Numerical Simulation Of The Effect Of River On Near-shore Hydrodynamics Using Unstructured Grid Model

Coastal waters are very closely related to human living and economic development in coastal areas; therefore the understanding of near-shore water environment are of great significance for people to use, develop and protect it. Usually, coastal waters are the main affected area by rivers which bring fresh water mixed with other materials, such as sediment, pollutants, etc. In the paper, three-dimensional finite volume hydrodynamic model with unstructured grid are adopted to study the impacts of rivers on the coastal water environment.To begin with, the paper introduces the unstructured triangular mesh generation technique. To generate a better unstructured grid, some improvements are made on grid quality judgments. Such improvements could not only achieve a smooth transition between regions with high and low resolution, but also ensure the greatest possible of generating equilateral triangle grids. Besides, the ordered list method was proposed to automatically add points to the computational domain; and this method could guarantee that new grid points are generating towards the high mesh quality. Then, the Laplacian algorithm was applied to smooth the generated mesh.The influence of rivers to the near-shore and coastal water can be affected by some factors which can be roughly categorized into two parts. One is internal factors, including river runoff, the concentration of pollutants and the diffusion coefficient of pollutants in rivers, etc. The other is the external factors, such as winds and tides. In the forth chapter, the effects of river off, the concentration of pollutants and the diffusion coefficient are simulated and analyze one by one. The residual current field, pollutants concentration and particle tracking method are used in order to explain the effects in different views. Then, the model is applied to the real sea condition in the fifth chapter. The residual current pattern are analyze in detail to compare the relative contributions of different external factors. Finally, the river effects are studied based on different methods.The results show the relationship of runoff and it's effects on near-shore hydrodynamics is nearly liner without any other external factors, and the concentration of pollutants in rivers would not change the relative concentration and it's distribution of pollutants in near-shore area. The diffusion coefficient has a little effect on the distribution of pollutants if runoff is big, on the contrary, it is important to the distribution of pollutants if there was no runoff. The near-shore hydrodynamics is very complicated under the real wind, tide, runoff and so on. The hydrodynamics of different areas are controlled by different factors. The wind has a great influence on the residual current field of the whole area, while the tide just has a weak effect on the residual current field. The influence of river is so strong that it can reach to 35km in off-shore direction and 130km in along-shore direction. The interaction of wind current and density current enhances the influence of river on the outside of bay and offshore. The momentum of river runoff itself is strong enough to control the characteristics of hydrodynamics of the bay and the narrow waterway. The distribution of pollutants in the bay is controlled by two rivers, and has a high value. The distribution of pollutants in the outside of bay and offshore is controlled by wind, tide, runoff together, and has a low value.