Community Research and Development Information Service - CORDIS

Periodic Report Summary - STREAMLINE (Strategic research for innovative marine propulsion concepts)

Increasing environmental concerns and soaring oil prices create a new focus on fuel efficiency for the marine industry. The need for radically new propulsion concepts delivering a step change in efficiency becomes apparent. Maritime transport continues to grow at twice the rate of global gross domestic product (GDP), with between 80 to 90 % of all goods imported and exported by Europe being transported by sea. Within the European Union more than 40 % of goods are carried through water. With the World Bank predicting that world trade will triple over the next 25 years, it is clear that the world fleet must be able to adapt to service this unprecedented growth, as well as to tackle the environmental issues that will occur.

There has been little real change in the state of the art for conventional screw propeller propulsion for many years. More substantial progress was achieved through the use of better propulsor configurations and improved integration of the propeller with the vessel hull hydrodynamics, which achieved significant fuel savings.

The STREAMLINE project was the response of the marine community to these challenges. Radically new propulsion concepts, delivering an increase in efficiency of at least 15 % over the state of the art were developed. Maximisation of energy conversion combined with low levels of cavitation, noise and vibration was also achieved. The research looked at novel applications of large area propulsion, a biomechanical system and distributed thrust via multiple propulsors.

Moreover, STREAMLINE investigated methods to fully optimise current systems including conventional screw propeller systems, pods and waterjets. The key issue was the exploitation of new computational fluid dynamics (CFD) methods to pursue improvements without dramatic vessel configuration changes.

The third objective of STREAMLINE was to develop advanced CFD tools and methods to optimise the hydrodynamic performance of the new propulsion concepts, focussing on the analysis of integrated hull and propulsor.

The first 18 months of STREAMLINE were focussed on establishing the baseline configurations and data sets, tools and methodologies to evaluate and design the state of the art concepts. During this period a systematic evaluation of three possible hull configurations was carried out to establish where the large area propeller (LAP) would be most effective. The CFD code that was used to carry out the evaluations was validated using towing tank data generated for the 8 000 dead weight tonnage (DWT) hull that was selected.

The computational investigations established the optimum position behind the ship for the propeller and compared the effect of increasing the propeller size. As was hoped for, the results showed clearly that there was significant increase in propulsive efficiency to be gained by increasing the propeller diameter.

Further verification of the CFD methodology was obtained by experimentation on the effect of the propeller on the free surface. Experimental work with a propeller running near the free surface in a cavitation tunnel was carried out and compared to calculation so that this effect could be properly accounted for. Additionally, the inclined keel hull concept was investigated as a method to accommodate the LAP, involving model testing and CFD analysis. In order to properly baseline the LAP against the state of the art, a systematic study using CFD of the stern and propulsion arrangements was also carried out.

The developed 'Walvisstaart pod' (WSP) was a novel propulsion concept for inland water ways that mimicked the motion of a whale's tail to generate thrust with up to 30 % improved efficiency over a conventional arrangement. During this period the detailed design of the WSP was mainly completed.

The internal mechanism for driving the blades was significantly simplified and the design was anticipated to meet its requirement specifications not only in terms of performance, but also for 50 000 hours of operation. The redesign also significantly reduced the power required to position the blades compared to the initial concept. The three-dimensional and detailed manufacturing drawings of all the major components were completed and evaluated by the manufacturers.

Moreover, a ship form that was free from intellectual property rights was developed. Since there was no industry benchmark for an inland waterway vessel, this hull would be publicised to support other research into inland vessel optimisation. Testing of this form was carried out with two alternative configurations to investigate air suction into the propellers from the sides. Typically this phenomenon was prevented by a 'tunnel' design. Predicting the phenomenon proved to be very tricky and in the next period some innovative new tests were planned to investigate new hypotheses.

Furthermore, solutions to enhance the hydrodynamic efficiency of screw propeller systems were developed. During the first reporting period of the STREAMLINE project, the first release of the proposed CFD models were applied for the analysis of the hydrodynamic performance of ship hulls and propellers. Hull and propeller interaction was investigated both at model and full scale. In this context, both viscous flow models and hybrid viscous or inviscid models were applied to ship flow hydrodynamic studies.

Furthermore, advanced shape manipulation techniques and problem parameterisation schemes were applied for the optimisation of hull forms. The extension of this technique to shape optimisation of propeller blades represented an innovative result achieved in the project. Comparative analysis between model test data and results from CFD simulations highlighted that the proposed computational models were fully adequate to describe flowfield features.

The requirement specification for the new waterjet concept was written and a selection of alternative arrangements was evaluated with some use of CFD. These included the use of shape memory alloys that were developed for aerospace applications in the ADVACT project, passive multi-channel inlets and active conventional actuation of the inlet. The waterjet was also tested at high and low speeds using a special hull design that featured a 'hump' in the resistance curve for the hull that assisted in evaluating the new inlets through self-propulsion tests.

Moreover, contra rotating pod (CRP) design was undertaken and the propeller designs tested in a cavitation tunnel. The design was then installed on a modified hull model for a RoRo vessel and became subject to resistance, wake and self-propulsion tests. Compared to a conventional twin-screw design the model achieved a significant power reduction.

Investigation began into an integrated contra rotating pod (ICP) design. In particular, the boundary element method (BEM) was shown to generate blade loading and overall efficiency with good accuracy, even though both thrust and torque were likely underestimated.

Mesh coupling methods were developed and tested for both sliding grid and overlapping grid approaches. Through testing on well established classical geometries the efficacy of the methods was validated. Another more practical numerical test case was then investigated, involving a propeller interacting with a free surface, and showed that the adaptive grid refinement procedures combined with sliding grids was an efficient approach.

In the overlapping grid approach a problem with flickering pressure fields in some simulations was observed. Tracing this back to overset interpolation errors, this was significantly improved by implementing second order interpolation schemes.

Grid refinement algorithms were implemented for both FreSCo+ and ReFRESCO. Test cases were examined and compared with manually defined grids. The results were very favourable for the automatically refined grids, showing that the algorithms produced accurate results in a very efficient manner. Ongoing investigations established the optimum criteria for grids' refinement.

Parallelisation and load balancing algorithms were also implemented to the codes and test cases showed that significant gains in computational efficiency were made compared to the imbalanced code. This would allow the new algorithms to be run effectively.

During the present reporting period good progress was made in multi-phase flow modelling capabilities of solvers being used for design work throughout the STREAMLINE project. In particular, a cavitation model combined with hull free-surface flow modelling was implemented. This methodology allowed to investigate problems where the effects of free-surface and propulsor interactions were not negligible.

Furthermore, the inclusion of cavitating flow modelling in a compressible-flow solver was investigated. Early applications to simple problems demonstrated that the resulting multi-phase CFD model represented a powerful approach to accurately simulate the physics of cavitation like source of noise signatures and risk of erosion.

In parallel to enhancing the capability of CFD models to predict cavitating flow phenomena work was also devoted to the development of hydroacoustic models. Innovative approaches to describe noise emissions related with propeller wakes, propeller-rudder interaction and the scattering of rigid surfaces in the hull aftbody were developed and tested on representative case studies. To achieve a full exploitation of these hydroacoustic models, the coupling with viscous hydrodynamic models was investigated and suitable interfaces were developed.

The development of hybrid viscous and inviscid models by coupling RANS and BEM solvers was addressed. During the first reporting period, the improvement of existing hybrid solvers was carried on and validation studies were performed on representative case studies. Moreover, propeller-flow modelling by inviscid-flow BEM was assessed. Activity focused on improving the capability to describe blade loading over a wide range of operating conditions. To this purpose, wake alignment procedures and viscosity effects' corrections were addressed. In addition to that, an existing BEM solver for isolated propellers was extended to describe multi-body configurations like propeller rudder or contra rotating propeller systems. Validation studies were performed on test cases available from the literature and from model tests on the baseline vessel.

One of the major improvements was that the coupling between unsteady flow solvers became possible. This represented an important feature in view of the application of hybrid models to the analysis of complex configurations like propeller rudder, podded propellers and contra rotating propellers in which the unsteady interaction between the propeller and the surrounding flow was fundamental to characterise the system performance.

Progress was made on automated optimisation of hull forms with RANS codes, with two object functions, one to estimate the power delivered to the propulsor and the second to express the quality of the wake field and so avoid erosive cavitation. In the area of propeller optimisation, a new method for generating propeller variants from an existing database of propellers was developed, enabling efficient optimisation.

Free form deformation (FFD) techniques were developed to explore both hull and propeller optimisation and initial results from simplified meshes were very encouraging.

The main impact of STREAMLINE would be to substantially reduce fuel consumption and pollutant emissions on a variety of applications, making waterborne transport a cost effective, attractive, alternative to road and air transport. Novel, innovative solutions for short sea shipping and inland waterway operations, having the potential to deliver at least 15 % reduction in fuel consumption and emissions would be demonstrated. At the same time, reduced noise and pressure impulses would deliver improved crew health and passenger comfort.

In addition, the results of STREAMLINE would affect current fleet efficiency by providing smaller efficiency improvements on a much larger scale, through the optimisation of current propulsion systems without dramatic configuration changes to the vessels, enabled by the development of advanced CFD methods. At the end of the first reporting period, the main technical ambitions of STREAMLINE, i.e. the theoretical and experimental verification of the benefits of a LAP, distributed propulsion, WSP, advanced screw propellers, waterjets at low speed and advanced pods were still on track. Across these concepts it was expected that efficiency gains of 5 to 30 % could be achieved.

The project would lead to a demonstration of a vessel fitted with the WSP, which would not only show the industry and general public a radical new way to propel inland vessels, but would inspire the general public. Along with the distributed thrust concept, not only will the carbon dioxide (CO2) emissions for inland waterways would be reduced, but the air and water quality would also be improved. Moreover, STREAMLINE would ensure that the European maritime industry remained at the global forefront of predictive and optimisation methods.

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