Time-Domain Simulation of Second-Order Wave Diffraction in Irregular Wave

A time-domain second-order method is presented to simulate three-dimensional (3D) wave-body interaction. In the approach, Taylor series expansions are applied to the free surface boundary conditions, and Stokes perturbation procedure is then used to establish corresponding boundary value problem at first-order and second-order on the time-independent surfaces. A Boundary Element Method (BEM), based on Rankine source, is used to calculate wave field at each time step. Multi-Transmitting Formula coupled with Damping Zone method (MTF+DZ) is employed as radiation condition to minimize the wave reflection. A stable Integral form of Free surface Boundary Condition (IFBC) is used to update velocity potential on the free surface. The present method is applied to compute the second-order Stokes wave diffraction of bottom-mounted circular cylinder first, and then to compute the irregular second-order Stokes wave diffraction of truncated cylinder in infinite water depth with three wave components. It is shown that long time simulation can be done with stability, and the model can be used to time-domain simulation of nonlinear irregular wave-body interaction.