Numerical Studies On Water Environment Of The Yangtze Estuary

The study during the postdoctoral research period are included in the report, which consists of the following two parts. The research about water environment of the Yangtze estuary is done in the first part. The aim of the research is for the regulation project of the Yangtze estuary in these years. In order to finishing these projects successfully, the character of flow field of the Yangtze estuary must be understood fully, two dimension program with double sweep implicit methods are compiled to calculate the flow character of the Yangtze estuary firstly. But the three-dimension character is very clear to the flow filed of the Yangtze estuary. A mature three-dimension estuary and coastal model ECOM is used to simulate tidal current and residual field. The result shows the ECOM model is used successfully to simulate the current field character of the Yangtze Estuary. Using a dissolved conservative material as a tracer in the water, a three-dimension advection-diffusion water exchange numerical model was used to study the flushing time by discharge and the discharge dominated region of the Yangtze estuary based on the successful simulation of flow field. On the other hand, The hydrology experiment in the south and north branch are done many times during these period. The necessary data are used to adjust the parament used in the numerical simulation. The Second part is the study during the doctoral period. The result of the numerical and experimental are published in this paper. The wavelet method is applied to analyze the transient record of cavitation noise of bubble collapse successfully.Part One: Study on the flow character of the Yangtze estuary. Firstly some problems about estuary are discussed in the report. Secondly some phenomena such as tidal current, residual current, wind field, salt field and sediment concentration of the Yangtze estuary is described. Lastly ECOM Model is used to simulate the flow field of the Yangtze estuary. A detailed comparison of the measured and predicted water level showed that the simulation is very successful. On the other way, The effect of different runoff discharge to the residual current field was also studied in the part. The result shows the residual in the estuary is mainly affected by the discharge. Secondly numerical investigation on the flushing time of the Yangtze Estuary by discharge was done. Based on the comprehensive reviews about the developments in the field of flushing time of the estuary. Two numerical methods about water exchange are discussed in the part. Using a dissolved conservative material as a tracer in the water, a three-dimension advection-diffusion water exchange numerical model was used to study the flushing time by discharge and the discharge dominated region of the Yangtze estuary. The flushing time of the Yangtze estuary is an important eigenvalue, which denotes the water environmental capability of estuary. Understanding these processes is of critical importance for evaluating the water environment, arranging the sewage outlet, and selecting the position of water reservoir and regulation of the Yangtze estuary. The study has not only theory value but also practical value.Part two: Study on the cavitation noise. The extend work of my doctoral research is introduced in the part. Problems of cavitation noise are investigated with three methods such as theory analysis, numerical simulation and experiment research. Mixed boundary element method is put forward to solve acoustics of bubble collapse by author. The laser single bubble experiment is firstly finished to prove the result of numerical calculation at domestic.