NUMERICAL SIMULATION OF THE STORM SURGE AND ITS INDUCED CURRENTS
风暴潮流运动的数值模拟

Storm surge is one kind of severe disasters which often claim tens of thousands people's lives. Scientists have investigated this problem for decades. These works have been focused mainly on the prediction of peak surge formation and its evolution. However, some environmental impact is attributed to the unusual passive scalar transport by the energetic currents generated by the storm surge. Hence, further understanding of surge-induced currents is indispensable. This paper, therefore, emphasizes on the behaviour of a water body in case of storm surges, in order to set a solid foundation for studying dynamics of the passive scalar transport in this unusual flow field. To begin with, we have established a two-dimensional numerical model by using depth-averaged Navier-Stokes equations, including surface pressure, wind stress, bottom drag and Coriolis force terms. The wind stress and bottom drag are determined by the quadratic drag law. The surface pressure field is described by so-called Fujita and Takahashi formulae. The model is verified by comparing previous numerical results. Then we apply the model to an open sea, simulating spatial and temporal variations of water level and currents caused by surges. By case studies, we have discussed the influences of surface pressure, water depth, bottom slope and maximum wind radius on the variations of water level, flow pattern and current speed. Finally, some conclusions have been drawn as follows. The flow pattern is apparently affected by Coriolis force, especially for deep water. The depth-averaged current speed increases with the drop of the surface pressure. It also increases with the water depth in a shallower sea, but decreases with the water depth in a deeper sea. The current follows the wind with a time lag. The deeper the water depth is, the longer the lag time becomes. The water level goes high when the atmospheric pressure drops or the maximum wind radius increases. A storm causes higher surge in a shallower water area. In a very deep sea, the surface pressure becomes dominant and the effect of wind shear is negligible. Generally speaking, higher water level occurs to the right side of the typhoon and the peak surge occurs approximately at the maximum wind point when the typhoon lands perpendicularly to the coastline.