The nonlinear wave and current effects on fixed and floating bodies by a three-dimensional fully-nonlinear numerical wave tank

A three-dimensional, fully-nonlinear numerical wave tank (NWT) is developed and utilized to analyze the interaction between nonlinear waves and fixed or floating bodies with uniform current. The NWT is based on the potential flow theory and the boundary element method and simulates nonlinear wave-current-body interactions using MEL (Mixed Eulerian and Lagrangian) method. Moreover, the robust acceleration-potential approach is applied to evaluate the instantaneous wave-induced pressure acting on the body without using numerical time differentiation of velocity potential. In addition, artificial damping zone with gradually varying artificial damping coefficient is applied to prevent reflected waves from side walls and input and downstream boundaries. Using the developed NWT, current-affected incident waves are simulated and compared with measured wave elevations in both coplanar and adverse currents. Then, fixed bottom-mounted and truncated vertical cylinders are simulated in waves and currents and the wave run-up, wave-frequency, double-frequency and mean-drift forces are calculated and compared with published results from the second-order perturbation approach. The NWT is then further applied to freely-floating (with soft horizontal spring) truncated vertical cylinders and the wave-frequency and double-frequency motions for various current conditions and wave drift damping are analyzed. Based on the developed NWT, the validity of Aranha's semi-analytic solution for wave drift damping is assessed.