Numerical Simulation Of Water Waves In Yangtze Estuary And Adjacent Sea Area

Wind waves and swells are significant obvious in the Yangtze estuary and adjacent seas under the control of monsoon and typhoons.The wind waves are characterized by large energy,and water waves induced by typhoon could be great threaten to coastal structures and human lives,so the numerical simulations of wind waves are partially significant in practice to research and forecast the possible effects of surges.Theoretical researches and applications of wave models,especially those adopted in the Yangtze estuary and its adjacent seas are reviewed in this thesis.The advantages and disadvantages of three basic wave models(Wave Energy Balance Equation(WEBE),Mild Slope Equation(MSE)and Boussinesq Equation Model(BEM))are compared,analysized and discussed in this thesis.Considering that:(1)The WEBE model is more convenient than MSE model on dealing with various forms of energy inputs and dissipations and can be adopted in large areas from estuary scale to ocean scale,the MSE model can give better predictions in shallow water where the refraction and diffraction effects become significant but can only be applied in much smaller areas.Meanwhile,the MSE model can not take energy inputs and dissipations into account as convenient as what WABM model does;(2)The bathymetry of Yangtze estuary and adjacent sea area are shallow and the coastline is complicated,where wind wave undergo a number of transformations such as shoring,refraction,diffraction,dissipation and et al..In order to improve the precision of wave prediction,the nested run of WEBE model SWAN(Simulating waves nearshore)and the parabolic MSE model REF/DIF(Combined Refraction and Diffraction Model) has been adopted in simulating the wave fields in the Yangtze Estuary and adjacent seas.In such a mesotidal environment,the effects due to tidal current can not be ignored in wave field simulations in the Yangtze estuary.In the past,the tide and tidal current were taken into account in wave simulations by introducing measured tide or current,with ignoring the spatial variety of tide and tidal current.In this study,the tide and tidal current which are calculated by a 2-D flow model were considered as a background field when computing wave generating,dissipating and propagating over bathymetry.Comparisons between infield data and model results show that the precision of wave computation after considering the effects due to tide and tidal current can be improved.The nested calculation of SWAN and REF/DIF was driven by several kinds of wind processes to calculate wave field distribution in the Yangtze estuary and adjacent sea.The effects of tide and current in wave field simulating were discussed in the Yangtze estuary and adjacent seas.The spatial distribution of significant wave height and variation of wave propagation direction due to the refraction and diffraction effects were particularly discussed in order to possess the characteristics of the wind waves near the Yangtze estuary thoroughly.