Numerical Simulation Of Wave Transformation In The Nearshore Zone Withnon-hydrostatic Equations

It is very important to accurately describe the nearshore wave transformation for the determination of design waves in coastal engineering. Varoius numerical wave models, and especially the numerical wave models based on non-hydrostatic equations, have been rapidly developed for investigating the wave transformtion in recent years. In this paper, a complete three-dimensional numerical model based on the improved non-hydrostatic wave model SWASH has been established to describe wave transformation in the nearshore zone and the model is applied in wave transformation for a practical engineering problem. The main contents and conclutions are summarized as follows.A numerical wave generation method without re-reflection for non-hydrostatic wave model is developed through introducing different forms of source functions combined with the wave damping absorber by using improved sponge layer. The stability of the model and the accuracy of the target wave induced by different forms of the source functions have been discussed. It is shown that the distributed source is better than the line source for the stability and accuracy of the non-hydrostatic wave model.A method of generating non-uniform waves along the boundary through the internal source function has been developed. The method has been introduced for coupling a phase-averaged wave model based on the wave action spectra model in large simulation area and a phase resolving wave model based on the non-hydrostatic model in small simulation area. According to the simulation results of two ideal wave transformation cases, it is shown that the coupled model can predict the wave height, wave period and wave spectrum accurately, and it can describe wave transformation from large areas to small areas reasonably.The Darcy-Forchheimer equation is introduced into the non-hydrostatic wave model to describe wave interaction with porous structures. Comparisons between the numerical and experimental results, show that the model can reasonably reproduce the complex wave filed, including wave partially reflection, transmission and wave diffraction in the vicinity of a porous breakwater.Hydrostatic front approximation and a wave breaking model are adopted so as to reduce the number of vertical grids in non-hydrostatic model when simulating wave breaking in shallow waters. Comparisons between the numerical and experimental results of wave breaking in shallow waters, show that the model can obtain a reasonable result of wave breaking with a relative low-vertical resolution in shallow waters.The developed non-hydrostatic wave model is applied to analyze the wave conditions for berths in a real harbor. By comparing the result of the physical model test, it is shown that the non-hydrostatic wave model can describe the complex process of wave transformation for waves propagation into the inner harbor from a entrance, including wave diffraction, refraction, reflection around a rubble-mound breakwater and vertical piers as well as the superposition of multi-incident and reflected waves.