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Tools for Ultra Large Container Ships

Periodic Report Summary 1 - TULCS (Tools for Ultra Large Container Ships)

Project context and objectives:

The increase in world trade has largely contributed to the explosion in sea traffic. As a result, the market demand is leading to ultra large container ships (ULCS), which have a capacity up to 18 000 TEU with length up to 400 m, without changes of the operational requirements (speed around 27 knots). The particular structural design of the container ships, leads to open midship sections, resulting in increased sensitivity to torsional and horizontal bending loads which is much more complex to model numerically. At the same time, due to their large dimensions, the ULCS become much 'softer' and their structural natural frequencies become significantly lower so that the global hydroelastic structural responses (springing and whipping) can become a critical issue in the ship design and should be properly modelled by the simulation tools.

It is fair to say that the modelling of springing and whipping is still a challenge and that there are no fully satisfactory numerical tools able to deal with these issues in the general case. At the same time, the other available tools such as model tests and full scale measurements have their own drawbacks (high cost, limited number of the covered cases, representativity of the beam model) so that no definite opinion can be made on this subject for the moment. Anyhow, it seems to be clear that more attention will be given to these issues in the future because there is clear evidence (numerical, model tests and full scale) that these hydroelastic types of structural responses exist and that their effects can be important both for fatigue and extreme response issues.

The particular importance of whipping and the insufficient knowledge in its modelling is clearly reflected in the recent Marine Accident Investigation Branch (MAIB) report, following the loss of the MSC Napoli container ship:

- It is likely that the hull of MSC Napoli was subjected to additional load due to whipping.
- It is apparent that whipping effect is currently very difficult to reliably calculate or model.
- In view of the potential increase in wave loading due to whipping effect, further research is required to ensure that the effect is adequately accounted for in ship design and structural analyses, and that sufficient allowance is made for the effect when determining design margins.

The final goal of the present project is to deliver clearly validated design tools and guidelines, capable of analysing all hydro-structure interaction problems relevant to ULCS.

Project results:

At the beginning of the project, the consortium agreed to accept the Korean shipyard Hyundai Heavy Industry (HHI - the world biggest shipyard) as the associated partner under special conditions. The presence of HHI allowed having access to the detailed data of the reference ship (9200 TEU ULCS Rigoletto) which is used in the project and which was built by HHI. At the same time HHI design experience will help for better organisation of the different numerical developments and for more dedicated exploitation of the project results.

At the same time, the cooperation with another EU project EXTREME SEAS was established. This cooperation was planned at the beginning of the project in order to make the experimental database more complete. Even if the two projects (EXTREME SEAS and TULCS) have different final objectives there were several common points regarding the issues related to the ship structural response in extreme sea conditions. It was thus agreed to join the effort and significantly extend the initial test matrix. This led to a much more useful experimental database.

The final TULCS project consortium is composed of 13 full members:

1. Bureau Veritas - Registre International de Classification de Navires et d'Aeronefs SA BUREAU VERITAS France, http://www.bureauveritas.com
2. Stichting Maritiem Research Institut Nederland MARIN Netherlands, http://www.marin.nl
3. CMA CGM CMA - CGM France, http://www.cma-cgm.com
4. Canal de Experiencias Hidrodinamicas de El Pardo CEHIPAR Spain, http://www.cehipar.es
5. Ecole Centrale de Marseille ECM France, http://www.centrale-marseille.fr
6. Technische Universiteit Delft TUD the Netherlands, http://www.tudelft.nl
7. Sveuciliste u Zagrebu, Fakultet Strojarstva i Brodogradnje UNIZAG-FSB Croatia, http://www.fsb.hr
8. Danmarks Tekniske Universitet DTU Denmark, http://www.dtu.dk
9. University of East Anglia UEA UK, http://www.uea.ac.uk
10. Sirehna - Societe d'Ingenierie de Recherches et d'Etudes en Hydrodynamique Navale SA SIREHNA France, http://www.sirehna.com
11. Wikki Limited WIKKI UK, http://www.wikki.co.uk
12. Hydrocean HO France, http://www.hydrocean.fr
13. Brze Vise Bolje d.o.o. BVB Croatia, http://www.bvb.hr and one associated member
14. Hyndai Heavy Industry HHI Korea, http://www.hhi.co.kr

From technical point of view, the overall progress of the project is in line with the objectives in spite of the delay which was taken at the beginning of the project.

In particular, the first model test campaign on simplified elastic model was successfully performed by ECM and the planning for the second campaign is ready. At the same time, the experimental plan for the sophisticated model tests on 9200 TEU container ship was agreed in between the partners and the planning was coordinated with the EXTREME SEAS project. Thanks to the cooperation with EXTREME SEAS, the experimental campaign will be much richer and many important test conditions, which would not be possible without cooperation, were added to the planning and will allow for more detailed investigations of hydroelastic phenomena. At the same time, the experimental model is based on a new promising concept proposed by Marin and Cehipar. The experiments are planned in June 2011.

The numerical developments are also progressing well. The most critical part of the developments, which concerns the numerical solution of the seakeeping problem with forward speed (still an open problem!) is progressing well and the first parts of the numerical codes were built by BV, MARIN and TUD. Even if the approaches which were chosen by different partners are quite different, they are quite complementary and represent the state of the art on the subject. It is important to note that it was decided, at the beginning of the developments, that more accents will be put on the most difficult part of simulations which is the linear seakeeping problem with forward speed and the move to the time domain will be done using the classical approach following the method proposed by Cummings and Ogilvie. Indeed, developing the nonlinear time domain model from scratch was judged to be too ambitious and, at the same time the common practice nowadays is more oriented to the use of the hybrid frequency/time domain methods. This reduces the risk of not achieving the planned objectives and give confidence in having the practical tools at the end of the project. First validation of the numerical seakeeping codes was performed using the data available in the literature and the final validation will be done using the data from the TULCS experiments.

On the hydroelastic side of the modelling (springing and whipping), the progress is also very good. UNIZAG-FSB developed quite unique beam model for container ship which allows very good representation of the hydroelastic ship behaviour for first several elastic modes. The advantage of using the beam model is quite obvious because it allows for very quick modelling of the ship structure. Indeed, thanks to the beam simplification the modelling time of the ship structure is drastically reduced (from few months to few days) when compared to full three dimensional (3D) finite element (FE) models. The proposed model was validated on the case of 7800 TEU container ship and the validation is ongoing on 9200 TEU vessel. It is very important to note that this task is far from trivial because of the particular structure of the container ship (open sections) and the progress which has been done is really outstanding and several interesting publications were issued by UNIZAG. At the same time, the coupling procedure with hydrodynamic model was also developed and tested on existing hydrodynamic software (BV Hydrostar). Thanks to the method which is used the coupling with the hydrodynamic models which are under development within the WP3 is straightforward.

Concerning the hydroelastic method based on coupling of the 3DFE model and 3D hydrodynamic model the progress which was made up to now is also very good. Indeed, the existing numerical code from BV was upgraded to deal with any type of the FE model and all the checking were done, so that the code became extremely efficient. The coupling with the existing hydrodynamic code Hydrostar is also performed along the same line as the beam model.

Within the developments of the hydroelastic models, it is important to note that, thanks to the methodology adopted, the coupling of the structural part (both beam and FEM based) with any hydrodynamic code is straightforward. This point is very important because this will allow an easy coupling with the hydrodynamic codes developed in WP3.

Parallel to the above developments, relatively independent developments on slamming were undertaken in WP5. This is also one of the important critical issues in the context of whipping calculations. Due to the complexity of the modeling, several methods were chosen going from the simplified ones (two-dimensional (2D) strip approach, 3D MLM method, semi empirical 3D method, CFD VOF method and CFD SPH method). The final plan is to include the simplified method into the overall loop for whipping calculations, while the more complex methods based on CFD approach will be used first to check their domain of validity and after that for calibration of the simplified methods and eventually for the calculations in the specific design cases where the CPU time issues are not limiting factor. The progress of this WP is good especially on the side of the simplified methods. The developments on the CFD side were blocked for a while because of the unavailability of the exact hull form of the ship (see above discussions about the cooperation with HHI). However, the necessary preparations of the CFD tools were done and their use on the case of the TULCS example ship are ongoing.

On the experimental side (WP6), the progress is satisfactory even if some delay was observed due to the unavailability of the exact hull form data before HHI joined the project. First series of the simplified model (highly elastic model at zero forward speed) tests was performed in ECM and the final report was issued. Limiting validations of the hydroelastic model were done by BV showing the promising results for the methodology which was chosen. However, the final test of the methods will be the comparisons with sophisticated model tests on the real ship advancing with forward speed in realistic sea states including the important whipping response. The final design and planning of these sophisticated model tests, which will be done in CEHIPAR, were agreed in between the TULCS partners and combined with the needs of the EXTREME SEAS project.

Full scale measurement campaign (WP7) is also progressing well. All the additional sensors and the sea state measurement system are now operational and first measurement data are collected (12 months records for ship motion and stresses, seven months of sea state data). The analysis of data and their integration into the overall project scheme is under progress.

In the WP8 which deals with overall technical coordination and integration of different tools, the progress is also significant. The methodologies both for extreme and fatigue types of loadings and responses were proposed by DTU and the graphical interface for the integration of different tools was designed by BVB and waiting for the input from other WPs.

On the dissemination and exploitation side (WP9), in order to make aware the international community of the importance of the global hydroelastic ship responses (springing and whipping), the First International Workshop on Springing and Whipping of ships was organised in Dubrovnik, CROATIA, from 10 to 11 November 2010. More than 50 experts from all over the world were participating at this workshop. During the two days, the experience of each other was exchanged through 28 interesting presentations followed by the useful discussions.

In conclusion, we can say that the progress of the project is satisfactory and all WPs are performing well. No significant delays are expected in spite of some difficulties at the beginning of the project.

Potential impact:

The main final objective of the project is to increase the safety and security of sea transport by container ships. This will be done by proper analysis of all the aspects of ULCS particular structural design.

The end products of the project will be the dedicated numerical tools and guidance for their use within the dedicated design methodology. Specific accent is put to the validation of the tools and that is why an important part of the project concerns the experimental and full scale measurements.

The so-called direct approach design methodology will be built around these tools in order to have more rational design procedure as compared to the classical rule procedures of classification societies. This direct approach is necessary because the actual size of ULCS often exceed the size commonly covered by the rules. At the end of the project, a simplified procedures will also be investigated and amendment to the existing rules based practice will be proposed.

Important accent will be put on dissemination of the project findings. This will be done through the dedicated publications and two international workshops. Contact with IMO will be established and dedicated presentation proposed. At the same time, the executive summary of the project will be put in the form of BV information note and will be distributed to the IACS members.

It is also important to note that, even if the project is specifically oriented to ULCS the results of the project might be used for other ship types too. Indeed, the methodologies and the tools are only slightly dependent on the ship type and can be applied, with small modifications, to any ship type and also to the floating off shore platforms.

Project website: http://www.fsb.hr/tulcs

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