Fully Nonlinear 3-D Numerical Wave Tank Simulation

Transient and steady-state nonlinear free surface waves and wave-body interactions are investigated in a 3-dimensional Numerical Wave Tank (NWT) using an indirect Desingularized Boundary Integral Equation Method (DBIEM) and a Mixed Eulerian-Lagrangian (MEL) time marching scheme. The Laplace equation is solved at each time step by using Rankine sources distributed outside the solution domain, and the fully nonlinear free surface boundary conditions are integrated with time to update its position and boundary values. A regridding algorithm is devised to eliminate the possible instabilities without using artificial smoothing. The incident waves are generated either by a piston type wavemaker or by feeding analytic forms on the input boundary. The outgoing waves are sufficiently dissipated by using spatially varying artificial damping on the free surface of the damping zone before they reach the downstream wall boundary. In some cases, side beaches are also implemented to minimize the sidewall reflection. Computations are first performed for nonlinear long-crested regular waves in a 3-dimensional numerical wave tank without a body. Subsequently, the nonlinear diffractions by a bottom-mounted vertical cylinder and truncated vertical cylinders are investigated and the present NWT results are compared with available experimental results and second-order diffraction computations.