Study On Dynamic Coupling Analysis Method Of High CFRD And Reservior System

For the CFRD constructed in the strong earthquake zone in western China,the reasonable evaluation of the seismic performance of concrete slabs is an important part of the feasibility study and seismic design.Therefore,it is necessary to carry out a more detailed simulation of the slabs in the dynamic numerical analysis,and one of the important influencing factors to be considered is the hydrodynamic pressure.The existing three-dimensional dynamic fluid-solid coupling analysis of the CFRD generally does not consider the dynamic water pressure excited by the bottom and the bank slope of the reservoir,that is,the dynamic water pressure cannot be accurately calculated.And for the 250m-300m level CFRD,it is still to be considered whether it is feasible to ignore the hydrodynamic pressure.The existing results are difficult to meet the safety evaluation requirements of high CFRD under earthquake conditions.The Westergaard simplification method recommended by the seismic code has many limitations and cannot accurately calculate the hydrodynamic pressure.It is necessary to make a detailed analysis of the errors caused by the Westergaard simplification method by using accurate hydrodynamic pressure calculation methods.In the analysis of the interaction between dam and reservoir,the additional mass matrix obtained by the numerical method of scaled boundary finite element method(SBFEM),finite element method(FEM)or boundary element method(BEM)is full for the incompressible reservoir.When the degree of freedom of the coupling system reaches a certain scale,especially for numerical calculations with strong nonlinearity(elastic-plastic dam),solving equations consumes a lot of computation time.Moreover,the engineering application suitability of the frequency-independent wave energy absorption boundary needs further discussion when considering the reservoir water compressibility for the fluid-solid coupling analysis of the CFRD and reservoir.In view of the above problems,based on previous research results,SBFEM developed in recent years is used to simulate the reservoir in front of the dam,and the dynamic fluid-solid coupling analysis of the CFRD and reservoir nonlinear system under seismic conditions is carried out.The main contents of this study are as follows:(1)Using FEM discrete nonlinear dam,SBFEM is used to simulate the prismatic semi-infinite reservoir in front of the dam.The CFRD-reservoir time domain nonlinear dynamic fluid-solid coupling analysis method based on FEM-SBFEM is established.Furthermore,the influence of hydrodynamic pressure on the dynamic response of concrete slabs under seismic conditions is studied,and the distribution law of hydrodynamic pressure before dam and its influence mechanism on dynamic stress of slabs are revealed.The hydrodynamic pressure influences the dynamic stress in face slabs through the frictional force between the cushion and the slabs.In view of the limitations of the widely used Westergaard concentrated mass method,the error of dynamic stress of the slabs caused by the Westergaard method is studied,and the error mechanism is clarified.The error of dynamic stress in face slabs along the slope direction principally roots in the false slope direction force of a lumped additional mass and the inaccurate frictional force acting on the concrete face.(2)Using SBFEM discrete the finite-domain reservoir model,the calculation method of hydrodynamic pressure considering the complex shape of three-dimensional reservoir in front of dam is proposed,and the accuracy of the method is verified.The dynamic coupling analysis method of the CFRD-complex shape reservoir system is established.The influence of different reservoir shapes(narrow curved valley and prismatic river valley)on the dynamic characteristics of slabs is analyzed.At the same time,the applicability of the calculation method of hydrodynamic pressure in the prismatic reservoir to the narrow curved reservoir is verified.(3)The traditional hydrodynamic pressure calculation method can only calculate the triangular or quadrilateral mesh.The dam-foundation grid cross-scale analysis system may have a polygonal mesh on the upstream face of the dam.And the traditional hydrodynamic pressure method cannot be directly used for the dynamic fluid-solid coupling analysis of this system,and secondary mesh treatment of upstream face of dam is needed.Based on the SBFEM theory and the polygonal mean shape function,a prismatic semi-infinite domain polygonal fluid element and a finite domain polygon fluid element are constructed.The dynamic water pressure calculation methods of the prismatic semi-infinite domain reservoir and the three-dimensional finite domain complex shape reservoir based on SBFEM polygonal element are proposed,and their accuracy is verified.The two methods compensate for the vacancy in the dynamic water pressure calculation model of polygonal mesh,and are coupled with the existing dam(grid cross-scale)analysis system.And then the grid cross-scale nolinear dynamic fluid-solid coupling analysis method for CFRD and reservoir system based on SBFEM polygonal element are established.For prismatic semi-infinite domain reservoir,the calculation model is used to analyze the influence of hydrodynamic pressure on the dynamic response of the rockfill of CFRD under earthquake conditions.For complex shape finite domain reservoir,the calculation model can reduce the freedom of the reservoir to improve efficiency by using the polygon mesh cross-scale discrete reservoir water,and the accuracy of the coupling method is verified.(4)The hydrodynamic pressure is calculated by the SBFEM-based semi-infinite domain compressible reservoir model and the model is coupled with the CFRD FE model.A nonlinear dynamic time domain coupling analysis method for CFRD and semi-infinite domain compressible reservoir based on FEM-SBFEM is established.The influence of reservoir water compressibility on the dynamic water pressure distribution in front of the dam and the dynamic response of the CFRD are analyzed.Moreover,for the compressible reservoir model,the method of cutting off frequency is adopted to reduce the calculation amount of solving in the frequency domain,and the hydrodynamic pressure calculation method of the compressible reservoir is improved.And an improved nonlinear analysis method for dynamic coupling of CFRD and compressible reservoir is established,and its accuracy is verified.The applicability of the engineering application of the frequency-dependent wave energy absorption model of the sedimentary layer in the reservoir is also discussed.It is recommended to use the incompressible reservoir water model to calculate the hydrodynamic pressure before dam in the dynamic seismic analysis of the CFRD project.(5)For the incompressible reservoir model,the simplification of the mass matrix is adopted to improve the calculation efficiency under the premise of ensuring accuracy.An efficient dam-reservoir dynamic fluid-solid coupling simplification analysis method was established,and the accuracy of the method was verified.Based on the object-oriented design method,the SBFEM-based isoparametric/polygon reservoir element is integrated on GEODYNA software platform.A high-performance refined analysis for dam and foundation-reservoir(grid cross-scale)system interaction based on FEM(or SBFEM)-SBFEM is implemented and applied to the analysis of actual CFRD engineering.The results show that Westergaard lumped additional mass method can cause large errors in the slope stress of slabs.In the seismic design and research of CFRD engineering,the accurate hydrodynamic pressure calculation methods should be adopted to more rationally evaluate its seismic performance.