Research On A Motion Prediction Method For Hydrofoil Hybrid Trimaran In Viscous Flow On The Basis Of Overset Grid Approach

Although there had been no worldwide attention until 1990 s, trimaran has soon become one of the important hull forms that lots of countries develop competitively, due to its unique overall performance, and the hydrodynamic study of trimaran deepens increasingly as well. However, researches about the motion prediction method for trimaran in viscous flow and the development of trimaran stabilizer still lag behind, and there is great academic importance and engineering value to carry out related work. In this paper, the establishment of motion prediction method for trimaran in viscous flow is explored on the basis of overset grid technique, and the method is also applied to the motion prediction of hydrofoil hybrid trimaran. The mechanism of hydrofoil system reducing drag and stabilizing is also analyzed. Main works of this paper are as follows:Integrating RANS method, overset grid technique, the solution strategy of six degree of freedom(6DOF) motions and the numerical wave generation technology, overcoming matching and data transmission problem in the overlapping process between complex appendage grid and hull grid, a method for predicting ship 6DOF motions in viscous flow is established. Numerical simulation of model DTMB5512 advancing in regular head waves is firstly carried out. With the comparison between numerical results and experimental data, validity and reliability of method in ship motion prediction are validated.For the purpose of reducing CPU time of ship motion prediction in viscous flow, the motion response of DTMB5512 in waves is predicted with the attempt of a harmonic wave group single run procedure. Compared with regular wave procedure and experimental data, the results show that harmonic wave group single run procedure provides equivalent accuracy results as regular wave procedure, while the calculation time is reduced over 60 percent, which lays a good foundation for future deep research.To further verify the validity of 6DOF motions prediction method on trimaran, the motion response of a trimaran advancing in regular head waves is studied numerically. The numerical results fit well with experimental data, which shows that this numerical method can be applied to the motion prediction of a trimaran.Based on the hull form and motion response characteristics of a trimaran, a simplified model of the trimaran adapting hydrofoil system is established. Numerical calculation of the rapidity and seakeeping performance of the hydrofoil hybrid trimaran are also carried out. The rapidity results shows good agreement with model test data, demonstrating that this method can predict the resistance and navigation condition of a trimaran and hydrofoil hybrid trimaran relatively accurately. For the absence of related regular wave experimental results, only qualitative analysis of the hydrofoil system stabilization effect is made, which accords well with project experiences, indicating that this method can be used for the motion prediction of hydrofoil hybrid trimaran, and it preliminarily achieves the engineering application level and provides practical research method and tool for the hydrodynamics evaluation and optimization of a hydrofoil hybrid trimaran. Furthermore, the mechanism of hydrofoil system reducing resistance and ship motion is analyzed, which provides basis and reference for the design and adaptation of hydrofoil system.