Fully Nonlinear Waves and Their Kinematics: NWT Simulation Vs. Experiment

A 2D fully nonlinear NWT is developed based on the potential theory, mixed Eulerian-Lagrangian (MEL) time marching scheme, and boundary element method (BEM). Wave profiles and wave kinematics of highly nonlinear waves are calculated using the NWT and the results are compared with linear, Stokes second-order theory and experimental values. It is confirmed that the spatial variation of intermediate-depth waves along the direction of wave propagation is caused by the unintended generation of second-order free waves, which was originally investigated both experimentally and theoretically (3^rd order perturbation theory) by Goda. The various phenomena observed by Goda are clearly reproduced by the present fully nonlinear NWT. It is shown that the wave kinematics above mean water level can be significantly different from the perturbation-based prediction. It is also found that small mean positive or negative flows can be generated below mean water level depending on the water depth and wave condition.