Numerical Study Of Nearshore Circulation And Substance Transport In Coastal And Estuary Areas

Wave and tide are the two main dynamic factors of coastal and estuary area, they coexist and have interaction with each other. When wave propagates to the shore, it will be refraction, diffraction and shoaling until broken as the result of varied water depth and structure. With wave broking, the wave induced current produced. It can play an important role in sediment transport along shore. At present, the two dimensional wave-current model has applied mostly, but the current was not uniformed in the vertical profile, and the vertical distribution has significant effect on the stability of structure and terrain evolvement. So we not only need to understand the surface changement, but also to find out the vertical variation of current, which can be carried out by the three dimension model.The purpose of this dissertation is to improved the three dimensional wave-current model COHERENS-SED to advance its ability of simulation, especially on the vertical characteristics.Firstly, vertical varied radiation stress is introduced into the model by adding to the fluid government equations. Then setting up numerical simulations with ideal terrain which are uniformed slope to study the vertical circulation in and out the wave broken zone. The results are agreement with the theory and measurement.At the other hand, due to waves act on the water surface, it makes the velocity gradient which will lead to the turbulence to enhance the vertical mixing induced by waves. So wave induced vertical mixing also be introduced into the coupled model through eddy viscosity coefficient. Carrying out some one-dimention numerical simulations in vertical direction, we find out the turbulence mixing of water flow was intensified by wave motion, the vertical eddy viscosity coefficient has a significant effect on the distribution of velocity in the vertical profile.Finally, applying the improved coupled model to Huanghe Delta, to study the wave induced current of surface layer and bottom layer. We obtained some conclusions:wave induced current was stronger in shallow water with depth little to 5m, it can be ignored in deep water zone. Surface current velocity caused by vertical varied radiation stress was larger than vertical averaged velocity, and bottom velocity was smaller than vertical averaged velocity. More over, the sediment transport under wave induced current was studied, and sediment will transport further with the effect of wave induced current. Then the condition of fresh water flowing into sea with wave induced vertical mixing was discussed, and making conclusions as follows:the surface velocity became smaller and the bottom velocity increased when wave vertical mixing was included, which shows the effect of wave on vertical distribution of momentum and energy.