Numerical Simulation Of Water Structure In Taihu Lake Based On Unstructured Grid

Taihu Lake is located in the economically developed Yangtze River delta of China, which is the important freshwater source of this region. In the recent years, however, Taihu Lake is seriously polluted and confronted with long-term water eutrophication. Hence, it is necessary to carry out extensive and intensive research on the hydrodynamic characteristic since it is the driving force and foundation of physical transport.Firstly, the wave in Taihu Lake was simulated by the calibrated wave model, which is governed by the three-genetation dynamic spectrum balance equation, based on unstructured grid, which can easily fit the irregular coastal boundary and numerous small islands. Furthermore, the SWAN model can tack into account many wave factors, such as wave refraction, reflection, depth-induced dissipation, diffraction, wave-wave interaction, and so on. The results showed that the model produced good and reliable wave field results in Taihu Lake. On the basis of this, this paper further used this model to simulate the wave field distribution under prevailing wind in winter and summer, respectively. In that way, we obtained the distribution of wave characteristics in Taihu Lake, as well as the relationship with wind speed and direction, depth of water, etc.Secondly, an unstructured grid, finite-volume, three-dimensional primitive ocean model was used to simulate the flow field in Taihu Lake, and the results showed good simulation capability. After that, the model was used to study the circulation in Taihu Lake. With the analysis of wind, river runoff, baroclinic pressure, the Coriolis force and topography influence, the formation and characteristics of the circulation in the lake during summer is studied systematically. The modeling results showed that the horizontal circulation was mainly wind-driven current; the vertical velocity was about 10-6 m/s, much smaller than the horizontal velocity, and weak vertical circulation could be found in some profiles. Throughput flow couldn't result in horizontal circulation, while the density current couldn't keep stable and horizontal circulation seldom formed due to the shallowness of Taihu Lake. The topographical effect made the distribution of the flow field under average time-invariant wind downwind in shallow water while backward in deep water. In addition, the simulation data showed that circulation could be formed if the wind force is strong enough, even though the bottom topography of Taihu Lake was flat. Then, an unstructured grid, finite-volume, three-dimensional primitive equation ocean model was used to simulate the flow field in Taihu Lake. The results showed that the model simulate well. After that, the model is used to research the circulation of Taihu Lake. With the analysis of wind, river runoff, baroclinic pressure, the Coriolis force and topography influence, the formation and characteristics of the circulation of lake during summer was studied systematically. It was shown that the horizontal circulation was mainly wind-driven current; the vertical velocity was about 10-6 m/s, much smaller than the horizontal velocity. Weak vertical circulation can be found in some of the profiles. Throughput flow won't lead to horizontal circulation. Affected by the shallow water of Taihu Lake, the density current can't keep stable, so horizontal circulation seldom formed. The topographical effect made the distribution of the flow field under average time-invariant wind downwind in shallow water while backward in deep water. In addition, the simulation showed that circulation could be formed if the wind force was strong enough, even the bottom topography of Taihu was flat.Finally, a 3D numerical model, which could take account of the wave field and pressure field, was established by modifying the momentum equations on the basis of FVCOM. The model was put forward to simulate the storm surge current under the action of 9711 typhoon, in which the pressure field and wind field were obtained from Jelesnianski typhoon model and the wave field was calculated by the SWAN model. Through the comparison with the measured data, Jelesnianski typhoon model could effectively simulate both the pressure field and wind field. Through the validation of six Taihu lake water stations, the established storm flow model produced satisfactory results and the conclusion that wave field had little effect on the flow field in Taihu Lake was obtained.