Study On Overflow Capacity Of Broken Line Rolling Dam In Trapezoidal Channel

In the small watershed comprehensive management project,in order to solve the water problems such as production and ecology,rolling dams are often built to block the river in the ditch and river.The rolling dam is used to control the upstream water level,store water for irrigation,and discharge flood water at the same time.Trapezoidal section channel is a common open channel.When building a rolling dam on a trapezoidal cross section channel,the dam type can be designed directly according to the trapezoidal cross section.The design is simple and convenient,and the construction cost is low.At present,there is a lack of direct calculation method for the overflow capacity of trapezoidal channel rolling dam.The research on the overflow capacity of trapezoidal channel rolling dam not only has certain theoretical significance,but also has practical application value for the design of rolling dam project.In this paper,the calculation of overflow capacity of rolling dam on trapezoidal channel is studied by the combination of experimental research and numerical simulation.The experimental device is designed and manufactured.A three-dimensional turbulent mathematical model is established to simulate the overflow of the rolling dam.The experimental research and numerical simulation of the overflow of the rolling dam are carried out.The flow characteristics of rolling dam under the conditions of free outflow and submerged outflow are studied from the aspects of free surface shape,central profile water surface line and velocity distribution.The effects of the height P,crest width L,upstream dam face slope ratio mu,downstream dam face slope ratio md,trapezoidal channel slope coefficient m and other factors on the overflow capacity of the overflow dam are systematically studied.Based on the constant total flow energy equation,the basic calculation formula of overflow of rolling dam is established(?)According to the results of experimental research and numerical simulation,the empirical formulas of discharge coefficient Cd=0.365+0.049(1+m)(H/L)0.215(H/P)and submergence coefficient ?s=tanh19.526(1-hd/H)are obtained by multiple regression analysis.Using independent test data,the accuracy of the calculation formula of overflow capacity of overflow dam is analyzed.Comparing the calculated value of empirical formula with the experimental value,the relative error of free outflow flow calculation is within 5.00%,the relative error of submerged outflow calculation is within 15.00%,the empirical formula has high calculation accuracy.