| The 21th century is a century of ocean, and human activities in ocean life, mineral and water resources appear much more intense, so exploring and making use of ocean resource demand higher requirements to improve ship hydrodynamic performances. Now many countries pour huge amount of cost into making research about high performance ships, and as one kind of new high performance ships, the trimaran has been highly recognized. When ships are travelling at high speeds, the characteristics of flow field around ships and after stern will affect ship hydrodynamic performance. Researchers pursue all the time that through adopting various methods for improving the flow field around ships, making the ship possess the best characteristics of hydrodynamic performance. The flow field around the trimaran becomes more complicated due to the existence of the side hulls, and the hydrodynamics of trimaran has been changed considerably. So how to optimize the configuration and improve the hydrodynamic performance of trimaran is one of the focuses. In this paper, the flow field around a trimaran is simulated in order to analyze the change of the flow and hydrodynamic performance when the configuration of the side hull of the trimaran is changed.The grid is used to discrete space region and the quality of it will affect the stability, convergence and accuracy of the simulation. Because the shape of trimaran is considerably complicated, forming the grid on the trimaran is very difficult. So the way of gridding on the trimaran is very important. In the paper, the main-hull was simulated with different grid sizes on the ship surface, different distance of the first layer of the nodes and grid distribution of flow field. Comparison of the numerical simulation with the experimental data proposed some suitable set for forming the grid. And then on above basis, three sets of different grids were formed on the trimaran. Researches about CFD verification, validation and convergency were carried out. All prove the validity of some suitable set of the grid.Choosing suitable turbulence models is an important factor as well in ship CFD, the main-hull and trimaran which have been investigated were used as a test case to analyze the effects of seven different turbulence models in the aspects of flow details and resistance of the ship. Comparison of the numerical simulation with the experimental data shows that turbulence model SST k -ωis better suitable to the trimaran. Based on the research results on the grid and turbulence model, the flow field around the main-hull and trimaran were simulated for different velocities. The calculated wave contour showed the characteristics of the flow and the numerical result can generally agree with experimental data. In general, the above research results are largely agreeable and the methods are workable.In general, the side hull of trimaran are basically vertical,parallel in longitudinal direction and zero-trimed relative to the center hull, in calm water,(i.e. trim angleα=0,attach angle (β=0 and tilt angleγ=0 case). To investigate a new concept of trimaran, consider in this paper a trimaran with changes of one, and the combinations of changes ofα,βandγ, calculate the effects of these changes on the resistance and other hydrodynamic performances, to seek the feasibility of improving performances with this new concept trimaran.At the end of the paper, for the trimaran, the flow field around the ship was calculated when the side hulls is with lots of different configurations. The effect of resistance, lift and trim moment from different side hull configurations was analyzed in order to get a great side hull configuration. The author hopes that the researches could give some help for further investigation. |
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