Research On Body-exact Time Domain Strip Theory Algorithm To Ship Motion Based On Matched Boundary Element Method

Numerical simulation of ship motion response in waves is of great significance to ship seakeeping prediction.A body-exact time-domain strip theory based on matched boundary element method is developed to solve nonlinear ship motion problems.Firstly,two kinds of boundary element methods are introduced in this paper:simple Green function method and matched boundary element method.Under the linear theory,a simple Green function method is verified by the circular flow problem.The matched boundary element method is validated by solving the hydrodynamic coefficient and the incident wave force of the semicircle section.The free boundary condition is strictly satisfied by using the matched boundary element method and the instability of the free surface is avoided.At the same time,the time-domain Green function only needs to be integrated at the straight wall boundary,so the matched boundary element method can calculate the ship hull with large flare.Then a numerical model of large amplitude forced motion hydrodynamic calculation is established.The hydrodynamic model uses linearized free surface conditions and exact body boundary conditions.The linearized free surface condition simplifies the numerical computation and improves the numerical stability.The exact body boundary conditions can improve the accuracy of large amplitude motion simulation and capture events such as slamming and submergence.The surface and body meshing method and the time-stepping of free surface are proposed.The model is used to analyze the convergence and hydrodynamic calculation of the large amplitude forced motion of the wedge.After the research on forced motion,the numerical model of free motions of two-dimensional section is established.The concept of acceleration potential is introduced and this model is used to simulation the free motion problem of a square box section.Using acceleration potential not only improves the accuracy of numerical calculation,but also highlights the coupling between hydrodynamic and rigid body motion problems and improves the stability of numerical calculation.Finally,based on the above two-dimensional calculation program,the 2-DOF motion on waves numerical simulation of S175 container ship and numerical simulation of parametric rolling to C11 container ship is carried out.The three-dimensional problem is simplified to two-dimensional section by using the time domain strip theory which has advantages of stability and efficiency compared with the three-dimensional model and widely used in engineering.The numerical simulation results are in good agreement with the numerical results of other literatures and some experimental values.It is proved that the code is acccurate,robust and efficient and is very suitable for nonlinear motion response prediction of ships in waves.