Application of RANSE CFD for Ship Hydrodynamics
by M.Sc. (Naval Architecture), Phd. Claus D. Simonsen, Senior Specialist at FORCE Technology.
Advanced Computational Fluid Dynamics (CFD) appears to be a strong tool in the design phase of ships, because detailed evaluation of design alternatives can be done early in the design process. But, so far CFD has primarily been used to investigate hull and propeller in separate models.
Today, the most commonly used method for checking combined hull-propeller flows is towing tank or cavitation tunnel testing. However, due to the cost of model testing, the combined hull and propeller designs are checked relatively late in the design process, meaning that many design parameters has been locked. The question therefore is if CFD can be used as a supplement earlier in the design process.
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When is comes to insight in the flow details and understanding of the physics of the flow CFD is very strong, because it generates detailed flow field information which can be used to improve the design and to make sure that the flow behaves well before the physical model is build. The detailed information generated through CFD holds another advantage as the data can be used to calculate hydrodynamic loads like the resistance, which means that the performance of the ship can be quantified. This information is very useful early in the design process as it can guide the selection of design variants. Therefore, the aim of this project has been to gain further knowledge on the hydrodynamic loads on the fully appended ship quantified by CFD. Further, the aim has been to investigate the interaction between hull, propeller and rudder in relation to the effect on the flow field around the aft part of the ship in order to develop a commercial tool to be used in the early design stage. |
Computed breaking bow wave |
The application of CFD for design evaluation and optimization of marine structures is currently expanding rapidly and consequently the complexity of the considered problems is increasing. To meet the future challenges and requirements to applications, it is therefore required that solid experience with the CFD tools, is built up for complex and practical flow problems.
To test and demonstrate the capabilities of CFD in connection with complex ship flows, FORCE Technology, MAN Diesel A/S and Technical University of Denmark have been involved in the present project. In order to achieve the aim of the project, a complete CFD model of a ship including appendages and operating propeller has been build to study the flow field, compute the hydrodynamic loads and validate the results against experimental data.
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A set of typical towing tank scenarios were simulated: Resistance test setup with the hull appended with rudder, open-water setup for the propeller alone and finally a self-propulsion setup with the fully appended hull. Meshing and flow simulation were made with STAR-CCM+. The results of the present work look very promising and have shown how advanced CFD can be applied to solve practical flow problems in the marine industry. Via flow visualization it is illustrated how valuable insight into the physics of the flow problems can be obtained. Further, comparisons between calculated and measured hydrodynamic forces and moments show that the CFD results for both hull and propeller can be predicted within 3.5% of measured data. So, all in all the results look promising seen in relation to future application of CFD in connection with evaluation of design variants in the early design phase. |
Papers on the topic:
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