Study On Adaptive Remeshing Numerical Methods In Seismic Liquefaction Of Saturated Sand

The seismic liquefaction always causes sinking and flow of the ground. To learn the mechanism and levels of such disasters, numerical simulation is an efficient research technique to availably reproduce and predict the seismic liquefaction process. However, because of unsuitable mesh dividing in FEM, the deformation is so strong that some local mesh is distorted and aberrant, which gives a poor result and even stops the calculation. Therefore, two sets of adaptive mesh methods have been developed to study this problem in three parts.Firstly, against the deformation characteristics of liquefied soil, an error estimation based on SPR is adopted to present the relative error distribution of strain in the whole mesh. The bilinear recovered function is applied to triangular element mesh, which can give a more stable and accurate error distribution than the linear recovered function. The error estimation due to bilinear recovered function can exactly conduct local mesh refinement/regeneration, and also available for a multi-mesh of quadrilateral and triangular element.Secondly, a mesh refinement scheme due to parallel fission and a mesh regeneration scheme based on Delaunay triangulation are developed, respectively. Through testing and discussion, the average relative error, related to liquefaction level, is set as a suitable error threshold for adaptive indicator, to achieve a locally refined mesh with reasonable limited adaptive times.Finally, corresponding to the local mesh refinement and regeneration schemes, the data transfer from old mesh to new mesh is built for each scheme. Taking advantages of FEM basic rules, the plastic feature of soil is completely carried on from old mesh to new mesh, and the data is calculated continuously and accurately in adaptive mesh procedure.During the three parts, applicability and reliability of the two adaptive mesh schemes are explored, obtaining their superiority and imperfection.The work above can prove that the adaptive mesh scheme can exactly capture and smooth the sharp deformation, greatly avoiding the mesh distortion. This scheme can decrease the whole calculation error due to refining the target mesh locally, reasonably and orderly. Such scheme also can save more calculation resource than the uniformly refined mesh, and improve the numerical results of normal FEM, raising the efficiency of FEM.