A numerical model is developed for 3-D floating body motions in fully nonlinear waves using the BEM. This BEM solves simultaneously the boundary integral equations for the velocity and acceleration fields and the motion equations of a floating body with six-degrees of freedom. The movement of the nodes on the free water surface is evaluated in accordance with the 3-D motion of fluid particle by the Mixed Eularian Lagrangian method (MEL) and it satisfies strictly satisfy the dynamic boundary condition on the water surface. After that, by the coordinate transformation of the six-degrees of freedom motions, the movement of arbitrary nodes on the body surface is evaluated and updated for the next time step. Validity of this numerical model is verified through comparisons with theoretical solutions of nonlinear waves such as the 5th order Stokes and the 3rd order Cnoidal waves, computed results by a fully nonlinear 2D-BEM, and 3-D experimental results of a moored floating plant barge.
It is necessary to develop a numerical model capable of reproducing fully nonlinear 3-D interactions between a moored floating structure and nonlinear waves. However, such numerical model is still being confined to fully nonlinear 2-D interactions using BEM and FEM. Especially, for the BEM, using boundary surfaces alone, surrounding the fluid domain, the problem of boundary values can be solved. So, the efficiency of computation is much better than the FEM and the BEM is more suitable for 3-D computation. For correct evaluation of floating body motions, it is necessary to correctly calculate the time variation of the fluid pressure acting on a floating body. However, the fluid pressure are affected by the motion acceleration of a floating body. So, the motion equation of the fluid must be strictly coupled up with the motion equation of the floating body.
