The Moving Mesh Method In Solving Seepage Problem With A Free Surface And Application In Engineering

The seepage problem with a free surface is one of the hot research subjects in hydroelectric field. It has extensive use background, but solving the problem will have to encounter the specific difficulty. The free surface meets mixed boundary condition-Dirichlet boundary condition and Neumann boundary condition. Generally, the problem is solved numerically by iteration computation. In this paper, the steady dam seepage problem with a free surface was solved by iterative method using FEM with combined moving and fixed meshes.In the process of iterative calculation, the computational field was divided into moving mesh area which the free surface might cross and fixed mesh area which the free surface did not cross.In the area of moving mesh, when the position of the free surface changed in the iterative procedure, the nodal points of the mesh would be adjusted with that. This paper followed the idea of homogeneous compressing and stretching to reach the aim of moving meshes. Simultaneously, in order to realize the meshes' automatic moving, information of moving meshes was generated according to general dam body's structure based on traditional data of FEM.With proceeding of the iterative calculation, the spatial location of the meshes in the area of moving mesh would be changed so that the penetrability coefficient of each cell might be changed to different one. In allusion to this problem, some subregions of different physical properties were compartmentalized in dam body and dam foundation according to the different penetrability coefficients. The spatial locations of those subregions were changeless in the computational progress. When the meshes moved to the new position, the cells of the new position would be identified over again, so as to ascertain which subregion the cells belonged to and modified the cells' penetrability coefficient.In the iterative procedure of moving meshes, the deformation of the meshes might lead to monstrosity of the cells. Two types of the abnormal cells were analyzed in this paper. One is the great length-width ratio of the cell, the other one is the cell of irregular shape. According to the computation and analysis, the paper held that the latter abnormality did great harm to the precision of the calculation and to the convergence of the iterative procedure. Therefore, the paper put forward a new way of homogeneous moving mesh to avoid abnormality of the cells' shape.The paper takes example for the practical project-Antiseep and Reinforcement of JiLin Fengmang Concrete Dam, considering the exiting antiseep measures (including the impervious layer of the dam body, the drainage barrier of the dam body, the drainage passage, the impervious core of the dam foundation, the drainage barrier of the dam foundation), the impervious performance of the dam was numerically simulated before and after installing the impervious core. The computational results showed that (after installing the impervious core) the free surface descends greatly, the waterish parts of the dam body decrease significantly without increasing the lifting pressures of the dam foundation evidently, the head pressures of the spillpoints in the lower reaches do not decline obviously. The computational procedure shows that the method and the measures of the paper have good convergence property and stability, which is independent of selecting of the initial free surface.