Current effects on nonlinear wave-body interactions by a 2D fully nonlinear numerical wave tank

Nonlinear wave-current interactions with fixed or freely floating bodies are investigated by a two-dimensional (2D) fully-nonlinear numerical wave tank (NWT). The NWT is developed based on the potential theory and boundary element method (BEM) with constant panels. Mixed Eulerian-Lagrangian (MEL) time marching scheme (material-node approach) is used with fourth-order Runge-Kutta fully updated time integration, regriding, and smoothing techniques, and acceleration-potential formulation and direct mode-decomposition method. Specially devised phi(n)-eta type artificial damping zones (i.e., numerical beach) are implemented to prevent wave reflection from the end wall and wave maker. Using the developed NWT, nonlinear wave-current interactions (1) without bodies; (2) with a stationary body; and (3) with a floating body for various wave and current conditions have been investigated and some of the NWT simulations are compared with the results of Boussinesq's equation and perturbation theory. It is seen that the NWT results reproduce the general trend of linear or perturbation theory in free-surface profiles, runup, forces, and motions but their magnitudes can be appreciably different from the perturbation-based solutions as wave steepness and current velocity grow.