Study On Hydrodynamic Simulation And Optimization Inversion Of Roughness For Upstream Reach Of Wanjiazhai Reservoir In The Yellow River

Because of the unique temperature and river conditions,in the Inner Mongolia section of the Yellow River in winter,the ice condition and ice run disasters occurred frequently seriously,especially in the Tuoketuo County.For the influence factors of ice,the four major factors include: thermodynamic,dynamic,channel topography and human influence factors.Therefore,in order to carry out the research on the influencing factors of ice,this paper takes the upstream dam site of the Wanjiazhai Reservoir in the main Yellow River to the Toudaoguai river section as the research object.Based on the measured water level,flow,and river terrain data,combined with field prototype observation results,the hydrodynamic model of the river section was built by using HEC-RAS software,and to explore the spatiotemporal distribution characteristics of the hydrodynamic parameters in each typical period.In addition,according to the idea of optimal estimation and inversion,the Calman Filter and BP Neural Network are used to construct the roughness optimization model and inversion model,to improve method of parameter rate determination,further improve the accuracy of the hydrodynamic model and make the simulation results more reliable.Finally,the error of hydrodynamic simulation is also analyzed.The research results are as follows:(1)HEC-RAS can well meet the needs of hydrodynamic simulation,and the maximum relative error is less than 13%.(2)By analyzing the spatial and temporal distribution characteristics of the simulated water level and combining with the characteristics of the flow,there is a positive correlation between upstream and downstream water level differences and flow in each typical period of the river is studied.(3)The ice dam is easily formed during the ice formation period in the Caojiawan river section.The main cause of the ice disaster is that the cross-section of river is relatively narrow and the flow velocity is obviously reduced here.(4)Using the numerical simulation method to optimize and invert the coefficient of roughness can effectively reduce the error of hydrodynamic simulation.After comparison,the inversion method is most effective,and the maximum relative error of hydrodynamic simulation is about 10%.(5)The error analysis shows that the cumulative fractional error of ice formation period is relatively larger in the research period,especially in February and March,while the cumulative error in August is the smallest.The research shows that it is feasible to carry out hydrodynamic simulation with HEC-RAS software,and the optimization inversion method is successfully applied to improve the accuracy of the model.To provide a scientific basis and theoretical support for the research of the Yellow River Inner Mongolia section of the flood disaster reduction work.In the future research,many factors should be considered comprehensively,so as to further improve the mathematical model and make the research results more representative.