from the elaboration of the SHOPERA project as well as from the collaboration with the Japanese R & D Project on Maneuvering in Adverse Condition and Minimum Power Requirement of Ships.
List of presentations
1. Vladimir Shigunov (DNVGL), SHOPERA: Criteria, Assessment Framework and Guidelines.
2. George Zaraphonitis (NTUA), SHOPERA WP5: Optimization studies.
3. Martio Jussi (VTT), Detailed optimization studies in WP5 by VTT
4. Reddy Devalapalli (LR), WP6: Application / Case Studies.
5. Apostolos Papanikolaou (NTUA), Main Achievements.
6. Hironori Yasukawa (Hiroshima Univ.), Japanese R & D Project on Maneuvering in Adverse Condition and Minimum Power Requirement of Ships.
7. Johan de Jong (MARIN), MCRAW JIP, Minimum Power Requirements of Dutch Low-Power Full-Block Ships.
8. Sander de Heijer (Netherlands Maritime Technology), Study on minimum power requirements (MacRAW), submitted to IMO by the Netherlands.
9. Kim Rene Hansen (MAN Diesel & Turbo), IMO EEDI and Minimum Propulsion Power from an Engine Designer’s Point of View.
10. Torsten Mundt (GL) & Apostolos Papanikolaou (NTUA), Submissions to IMO, way ahead.
List of Websites:
http://shopera.org
The 2012 guidelines on the method of calculation of the attained Energy Efficiency Design Index (EEDI) for new ships (MEPC.212(63)) represent a major step forward in implementing the REGULATIONS ON ENERGY EFFICIENCY OF SHIPS (resolution MEPC.203(62)). There are, however, serious concerns regarding the sufficiency of propulsion power and of steering devices to maintain the manoeuvrability of ships in adverse conditions, assuming that the ship marginally passes the relevant EEDI criterion. This gave reason for additional considerations and studies at IMO (MEPC 64/4/13 and MEPC 64/INF7). Furthermore, whereas present EEDI regulations concern the limitation of gas emissions by ship operation, what may be understood as a new constraint in ship design and operation, it is urgent to look holistically into integrated ship design and operational environments and implement multi-objective optimization procedures, looking for the right balance between ship’s efficiency and economy, safety and greenness.
To this end, the SHOPERA consortium was put together representing the whole spectrum of stakeholders in the maritime industry and with superior expertise and scientific know-how in hydrodynamic tools development, validation of software tools, experimental techniques and expertise in ship design and international maritime rule making. Project SHOPERA addressed the above raised, urgent regulatory issues by:
• Further development and refinement of existing high fidelity, hydrodynamic simulation software tools for the efficient analysis of the seakeeping and manoeuvring performance and safety of ships in complex environmental and/or adverse sea/weather conditions (including the consideration of winds and extreme sea events). The efficiency of steering devices and the effect of restricted waterways in port areas have been considered. Extensive use has been made of state-of-the-art numerical simulation tools available to the consortium, which have been adapted to the needs of the project and have been supported by a comprehensive model testing programme.
• Performing seakeeping/manoeuvring model tests in combined seaway/wind environment by use of a series of prototypes of different ship types (tanker, containership, RoRo ferry), to provide the required basis for the validation of employed software tools and the results obtained by numerical simulations.
• Integrating validated software tools for the hydrodynamic/manoeuvrability assessment of ships in adverse seaway/weather conditions into ship design software platforms and set-up of optimization procedures in which ship’s performance is assessed holistically, thus, looking for the minimum powering requirement to ensure safe ship operation in adverse seaway/weather conditions, while keeping the right balance between ship economy, efficiency and safety of the ship and the marine/air environment.
• Putting together design teams that comprise designers, shipyards, owners and class societies to conduct investigations on the impact of the proposed new guidelines for the assessment of the minimum propulsion power to maintain manoeuvrability in adverse conditions (MEPC 64/4/13) on the design and operational characteristics of various ship types.
• Developing new guidelines for the required minimum propulsion power and steering performance to maintain manoeuvrability of ships in adverse environmental conditions.
• Establishing minimum propulsion power ensuring safe operation for various types of ships.
• Preparing and submitting to IMO a summary of results and recommendations for further consideration.
Project Context and Objectives:
The 2012 Guidelines on the method of calculation of the attained Energy Efficiency Design Index (EEDI) for new ships, resolution MEPC.212(63) represent a major step forward in implementing the regulations on energy efficiency of ships, resolution MEPC. 203(62). However, concerns had been expressed regarding sufficiency of propulsion and steering abilities of ships to maintain their manoeuvrability in adverse conditions if the EEDI requirements are achieved by simple reduction of the installed engine power. This gave a reason for additional considerations and studies by IACS, which served as a basis for the Interim Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions, MSC-MEPC.2/Circ.11 (2012), which were updated in annex 1 to document MEPC 65/4/3 and subsequently adopted by resolution MEPC.232(65) and was further updated by resolutions MEPC.255(67) and MEPC.262(68).
To address these challenges, several research projects were initiated at international level, among them the 3 years research project SHOPERA (Energy Efficient Safe SHip OPERAtion, www.shopera.org 2013-2016), funded by the European Commission in the frame of FP7 and representing the whole spectrum of the European maritime industry, including classification societies, universities, research organisations, model basins, ship designers, shipyards and ship operators.
Scenarios of adverse conditions and manoeuvrability criteria
In SHOPERA, a review of existing regulations, interviews of ship masters and analysis of accident statistics and detailed accident investigations were conducted to identify relevant scenarios, criteria and corresponding standards (environmental conditions) which should be employed to assess the sufficiency of propulsion and steering systems of ships for manoeuvrability in adverse conditions. Three scenarios of adverse conditions were identified, in which manoeuvrability characteristics of ships are challenged in different way:
1. Weather-vaning in the open sea, which imposes less strict requirements on the manoeuvring, albeit in more severe weather conditions. Arguably, the inability to manoeuvre in the open sea should not lead to a loss of the ship anyway, because safety of ships, which are unable to manoeuvre and are drifting in beam sea, should be ensured by the Severe Wind and Rolling Criterion (Weather Criterion), MSC.267(85).
2. Manoeuvring in coastal waters imposes strong functional requirements on ship’s manoeuvrability: in principle, any manoeuvre may be required, perhaps in a complex navigational situation and in a seaway from a direction unfavourable for manoeuvring. However, the relevant weather conditions are rather moderate, because in an increasing storm, ship masters timely search for shelter or leave to the open sea. Therefore, this scenario requires both a sufficient steering ability, to avoid grounding, collision or contact, in seaway headings not always favourable for steering, and a sufficient propulsion ability, to enable timely leaving coastal area.
3. Manoeuvring at limited speed in restricted areas, typically during approaching to or entering ports, where the ship’s speed is restricted due to navigational requirements. Because this scenario does not lead to any restriction on the installed minimum power, it is not considered here.
Correspondingly, three criteria are proposed to assess the sufficiency of propulsion and steering systems of ships for manoeuvrability in adverse conditions: Weather-vaning ability, i.e. the ability of the ship to change and keep heading in head to bow-quartering waves; Steering ability, i.e. the ship’s ability to perform any manoeuvre in seaway from any direction; and Propulsion ability, understood as the ship’s ability to maintain some speed (proposal: 6 knots) in seaway from any direction.
Assessment framework and evaluation methods
Compliance with the IMO Manoeuvrability Standards, MSC.137(76) is demonstrated in full-scale calm water sea trials; full-scale trials are, however, impossible to conduct for the evaluation of manoeuvrability in adverse conditions. Evaluation of the proposed criteria in transient model experiments with self-propelled models in simulated irregular waves and wind, or with corresponding numerical simulations, is presently unfeasible for regulatory purposes. The assessment procedures proposed by SHOPERA are based on a combination of freely chosen evaluation methods (experimental, numerical or empirical) for different components of the assessment procedure, and a combination of these components in a simple assessment procedure. The assessment procedure itself can also be freely chosen between three complexity levels:
1. Comprehensive Assessment, allows the best accuracy. Still, the designer can choose between numerical, experimental or empirical methods, which should, however, all ensure satisfactory accuracy of results.
2. A less complex, Simplified Assessment, which still takes into account the physics of the problem, but uses a reduced number of assessment scenarios and reduced complexity of equations; this assessment also allows the choice between experimental, numerical or empirical methods to evaluate different elements of the procedure and has the complexity of a spreadsheet calculation.
3. The simplest assessment procedure, a Sufficient Propulsion and Steering Ability Check, is based on pure empirical / statistical formulae, which define the required installed power as a function of main ship parameters and require few simple pocket computer calculations.
Both the Comprehensive and Simplified Assessments require the definition of time-average forces due to waves including added resistance, wind forces, calm-water reactions, rudder-induced forces and propeller characteristics. According to the SHOPERA approach, these contributions can be defined separately, with different methods (experimental, numerical or empirical) as necessary. According to the performed sensitivity analysis, the most important contributions for the propulsion and steering in adverse conditions are the time-averaged surge and sway forces due to waves, the surge and sway force and yaw moment due to calm-water reactions and the lateral rudder force. Especially important for practical approval is the availability of suitable empirical methods for all elements of the assessment procedure. SHOPERA has undertaken a thorough validation of empirical methods for calm-water reactions, wind forces and rudder forces, including bi-lateral benchmarking with the JASNOE project and concluded that such methods are in principle available for practical use, if used within their applicability limits, with the exception of the time-average wave forces.
The development and validation of numerical and empirical methods for the time-average wave forces, including added resistance, was one of the most important research issues of SHOPERA and was addressed as following:
1. Extensive model tests were performed for three ship types (a 14,000 TEU container ship, a standard VLCC tanker and a small RoPax) in over 1,300 conditions, including various draughts, water depths, forward speeds and wave directions, lengths and heights to generate a validation database for numerical and empirical methods.
2. Several evaluation methods were developed and validated, ranging from high-fidelity CFD methods to 3D panel codes and simple empirical formulae.
3. To evaluate the availability of methods that can be used in practical assessment, SHOPERA conducted an international benchmark study of numerical and empirical methods. The results showed a notable progress in the development of both numerical and empirical methods in the last years and availability, in principle, of numerical methods for practical regulatory purposes, if their application is properly verified.
A critical aspect of manoeuvrability of ships in adverse conditions is the correct modelling of the main engine and the propulsion system under high load in adverse conditions. Frequently used assumptions of constant torque, constant power or constant rotation speed may lead to misleadingly optimistic predictions. In SHOPERA, output limits of diesel engines under high load were investigated, and recommendations for the practical assessment were provided.
Case studies of existing fleet and optimization exercises
The aim of the case studies and optimization exercises carried out by SHOPERA was, first, to systematically compare the proposed criteria with each other and to identify possible redundancies or loopholes. The studies concerned bulk carriers, tankers, general cargo vessels, container ships, LNG and gas carriers, reefers, RoRo cargo vessels, RoPax vessels and cruise vessels, chosen within the whole range of representative sizes and installed power.
The systematic comparison between the three proposed criteria shows that the marginal wave height (i.e. maximum wave height, up to which the vessel can fulfil the respective criterion) according to the weather-vaning criterion is very well correlated with the marginal wave height according to the propulsion criterion, which means that one of these criteria may be redundant. The marginal wave heights according to the propulsion and steering criteria also correlate with each other to some degree.
Results from the conducted case studied show that the marginal wave heights are ship size-dependent for all three criteria: larger vessels are able to satisfy the proposed criteria at greater wave heights than smaller vessels. Whether the standard wave height should also be ship size-dependent, however, may be a subject of discussion with all interested stakeholders. The arguments for ship size-dependent standard wave height are:
1. The dependency of the marginal wave heights on the ship size was revealed from the application of manoeuvrability criteria to existing vessels, thus it reflects existing design and operational practices.
2. Consequences of accidents are generally greater for larger vessels, thus the frequency of accidents implied by the standard wave heights should be for them lower.
3. The impact of seaway on ship’s motions and manoeuvrability in waves diminishes with increasing ship size.
Results show also that the marginal wave heights differ substantially, between ship types. Bulk carriers and tankers show very similar marginal wave heights, which are lower to significantly lower than the marginal wave heights of other vessel types; this is mostly due to their lower specific installed power compared to other vessel types, like container ships, and due to advanced propulsion and steering concepts typical for other vessel types, like twin screw, diesel-electric propulsion, controllable pitch propellers or pods.
Concerning possible conflicts between the requirements to safe manoeuvring in adverse conditions and the strengthening of EEDI requirements, especially at the later Phases of EEDI implementation, the following results were obtained:
1. If existing vessels, satisfying requirements of a certain Phase of EEDI implementation, are compared across all ship types, bulk carriers and tankers show remarkably similar marginal wave heights, which are also lowest among all ship types.
2. If vessels are selected that satisfy the proposed by SHOPERA criteria for manoeuvrability in adverse conditions at the standard wave heights according to the 2013 Interim Guidelines, bulk carriers and tankers seem to marginally fulfil the requirements of Phase 2 EEDI implementation, but not of Phase 3, whereas vessels of other types are able to satisfy or even over-satisfy the requirements of Phase 3.
3. For EEDI Phase 3-compliant bulk carriers and tankers to pass the proposed manoeuvrability requirements, the standard wave heights need to be lowered compared to those in the 2013 Interim Guidelines.
4. The conducted parametric optimisation studies for RoPax ships revealed ample manoeuvrability margins in adverse conditions, but problems of compliance with the EEDI Phase 3 requirements, whereas the Phase 2 requirements appear marginally fulfilled. This finding is also confirmed by other studies of the European passenger shipping industry and should be an additional subject of discussion among all interested stakeholders.
Dissemination of results
A large number of papers and conference presentations were produced by the SHOPERA consortium; a list of selected papers is given in the Annex. Additionally, four public workshops were organized by the project for open discussion or results and exchange of opinions with the maritime industry, other projects and maritime safety stakeholders.
Submissions to IMO
SHOPERA had a close collaboration with a research project of the Japanese maritime industry, coordinated by the Japan Society of Naval Architects and Ocean Engineers (JASNOE) with the aim to exchange information about the progress of work of both projects and ultimately to prepare and submit a joint proposal for the draft revised Guidelines to MEPC 70/71. The joint proposal of the two projects has being submitted with the document MEPC 70/5/20, with supplementary information submitted in a series of INF documents.
Independently of the above joint submission with Japan, which refers to tankers, bulk carriers and combination carriers, an additional document (MEPC 70-INF.33) was submitted, aiming to inform all interested stakeholders about the whole range of results of the project SHOPERA, which covered all types of ships affected by the EEDI framework.
Project Results:
1 Introduction to project SHOPERA – Objectives
The introduction of the Energy Efficiency Design Index (EEDI) was a major step towards improving energy efficiency and reducing greenhouse gas (GHG) emissions of shipping. It has also raised concerns that some ship designers might choose to lower the installed power to achieve EEDI requirements instead of introducing innovative propulsion concepts. This can lead to insufficient propulsion and steering abilities of ships to maintain manoeuvrability under adverse weather conditions, thus to a serious ship safety problem. Work carried out by IACS highlighted this issue and led to the development of first draft guidelines for consideration by IMO in 2011, IMO MEPC 62/5/19 and MEPC 62/INF.21 which resulted later in 2012 Interim Guidelines, see IMO MEPC 64/4/13, MEPC 64/INF.7 updated in 2013 in Res. MEPC.232 (65). Even though the 2013 Interim Guidelines prevent irrational reduction of installed power, their sufficiency was disputed, especially concerning the definition of the minimum power lines, adversity of the weather conditions to be considered in the assessment and removal of comprehensive assessment. Several research initiatives in various European countries as well as Japan and the Republic of Korea, aiming at updating these guidelines (see, e.g. IMO submissions MSC 93/21/5 and MSC 93/INF.13 by Greece, MEPC 67/INF.22 by Japan, MEPC 67/4/16 by Denmark, Japan and the Republic of Korea, and MEPC 67/INF.14 by Germany, Norway and the United Kingdom) were started and are expected to lead to the rationalization of the interim guidelines.
To address the above challenges by in-depth research, the EU funded project SHOPERA (Energy Efficient Safe SHip OPERAtion) (2013-2016) was launched in October 2013, aiming to develop suitable numerical methods and software tools and to conduct systematic case studies, which will enable the development of improved guidelines and their submission for consideration to IMO. A strong European RTD consortium was formed, representing the whole spectrum of the European maritime industry, including classification societies, universities, research organisations and model basins, ship designers, shipyards and ship operators. The project's objectives were to:
• Develop criteria and corresponding environmental conditions for the assessment of the sufficiency of propulsion and steering systems of ships for manoeuvrability in adverse conditions, including open sea, coastal waters and restricted areas.
• Develop and adapt existing high fidelity hydrodynamic simulation software tools for the efficient analysis of the seakeeping and manoeuvring performance of ships in complex environmental and adverse weather conditions.
• Perform seakeeping and manoeuvring model tests in seaway by using a series of prototypes of different ship types to provide the required basis for the validation of employed software tools.
• Develop simplified assessment procedures, to the extent feasible, which should enable a quick assessment of the safety margins of ship designs with respect to the minimum propulsion and steering requirements for manoeuvrability in adverse weather conditions.
• Integrate validated methods and software tools for manoeuvrability assessment of ships in adverse weather conditions into a ship design software platform and combine it with a multi-objective optimization procedure, targeting sufficient propulsion and steering requirements for safe ship operation in adverse weather conditions while keeping the right balance between ship economy, efficiency and safety.
• Conduct investigations of the impact of the proposed requirements on the propulsion and steering abilities of ships for manoeuvrability in adverse conditions on the design and operational characteristics of various ship types by design teams comprising designers, shipyards, ship owners, classification societies, research institutes and universities. The impact on EEDI was also investigated by implementation of the developed holistic optimisation procedure in a series of case studies.
2 Scenarios and Criteria
2.1 Existing Regulations
Manoeuvrability of ships is presently normed by IMO Standards for Ship Manoeuvrability, IMO (2002), which address turning, initial turning, yaw checking, course keeping and emergency stopping abilities, evaluated in simple standard manoeuvres in calm water. These Standards have been often criticized for not addressing ship manoeuvring characteristics at low speed, in restricted areas and in adverse weather conditions; the importance of the latter increased after the introduction of EEDI. In EE-WG 1/4 (2010), IACS put together the requirements of classification societies related to the redundancy or duplication of the propulsion system to indicate relevant criteria and environmental conditions for steering and propulsion in adverse weather conditions. Studies by IACS on minimum power requirements for manoeuvrability in adverse weather conditions started with analysis of functional requirements to manoeuvrability in the open sea and coastal areas, MEPC 62/5/19 (2011) and 62/INF.21 (2011), concluding that manoeuvring in coastal waters is more challenging than in the open sea; the resulting criteria for ship propulsion and steering abilities were formulated in MEPC 64/4/13 (2012) and 64/INF.7 (2012): the ship should be able, in seaway from any direction, to (1) keep course and (2) keep advance speed of at least 4.0 knots. The corresponding weather conditions are not too severe, because ship masters do not stay near the coast in an increasing storm and either search for a shelter or leave to the open sea and take a position with enough room for drifting. The standard environmental conditions defined by IACS (wind speed 15.7 m/s at significant wave height 4.0 m for ships with Lpp=200 m to 19.0 m/s and 5.5 m, respectively, for Lpp=250 m and greater) were derived by benchmarking of tankers, bulk carriers and container ships in the EEDI database against these two criteria.
2.2 Accidents
In SHOPERA, available detailed investigations of accidents related to insufficient manoeuvrability in adverse weather conditions were studied. Summarising, as the most frequent cause of heavy weather-related grounding accidents is waiting at anchor in heavy weather and too late starting of the engine. In several accidents, vessels were not able to move away from the coast or turn into seaway despite full engine power applied. Regarding adverse weather conditions related to accidents, we may recall the well-known statistics of the HARDER project indicating that more than 80% of the collisions happened at significant wave height below 2 m, whereas significant wave heights exceeding 4 m were practically not recorded. Similar results were obtained from a comprehensive statistical analysis of ship accidents in adverse sea conditions, conducted in SHOPERA. From these statistics it is evident that:
1. The most vulnerable ship types with respect to navigational accidents in adverse conditions are general cargo ships, followed by Ro-Ro ferries, bulk carriers and tankers.
2. For these ship types, the accident location varies between port areas (almost exclusively for Ro-Ro ferries) and generally limited waters, such as port and restricted waters (for general cargo vessels and bulkers); for tankers, we observe some increased sensitivity in route (open seas) conditions.
3. Inclusion in the statistical analysis of very rare abnormal weather events (hurricanes, typhoons etc.) does not significantly alter the statistics.
4. Observed mean wind speeds of about 10 m/s and significant wave heights of 1.49 m are remarkably low; this also applies to the statistical quartiles, with lower values observed for collisions and groundings and the highest recorded values related to contacts.
5. There is a statistically significant difference in mean wave height between ship types, which means that some ship types are more affected by wave height than the others.
6. The calculated accident rates, related to the Fleet at Risk, are in the range of 10-5 to 10-3 accidents per ship per year, i.e. by one order of magnitude lower than accident rates calculated in Formal Safety Assessments, which do not consider the prevailing weather conditions.
7. Among the three navigational accident types, groundings exhibit the highest rates for cargo carrying ships in general, whereas for Ro-Ro ships contacts are associated with the highest rates.
8. Based on the available information, hull damage was selected as a main consequence variable for the risk analysis. The collected data were organized in categories of increasing level of severity, considering their qualitative nature.
9. The risk analysis implemented the concept of risk triplets defined by Scenario, Frequency, and Consequence, and enabled the generation of three distinct types of risk-related curves, based on accident frequencies per ship type, per ship type and size class, and per ship and accident type.
10. Overall, groundings and contacts in heavy weather conditions are the accident types with the highest risk across all ship types.
11. Comparison of risk levels between ship types shows that Ro-Ro Ferries and RoRo Cargo ships exhibit high risk values due to high accident frequency and medium level of consequences, whereas Gas Carriers, Tankers and Bulk Carriers exhibit high risk values due to the observed high level of accident consequences.
2.3 Interviews of Ship Masters
Interviews of masters of about 50 container ships, bulk carriers and tankers conducted in the projects PerSee and SHOPERA indicate that in the open sea, the captain usually has more freedom and can decide what severity of weather conditions is acceptable for his ship, depending on the freeboard, cargo, stability and propulsion and steering characteristics of the vessel. On the other hand, when caught in most violent storms, steering against seaway may be impossible for any vessel; in such circumstances, drifting with seaway was considered as an acceptable option for a limited time if there is enough room for drifting. However, the available power is important for escaping the storm and bringing the ship into safe weather conditions. Manoeuvring in coastal areas was reported as more challenging than manoeuvring in the open sea, because, in principle, any manoeuvre, sometimes in unfavourable seaway direction with respect to the ship, may be required. Environmental conditions are, however, less severe than in the open sea, because ship masters do not remain near the coast in a growing storm, but either search for shelter or leave to the open sea. As relevant manoeuvring problems, steering problems were mentioned in the interviews insignificantly more often than propulsion problems (83% vs. 60% of cases, respectively); insufficient engine power was mentioned more frequently for bulk carriers and tankers, whereas insufficient rudder capability more frequently for container vessels. As a very specific manoeuvring problem in restricted waters, manoeuvrability at limited speed (due to navigational restrictions, e.g. during approaching ports) was mentioned, in strong wind and, sometimes, strong current, but usually without large waves because of protected areas.
2.4 Proposal for Scenarios and Criteria
Based on the above results, Shigunov and Papanikolaou (2014) proposed three scenarios, in which steering and propulsion abilities of ships are challenged in a different way and which require, therefore, specific criteria: open sea, coastal areas and restricted areas at limited speed. For the open sea, the ability of ship to weather-vane, i.e. keep heading in head to bow-quartering seaway, was proposed as a criterion. Regarding corresponding environmental conditions, it was noted that none of the existing ships can steer against waves and wind in most severe possible storms, therefore, benchmarking of the existing world fleet with respect to the weather-vaning criterion was proposed to define the standard wave height. For the coastal areas, two criteria were proposed: the ability of the ship to perform any manoeuvre and the ability to maintain some speed over ground to enable leaving the coastal area before the storm escalates; due to navigational restrictions, both criteria should be possible to fulfil in seaway from any direction. The corresponding environmental conditions are less severe than in the open sea and should also be defined by benchmarking of existing ships against these criteria. Manoeuvrability at limited speed in restricted areas refers to situations where the ship master has to reduce the applied engine power (and thus forward speed) significantly below available power because of navigational restrictions, e.g. during approaching to or entering ports, navigation in channels and rivers etc. Because full available power cannot be applied in this scenario, the corresponding manoeuvrability criteria will not impose any restrictions on minimum propulsion power, thus this scenario is not considered here. Based on this, SHOPERA proposed the following criteria for manoeuvrability in adverse weather conditions: weather vaning ability in heavy weather in the open sea and steering and propulsion abilities in increasing storm in coastal areas.
In the practical assessment, weather-vaning ability was treated in a simplified way, as the ability of the ship to keep position in bow to bow-quartering seaway; this simplification follows from the observation, confirmed by model tests, that the ship will not be able to keep heading under the action of environmental forces if the forward speed is not sufficiently large, because of significantly reduced manoeuvring reactions on the hull and steering force on the rudder.
The steering ability in increasing storm in coastal areas is understood as the ability of the ship to perform any manoeuvre in seaway from any direction. An equivalent, but easier to verify in practice criterion is proposed, that the ship should be able to start or continue course change in seaway from any direction. This formulation should be distinguished from the traditional course-keeping problem: the steering ability is understood here as the ability of the steering system to overcome environmental forces and start (or continue) course change during an arbitrary manoeuvre (i.e. capability of the steering system); for this ability, it does not matter whether each intermediate state during manoeuvre is stable or not, thus the stability of the ship on each particular course is not addressed, whereas the traditional definition of course-keeping addresses stability of straightforward motion. Note that the proposed criterion does not exclude the ship’s ability to perform also straightforward motion (which is one of “all” required manoeuvres): even if a ship is directionally unstable on some course, it will still be able to follow this course using rudder for continuous course corrections.
The propulsion ability in increasing storm in coastal areas ensures that the ship is able to leave coastal area in a sufficient time before the storm escalates. As the minimum required advance speed, 6.0 knots was chosen by SHOPERA, instead of 4.0 knots used in 2013 Interim Guidelines, to take into account possibly strong currents in coastal areas. The corresponding environmental conditions for these three criteria need to be defined by benchmarking of existing vessels.
2.5 Environmental Conditions
Wave Height
The existing 2013 Interim Guidelines do not consider manoeuvring criteria for the open sea. SHOPERA has introduced the weather-vaning criterion for the open sea, which requires corresponding standard environmental conditions. A straightforward choice of the North Atlantic scatter table, IACS (2001), is not fully suitable to define the weather conditions to be used with the weather-vaning criterion as although this scatter table is based on visual onboard observations, BMT (1986), it is unknown whether ships were able to manoeuvre in the reported sea states and what manoeuvres they were able to perform; in particular, it is unknown whether existing ships can or cannot weather-vane in such sea states. Finally, safety of a ship that is not able to weather-vane in a certain sea state in the open sea and thus has to drift in beam seaway will still be ensured due to the IMO Severe Wind and Rolling Criterion (Weather Criterion), IMO (2008). Therefore, benchmarking of the existing fleet with respect to the weather-vaning criterion appears as the most rational way to define the standard wave height: the standard wave heights should be defined in such a way that the majority of the existing vessels fulfil the related requirements, taking into account that the present safety level with respect to manoeuvrability-related accidents in heavy weather is satisfactory, Ventikos et al. (2014).
For increasing storm in coastal waters, the 2013 Interim Guidelines use two criteria, course keeping and advance speed. The corresponding standard wave heights were defined by benchmarking of tankers, bulk carriers and container ships in the EEDI database against these two criteria, which led to the significant wave height of 4.0 m and wind speed of 15.7 m/s for ships with Lpp=200 m and significant wave height of 5.5 m, and wind speed of 19.0 m/s for Lpp=250 m and greater, with a linear interpolation of wave height and wind speed for Lpp between 200 m and 250 m. SHOPERA aimed at validation of the proposed weather conditions with respect to available measurements and other data sources. The problem is, on the one hand, that there are no fully unified recommendations for the seaway parameters for coastal areas. Second, met-ocean climate of coastal areas strongly depends on the region and local bathymetry, which maybe difficult to fully account for in regulations.
The coastal areas considered by SHOPERA included: access channel to the port of Antwerp, Scottish waters and the port of Leixões, Bitner-Gregersen et al. (2016). The 40 nautical mile long access channel to the port of Antwerp is dredged in a rather protected sand banks area, whereas both the Scottish coastal waters and the port of Leixões are not as protected. Correspondingly, the former area indicates milder wave heights than the latter two. Note also that the observations for these three areas were not uniformed, they had different duration. The maximum observed significant wave heights occurred with different probabilities in these areas and had different values; for the access channel to the port of Antwerp, Scottish waters and the port of Leixões of about 4.5 m, 5.5 m and 6.0 m, respectively.
Noting that the available data refer to fixed locations, whereas ship masters do not remain on the same position near the coast in a growing storm, but either search for shelter or leave to the open sea, SHOPERA has used also several other sources to estimate rationally the required standard wave heights. Statistics of the weather conditions during manoeuvring-related accidents in adverse weather conditions, Ventikos et al. (2014), shows remarkably mild environmental conditions during accidents (mean wind speed of about 10 m/s and mean significant wave height about 1.5 m), which agrees with the earlier statistics from the HARDER project, indicating significant wave height below 2.0 m in 80% of collisions and absence of collisions at significant wave heights greater than 4.0 m. The study by IACS, EE-WG 1/4 (2010), also identifies rather mild standard wave heights for weather-vaning (wind speed up to 21 m/s and significant wave height up to 5.4 m) and advance speed (wind force up to Bft 8 at 6.0 knots advance speed) requirements. On the other hand, maximum significant wave heights and wind speeds during manoeuvrability-related accidents achieve, according to SHOPERA statistics, in rare cases 7.0 m and 20 m/s, respectively. Detailed accident reports indicate wind force up to Bft 10 (in excess of 23 m/s) and significant wave heights above 6.0 m during few accidents in coastal areas. However, the well-documented case ATSB (2008), where the significant wave height exceeded 6.0 m, clearly indicates unacceptably long waiting of the vessel at anchor in an increasing storm as the reason of the accident. Similar conclusions follow from the interviews of ship masters: 50% of the ship masters prefer to leave coastal areas before wind increases to Bft 8 and significant wave height achieves 5.0 m.
The scatter between the wave heights relevant for manoeuvrability in coastal areas from different sources is not really surprising if we take into account that manoeuvrability performance depends, to a large extent, on characteristics of the vessel and on the operational experience and practices of the ship master. Therefore, benchmarking of the existing fleet with respect to the new criteria appears as the most rational way to define the standard wave height, for several reasons. In SHOPERA, dedicated case studies were undertaken concerning all ship types considered in the EEDI regulations.
Wind Speed
The influence of wind forces on propulsion and steering ability in seaway is comparable to the influence of the time-average wave forces for ships with a large windage area, such as container vessels and pure car and truck carriers, and is less important, but not negligible, for vessels with moderate windage area, such as bulk carriers and tankers, Shigunov (2015). For practical assessment, it is convenient to use a unified wind speed-wave height relationship (perhaps different for the open sea and coastal areas) rather than use wind speed as an additional standard. The problem in the derivation of such a unified relation is that the relation between wind speed and wave height strongly depends on the fetch, wind duration and presence of wind sea and swell. Because these factors depend on location, the relation between the wind speed and wave height is location dependent, even when considered in a statistical sense. In SHOPERA, various alternative formulae, expressing the relationship between the wind speed and the significant wave height have been reviewed and proposals have been made both for open sea and for coastal areas.
Other Sea State Parameters
In severe to very extreme sea states, the influence of swell maybe less significant compared to the wind sea, whereas in small to moderate seaways, the influence of swell may be significant. For the open sea, it is feasible to assume a situation of a ship weather-vaning for a prolonged time until the storm finishes, i.e. a developed storm situation is relevant for the assessment of the weather-vaning ability in the open sea. For a fully developed sea state, the Bretschneider spectrum (also referred to as a two-parameter ITTC spectrum) is generally recommended by ITTC while the Pierson-Moskowitz spectrum is widely used by the marine industry.
For coastal waters, the assumed scenario, confirmed by the interviews of ship masters undertaken by SHOPERA, is that ship masters do not remain near the coast in a growing storm until it escalates, but either search for shelter or leave to the open sea. Therefore, the feasible scenario to be applied with the steering and propulsion criteria is a developing storm. For a developing storm a general recommendation is to use the JONSWAP spectrum with the peak parameter of 3.3 i.e. as used in the 2013 Interim Guidelines for the evaluation of ship manoeuvrability in coastal areas. As a realistic assumption, directional spreading of wave energy with respect to mean wave direction is recommended; as the spreading function, cos^2-spreading was used in SHOPERA.
The range of characteristic wave periods (for clarity, the peak wave period will be used) used in the assessment has a significant influence on the assessment results. For the propulsion ability criterion, as well as for the weather-vaning criterion, the upper (long waves) boundary of the used peak wave periods defines whether and how much of the added resistance peak is taken into account, whereas the lower boundary (short waves) is important for larger, especially blunt, vessels for which a significant part of added resistance comes from short wave components. For the steering ability criterion, external excitation increases with increasing wave frequency, therefore, it is important how the lower boundary (short waves) of the peak wave periods is defined. The lower boundary of peak wave periods used in the 2013 Interim Guidelines, 7.0 s, is slightly conservative, because it crosses the theoretical maximum storm steepness boundary in the relevant range of significant wave heights. The upper boundary, 15.0 s, although theoretically possible, is unnecessary large, because such large wave periods are not critical for propulsion or steering ability. SHOPERA proposed suitable formulae for the lower and upper boundaries of peak wave periods as functions of significant wave height.
3 Assessment Procedures
The general assessment concept proposed by SHOPERA is to allow free choice of assessment procedures of different complexity (similarly to 2012 Interim Guidelines), ranging from simple empirical formulae to advanced assessment procedures, so that the designer can select the most suitable procedure depending on the particular design needs. Simple assessment procedures are sufficient for the majority of conventional vessels, whereas more accurate assessment procedures and evaluation methods are required for cases with large uncertainties, such as innovative propulsion and steering solutions, which are intended to be promoted by the EEDI regulations. SHOPERA proposes three alternative assessment procedures:
• Comprehensive Assessment allows the best accuracy, solving coupled nonlinear motion equations. Still, the designer does not have to use tedious/expensive evaluation methods for different components, but can choose between numerical, experimental or empirical methods for different elements. This type of assessment is anyway necessary for ships with innovative propulsion and steering arrangements.
• Simplified Assessment, a first-principle assessment with reduced number of considered situations and reduced complexity of motion equations, also allowing choosing between experimental, numerical or empirical methods to evaluate force components, and having complexity of a spreadsheet calculation.
• Sufficient Propulsion and Steering Ability Check is based on pure empirical formulae to define the required installed power as a function of main ship parameters (deadweight, block coefficient, windage area, rudder area, engine and propulsion type), of a complexity of a pocket calculator.
3.1 Comprehensive Assessment
Compliance with the IMO Manoeuvrability Standards, IMO (2002), is demonstrated in full-scale trials, which is impossible for ship manoeuvrability assessment in adverse weather conditions. Alternatively, the proposed criteria (weather vaning, steering and propulsion abilities) can be evaluated, in principle, directly in transient model experiments with self-propelled ship models in simulated irregular waves and wind, for all required combinations of wave directions and periods. This is, however, presently unfeasible for practical purposes for several reasons: First, providing reliable statistical predictions in irregular seaway requires repeating tests in multiple long realisations of each seaway, which is too expensive. Besides, few facilities exist worldwide, able to perform such tests, making such tests impractical for routine design and approval. Third, verification of such tests by the Administration is impossible (unless the test program is repeated), which makes this approach impractical for approval. Finally, results of such tests depend heavily on the time history of steering, causing too large variability and uncertainty of test results, which therefore cannot be reliably verified especially in marginal cases (i.e. cases near the failure boundary, which are the actual cases of interest in approval). Alternative to such model tests, direct numerical simulations of transient manoeuvres in irregular seaway, are not mature enough yet for routine design and approval, ITTC Manoeuvring Committee (2008). The approach proposed by SHOPERA is based on separate evaluation of different acting forces (waves, wind, propeller, rudder etc.) using simple model tests, numerical simulations or empirical formulae, and combination of the defined forces in a simple numerical model. Whereas the resulting procedure is based on first principles and takes into account all relevant physics, it is at the same time
• verifiable by Administrations or Recognised Organisations,
• based on technology presently available in the industry,
• inexpensive and as accurate as presently practicable,
• flexible, since designers and administrations are free to choose alternative methods (experimental, numerical or empirical) depending on designer needs,
• open for updates when new numerical or experimental methods are developed, without the need to revise the Guidelines.
The Comprehensive Assessment procedure proposed by SHOPERA is based on neglecting oscillatory forces and moments due to waves and thus considering only time average forces and moments, assuming that the time scale of such oscillations is shorter than the time scale of manoeuvring motions. This effectively reduces the evaluation of manoeuvrability criteria to a solution of coupled motion equations in the horizontal plane under the action of time-average wave-induced forces, as well as wind forces, calm-water forces, rudder forces and propeller thrust. Adequate procedures for the evaluation of steering ability and propulsion ability criteria have been developed and proposed. The advantage of the proposed Comprehensive Assessment, and the main difference from the Comprehensive Assessment in the 2012 Interim Guidelines is that the different effects (wind, waves, calm water, rudder, propeller and engine) can be measured or computed separately, if necessary with different methods (experimental, numerical or empirical). Note that even if model tests or complex numerical computations are used for some of contributions, they are done in stationary setups under well-controlled conditions and combined in a simple mathematical model.
3.2 Evaluation Methods for Components of Forces and Moments
Opposite to the transient manoeuvring tests in simulated wind and irregular waves, the proposed procedure relies on measurements of separate forces in well-controlled steady conditions. For calm-water, wind, rudder and propeller forces, such experiments are well established and can be done in many facilities world-wide (note that calm-water resistance and propulsion characteristics, including open-water propeller characteristics and hull-propeller interaction coefficients can be taken from the model tests that are required for EEDI verification anyway). However, measurement of the time-average wave forces requires advanced measurements in a seakeeping basin, therefore, cannot be used routinely.
Numerical methods are presently available, in principle, for the same forces (calm-water, wind, rudder and propeller) as well; however, their use in regulatory assessment requires a significant effort by administrations and recognised organisations. Availability of numerical methods for time-average wave forces is one of the most critical issues: the absence of suitable numerical methods for added resistance led to the removal of numerical methods from the 2013 Interim Guidelines. Development and validation of numerical methods for time-average wave forces and moments was one of the major tasks of SHOPERA. Model test measurements of such forces were done for three ship models (a 14000 TEU container vessel, a VLCC tanker and a RoRo) for various ship speeds and wave directions and periods (with particular emphasis on short waves); results of these measurements were used for an international benchmarking of the available numerical methods for time-average wave forces. The results of this benchmarking show a significant progress of numerical methods in the last years and indicate the principal availability of numerical methods for regulatory purposes, if applied correctly.
Especially important for the practical implementation of any practical procedure is the availability of empirical methods for different force components. In addition to the well-established empirical methods for wind forces, Blendermann (1993), Fujiwara et al. (2006), extensive validation studies were carried out together with the project from Japan for calm-water reactions and rudder forces in propeller race, which indicate availability of such empirical methods for the practical use; however, designers and Administrations should ensure that empirical methods are used within their applicability limits.
An important aspect of propulsion and steering in adverse conditions is a correct description of the engine under high load. In SHOPERA, air/surge limits of diesel engines (two- and four-stroke) were verified and recommendations were provided for practical assessment procedures.
3.3 Simplified Assessment
The aim of the development of the Simplified Assessment was to have a simple enough procedure for routine use by Administrations by reducing the number of calculations (solution cases) as well as the number of terms in motion equations, while keeping all relevant physics. In particular, the Simplified Assessment addresses the same criteria as those enforced in the Comprehensive Assessment (weather-vaning, steering and propulsion). The simplified procedures for steering ability (ability to start or continue course change in any seaway direction) and propulsion ability (ability to keep a minimum advance speed in all seaway directions) were proposed in Shigunov et al. (2014).
Simplified Steering Ability Assessment
The starting point is the system of coupled motion equations in the horizontal plane, solved for all relevant forward speeds and all seaway directions to check that the ship is able to start or continue course change in seaway from any direction. Note that for the steering ability, both the steering system and propulsion (which influences steering ability) are required and should be integral parts of the assessment: e.g. ships with powerful propulsion may have a smaller rudder, whereas ships with weaker propulsion may compensate this with larger or more effective steering devices. Results of Comprehensive Assessment for many ships show that the dimensioning condition for the installed power, i.e. the condition at which the ratio of the required to available delivered power is maximised along the line of maximum steering effort (further referred to for brevity as critical condition for steering) is close to beam seaway. Note that from experience, as well as from the results of Comprehensive Assessment for many ships, critical conditions for steering occur most frequently in stern quartering waves; however, in such situations the required power is less than the required power defined by the Propulsion Ability. When the Steering Ability is dominating for the definition of the installed power, the critical conditions are always close to beam seaway situations. This allows reducing the evaluation of the time-average wave and wind forces to beam seaways. The second simplification stems from the observation that the levers of time-average wave and wind yaw moment are negligible compared to the lever of the calm-water yaw moment in critical conditions for steering.
As a result, the system of coupled motion equations in the horizontal plane is significantly simplified. To define the components of forces and moments in the Simplified Assessment of Steering Ability, any of the methods used in the Comprehensive Assessment can be applied; in addition, application of simplified empirical formulae seems suitable for this assessment level. Such formulae and their validation are proposed.
Simplified Propulsion Ability Assessment
The starting point is the system of coupled motion equations in the horizontal plane, which has to be solved for all possible seaway directions to demonstrate that the ship is able to keep forward speed of at least 6.0 knots in seaway from any direction. Noting that bow seaways are most critical for required power at a given speed, it is enough to consider only seaways from 0 to about 60 degrees off-bow in the assessment. Further, neglecting the influence of drift on the required thrust and required power allows omitting equations for the lateral forces and yaw moments. Thus only the equation for the longitudinal forces needs to be considered, and only in head waves. However, it is important to keep in mind that the time-average longitudinal force due to waves should be taken as the maximum force in mean wave directions between 0 and 60 degrees off-bow. The various force components can be found using any method from the Comprehensive Assessment (empirical, numerical or experimental). However, it seems logical to allow using also simpler approximations for these terms in the Simplified Assessment.
3.4 Sufficient Propulsion and Steering Ability Check
The simplest assessment procedure, Sufficient Propulsion and Steering Ability Check, is based on pure empirical formulae to define the required installed power as a function of main ship parameters. Three different groups of formulas have been developed in SHOPERA. The formulae proposed by SHOPERA are based on the application of the comprehensive propulsion and steering assessment procedures to over 400 bulk carriers, tankers, container ships and general cargo vessels equipped with two-stroke low-speed diesel engines, a fixed-pitch propeller and a conventional rudder. For each ship, the maximum significant wave height was found, at which the required brake power is equal to the available brake power, separately for steering and propulsion criteria. Based on these results, MCR was approximated as empirical formulae of significant wave height, for each combination of main ship parameters, and then, the required installed power was found that satisfies the standard significant wave heights for propulsion and steering. The resulting empirical formula, for propulsion ability requirement is:
MCT=0.21*SQRT(CB)*LPP^2
where MCR, kW, is the required installed power in terms of the maximum continuous rating of the engine, CB the block coefficient and LPP the length between perpendiculars. The corresponding empirical formula for the steering ability requirement is:
MCR=0.15*CR*LPP^2
Where CR is an appropriate coefficient depending on the ship characteristics. Testing of the proposed formulae by all interested stakeholders and its validation are required to approve / improve them; it should be noted that these formulae are suitable only for vessels equipped with two-stroke low-speed diesel engines, a fixed-pitch propeller and a conventional rudder; for other types of engine, propulsion and steering the simplified or comprehensive assessment should be used.
3.5 Engine and Propulsion
Within the comprehensive and simplified assessment procedures, a steady engine model can be used to define available brake power as a function of the engine rotation rate, defined by the engine diagram: Several propeller curves are superimposed on the engine diagram among which a light propeller curve, corresponding to clean hull in calm water; along this curve, engine’s power is nearly proportional to the cubic power of the engine’s rotational speed. Heavy propeller curves are assumed for fouled hull in seaway and are obtained by increasing the light propeller curve power by an appropriate sea margin. In the assessment of the sufficiency of the installed diesel engine for manoeuvrability in adverse conditions, it is necessary to take into account that the maximum continuous output of a diesel engine is bounded, depending on its rotation speed, by several limits:
• Power limit, at the maximum rotation rates. At the power limit, maximum power continuously provided by the engine is constant and equal to MCR.
• Maximum torque limit, defined by the shafting system bearing strength, at the moderately reduced rotation rates. At the maximum torque limit, torque is constant and thus the maximum engine output is proportional to rotation speed.
• Surge limit, at low rotation rates. To the left of the surge limit, the engine will lack air from the turbocharger for the combustion process.
Due to increased resistance in adverse conditions or during manoeuvres, the propeller curve shifts upwards, and the maximum engine output is defined by the intersection point of this curve with one of the engine limit curves (either the Maximum torque limit or the Surge limit). At low added resistance, e.g. in normal operation in low to moderate sea states, maximum torque is relevant, whereas for propulsion and manoeuvring in heavy weather, surge limit becomes the limiting curve. At this point, the available delivered power is reduced compared to MCR. This available delivered power is compared with the required delivered power defined from the propeller model.
SHOPERA has performed case studies for vessels with various types of engine and propulsion besides the low-speed two-stroke diesel engine working directly on a fixed-pitch propeller. Although in the practical approval, verified manufacturer data describing engine limit curves and propeller characteristics should be used, a summary of approaches used to consider other types of the engine and propulsion in the SHOPERA case studies is given below:
• For 4-stroke diesel, the air-surge limit curve is much more restrictive than the air-surge limit curve for 2-stroke engines. In SHOPERA, measurement data were used for 4-stroke diesels.
• For a diesel-electric propulsion, it was assumed that the power output of an electric motor is independent from the rotation speed, i.e. the output of the engine was assumed constant at all rotation speeds. In emergency situation, 100% of MCR can be considered as the maximum available power.
• For a vessel equipped with a controlled-pitch propeller, it was assumed that the propeller operates at a constant rotation rate, and the pitch of propeller blades was varied to adjust the propeller to the actual forward speed and required thrust.
The propeller thrust is found from the equilibrium of forces in the x-direction. Using the known thrust, the advance ratio J is found using known open-water propeller characteristic KT(J) along with the propeller advance speed. From the advance ratio J, the torque coefficient KQ(J) is found using the open-water propeller characteristics. After that, the propeller rotation speed and the required delivered power to the propeller are readily obtained.
3.6 Development and Refinement of Numerical Tools
Numerical hydrodynamic tools are essential to predict the dynamics of ships in various conditions of interest and an abundant choice of tools is available, each one with its specific characteristics as to the problems addressed and the formulation adopted for the solution. Consequently each tool has its level of accuracy and its limits of application. During this project, different types of hydrodynamic codes have been further extended in order to better deal with the specific problems considered in the project. One type is potential flow seakeeping codes used for predicting added resistance in waves and for loss of stability in waves; other potential flow codes deal with methods for manoeuvring prediction both in waves and in confined waters, which represent two extreme situations to which the usual deep water manoeuvring codes need to be further developed. Another type of codes is based on field methods, which include different types of CFD codes. Many applications of these codes have the objective of determining off-line databases for describing second-order wave forces, approximations of manoeuvring hull forces in shallow water, rudder forces behind the propeller in waves, simplified unsteady model for a screw propeller and peculiarities of hull-propeller interaction coefficients in waves. These databases are meant to augment the manoeuvring potential codes with those features, improving their prediction ability while keeping the speed of computation in acceptable limits. Other applications aim at direct predictions of ship motions by coupling with the 6DOF ship motion simulator other features such as of engine dynamics and automatic controllers and coupling with a propeller model. Several developments have being made in parallel by various SHOPERA partners and thus only some typical results are herein presented.
Potential Flow Methods
The calculation of the added resistance of ships in waves is a very important scientific and practical aspect of the project, as it directly addresses the required minimum powering for the ship to advance at certain speed in waves, while it leads to the estimation of the fuel consumption during ship voyages; three different project teams are working on this subject on the basis of potential theory and associated software tools. An existing numerical model of added resistance calculation and speed loss estimation developed by Prpić-Oršić and Faltinsen (2012) has been improved by accounting for the effect of air resistance. The total wind velocity is a combination of a steady-state or mean velocity and a turbulent (gust) velocity. The mean speed is calculated as a function of significant wave height according to the one-parameter Pierson-Moskowitz spectrum. The gust component is a random process with zero mean represented by a gust spectrum. The wind direction is assumed to be the same as wave direction. The numerical model has been extended for the effect of various dynamic effects (slamming, deck wetness, bow acceleration and propeller emergence) on voluntary ship speed reduction and so arranged to allow the prediction of ship’s behaviour for the whole range of ship speeds and heading angles, which is an essential part of weather routing systems (Vettor and Guedes Soares, 2015).
The 3D seakeeping code HYBRID of NTUA has being further developed for simulating the 6 DoF nonlinear ship motions in adverse sea states and for studying the parametric rolling problem. The HYBRID code has been applied to the study of parametric rolling problem of the ITTC-A1 ship and the calculation of drift forces and added resistance of RoPAX, KVLCC2, and DTC ships. The HYBRID code is essentially a nonlinear time domain method based on the impulse response function concept and incorporates the nonlinear Froude-Krylov force and hydrostatic force to simulate the six DoF ship motions, Liu et al (2014). For the calculation of drift forces and added resistance, a far-field method and a proper semi-empirical formula for short wave region correction are used.
The OceanWave3D software of DTU solves the linearized, forward-speed potential flow problem to predict seakeeping and added resistance in waves. The tool is based on an arbitrarily high-order finite difference method, and two gridding approaches are under development: 1) overlapping boundary fitted structured grids; and 2) an immersed boundary technique based on the method of weighted least-squares. The overlapping grid approach has been validated for linear seakeeping and added resistance both with Neuman-Kelvin and double-body flow linearization (Amini Afshar et al. 2015) and is currently being tested with real ship geometries. The immersed boundary technique has been validated for wave-less problems, and is being extended to solve the linear seakeeping problem. In order to extend both of these methods to treat fully nonlinear wave structure interaction, a new automated derivation procedure has been developed for implementing arbitrarily high-order Weighted Essentially Non-Oscillatory (WENO) schemes on uniform and non-uniform finite difference grids. Such a WENO treatment of the convective terms in the nonlinear, forward-speed free surface boundary conditions is shown to be robust and stable for all combinations of ship speed and wave celerity. This paves the way to extending the code to nonlinear wave-ship interaction. Future developments include parallel implementation and extensions to nonlinearities
A time domain code ‘Waqum2’ has been developed to simulate ship manoeuvring in waves. Based on the state of the art of maneuvering models and sea-keeping theory, a unified theory is used herein to develop this code, which can simulate ship responses in a sea state in time domain. The fluid memory effect is included in this code through a convolution function. The considered environment loads include wind and wave loads. The actuator force is composed of propeller force and rudder force. All the loads and actuator forces are given in individual force module, and they can be enabled or disabled based on the analysis requirement for a particular case. An engine model is also available in the code, which enable us to study ship responses in adverse sea more accurately and systematically. A PID controller is implemented in this code to control rudder angle and rpm of propeller or power output from engine. The verification of this code is performed (Guo, et al., 2016).
Field Methods
Several simulations were performed for different ships in waves using the RANS solver OpenFOAM. Drift forces were computed for different heading angles and compared with available experimental data. Ships under investigation were the Wigley hull III, the Duisburg Test Case (DTC) containership, described by el Moctar et al. (2012) and a Cruise-Vessel. During these first studies, influencing parameters such as discretization, numerical setups and modes of motion were investigated. Achievements have been obtained with respect to the following aspects: Grid and convergence study, preliminary validation study for the calculation of second order wave forces and comparison between fixed and spring constrained surge motions on added resistance (Ley et al 2014). The final objective is to develop off-line databases for second order wave forces, approximations of manoeuvring forces in shallow water, rudder forces behind the propeller in waves, a simplified unsteady model for a screw propeller and peculiarities of hull-propeller interaction coefficients in waves, obtained by a RANS solver.
The RANS code Neptuno (Cura Hochbaum & Voigt, 2002) has been enhanced with a new body force propeller model, allowing a better approximation of the rudder inflow and propeller torque. The code can be used to calculate forces on the hull due to waves, current and wind to derive a coefficient set including these environmental effects. The new body force model is based on a large set of RANS calculations for the isolated propeller rotating in homogenous inflow. The present calculations were made for a stock propeller with six blades. The advance coefficient J and the angle of incidence α were varied in a range of 0.1 to 0.9 and 0° to 30°, respectively. For each time step of the calculated case – which corresponds to a specific rotation angle of a considered propeller blade – the resulting pressure and shear stresses in each cell of a triangular grid on both the suction and pressure side of the blade are saved. The propeller disk is then discretized with a polar grid and for each cell of this grid the three components of the mean force per unit area caused by all propeller blades over a complete revolution are calculated and stored in a database for each considered pair J and α. In addition, the corresponding induced velocities of the propeller in an upstream reference plane are saved as well. When setting up the RANS calculation of a forced motion test, each cell of the polar grid on the propeller disk gets mapped to a cell in the computational domain and vice versa. The individual inflow condition at this cell is then evaluated from the total local wake field. There are three inflow parameters considered – the inflow speed and two angles, the first angle corresponding to the angle α mentioned above and the second one, which allows for turning back the current situation at the considered cell to the general situation assumed when generating the database, where the oblique propeller inflow was always horizontal. This makes it possible to take into account any inflow condition to the propeller as occurring for instance during sway and yaw motions of the ship. The body forces for each cell within the propeller region foreseen in the computational grid for the RANS simulation of virtual captive model tests are obtained from the database depending on the current inflow condition using a two-dimensional interpolation on J and α.
Another approach that is being pursued is the simulation of ships in manoeuvring conditions by coupling a potential flow method for the representation of the propeller with a RANS solver, which simulates the bulk flow around the hull. The objective is to find a correction factor for the propeller wake in varying inflow conditions, in order to have the real wake field and propeller forces during manoeuvres. In the present research the propeller suction is modelled as the suction of an equivalent actuator disk with angular varying loads. Only a one-cell layer of body forces is used in the propeller axial direction, even though more layers could be used if needed. The RANS code FINFLO was coupled with a propeller lifting line method for the prediction of the effective wake. The correction factors were calculated for a relatively light loaded propeller condition using circumferentially averaged values. Future work will consist of applying the correction factor approach to ship flow in manoeuvring conditions.
3.7 Validation of Evaluation Methods
One of the most important gaps in the state of the art of ship hydrodynamics before the project was the absence of validated numerical and empirical methods for the computation of time-average wave forces and moments, including the added resistance in waves. Although some measurements were available for the longitudinal component of such forces, both at zero and non-zero speeds, most data were available for head waves only; virtually no systematic measurements were freely available for the added resistance in oblique waves, as well as for the side drift force and yaw drift moment on ships, especially for non-zero forward speed. Providing experimental data for the validation of advanced methods or simplified models for rudder forces in propeller race, not sufficiently available yet in the open literature, was an additional objective of the experimental studies. Finally, validation of the proposed criteria for manoeuvring in waves (weather-vaning, steering and propulsion) can be done using direct transient simulations of manoeuvres in waves in time domain. However, such simulation methods themselves require validation by comparison with experiments; in the open literature, only limited amount of such experimental results is available. To close this gap a test matrix was defined, which specifies test conditions and values to be measured; summarizing, the following model tests were performed in deep and shallow water to provide validation data for the developed numerical models:
• Time-average wave forces including added resistance in regular waves;
• Added resistance in irregular waves;
• Propulsion and speed loss in regular waves;
• Rudder forces in regular waves;
• Rudder forces in propeller race at high propeller loading;
• Turning circle in regular waves;
• Zig-zag manoeuvres in regular waves.
Three vessel types of significantly different hydrodynamic characteristics were selected to provide a sufficiently broad variety of hull geometries for the validation of numerical tools: a VLCC tanker (the KVLCC2 tanker designed by MOERI), a post-panamax container ship (the Duisburg Test Case (DTC) container vessel designed by the Institute of Ship Technology) and a RoPax ferry. For these three hullforms, a comprehensive test program consisting of more than 1,300 different model tests has been carried out by four SHOPERA partners:
• At Norsk Marinteknisk Forskningsinstitutt (MARINTEK), 390 model tests for deep water conditions were performed in the large Towing Tank and the Ocean Basin.
• At the Canal de Experiencias Hidrodinámicas de el Pardo (CEHIPAR) 220 model tests were performed for deep water conditions in the Ship Dynamics Laboratory.
• In the Seakeeping Basin of the Technische Universität Berlin (TUB), a facility of the former VWS Berlin, another 180 model tests were conducted in shallow and intermediate water depth.
• Finally, Flanders Hydraulics Research (EVFH) unique towing carriage facility was exploited, which allows to run a significant number of tests in fully automated mode. Due to this unique feature, the major share of the test program – 560 experiments (added resistance, drift force, propulsion and manoeuvring tests in waves) – were conducted in shallow water conditions at the EVFH towing tank.
Model Test Specification
While the RoPax vessel was exclusively tested in deep water conditions at MARINTEK, both deep and shallow water tests were conducted for the KVLCC2 and DTC at all four participating partner institutions. The SHOPERA test campaign focused on the following test types:
• Added Resistance and Drift Force Measurements: For the added resistance and drift force tests at forward speed, the models were towed at predefined forward speed without propeller by a carriage with a spring frame, which had also integrated force transducers. For the zero-speed drift force tests, the models were moored by a spring system with integrated force transducers. Heave, pitch and roll motions were unrestrained, while surge, sway and yaw were restrained by springs. An exception was the drift force/added resistance tests at forward speed performed at TUB, in which the model was self-propelled and held captive by a measuring device consisting of spring held sleds. This newly developed measuring device consists of a frame with a pair of y-sleds, which carry an x-sled each, so that the model can surge, sway and yaw within certain limits determined by the stiffness of the attached springs. The sleds allow for motions both alongside and perpendicular to the direction of the towing carriage, as well as yaw motions. Parameters of variation for the added resistance and drift force tests were the under keel clearance, the ship forward speed, the loading condition and the heading over a relevant range of wave periods.
• Propulsion Tests in Waves: For the propulsion tests in waves the models were self-propelled and free running. Course was kept by an autopilot controlling the rudders. The purpose was to determine propulsive coefficients and speed loss in regular waves over a range of periods as well as in selected irregular sea states. By variation of the propeller revolution a constant mean forward speed in waves was achieved.
• Rudder Force Tests: For rudder force tests in calm water, the models were self-propelled and captive. The rudders were equipped with sensors for forces and shaft moments. For different propeller revolutions, the rudder angle was slowly varied from zero to 35°.
• Manoeuvring Test in Waves: The experimental determination of manoeuvring characteristics in selected wave scenarios was a further focal point of SHOPERA. The setup for the manoeuvring tests was similar to the one for the propulsion tests in waves - the models were self-propelled and free running with predefined constant propeller revolutions set. Parameters of variation for turning circles encompass the initial heading and the regular wave period. For zig-zag tests, only the wave period was varied. During PMM and Circular Motion tests, the models were being kept captive.
The effects of various characteristics of ship’s hull form on the added resistance in waves were investigated to derive new empirical formulae for the time-average wave forces, including added resistance, based on best fitting of available experimental data for different types of hull forms. Extensive validations of the proposed empirical formulae were carried out for different types of ships and in comparison with other empirical methods as well as more advanced approaches. An extensive study on second order forces in regular waves was also performed by field methods. Quadratic response amplitude operators (RAOs) for the forces were compared with experimental results for two different ship types. The ratio between wave and ship length was varied from 0.2 to 2.5. Thus, both, relatively short waves and long waves were considered.
Several semi-empirical methods for the forces on full-spade and semi-spade rudders in propeller race were developed and tested, based on the approach described in Brix (1993). In addition, a model was developed for the forces acting on podded drives during manoeuvring.
Validation of the proposed criteria for manoeuvring in waves (weather-vaning, steering and propulsion) can be done using direct transient simulations of manoeuvres in waves in time domain. To do this, such simulation methods themselves require validation by comparison with experiments. In the open literature, few such experimental results are available. For the comparison with the conducted manoeuvring experiments for the DTC container ship, a complete set of calm water manoeuvring coefficients was computed using RANS-CFD simulations. Numerical predictions agreed fairly well with the free running experiment to the starboard side. Differences of the free running test to port and to starboard side, have still to be clarified and may be related to the fitting of the twisted rudder. Turning circle manoeuvring tests were performed at different ship speeds in regular waves of different heights and headings. The nonlinear equations of motion for six degrees of freedom or, alternatively, four degrees of freedom, were solved in time domain. The hydrodynamic coefficients for calm water reactions were computed using virtual PMM tests with viscous field methods. Turning circle tests were performed in regular waves of height 2 m, period 12.5 s with the initial heading from head. The computed and measured trajectories for the DTC and S175 container ships agree fairly well with the experiments.
4 Benchmarking of Time-Average Wave Forces & Moments
An open blind international benchmark study has been organized by SHOPERA using for validation selected tank test results, which were obtained within the SHOPERA project, while some benchmark test data were made available from experimental studies in Japan. The aim of this benchmark study was to assess the accuracy/reliability of current numerical simulation methods on calculating the mean second order forces/moment and simulating the manoeuvrability of a ship in waves of varying complexity; simplified formulas, potential flow methods, motion simulators and viscous field methods, were compared with each other and with model tests for selected cases. The comparative experimental data were not known to the study participants, hence it can be concluded that the present benchmark assessment was based on a solid foundation and allowed an assessment of the genuine capabilities of benchmarked codes. The submitted simulation results were analysed and compared with corresponding model experimental data to conclude on the accuracy and efficiency of the methods. The outcomes of the study were presented at a public workshop on April 15, 2016, Lloyds Register, London (see http://www.shopera.org/benchmark-study/eedings/presentations of the workshop). Two well-known hullforms were used for the study:
The Duisburg Test Case (DTC) containership design is a modern post Panamax 14,000 TEU container vessel. It was developed by the Institute of Ship Technology, Ocean Engineering and Transport Systems (ISMT) of the University of Duisburg-Essen in collaboration with Germanischer Lloyd for benchmarking and validation of numerical methods; its lines and other characteristics are available to the public.
The KVLCC2 is a VLCC type tanker vessel, representing the second variant of a modern tanker design developed by the Korean Institute of Ship & Ocean Engineering (KRISO) with bulb bow and U-shaped stern lines. The hull lines have been exclusively developed for testing and benchmarking and this ship has been widely used benchmarks of international scientific committees, like ITTC and SIMMAN.
4.1 Added Resistance in Waves
For the added resistance of the DTC ship, 13 participants made 15 submissions; for the added resistance of KVLCC2 ship, 10 participants made 11 submissions. At higher speed in head waves, the spreading of results among the various methods and in comparison to the experimental data is moderate, while most methods seem to deliver results with good agreement with the experimental data. It should be herein noted that the test range of frequencies/wave lengths, extending to very short waves of λ/L ≈ 0.2 is quite demanding introducing uncertainties both to the experiments and computations. At lower speeds in head waves, the spreading among the numerical results gets larger, and the deviation from experimental results is also significant. The quality of the numerical predictions by some methods is poor, but several others are satisfactory. It should be noted that the range of tested scenarios refers to a great extent to the short waves region, where the physics of the problem become very complicated for both the numerical and experimental methods (breaking waves, viscous effects, etc.). For oblique waves, tank tests have been conducted only for low speeds and 60 deg heading. In general, a relatively good agreement has been observed for the DTC ship, whereas for the KVLCC2 ship the performance is similar.
4.2 Drift Forces and Moments
For the mean side force and yaw moment of the DTC ship, 10 participants made 13 submissions. For the KVLCC2 ship, 8 participants made 9 submissions. The convergence of results on the drift force in the transverse direction is general good, while the results for the mean yaw moment are less satisfactory. This may have been expected, as the yaw moment is the combined effect of forces both in the longitudinal and the transverse direction, and any discrepancy in the mean force in the longitudinal direction trivially leads to unsatisfactory results in the mean yaw moment. The performance of the various methods is similar to that observed in the previous tests.
4.3 Benchmarking Conclusions
The benchmark study concerned two large ships, the DTC containership and the KVLCC2 tanker, which are both well over 300m in terms of length. For such large ships, the encountered waves in actual sea conditions are mostly ‘short’, namely λ/L < 0.5 where the benchmark study focused on. The study delivered a good insight into the predictability of complicated hydrodynamic phenomena on the basis of experimental and numerical studies. It provided also valuable benchmark data to the international scientific community for future research on a subject with strong scientific and engineering background linked to international maritime regulations. Some essential aspects of the subject were noticed and should be further studied in the future. In particular, examining the numerical simulation results in comparison to model experimental data, the following may be concluded:
1. The predictability of the added resistance is generally decent to good. The performance of the tested methods is better for moderate speeds and worsens with decreasing speed. Also, the agreement is better for the tested full type ship (KVLCC2) than for the DTC containership hull form.
2. The predictability of the second order forces/moments (drift forces and yaw moment), is generally worse than for the added resistance and again worse for the DTC ship than the KVLCC2 ship.
3. For the manoeuvrability simulations, the behaviour of various employed numerical methods is not consistent. Despite the large spreading among the numerical methods and deviation from experimental results, some methods, performing well in one case, were not good for another case, thus conclusions could not be drawn, except for some qualitative effects of the impact of incoming waves.
4. The overall impression of the submitted results based on strip theories was not satisfactory. This is mainly due to its insufficiency in accounting the 3D and end effects (bow and stern) of the hull form, which are significant in the present study subject.
5. BEM methods implementing various theories performed as category of methods best in the present benchmark due to their essential merits: comparatively easy to use, when the code is properly programmed and validated and with decent results for non-extreme designs and loading/environmental conditions.
6. A reliable assessment of CFD/RANS methods was not possible due to limited participation and some delivered odd results. This may be attributed to improper use of codes (meshing etc.), allowing the conclusion that CFD codes are highly dependent on their usage, rather than on the physics of the studied problem or the code itself.
7. There was also one empirical method participating in the benchmark study by submitting results on the prediction of added resistance. For the studied cases, the empirical method delivered good results, showing a promising performance.
Some additional general comments may be concluded:
a. Limitations of the numerical methods: CFD tools are highly dependent on the end-users’ skills (background, experience with the type of problem, etc). In general, however, the quality of predictions is solely dependent on the code developer’s know-how and the code user’s experience.
b. The particularity of hull form: The scattering of the numerical results is more serious for the DTC ship than for the KVLCC2 ship. This can be credited to the effect of their hull form. The DTC ship disposes a relatively small draft (in comparison with other main particulars), an extended bulbous bow close to the free surface and a transom stern with long overhang near the calm water free surface. It is well known that these are two critical issues, namely, an emerging bulbous bow and immersing transom stern, with the associated complex wave phenomena and rapid change of the wetted part of the ship. Potential flow, panelling methods are not performing well in these conditions due to their essential limitations. However, even RANS methods are challenged under similar conditions and may fail, if not properly used.
c. The tested waves: As the size of the tested ships is large (>300m), representative sea states fall into the relatively short waves. In order to measure the small absolute values during model tests, quite steep waves were generated and tested. This may have created additional uncertainty in the benchmarked results, independently of the specific hull form. This uncertainty can only be partially controlled by using larger ship models for testing or applying full scale CFD simulations in future work.
d. Uncertainty of experimental data: The studied complex hydrodynamic phenomena put great challenges not only to numerical methods, but also to model experiments. This is obvious, when observing the spread of comparative model experimental data for similar conditions. This may be attributed to limitations of the used hardware, which is sometimes tested to its limits (e.g. measurement of very small force values of few Newtons), the inherent limitations of the size of tested ship models and generated scaled waves, the lack of repeatability of test measurements, etc.
5 Case Studies
It is not realistic and not necessary to design ships for operation in the worst possible storms that can be theoretically encountered, given that ships can nowadays timely avoid such stormy conditions by improved weather forecasts and satellite information systems. The standard operational wave heights of ships should be defined in such a way that the majority of the existing vessels fulfils the related requirements, because, first, present design and operational practices cannot be changed abruptly, for example, because of the introduction of EEDI and, second, the present safety level with respect to manoeuvrability-related accidents in heavy weather is satisfactory, Ventikos et al. (2014). Notably, to similar conclusions comes a study by IACS, EE-WG 1/4 (2010), which identifies rather mild standard wave heights for weather-vaning (wind speed up to 21 m/s and significant wave height up to 5.4 m) and advance speed (up to Bft 8 at 6.0 knots advance speed) requirements. Therefore, benchmarking of the existing fleet with respect to the herein proposed new criteria appears as the most rational way to define standard wave heights. Such an approach was also used in the IACS studies on minimum power requirements and led to the environmental conditions in the 2013 Interim Guidelines: wind speed 15.7 m/s at significant wave height 4.0 m for ships with length BP up to 200 m to 19.0 m/s and 5.5 m, respectively, for length BP of 250 m and greater. Therefore, case studies were undertaken in SHOPERA concerning all ship types considered in the EEDI regulations.
5.1 Comparison between Criteria
The weather-vaning ability was treated using a simplified criterion, as the ability of the ship to keep position in bow to bow-quartering seaway; this simplification follows from the observation that the ship will not be able to keep heading under the action of environmental forces if the forward speed is not sufficiently large, because of significantly reduced manoeuvring reactions on the hull and steering force on the rudder. Comparisons of marginal significant wave heights according to comprehensive propulsion assessment using 4.0 knots advance speed with marginal significant wave heights according to the comprehensive position keeping assessments for bulk carriers, tankers and container vessels have been performed verifying that marginal wave heights for position-keeping are consistently greater than those for 4.0 knots propulsion; the deviation between results decreases with increasing ship size, according to Froude law. Note, however, that the marginal wave heights according to these assessments are very well correlated, which means that for norming, one of the criteria is redundant. Before making the final choice, a comparison with assessment based on other weather-vaning criteria would be useful, e.g. with the more comprehensive “heading recovery” criterion proposed by the project conducted in The Netherlands.
Comparisons have been also performed between the marginal wave heights according to comprehensive propulsion assessment (here, 6.0 knots advance speed was used) with marginal wave heights according to steering assessment for bulk carriers, tankers, general cargo vessels and container ships. The marginal wave heights according to these two criteria are also correlated to some degree, however, with significantly more spreading than for the position keeping vs. propulsion. It can be concluded that fulfilment of the propulsion ability requirement at a certain marginal significant wave height guarantees fulfilment also of the steering ability requirement at a marginal significant wave height of about 1.0 m smaller. The difference becomes slightly greater than 1.0 m at the propulsion marginal significant wave heights above about 5.5 m, which are, perhaps, not relevant anyway. Note, however, that this correlation between the propulsion and steering abilities stems from the fact that the steering systems of the considered ships are properly dimensioned according to other requirements, e.g. IMO Manoeuvrability Standards (2002).
5.2 Definition of Standard Wave Heights Using Comprehensive Assessment
One of the aims of the Case Studies was to provide recommendations for the standard wave heights using Comprehensive Assessment. This study was done as follows: first, a sample of representative vessels was selected; after that, the Comprehensive Assessment of Propulsion and Steering Abilities was applied to find the marginal wave height (separately for Propulsion and Steering and for different ship types and sizes); finally, a fit of the determined marginal wave heights vs. length BP was done to define the standard wave height per ship type and overall for all ship types; note that the marginal wave heights were considered separately for the Propulsion and Steering Abilities.
To select representative vessels, several series of designs were generated:
1. Series of bulk carriers and tankers along the defined boundary lines MCR=f(Lpp), which exclude a certain percentage of vessels with lower power. As the “bottom line”, a line corresponding to the limit of 5% of the low-powered vessels was used; besides, 10%-, 20%- and 30%-lines were defined and series of ships were generated. For comparison, low-power series were generated also for container ships and general cargo vessels. These series were generated using the IHS-FairPlay data for each vessel type.
2. Series of bulk carriers and tankers along the lines MCR=f(Lpp) corresponding to vessels marginally fulfilling the requirements of EEDI Phase 1, 2 and 3.
3. Series of bulk carriers and tankers along the Minimum Power Lines according to the 2013 Interim Guidelines, Res. MEPC.232(65) as amended by Res. MEPC.255(67) and MEPC.262(68).
The marginal significant wave heights obtained with Comprehensive Propulsion and Steering assessment were plotted vs. the Length BP, for the bulk carriers and tankers (in some cases results for low-power container ships and general cargo vessels were included for comparison) with the installed power corresponding to the 5% and 20% of low power vessels of the FairPlay database. Bulk carriers and tankers look very similar with respect to the marginal wave heights and are significantly below container ships. The results indicate that, if only the propulsion ability is taken into account, bulk carriers and tankers with a power at about the 20% MCR line of the FairPlay database are slightly above the current standard (hs=5.5 m at Lpp=250 m); Steering Ability appears to be more critical, i.e. it corresponds to lower marginal wave heights than Propulsion Ability. Similar plots have been produced for bulk carriers and tankers marginally satisfying the requirements of EEDI implementation Phase 3, 2 and 1, respectively. The results show that if only propulsion ability is taken into account, the current standard hs=5.5 m at Lpp=250 m is fulfilled by Phase 1-compliant tankers and bulk carriers and, marginally, by Phase 2 compliant tankers and bulk carriers. In addition to the above, plots have been produced for the marginal significant wave heights according to comprehensive propulsion and steering abilities assessments for bulk carriers and tankers, which marginally satisfy the Minimum Power Lines of 2013 Interim Guidelines. Based on the obtained marginal wave heights for bulk carriers and tankers, and requiring that the standard wave height for the propulsion ability assessment is equal to the standard wave height according to the 2013 Interim Guidelines of 5.5 m for vessels with Lpp=250 m, the following can be proposed:
hs=min(2.2+Lpp/75 5.5)
or alternatively the standard wave heights can be set equal to those (slightly less conservative for vessels of Lpp < 250 m) in the 2013 Interim Guidelines.
To define standard wave heights for the steering ability assessment, it was assumed that, on the average, the same percentage of vessels from the total number of vessels used should fail the steering ability assessment as the propulsion ability assessment (for the individual vessels, one or the other requirement can be dominating). This led to the following proposal:
hs=2.0+Lpp/100
One observation from these results is that the marginal wave heights are ship size-dependent: larger vessels are able to fulfil both propulsion and steering requirements at greater significant wave heights than smaller vessels. This is understandable physically; in principle, ship size dependent standard wave heights may be acceptable from the pragmatic point of view: because consequences of accidents are greater for larger vessels, acceptable probability of accidents should be lower for larger vessels. Besides, ship size-dependent standard wave height would reflect existing design and operational practices: smaller vessels, obviously, do not operate in storms of the same severity as larger vessels. Note that standard wave heights in the 2013 Interim Guidelines are also ship-size dependent, however, this is a subject of ongoing discussion. Another conclusion is that the marginal wave heights differ, partly substantially, between different ship types. A final note concerns the possibility of contradiction between fulfilling the proposed requirements to manoeuvrability in adverse weather conditions and the possibility to fulfil EEDI requirements, which are progressively strengthening from Phase 1 to Phase 3. It is interesting to note that whereas the selected low-power general cargo vessels and container carriers satisfy the standard wave heights corresponding to the 2013 Interim Guidelines and, at the same time, easily fulfil the requirements to Phase 3 of EEDI implementation (as presently formulated), the selected bulk carriers and tankers, marginally satisfying standard wave heights of the 2013 Interim Guidelines, are able to marginally fulfil requirements of Phase 2 of EEDI implementation, but not the requirements of Phase 3. Note, however, that standard wave heights can be adjusted to the marginal wave heights of Phase 3-compliant bulk carriers and tankers, i.e. effectively, slow-steaming designs; whether such vessels can be considered as representative vessels of fleet in service requires a prolonged discussion with all interested stakeholders.
5.3 Comparison between Ship Types using Simplified Assessment
The simplified assessment of propulsion and steering ability is more conservative than the comprehensive assessment, therefore, it was not applied to define the standard wave heights. On the other hand, it can be used to compare performance of vessels of different types with respect to EEDI requirements, when selected vessels of different types have comparable performance with respect to manoeuvrability in adverse conditions. In this study, vessels of different types were selected, which have the same marginal wave heights (computed using simplified assessment procedure) as bulk carriers and tankers, marginally compliant with the requirements of either Phase 1, 2 or 3 of EEDI implementation. The analysis identified EEDI phase that these selected vessels were able to satisfy. The analysis showed that the general cargo vessels satisfy either the same EEDI phase as the bulk carriers and tankers with the same marginal wave heights (this concerns old designs of general cargo vessels), to “higher” Phases; all other vessel types (Cruise Vessels, LNG and Gas Carriers, RoRo Cargo and RoPax) achieve significantly “higher” phases of EEDI implementation than bulk carriers and tankers if they have comparable marginal wave heights with respect to manoeuvrability in heavy weather. Plots have been elaborated showing marginal significant wave heights according to simplified propulsion and simplified steering abilities assessment for bulk carriers, tankers, container vessels, general cargo vessels, LNG and gas carriers, RoRo cargo vessels, reefers and RoPax vessels. In each of these plots, only vessels satisfying requirements of a certain EEDI implementation phase are shown. The plots show that for each EEDI phase, bulk carriers and tankers show remarkably similar marginal significant wave heights, which are lowest over all ship types. Container vessels demonstrate high marginal wave heights due to high installed power; passenger vessels (RoPax and cruise vessels) show significantly higher marginal wave heights than other vessel types due to advanced propulsion and steering systems (twin screw, diesel-electric main propulsion, controlled pitch propeller, pods).
A final note concerns the question whether the standard wave heights should depend on ship type. On the one hand consequences of accidents, as well as operational practices, differ between different ship types, especially between passenger and cargo vessels. Besides, the revealed differences in the marginal wave heights between different ship types reflect established design and operational practices, which should not be drastically changed by new regulations, assuming that the present level of safety is satisfactory. Both these arguments are in favour of correspondingly different standard wave heights per ship type. On the other hand, the revealed difference in the manoeuvring characteristics in heavy weather reflects, obviously, different requirements to the operational performance of the propulsion and steering systems of ships of different types, not related to safety. Obviously, reaching a conclusion regarding ship type-dependency of standard wave heights requires a prolonged discussion with all interested stakeholders.
5.4 Study of redundancy of proposed criteria with respect to existing standards
The criteria proposed by SHOPERA have been evaluated regarding their redundancy with respect to existing regulations, as a function of ship type and size.
First, the redundancy of weather-vaning criteria with respect to Intact Stability code (IS code) is investigated. The results of numerical simulations of motions in waves were combined with the assessment of steering and propulsion ability in seaway for a 8400 TEU post-panamax container ship. Bases on the analysis, it could be concluded that ship can drift in open sea without capsizing, if there is enough room; thus, the IS code seems to ensure that at least the investigated ship types will not capsize. The large roll motions could lead to a shift of the center of gravity of some ship types, such as, bulk carriers, general cargo ships and RoRo vessels, which are not considered in the existing IS code. In such cases, the ships may capsize, but this is not an issue of the minimum powering in waves, EEDI regulatory provisions. To make sure the safety of these ships in open sea, the IS code should be improved to take care of this, or ship’s ability to change heading in open sea needs to be required.
Regarding the steering criteria, it has been verified whether Vck- solution in the simplified assessment of 2013 Interim Guidelines, class requirement on minimum rudder areas and the IMO Manoeuvrability Standards ensure good correlation of steering and propulsion criteria to render the steering criterion redundant. The investigations show that:
• The Vck – solution used in the Simplified Assessment of 2013 Interim Guidelines seem not to lead to a redundancy of the steering criteria.
• The marginal wave heights of propulsion and steering criteria are still correlated to some degree with minimum rudder area required by DNV Rule (2005). The spreading of the results with minimum required rudder areas is larger than that with installed rudder areas. With the minimum required rudder areas, the fulfilment of propulsion ability at certain wave height ensures the fulfilment of the steering ability at a wave height of about 2.0 m smaller. In the joint SHOPERA-Japan submission to IMO for bulkcarriers, tankers and combinations carriers over 20,000 t DWT, the resulting wave heights for the propulsion ability were maximum 1.5m larger than for the steering ability. Thus, the results show that the minimum rudder areas given by DNV Rule (2005) lead to a slightly less wave heights for the steering criterion.
• IMO Manoeuvrability Standards have been developed to evaluate the manoeuvring performance of ships with traditional propulsion and steering systems (e.g. driven ships with conventional rudders). The results of the investigations show that the IMO Manoeuvrability Standards ensure good correlation of steering and propulsion criteria for the investigated case study ship. Further case studies are needed to verify this for other ship types and sizes.
Regarding the propulsion criterion, the analysis shows that IMO Manoeuvrability Standards cannot make the propulsion criterion proposed by SHOPERA redundant.
5.5 Sensitivity studies
The sensitivity studies were performed using a comprehensive assessment to provide recommendations for allowed tolerances for numerical, empirical and experimental methods concerning the propeller curves (KT, KQ curves), propulsion coefficients (wake fraction and thrust deduction), time-average wave-induced forces, wind forces and calm water forces.
The effect of the minimum required forward speeds (4 knot vs. 6 knot) on the results is studied with the comprehensive method. The results show that an effect of the forward speed on the marginal wave heights of different ship types is very similar. The change of the marginal wave heights is about 0.5m. The change of the required power for bulk carriers, tankers and container ships is about 26% - 33% of the required power compared to a ship speed of 4 knots. However, the change is larger for general cargo ships, namely about 27%- 37% of the required power compared to a ship speed of 4 knots.
6 Optimisation
The challenge of identifying a suitable and efficient path between the conflicting requirements of reducing greenhouse emissions and at the same time maintaining adequate safety of ships in adverse sea conditions is the main objective of the SHOPERA project. To this end, a specific work package is foreseen in SHOPERA for the development of a multi-objective optimization procedure, in which a ship’s performance is assessed holistically, thus, looking for the minimum powering requirement to ensure safe ship operation in adverse seaway/weather conditions, while keeping the right balance between ship economy, efficiency and safety of the ship and the marine/air environment. The planned optimization studies were implemented in two phases: The first phase consists of a Global Optimization, aiming to identify most favourable combinations of main dimensions, form parameters and other integrated characteristics of the ship. The second phase consists of a Detailed Optimization, including hullform details. These studies should be carried out applying refined and more accurate methods than those used for the global optimization.
6.1 Parametric Model for the Global Optimization
Parametric models for RoPax ships, tankers and bulk carriers were developed within the NAPA software. Additional parametric models for cruise ships, container ships, general cargo carriers and LNG carriers were developed within the CAESES software. These parametric models are able to perform in a fully automatic way and without the need of any user intervention a series of basic tasks:
1. Hullform development
2. Resistance and propulsion estimations
3. Development of internal layout
4. Weights estimation - Definition of Loading Conditions
5. Evaluation of transport capacity (e.g. payload and, depending on ship type, lanes length, number of cars/trucks, cargo holds or cargo tanks volume, number of TEUs)
6. Evaluation of Stability Criteria and other Regulatory Requirements (e.g. oil outflow index for tankers etc.)
7. Assessment of Building and Operational Cost, Annual Income and Selected Economic Indices (e.g. NPV, RFR based on a specified operational scenario)
8. Evaluation of Energy Efficiency Design Index (EEDI)
9. Evaluation of hydrodynamic/manoeuvring performance in adverse seaway/weather conditions based on the criteria and procedures developed by SHOPERA.
6.2 Global Optimization studies
The developed parametric model has been applied for the design and optimization of two RoPax ships. The objective of these studies was to maximise the Net Present Value of the investment, while ensuring compliance with safety regulations, EEDI Phase I or Phase II requirements and the SHOPERA criteria for manoeuvrability in adverse weather conditions, as well as various operational constraints such as draught and trim constraints for the various loading conditions, upper limit on building cost, lower limits on DWT and lanes length requirements, constraints on the average truck weight etc. The smaller of the two RoPax ships is designed for a roundtrip length of 320 sm, with a transport capacity of 1,200 passengers, 200 private cars and 21 trucks and a service speed of 23.8 kn. The second ROPAX ship is designed for a roundtrip length of 514sm, with a transport capacity of 1,800 passengers, 640 private cars and 130 trucks and a service speed of 27kn. The results from the optimization of the two ROPAX ships indicate that compliance with the EEDI Phase II requirement was quite demanding, as most of the unfeasible designs failed to satisfy this criterion. However, in the case of the small ROPAX ship, a number of 161 designs were identified, capable of complying with Phase II requirement while at the same time, only two of them were identified, marginally fulfilling Phase III requirement. For the larger ROPAX ship, a number of 293 designs were identified, capable of complying with Phase II requirement while no design was found complying with Phase III. In contrast to what was observed in the case of tankers and bulk carriers, compliance with the SHOPERA propulsion criterion in adverse weather conditions was easily achieved, even by the designs with reduced propulsion power, complying with EEDI phase III. This of course was not an unexpected result, since RoPax ships are highly powered in comparison with other types of ships of equal displacement.
Two Crude Oil Carriers have been optimized using the developed optimization platforms. The smaller of the two Oil Carriers is a SUEZMAX tanker, fitted with a main engine delivering 18,660 kW MCR at 91 RPM. The larger Oil Carrier is a VLCC (actually, the larger designs obtained had a size at or above the limits of existing VLCCs), fitted with a Wärtsilä 7RT-flex84T-D main engine delivering 29439 kW MCR at 76 RPM. For both ships, a significant number of designs was identified complying with the EEDI Phase I requirement and with the SHOPERA propulsion criterion. No design was found complying with Phase II. To investigate the possibility of achieving compliance with EEDI Phase II requirement, calculations have been repeated with smaller engines, resulting in a reduction of service speed of approximately 0.44 kn in the case of the Suezmax tanker and 0.8kn in case of the VLCC. With the smaller engines, both the EEDI Phase II requirements and the SHOPERA propulsion criterion are fulfilled.
Two Bulk Carriers have been optimized. The smaller of the two Bulk Carriers had a DWT in the area of 37,000t and was fitted with a main engine delivering 6,900 kW MCR at 129 RPM. The second Bulk Carriers had a DWT in the area of 58,600t DWT and was fitted with a main engine delivering 9,020 kW MCR at 125 RPM. For the smaller bulk carrier, EEDI Phase I requirement and the SHOPERA propulsion criterion was easily fulfilled, while a number of designs was found complying with EEDI Phase II. To investigate the possibility of achieving compliance with EEDI Phase III requirement, calculations have been repeated with a smaller engine, resulting in a reduction of service speed of approximately 1.2 kn. With this new engine, both the EEDI Phase III requirements and the SHOPERA propulsion criterion are fulfilled. For the larger bulk carrier, it was also possible to find a series of designs complying with the EEDI Phase I requirement, although by a relatively small margin, and at the same time fulfilling the SHOPERA propulsion criterion. No design was found fulfilling Phase II requirement. A smaller engine has been selected and calculations for the obtained feasible designs were repeated, resulting in a service speed reduction of approximately 0.7 kn. With this new engine, both the EEDI Phase II requirements and the SHOPERA propulsion criterion are fulfilled.
Two containership case studies have been examined: a 5,000 TEU and a 10,000 TEU containership. The optimization studies resulted in a series of designs complying with EEDI Phase II requirements, as well as with the SHOERA propulsion and steering criteria. In contrast to what was observed for tankers and bulk carriers, for the smaller Container ship the steering criterion was easier to comply with than the propulsion criterion. In the case of the larger Container ship optimization, some ships (particularly those with DWT around 90 kt) are also exhibiting a larger margin with respect to the steering criterion, while for those with a DWT above 110 kt the opposite seems to be true.
The optimization of a 46,000 ton DWT General Cargo ship has been also carried out, resulting in a series of design alternatives complying with EEDI Phase II requirements, as well as with the SHOERA propulsion and steering criteria. Also in this case, the steering criterion was easier to comply with than the propulsion criterion.
The Cruise Ship global optimization study was carried out for a ship designed for worldwide and year-round operation following the summer season in Europe and Caribbean areas, thus assuming a constant number of passengers and revenue. Initially 50 feasible designs were found. However after careful screening of the candidates the number of feasible designs has decreased to 37. Some designs have been rejected due to poor resulting geometry. The obtained results indicate that compliance with EEDI Phase II & III was easily achieved. Compliance with the SHOPERA criteria for manoeuvrability in adverse weather conditions was also achieved. The results were obtained with Level 2 criteria as developed for Cruise Ships with CPP propulsion.
The LNG global optimization study was carried out for a ship designed for worldwide and year-round operation. Initially 60 feasible designs were found. However after careful screening of the candidates the number of feasible designs has decreased to 34. Some designs have been rejected due to poor resulting geometry. The obtained results indicate that compliance with EEDI Phase II & III was not easily achieved, many designs passed Phase II but almost all failed to pass Phase III. Compliance with the SHOPERA criteria for manoeuvrability in adverse weather conditions was achieved, with no particular problems observed to pass the 6 knots propulsion threshold. The results were obtained with Level 2 criteria as developed for Single Screw FPP propulsion.
6.3 Local hullform optimizations
Five ship types were selected for detailed hullform optimization. Three of them have been extensively studied in the other WPs of SHOPERA; the Calmac RoPax, the DTC container ship and the KVLCC2 tanker. A Cruise Ship, derived by the global optimization was the 4th ship selected for detailed hullform optimization studies and finally the D-Bulker of NAPA was also used by courtesy of NAPA Ltd. The Calmac RoPax represents a small Roro Passenger ferry, which is operating in area where both confined waterways and adverse open sea weather conditions prevail. Two versions were analysed: with and w/o a bulbous bow. For the KVLCC2 tanker and the D-Bulker, along with the original version, featuring a bulbous bow, two alternatives were tested, one with a bulbous bow of increased size and one w/o a bulbous bow.
The hydrodynamic performance analysis both for the tanker and the bulk carrier revealed that the larger bulbous bow section seemed to decrease the resistance both in shallow and deep water. The difference of resistance in shallow and deep water was significant. The versions without the bulbous bow provided the largest resistance in all conditions.
The added resistance in waves of the tanker ship was minimized with the non-bulbous bow version. This version, however, produced clearly the highest resistance values in calm water. Quite the converse trend was observed with the bulkers, as the version with no bulbous bow, had clearly the highest value for the added resistance in waves.
The bow form optimization of the Cruise ship and the Container ship has been conducted to ascertain the performance of their hull in terms of the added resistance in waves. The step-wise modifications were done on the hull and the added resistance in waves of different frequencies were calculated. An in-house code was used based on the pressure integration method. In the first stage of the work for the cruise ship optimization, a sensitivity analysis of 15 parameters was made by changing by ±10% the original values. Next the most influent parameters were identified and a response surface was fit to the results, using a linear polynomial approximation. Finally by determining the minimum value of the added resistance, the optimum combination of the parameters was obtained. In the bow form optimization of a Container ship hull, all the form parameters were used. Next a response surface was fit to the results of a systematic variation conducted by altering the hull parameters by a factor of ±10%. Finally, by determining the minimum value of the added resistance, the optimum combination of the form parameters was obtained.
References
• Papanikolaou, A., Zaraphonitis, G., Bitner-Gregersen, E., Shigunov, V., El Moctar, O., Guedes Soares, C., Reddy, D.N. Sprenger, F., “Energy Efficient Safe Ship Operation (SHOPERA)”, 2015 World Maritime Technology Conference (WMTC150), 3-7 Nov. 2015, Rhode Island (USA).
• Papanikolaou, A., Zaraphonitis, G., Bitner-Gregersen, E., Shigunov, V., El Moctar, O., Guedes Soares, C., Reddy, D.N. Sprenger, F., “Energy Efficient Safe Ship Operation (SHOPERA)”, Proc. 12th Int. Marine Design Conference (IMDC2015 ), 11-14 May 2015, Tokyo (Japan)
• Papanikolaou, A., Zaraphonitis, G., Bitner-Gregersen, E., Shigunov, V., El Moctar, O., Guedes Soares, C., Reddy, D. N., Sprenger, F., “Minimum Propulsion and Steering Requirements for Efficient and Safe Operation (SHOPERA)”, Invited paper, 37th Motorship Propulsion and Emissions Conference, 4-5 March 2015, Hamburg (Germany).
• Shigunov, V., Papanikolaou, A., “Criteria for Minimum Powering and Maneuverability in Adverse Weather Conditions”, 14th Int. Ship Stability Workshop (ISSW), 29th Sept.- 1st Oct. 2014, Kuala Lumpur, Malaysia.
• V. Shigunov (2015), “Manoeuvrability in adverse conditions”, Proc. 34th Int. Conf. on Ocean, Offshore and Arctic Engineering OMAE2015, St. John's, Newfoundland, Canada; Paper Nr. OMAE2015-41628.
• Bitner-Gregersen, E.M Guedes Soares, C. and Vantorre, M., “Adverse weather conditions for ship manoeuvrability”, Transportation Research Procedia 14 (2016) 1631–1640. (Presented also at the 6th EC Transport Research Arena April 18-21, Warsaw, Poland 2016).
• Bingjie Guo, Eivind Ruth, Håvard Austefjord, Elzbieta M. Bitner-Gregersen, Olav Rognebakke, “Time domain Analysis on Ship Maneuvering in Adverse Sea State”, OMAE2016 – 54589, Proceedings of the ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering OMAE2016, 19 – 24 June, 2016, Busan,South Korea.
• N . P . Ventikos , A . Koimtzoglou , K . Louzis , and E . Eliopoulou, “Statistics for marine accidents in adverse weather conditions”, Maritime Technology and Engineering (MARTECH) 2014.
• Prpić-Oršić and Faltinsen (2012) Estimation of ship speed loss and associated CO2 emissions in a seaway, Ocean Engineering, 44, 1, 1-10 .
• R. Vettor & C. Guedes Soares, “Multi-objective Route Optimization for Onboard Decision Support System”, 11th International Conference TRANSNAV 2015 on Marine Navigation and Safety of Sea Transportation - Gdynia (17th - 19th June, 2015).
• Papanikolaou, A., Liu, S. Zaraphonitis, G. (2014), “Time Domain Simulation of Nonlinear Ship Motions Using an Impulsive Responsive Function Method”, 2nd International Conference on Maritime Technology ICMT2014, Glasgow.
• Amini Afshar, H.B. Bingham and R. Read. (2015), “A high-order finite-difference linear seakeeping solver tool for calculation of added resistance in waves”, 29th International Workshop on Water Waves and Floating Bodies, Bristol, UK. Available from: http://www.iwwwfb.org.
• el Moctar, O., V. Shigunov and T. Zorn, “Duisburg Test Case: Post-Panamax Container Ship for Benchmarking”, Journal of Ship Technology Research, Vol.59 No.3 pp. 50-65, 2012.
• Ley, J., S. Sigmund and O. el Moctar, “Numerical Prediction of the Added Resistance of Ships in Waves”, Proc. 33rd ASME Int. Conf. on Ocean, Offshore and Arctic Engineering, San Francisco, USA. - Paper Nr. OMAE2014-24216, 2014.
• Cura Hochbaum, A. and M. Voigt, “Towards the Simulation of Seakeeping and Manoeuvring based on the Computation of the Free Surface Viscous Ship Flow”, Fukuoka, Japan, 24th ONR Symposium on Naval Hydrodynamics, 2002.
• Brix, J. E. (1993),” Manoeuvring Technical Manual” – Seehafen Verlag, Hamburg.
• Blendermann, W. (1993), “Parameter identification of wind loads on ships”, Journal of Wind Engineering and Industrial Aerodynamics, 51 (1993), p. 339.
• Fujiwara, T., Ueno, M. and Ikeda, Y. (2006), “Cruising performance of a large passenger ship in heavy sea”, Proc. 16-th Int. Offshore and Polar Engineering Conf., Vol. III, pp. 304-311
Potential Impact:
1 Potential Impact
The ultimate aim of the project is to develop revised guidelines for various types of ships to evaluate the ability of ships to maintain manoeuvrability under adverse conditions. The proposal for the guidelines has been prepared and submitted to IMO-MEPC 70 with the aim of their finalisation and adoption at MEPC 71. The key results and conclusions of the project have been submitted as an accompanying information paper. The submission was done through the flag state delegation of Norway and supported by the member states Denmark, Germany and Spain.
The revised guidelines for definition of the minimum required power and steering performance to maintain manoeuvrability under adverse conditions, submitted to IMO-MEPC 70 for consideration and possible adoption at MEPC 71, will, if adopted, shape ship designs in the post-EEDI era, will have significant contribution towards the preservation of the current levels of safety of ships operating in adverse weather condition and will ensure widest possible exploitation of the project results. Besides, the new numerical methods, software tools and testing techniques developed in the project would be urgently required in the industry upon adoption of the updated guidelines, which will ensure their world-wide exploitation. In addition, the developed optimisation techniques, which allow combining safety in adverse conditions with EEDI requirements, would also be demanded by the industry.
Existing software tools, already developed by a project partner before the project start, that were validated, refined, adapted or extended during the project, remain at the disposal of this partner. New software tools that have been developed during the elaboration of the project will remain for their exploitation at the disposal of the partners that were involved in their development with a positive impact on the competitiveness of the corresponding partners as well as on the design of safer and more efficient ships. In both cases, the software tools will be exploited after the end of the project by providing services to the industry and by using them in research, development and education.
Innovative experimental techniques and procedures developed in the project will be further exploited by the partners that were responsible for their development.
The optimized ship designs will be exploited by the partners involved in their development, whereas the new knowledge and understanding of the behaviour of various types of ships at low speed under adverse sea conditions will be openly available to the scientific community.
2 SHOPERA - Exploitation Plan
Activities and measures for the exploitation of the research output were coordinated by the Exploitation Committee, consisting of the Project Coordinator, the WP1, WP6 and WP7 leaders (DNV, LR and GL, respectively) and, additionally, RINA as a representative of classification societies and also DAN and FSG as representatives of the participating ship operators and yards. A preliminary Exploitation Plan has been issued with the Mid-Term Assessment Report. In this deliverable, the Exploitation Plan is finalised.
2.1 Exploitable Results
2.1.1 Revised Guidelines
The ultimate aim of the project is to develop revised guidelines for various types of ships to evaluate the ability of ships to maintain manoeuvrability under adverse conditions. The proposal for the guidelines has been prepared and submitted to IMO-MEPC 70 with the aim of their finalisation and adoption at MEPC 71. The key results and conclusions of the project have been submitted as an accompanying information paper. To ensure awareness of the key stakeholders at IMO about the project’s objectives, methods and results and to facilitate acceptance of the results by IMO, the following activities have been conducted:
1. During the project, five papers have been submitted to IMO-MEPC sessions from MEPC 67 to MEPC 70 regarding objectives and the time plan of SHOPERA, its aims, deliverables and results to ensure awareness of the key stakeholders at IMO about the project and facilitate acceptance of the results by the IMO at the end of the project. Moreover, two presentations were done at IMO MEPC to support the submissions with personal explanations and feedback. As a result, IMO-MEPC 67 decided to wait up the completion of the project SHOPERA before updating the 2013 Interim Guidelines. Several IMO delegations referred to the project and its anticipated contribution.
2. The project SHOPERA has closely collaborated with the parallel RTD project conducted in Japan, funded by the Japan Government, NKK class and Japan Shipyard Research Association, and coordinated by the Japan Society of Naval Architects and Ocean Engineers. The two projects have been able to submit a common proposal to IMO-MEPC 70 with agreed contents of the revised guidelines.
3. Four public workshops were organised by SHOPERA and two international workshops were organised by Japan, which included presentations of the project plans, contemporary results and outlined the final guidelines.
2.1.2 Assessment Procedures
The proposal for the revised guidelines developed by the project allows free choice between three assessment procedures: Comprehensive Assessment, Simplified Assessment, and the Sufficient Propulsion and Steering Ability Check.
The Comprehensive Assessment allows for the best accuracy by solving coupled nonlinear motion equations in the time domain, and can be implemented in a dedicated software tool. Several partners have developed such software tools during the project; these tools will remain at the disposal of the partners that were involved in their development and will be exploited by providing services to the industry and by using them in research, development and education.
The Simplified Assessment, a first-principle assessment with reduced number of considered situations and reduced complexity of motion equations, can be implemented as a spreadsheet calculation. The MS Excel spreadsheets developed by Germanischer Lloyd were distributed to the ship yards, design offices, classification societies and universities to be used in case studies and optimisation exercises during the project and will be freely available after the end of the project.
The Sufficient Propulsion and Steering Ability Check is based on pure empirical formulae, defining the required installed power as a function of main ship parameters and having a complexity of a pocket calculator, thus this assessment level can be easily used by anybody once adopted.
Project results will also be used for the development of classification rules by the classification societies.
2.1.3 Evaluation Methods
Both Comprehensive and Simplified Assessments are based on a modular principle, so that the designers and administrations can choose between numerical, experimental or empirical methods for different input elements to the procedure. From the required input elements (time-averaged surge and sway forces due to waves, wind forces, calm-water manoeuvring reactions, rudder forces, propeller forces and engine characteristics), the time-average surge and sway forces due to waves and the rudder forces were found to be the most uncertain among the most important contributions.
Therefore, significant effort was dedicated in the project to the development, validation and exploitation of the numerical and empirical methods for the time-average wave forces (including added resistance) and rudder forces. For the time-average wave forces (including added resistance), extensive model tests were performed for three ship types (a modern 14,000 TEU container ship design, a standard VLCC tanker and a small European RoPax) in over 1,300 conditions, including various draughts, water depths, forward speeds and wave directions, lengths and heights to generate a unique validation database for numerical and empirical methods. The results are available to all project partners for the validation of numerical tools. Several numerical methods were developed and validated, which will remain at the disposal of the partners that were involved in their development and will be exploited after the end of the project by providing services to the industry. In addition, several empirical formulae were developed of various degree of complexity, which are simple enough to be used by any designer or administration.
Moreover, to evaluate the world-wide availability of methods that can be used in the practical assessment, SHOPERA conducted an international benchmark study of numerical and empirical methods for the time-average wave-induced forces and moments and simulation of ship manoeuvres in waves. Sixteen organizations (six SHOPERA partners and ten external participants) from all over the world participated in the study, including industry, research institution and academia, therefore, this exercise represents an important exploitation activity. The results of this benchmarking exercise have been published at the joint SHOPERA-ITTC workshop in London and will be described in a detailed public report soon.
Another open benchmarking exercise dedicated to ship motions and time-average wave-induced forces in shallow water will be carried out shortly after the end of SHOPERA, using measurement data from captive and free-running model tests in waves in medium deep and shallow water obtained in SHOPERA. The results of this benchmarking should be presented at the 5th MASHCON Conference which will be held in 2019 in Ostend.
The experimental results used within these benchmarking exercises will be publicly available; other experimental results remain available only to SHOPERA partners, but will become publicly available once SHOPERA partners publish them in the open literature.
2.1.4 Optimisation Results
In the project, optimisation techniques, software tools and software have been developed, which allow combining sufficient safety in adverse conditions with EEDI requirements. These techniques and tools will remain at the disposal of the partners that were involved in their development and will be exploited after the end of the project by providing services to the industry and by using them in research, development and education.
The optimized ship designs will be exploited by the partners involved in their development, whereas the new knowledge and understanding of the behaviour of various types of ships at low speed under adverse conditions are openly available to the scientific community for further exploitation through publications.
2.2 Exploitation Plan
The key project outcomes, their exploitation area, exploitation timeline and responsible partners are listed below.
Exploitable product(s) or measure(s): D1.1.1 Environmental data sets
Sector(s) of application: Ship design, Rule development, Education
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: DNV, IST, GL, EVFH
Exploitable product(s) or measure(s): D1.2.1 Accident data
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: NTUA, GL
Exploitable product(s) or measure(s): D1.3.1 Safety criteria
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: GL
Exploitable product(s) or measure(s): D2.1.1 Potential flow methods for seakeeping and stability in waves
Sector(s) of application: Ship design, Ship operation (routing, SEEMP), Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: IST, GL, NTUA, SU
Exploitable product(s) or measure(s): D2.2.1 Potential flow methods for manoeuvring in waves
Sector(s) of application: Ship design, Ship operation (routing, SEEMP), Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: DNV, GL, IST, NTUA, RINA, DTU
Exploitable product(s) or measure(s): D2.3.1 Potential flow methods for manoeuvring in confined waters
Sector(s) of application: Ship design, Ship operation (routing, SEEMP), Rule development
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: IST, SU
Exploitable product(s) or measure(s): D2.4.1 Field methods to determine ship hydrodynamic characteristics
Sector(s) of application: Ship design
Timetable for commercial use: In use
Owner and other partner(s) involved: TUB, VTT, IST, SU, UDE, GL
Exploitable product(s) or measure(s): D2.5.1 Field methods to determine ship hydrodynamic characteristics
Sector(s) of application: Ship design
Timetable for commercial use: Direct commercial use is not planned
Owner and other partner(s) involved: UDE, IST, LR, NTUA
Exploitable product(s) or measure(s): D3.1.1 Innovative experimental techniques
Sector(s) of application: Ship design
Timetable for commercial use: In use
Owner and other partner(s) involved: MARINTEK, CEHIPAR, EVFH, TUB
Exploitable product(s) or measure(s): D3.1.2 Model test data
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: In use
Owner and other partner(s) involved: MARINTEK, CEHIPAR, EVFH, TUB
Exploitable product(s) or measure(s): D4.5.1 Comprehensive Assessment software tools
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: Finalisation of guidelines (April 2017)
Owner and other partner(s) involved: GL, UDE, DNV, NTUA, RINA
Exploitable product(s) or measure(s): D4.5.2 Simplified Assessment tools
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: Finalisation of guidelines (April 2017)
Owner and other partner(s) involved: GL
Exploitable product(s) or measure(s): D5.1.1 Integrated optimization platform
Sector(s) of application: Ship design
Timetable for commercial use: In use
Owner and other partner(s) involved: NTUA, IST, UDE, FSG, ULJ, VTT, DUT, NAP
Exploitable product(s) or measure(s): D5.3.1 Optimisation know-how to combine safety with EEDI requirements
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: In use
Owner and other partner(s) involved: NTUA
Exploitable product(s) or measure(s): D7.7.1 Revised guidelines for sufficient manoeuvrability in adverse conditions
Sector(s) of application: Ship design, Rule development
Timetable for commercial use: October 2016 (submission to IMO) – April 2017 (finalisation)
Owner and other partner(s) involved: GL, LR, NTUA
3 SHOPERA-Dissemination Activities
Dissemination of the research output has been facilitated mainly through technical publications in international scientific journals, conferences and workshops. The consortium also facilitated the dissemination of the research output to a wider audience through a series of articles and presentations in public mass media. A project-specific web site has been created and is constantly updated and maintained by the coordinator during the elaboration of the project and for at least 3 years after the project’s end. A public area is maintained on the project’s web site, allowing free access to selected deliverables, reports and publications resulting from the elaboration of the project. To exchange views with external experts in ship design, hydrodynamics, safety and operation, shipowners, regulators and other stakeholders on hydrodynamic, design and regulatory aspects of norming manoeuvrability in adverse conditions, fine-tune the objectives of the project and the way ahead and, at the same time, facilitate acceptance of the project outcomes by the key stakeholders, four public workshops have been organised within the project.
3.1 Peer Reviewed Journal Papers
20 Papers, full list in D.7.6
3.2 Peer Reviewed Conference Papers
58 Papers, full list in D.7.6
3.3 Submissions to IMO
1. IMO MEPC (2014) EU Project “Energy Efficient Safe SHip OPERAtion” (SHOPERA), Paper MEPC 67/INF.14 submitted by Germany, Norway and United Kingdom
2. IMO (2016) Progress report of SHOPERA and JASNAOE projects for development of the revised minimum propulsion power Guidelines, Paper MEPC 69/INF.23 submitted by Denmark, Germany, Japan and Norway 12 February 2016
3. IMO (2016) Progress report of SHOPERA and Japan's projects and outline of draft revised Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions, Paper MEPC 70/5/20 submitted by Denmark, Germany and Japan
4. IMO (2016) Supplementary information on the draft revised Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions, Paper MEPC 70/INF.30 submitted by Denmark, Germany and Japan
5. IMO (2016) Results of research project "Energy Efficient Safe Ship Operation" (SHOPERA), Paper MEPC 70/INF.33 submitted by Denmark, Germany, Norway and Spain 19 August 2016
3.4 SHOPERA Presentations
5 submissions, full list in D.7.6
3.5 Mass media
The SHOPERA project was selected among EU funded projects for presentation at the EURONEWS channel. The video was produced by EURONEWS Science with films/interviews at ULJANIK shipyards, Croatia and CEHIPAR, Spain. The video was first transmitted by EURONEWS on Monday 26/09/2016 and broadcasted the whole week after. The program is now available in all the 13 languages on EURONEWS' website: http://www.euronews.com/programs/futuris/ and, on the EURONEWS' YouTube channels (http://eurone.ws/MMZbq and https://www.youtube.com/user/euronewsknowledge/videos).
3.6 First Public SHOPERA Workshop
The first workshop “Introduction of the Project to Key Stakeholders” was organised by GL with the assistance of NTUA on October 30, 2014, in Hamburg, to communicate the objectives of the project to the wider scientific and technical community and to the various stakeholders.
The first part of the workshop included presentations by external speakers, representing the majority of views of industry and experts at IMO (BIMCO, Greek and Danish Shipowners Associations, IACS, ITTC), industry research groups in the subject area (Common Research Ships), as well as overseas research views from Japan and India. Industry representatives underlined very high expectations about the outcome of the project regarding the future regulatory work on EEDI at IMO.
In the second part, SHOPERA partners presented challenges addressed by SHOPERA along with the state of work and the proposed way ahead. Discussions were lively and most valuable in the substance. The common feeling was that the workshop greatly contributed to the understanding of some controversial matters and clarified the view of how to proceed in the next few years, even if the subject is politically very tricky and scientifically very demanding.
The main output from this workshop was the awareness of the key stakeholders of the project and facilitation of the acceptance of the expected results. The feedback from the external participants has been used to refine the objectives of the project and shape the way ahead.
List of Presentations:
1. Jeppe Skovbakke Juhl (BIMCO) EEDI – Minimum power to ensure safe maneuvering in adverse conditions
2. George A. Gratsos (Hellenic Chamber of Shipping) Minimum power requirements for safe navigation
3. Hans Otto Kristensen (Danish Shipowners’ Association) Some thoughts about minimum power for safe manoeuvring in adverse weather conditions
4. Torsten Mundt (DNV GL) IACS contribution on the minimum required power issue: A retrospection
5. Frans Quadvlieg (Cooperative Research Ships, Group on Manoeuvrability in Waves) Manoeuvring in adverse weather
6. Reint Dallinga, Olav Rognebakke (Cooperative Research Ships, Added Resistance in Waves Group) Added resistance - physical insights. Cooperative Research Ships JIP results
7. Masaru Tsujimoto (National Maritime Research Institute) Japan's research activities on minimum propulsion power requirement - Hydrodynamic approach
8. Apurba Ranjan Kar (Indian Register of Shipping) Ship Manoeuvrability: An overview of ongoing studies by Indian Register of Shipping
9. Anton Minchev (FORCE Technology) Manoeuvring aspects at ultra-slow speeds
10. Apostolos Papanikolaou (SHOPERA, NTUA) Introduction: Overview SHOPERA
11. Elzbieta M. Bitner-Gregersen (SHOPERA, DNVGL) Met-ocean description
12. Koimtzoglou A., Louzis K., Eliopoulou E., Ventikos N.P. (SHOPERA, NTUA) Identification of ships and risk analysis of relevant marine accidents
13. Vladimir Shigunov (SHOPERA, DNVGL) Manoeuvrability criteria
14. Carlos Guedes Soares (SHOPERA, IST): Development and Refinement of Numerical Hydrodynamic Tools
15. Ould El Moctar (SHOPERA, UDE): Numerical Investigation of Added Resistance in Waves
16. Florian Sprenger (SHOPERA, MRTK) Experimental Studies
3.7 Second Public SHOPERA Workshop
The second public SHOPERA workshop was organized by IST with the assistance of NTUA on October 15, 2015 in Lisbon. The aim of this workshop was to communicate the findings of the first two years of the elaboration of the project to the wider scientific and technical community as well as to the various stakeholders and to obtain valuable feedback from the external participants regarding the set objectives and the procedures adopted in order to meet these objectives. Besides representatives of the SHOPERA consortium, there were also presenters and participants form outside the consortium and members of the SHOPERA Advisory committee, such as the International Maritime Organisation (IMO), the European Maritime Safety Agency (EMSA), the Ministry of Land, Infrastructure, Transport and Tourism of Japan, flag administrations (Netherlands) and the Association of the Netherlands Shipbuilders.
During the morning session of the workshop, external experts and SHOPERA partners addressed topics related with the general SHOPERA objectives, such us regulatory work in IMO related to the minimum powering requirements of ships in relation with the EEDI requirements, and prediction of added resistance of ships in waves. In addition, the project coordinator, Apostolos Papanikolaou presented an overview of the objectives and rational of the SHOPERA project, its workpackages and current status of work.
During the afternoon session, the progress of work of workpackages 1, 2, 3 and 4 was presented. WP1 was presented by Dr. E. Bitner-Gregersen (Task 1.1 Environmental Conditions) and Dr. Vladimir Shigunov (Criteria and Assessment Framework, Task 1.3). Then Prof. Carlos Guedes Soares and Prof. Ould el Moctar provided an overview of the software tools for the assessment of the hydrodynamic performance of ships with respect to their manoeuvring characteristics and added resistance in waves that are refined and extended in WP2 and their validation, carried out in WP4, using experimental results derived in WP3. Finally, the large program of tank tests, carried out in WP3 by MARINTEK, CEHIPAR, EVFH and TUB was presented by Dr. Florian Sprenger and Messrs. Adolfo Maron, Thibaut Van Zwijnsvoorde and Antonio Lengwinat respectively.
List of presentations
1. Masao Yamasaki, International Maritime Organisation (IMO) Marine Environment Division, Interim Guidelines for determining minimum propulsion power to maintain the manoeuvrability of ships in adverse conditions.
2. Takahiro Kijima, Director for Environment Policy, Ministry of Land, Infrastructure, Transport and Tourism, JAPAN, Revision of the Interim Minimum Power Guidelines, based on the project results such as SHOPERA and JASNAOE.
3. Torsten Mundt, DNVGL, The “min. req. Power issue” and the desire to manoeuvre out.
4. Reint Dallinga, MARIN & CRS, Netherlands, Added resistance from a linear theory.
5. Masaru Tsujimoto, NMRI, Japan, Progress of Japan's Research Activities on Minimum Propulsion Power Requirement.
6. Apostolos Papanikolaou (NTUA), Introduction-Overview SHOPERA
7. Elzbieta Bitner-Gregersen (DNVGL), Environmental Conditions
8. Vladimir Shigunov (DNVGL), Criteria and Assessment Framework
9. Carlos Guedes Soares (IST), O. El Moctar (UDE), Development and Refinement of Numerical Hydrodynamic Tools
10. Florian. Sprenger (MRTK) and other Exp. Tanks representatives, Experimental Studies
3.8 Third Public SHOPERA Workshop
The third public SHOPERA workshop was hosted by LR and jointly organised by LR, NTUA and ITTC Manoeuvring Committee on April 14, 2016 in London with representatives from the ITTC Seakeeping, Stability and Performance Committees. The aim of this workshop was to communicate the findings from the elaboration of the project to the wider scientific and technical community, to enhance collaboration of the SHOPERA partners with other research teams working on the same or similar research topics in Japan, Korea, The Netherlands as well as with the ITTC Manoeuvring Committee and Seakeeping Committee and to obtain valuable feedback from the external participants regarding the set objectives and the procedures adopted in order to meet these objectives.
Along with representatives of the SHOPERA consortium, there were also presenters and participants from the ITTC Committees for Manoeuvring, Seakeeping, Stability and Performance, members of the SHOPERA Advisory committee and other external experts. The objectives of the workshop were presented by Apostolos Papanikolaou, NTUA.
List of presentations
1. Vladimir Shigunov (DNVGL), SHOPERA: Criteria, Assessment Framework, Methods
2. Hironori Yasukawa, (Hiroshima University), Japanese R & D Project on Manoeuvring in Adverse Condition and Minimum Power Requirement of Ships.
3. Yeon Gyu Kim, Dong Jin Yeo (KRISO), Sang Hyun Kim (Inha Univ.) Research Activities on Manoeuvring in Waves in Korea.
4. Pierre-Emmanuel Guillerm (Ecole Centrale de Nantes), How to develop manoeuvring in waves standard for model tests and numerical simulation methods.
5. Yonghwan Kim (Seoul National University), Seakeeping Analysis Coupled with Manoeuvring Problem.
6. Gregory Grigoropoulos (NTUA), Towards more rational guidelines to determine minimum propulsion power for Safe Operation under adverse Weather Conditions
3.9 Fourth Public SHOPERA Workshop
The fourth public SHOPERA workshop was hosted and organised by NTUA on September 28, 2016 in Athens. The aim of this workshop was to provide the overall presentation of the elaboration of the project, with emphasis on the set objectives, adopted procedures towards the objectives, major achievements, key results, collaboration with similar studies in Japan and the Netherlands, conclusions and recommendations. In particular, the developed new guidelines for the required minimum propulsion power and steering performance of various types of ships to maintain manoeuvrability under adverse conditions were presented and discussed with the scientific community and key stakeholders. The main output from this workshop was the wide awareness of the key stakeholders, particularly IMO members, of the proposed updated guideline, and better acceptance of the project results, on the one hand, and the feedback received at the workshop on the other hand.
The first part of the workshop was devoted to presentations by SHOPERA partners presenting the major achievements of the last 12 months of the elaboration of the project, while the second part included presentations by representatives of the SHOPERA Advisory Committee and other invited external speakers, representing views of the industry. The workshop was closed by Prof. Apostolos Papanikolaou (NTUA) who discussed the submissions to IMO that resulted from the elaboration of the SHOPERA project as well as from the collaboration with the Japanese R & D Project on Maneuvering in Adverse Condition and Minimum Power Requirement of Ships.
List of presentations
1. Vladimir Shigunov (DNVGL), SHOPERA: Criteria, Assessment Framework and Guidelines.
2. George Zaraphonitis (NTUA), SHOPERA WP5: Optimization studies.
3. Martio Jussi (VTT), Detailed optimization studies in WP5 by VTT
4. Reddy Devalapalli (LR), WP6: Application / Case Studies.
5. Apostolos Papanikolaou (NTUA), Main Achievements.
6. Hironori Yasukawa (Hiroshima Univ.), Japanese R & D Project on Maneuvering in Adverse Condition and Minimum Power Requirement of Ships.
7. Johan de Jong (MARIN), MCRAW JIP, Minimum Power Requirements of Dutch Low-Power Full-Block Ships.
8. Sander de Heijer (Netherlands Maritime Technology), Study on minimum power requirements (MacRAW), submitted to IMO by the Netherlands.
9. Kim Rene Hansen (MAN Diesel & Turbo), IMO EEDI and Minimum Propulsion Power from an Engine Designer’s Point of View.
10. Torsten Mundt (GL) & Apostolos Papanikolaou (NTUA), Submissions to IMO, way ahead.
List of Websites:
http://shopera.org
