ABSTRACT

To predict the motions and wave loads for ships and floating structures under extreme sea-state, a fully nonlinear time-domain computation program base on the Mixed Eulerian-Lagrangian method with high-order boundary element approach is developed and the validity of computational system is analyzed. The standard Runge-Kutta method and the fourth order Adams-Bashforth-Moulton method are used for the time step method. The NURBS based high order BEM method is used to calculate the velocity potential at each time step. An artificial damping layer is adopted as the far field radiation condition on the free surface to avoid the wave reflection from the outer boundary, and the present method is found to be numerically stable. The pressure on body can be obtained by solving a boundary integral equation of time derivative of velocity potential.

INTRODUCTION

Numerical simulation and analysis of motions and loads of ship and ocean structure under waves with large amplitude are very important in either theory or engineering application. With the wide use of three-dimensional FEM method, the calculation of wave loads on floating body in the waves is in need more and more. In this paper, the interaction between non-linear waves and surface-piercing body with arbitrary shape in three dimensions is investigated on the basis of the potential theory. The Rankine source Green function method both in time-domain with considering of fully non-linear effect is used in the calculation.

Generally, two categories of methods are used in simulations of time-domain 3-D wave-body interaction. One approach is the perturbation based high-order method. In this method, Taylor series expansions and the Stokes perturbation procedure are applied to the free surface and body surface boundary condition, and the problem can be solved in a time invariant computational domain.

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