The Numerical Simulation Research Of Earth And Rockfill Dam's Breaking Process And Its Downstream Advance Of Freshet

The research about the breaking process of earth and rockfill dam and its downstream flood routing is very important to handle the sudden dam-breaking flood disaster and enhance the safety of agricultural water conservancy projects in China.The dam failure research progress and its trends are reviewed in this article. On the basis of previous studies, a mathematical model of flood routing by dam failure is established, which adopts the finite volume method and TVD-MacCormack format. The model adopts irregular local discontinuous grids to divide the computational area, adopts the unstructured grid managing mode to organize the computational grids, adopts the dynamic boundary processing technology to treat wet-dry boundary, which is based on unit properties and interface properties. After validated by using the test data of two dam-breaking physical models, this mathematical model simulates the dam-breaking flood routing processes of Weishui reservoir and Lushui reservoir.The model verifying results show that the model can reasonably simulate the dam-breaking waves'routing, reflection and refraction in the reservoir and flood storage area after dam failure. The model exhibits the good ability to capture the intermittent wave in the rapid-tranquil flow transition zone and discontinuous flow zone near the breach. In breach zone where exists greater water level gradient and strong three-dimension flow, due to the connatural simulating deficiency of two-dimension and three-dimension mathematical models, there is some difference between the computing value and experimental value from individual water level measuring point. As a whole, the numerical simulating results match the physical model test results perfectly.The test results of model sensitiveness show that the superbee limiter exhibits the excessive compressing to intermittent waves, but the calculated water level processes from the minmod limiter are relatively smooth. In addition, frequency from the appropriate flux limiter can reduce the unnecessary computing effort while the computational stability is maintained. Adopting irregular local discontinuous grids to divide the computational area, adopting the unstructured grid managing mode to organize the computational grids, can provide the model a good ability to adapt to the complex terrain, also reduce the amount of invalid grids, maximize the effective computing grid, so the model computing efficiency increases.The numerical computing results of project cases show that the mathematical model simulates reasonably the flow pattern of the reservoir, the breach and the downstream area, the water surface changing process during dam breaking and breach forming. The model also exhibits the good ability to capture the intermittent wave in the rapid-tranquil flow transition zone near the breach, the good stability in the great water level gradient zone. The dynamic boundary processing technology based on unit and interface properties has a strong simulating capability of the dramatic dry-wet changing zone.According to the numerical computing results of project cases, the flow discharge process of the dam breach and the downstream cross-sections is reasonable, so is the variation of the flood peak discharge with the reservoir level. The analysis of arrival time of the flood, the flood period, and the contour chart of maximum submerged depth show that with the released discharge decreasing, the moment when the flood reaches the same downstream location delays accordingly, the flood submerging period reduces. The maximum submerged depth trends to decrease along the flood moving path as a whole. The maximum submerged depth of the zone with lower elevation in the same section is big generally.The numerical computing results of the verifying cases and project cases show that the mathematical model introduced in this article has the good property of water amount conservation.