Research On Mathematical Model And Hydrodynamic Characteristics Of Flow Field In Lakes

Lake is an important part of the water cycle on the Earth. Huge changes have taken place in the hydrologic process and ecosystem structure of city lakes under human activities. It is an important and urgent reasearh subject of studying on evolution process of lake water circulation system driven by multiple factors such as natural environment and human activities, analysizing on distribution pattern of the flow field constrained by different water-land, water-gas and substrate facotors, and researching on the spatial-temporal law of motion of lake water body, and therefore providing scientific basis for lake water environment goverment, lake ecology control and optimal operation of large scale connection projects of lakes. And it provides crucial approach to accomplish this research subject by establishing a hydrodynamic model of lake and simulating lake system precisely and efficiently. However, the study on high-efficiency simulation of lake hydrodynamic process is not systematic and thorough in our country, which is not sufficient to make an effective decision to improve water quality and water ecological system in lakes. As a result, it is imperative to conduct in-depth study on numerical simulation of hydrodynamic and water quality model, establish an efficient and stable flow field mathematic model, reveal the hydrodynamic characteristics for large scale lakes with irregular boundaries, and provide scientific basis for decision making by water resource administration authorities in regard of water ecological restoration and control.Basing on the theory of shallow water dynamics, this paper establishes a high-performace two-dimension mathematic model, which could be applied to lake water with irregular land-water boundaries and complex topography. Using this model, analysis on characteristics under different natural environmental factors and different tactics of water diversion was made. Furthermore taking the Wuhan Donghu Lakes as research area, this paper made an analysis on water flowing characteristics and main driving forces of the lakes, and discussed some efficient ways to improve the refresh rate of stagnant water area. Relevant achievements have been applied to the project of Research and Application of Critical Technology on Water Network Control of Donghu Lakes, which is a special scientific research project for public welfare industry conducted by the Ministre of Water Resources. The main work and innovation of this paper includes:(1) A model with flexible structure and adaptive grid was established, and the grid self-adaption criterion based on local flow pattern was developed. The model could modify the grid density dynamically, and make a balance between the solution accuracy and computational efficiency. It would be beneficial to resolve the contradiction between the time-consuming and high precision numerical anslysis on large scale water simulation.(2) A well-balanced numeric scheme was propsed for two-dimensional shallow water equations. Concerning the problem of illusive flow during dealing with dry-wet interface, which is introduce from discretization of bottom slope terms and evation of flux across cell interfaces in traditional methods, this paper proposed a well-balanced numeric scheme, and verified that the model satisfies the C-property through theoretical derivation and validating against several numerical tests, which proves the numerical model is capable for simulation with moving wet/dry interfaces.(3) The proposed model is validated by a set of benchmarks, including ideal test cases with theoretical solutions, laboratory experiments with measured datas, and so on. The results show that the model is accurate, stable, well-balanced and mass conservative, and has a good performance in modelling irregular boundaries of computational domain.(4) The influence on the establishing time, distribution of velocity, lakeshore boundaries, surface wind-stress, initial lake water surface elevation and islands was analyzed.(5) Using a hydrodynamic model, simulaion of water flow in Donghu lakes was made, which revealed the characteristics of water movement in the lakes and the contribution of different environmental driving forces on lake flow field. Combined with these driving forces of stagnant zones, an efficient control strategy is proposed to improve the water velocity in stagnant area.