Numerical Simulation Of Hydrodynamics And Flushing Water In The Yangtze Estuary

This paper reviews the history and present situation of the research on the Changjiang diluted water at home and abroad.It is found that the expansion of the Changjiang diluted water is affected by many factors,but the dominant factors are not clear.In addition,the Yangtze River Estuary suffers from typhoons all the year round,and there are few studies on the continuous typhoon transit on the expansion of the Changjiang diluted water.In response to the above problems,a high-resolution salivation Model of the Yangtze River Estuary was established based on the FVCOM（An Unstructured Grid,Finite-Volume Coastal Ocean Model）,and a three-dimensional barobaric hydrodynamic model was established on the basis of good verification results.The results show that the model can well simulate the water level,salinity,flow field and other variables in the Yangtze River Estuary,and can accurately simulate the tidal current and the expansion of the Changjiang diluted water in the Yangtze River Estuary.The main results are as follows:（1）A high-quality unstructured triangular grid is generated based on the high resolution shoreline and terrain data of the Yangtze River Estuary.The hydrodynamic model of the Yangtze River Estuary area is established under the condition that only open boundary water level is added to drive.The model has been verified to have high accuracy and accuracy.The average absolute error of the tidal level of the model is less than 0.1 m,and the error of the velocity and flow direction of the model is less than 10%.Then,forced fields such as temperature,salinity,heat flux and wind field were added to build a three-dimensional baroclinic hydrodynamic model based on the open boundary water level drive to simulate the change of the Changjiang diluted water.Through the validation of salinity data,it can be seen that the change of salinity in the model is basically consistent with the actual situation,and the correlation between the measured data and simulation at the two stations is 0.95 and 0.88,respectively.（2）It is found that the iso-amplitude lines of K₁ and O₁ in the Yangtze River Estuary are about 0.3 m and 0.18 m respectively,the amplitude of M₂ and S₂ is about 1.5 m and 0.75 m respectively,and the phase is basically perpendicular to the shoreline.In the eastern sea area outside the estuary,the tidal current is rotary current,and most of the flow in the estuary is rectilinear current.The velocity of the residual current in the estuary is larger,and the maximum residual current is found in the sea area on the south side of the upper part of Chongming island,the sea area on the north side of the middle part of Chongming island and the estuary area of the south and north channels.The residual flow outside the port is slightly larger than that outside the port in summer,and the residual flow inside the port into the north trough to the northeast direction is obviously weakened,and another part of the residual flow flows south along the south trough into the Hangzhou bay.（3）In 2019,the core area of the Changjiang diluted water mainly extends to the northeast and northwest in summer,and mainly extends to the south in autumn.The change of the wind field has an impact on the expansion of Changjiang diluted water in summer and autumn.The typhoon caused the abnormal diversion of the Changjiang diluted water.Continuous typhoons accelerated the southward expansion of the Changjiang diluted water in autumn.The results of this study are conducive to reveal the expansion mechanism of the Changjiang diluted water,and provide a scientific basis for further research on the expansion of the Changjiang diluted water.