Study On Numerical Simulation Of Seawater Exchange Based On Flux Function

The ocean plays a vital role in the life and development of human beings.In recent years,owing to the shortage of land resources and the rapid economic development,human activities on marine development are increasing,which inevitably has an impact on the marine environment.Water exchange capacity and water self-purification capacity are two important indexes to determine the quality of water environment,and it is the basic problem in the research of marine environmental science.It is of great significance to study and evaluate the water environment quality of the bay by studying the water exchange capacity and self-purification capacity of the bay.Water exchange capacity is only related to the flow of water.At present,most of the researches on water exchange rely on the concentration of indicator material to calculate water exchange rate and exchange time,and the results cannot accurately reflect the exchange capacity of seawater.Taking a simple T shaped area as an example,the paper proposes a water exchange calculation method based on the flux function,which is analogous to the stream function.Since the stream function is usually only used for two-dimensional plane flow.Therefore,the two-dimensional shallow water equation with the average depth of water is obtained by integrating the three-dimensional continuity equation along the direction of water depth,which transforms the three-dimensional problem into the two-dimensional problem.After that,the two-dimensional shallow water equation is integrated and the flux function is derived analogy with the flow function.Then the double opening model and the single opening model are established respectively to get the data of velocity,depth and so on.Finally,according to the simulated data,the flow value is calculated,and the streamline distribution corresponding to the flux function is made.It can be clearly seen from the streamline map that more than half of the water in the simulated area can be exchanged out of the area and It is calculated that the seawater exchange rates in the first and second half cycles of the double opening model are 0.6396 and 0.6465,and the seawater exchange rate in the first half of the single opening model is 0.7847.The result shows that it is simple and feasible to evaluate the water exchange capacity of a certain area by using the numerical simulation method based on the flux function.The streamline distribution map can directly reflect the water exchange capacity,which will provide some references for future water exchange research and comprehensive improvement of the Gulf.The water self-purification ability is not only related to the fluidity of water bodies,but also to the proliferation of materials.In order to distinguish with the water exchange capacity,the paper also studies the self-purification ability of the double door model.Firstly,the convection-diffusion model is used to simulate the change process of concentration of a landmark substance in the region over time.Then the water self-purification capacity in the simulated area is calculated and analyzed.It is also proposed that effective supervision and management should be carried out in the important sewage stage during the construction and operation of the Bay and port so as to prevent the pollutants from entering the areas where the water exchange capacity and the self-purification ability are weak,thereby endangering the quality of water environment.