Numerical Analysis Of Breach s Surge waves

Surge waves resulting from dam breaks have been responsible for numerous losses of life. Sudden reservoir drawdown caused by partial breach of a dam can create a surge within the reservoir. Positive and negative surges are generally observed in open channels. Positive surges that occur due to tidal origins are referred to as tidal bores. A positive surge occurs when a sudden change in flow leads to an increase of the water depth, while a negative surge occurs due to a sudden decrease in water depth. A negative surge is an unsteady flow characterised by a decrease in water depth. Negative surges can occur downstream of a control structure when the discharge is reduced. They also occur upstream of a control structure that is opened rapidly or The failure time is very low. For a stationary observer the negative surge appears to be a gentle lowering of the free surface. The Hec-ras model based on the linearized implicit finite-difference model which based on the De St. Venant equations. The various implicit methods of finite differences that have been developed, the Preissmann-type schemes. When the surge occurs, the De St. Venant differential equations are not valid in the neighborhood of the surge So In most cases the partial differential equations may be solved to obtain The Explicit MacCormack (MOC) model by Method of Characteristics in the neighborhood of the surge. According to This paper provides the Parametric Models methods and numerical model such as MacCormack Explicit scheme and Preissmann Implicit scheme using Hec-Ras to simulate dam break furthermore it used to predict breach outflow hydrographs .Unsteady flow modeling is often used in dam breach analysis due to the need to obtain more detailed or accurate results. The breach parameters will directly and substantially affect the estimate of the flows. Due to this illustrate the failure time is very low, as a result the negative surge occurs, However De St. Venant differential equations are not valid in the neighborhood of the surge. In order to evaluate the effective of negative wave on the outflow hydrograph. according to this, the outflow computed by the simplified model with The explicit method of characteristics (MOC). The results of the Hec-Ras simulation, present that it was relatively closely to estimate peak breach discharges with The Explicit McCormack model

کلیدواژه ها:

MacCormack ، implicit ، finite-difference model ، overtopping ، peak breach discharge ، De St. Venant ، Explicit.