Numerical Simulation Of Tidal Shear Front And The Influence Of Topography Evolution On The Hydrodynamic Characteristics Around Yellow River Estuary

The Yellow River estuary is in the place where the Laizhou bay and Bohai bay meet, locating in the Dongying city, Shangdong province. Yellow River plays a significant role in human’s activity. The tremendous sediment transportation of Yellow River results in the dramatical changes of the topography, which exerts important influences on the hydrodynamic force. The special hydrodynamic phenomenon, tidal shear front, also serves as a crucial role in the hydrodynamic force as well as the topography evolution. This dissertation adopted the numerical simulation method to study the tidal shear front and the influence of topography evolution on the hydrodynamic characteristic around Yellow River estuary.First of all, a three dimensional numerical model based on the hydrodynamic module of FVCOM was established for Yellow River estuary. The model has been calibrated by observed data, such as elevation, flow direction, flow velocity and salinity. The results of comparison showed the model is suitable to reflect the hydrodynamic force in the research area.In addition, the model built above is employed to simulate the tidal shear front around Yellow River estuary numerically. The outcome illustrated that the model reproduced tidal shear front very well. The formation, spread and duration of two different types of tidal shear front are discussed and analyzed. The influences of wind, river runoff, topography, bottom friction and wave on tidal shear front are studied by comparing shear front in different experiments horizontally and vertically. In the process of studying the influence of wave on the tidal shear front, the wave model SWAN was coupled with the three dimensional numerical model. In the process of studying the influence of topography on the tidal shear front, subaqueous topography of Yellow River estuary was changed according to the changing patterns obtained from the past few years. Wind only exerts small effects on the surface of the tidal shear front. The runoff of Yellow River would push tidal shear front to some extent, and change the position of shear front via varying the vertical stratification of velocity. Bottom friction performs little function on the position of shear front, but plays an important role on the intensity. The large bottom friction will weak tidal shear front, while the small bottom friction will strengthen it. Wave has no relationship with tidal shear front. Topography performs an important role in the position of tidal shear front. The position of shear front moved from a shallow to a deep area due to the deposition of topographyThe three dimensional model was employed to simulate the salinity distribution on the changed topography and original topography. Compared with the salinity distribution on original topography, the diluted water can spread further away from Yellow River estuary on the changed topography. This phenomenon is especially obvious on the south and east of the Yellow River estuary. The particle tracking around Yellow River estuary was modeled on the original topography and changed one via the numerical model. The results showed that the tracers moved towards two main directions. The one is the northeast of Laizhou bay, while the other is the southwest of Laizhou bay. The particles on the surface, middle and bottom layers can move further on the changed topography than that on the original one. This phenomenon becomes intensify as the time passing by.