Analysis Of Dynamic Characteristics Of Railway Ballast Bed With Coupled DEM-FEM Method

With the development of high-speed railway,the dynamic study of railway is very important for train safety.According to the structural characteristics of the railway track that includes varieties of composition of sleeper,ballast,embankment and so on.This paper build a coupled DEM-FEM numerical algorithm to simulate railway structure that contains both continuous and discontinuous materials.Discrete element method(DEM)shows distinct advantage in the simulation of dynamic behavior of granular materials,which can effectively obtain the mesoscopic dynamic information,but the computational efficiency of discrete element method is low.Finite element method(FEM)is one of the most effective numerical algorithm to simulate continuum structures,and FEM has great advantages in computational efficiency.Therefore,to give full play to advantages of the two method,this paper presents a coupled discrete-finite element method to simulate railway structure that contains both ballast and continuum structure.The discrete element method and the elastic-plastic finite element method are employed to model the ballast and compact continuum structure of railway,respectively.Clumps are employed to construct real ballast.To build coupled DEM-FEM algorithm in plane,the contact force in plane is obtained according to principle of conservation of energy so that the contact force can transfer to finite element areas as equivalent nodal force.The displacement of finite element on coupled surface can participate in DEM calculation as displacement boundary conditions.In the coupling region that discrete elements overlap with finite element,Discrete element local coordinates can be obtained by newton iteration method so that the force of discrete element in coupling region can transfer to finite element areas as force boundary conditions.According to the displacement continuous condition,the discrete elements are consistent with finite elements motion in coupling region,so displacements of DEM is determined and can participate in DEM calculation to realize DEM-FEM coupling in volume..According to the structural characteristics of the ballasted-ballastless transition zone of railway track,this paper build three numerical models of different construction way based on coupled DEM-FEM numerical algorithm to simulate its dynamic behaviors of settlement under train loading.The results show that the way ballast embedded slab track and track embedded ballast can improve the stability of ballast track and reduce differential stiffness and settlement effectively.Numerical model of railway track where ballast interact with embankment are built based on coupled DEM-FEM numerical algorithm to analysis micromechanical characteristics of track.The motions of DEM in coupling region are determined by constitutive model of ballastembankment.The model considers plastic deformation of embankment caused by the ballast at the same time.The results show that ballast can transfer train load to the embankment scatteredly and improve the stability effectively.Moreover,the bearing capacity of ballast bed are determined by plastic deformation in the top of embankment.Also,the results verify the reliability of the coupled DEM-FEM model of interaction between ballast and embankment.