The Study Of Coast Hydrodynamics Along Reef Islands Using A Multi-layer Non-hydrostatic Wave Model

The study of hydrodynamics at reef islands is of great significance for the reef engineering.The unique topography of the reefs is characterized by the steep reef-face slope,the reef flat with shallow water and large bed roughness;the resulting hydrodynamics are thus obviously different from that on common coastal regions and even more complex.For two-dimensional reef island profiles,a multi-layer non-hydrostatic model is developed to investigate the coastal hydrodynamics along reef islands.The model solves 2DV-Euler equations in terrain and surface-following coordinates and defines the elevation as a single-valued function of horizontal positions.A combined finite-volume and finite-difference scheme is applied for the spatial discretization of t he governing equations.The two step predictor-corrector method is adopted for the adaptive time stepping.The momentum equations are handled using a high resolution Godunov-type finite volume scheme.The fluxes at cell faces are estimated by central upwind scheme.The breaking wave was treated as discontinuities and this model has the capability of handling discontinuities,so there is no wave breaking parameters are employed.The moving boundaries are handled by using a simple wetting-drying scheme directly.A series of numerical experiments are performed by using this model.The correct discretization and accurate time marching of the governing equations is tested by long distance propagation of solitary wave in a channel with constant water depth;solitary wave breaking and run-up over a slope bench denotes the model's capability in modeling solitary wave breaking and handling moving shoreline;then the model is applied to simulate solitary wave propagation over reef profiles and the change of wave transformation and the velocity fields are analyzed,furthermore the relationship between the solitary wave run-up over the back-reef slope and the reef morphology is concluded.Regular wave transformation over a submerged bar denotes the model's capability in handling non-linear and dispersion and regular wave breaking over a bench slope indicates the model can well simulate regular wave breaking;then regular wave transformation over reef profile is investigated,the wave height attenuation and the wave-induced setups and set downs are analyzed.Irregular wave transformation over reef profiles is also investigated.