Research On Unstructured Finite Element Mesh Generation Method And Its Application

The numerical calculation method represented by finite element method is usually used to study various geological phenomena such as fluid,solid,electric and magnetic which affect the safety of mine production in engineering practice.On the one hand,the efficiency and accuracy of numerical calculation mainly depend on the mesh;on the other hand,too many manual operations in the process of mesh generation greatly limit the application of numerical calculation in complex engineering problems.Mesh generation has always been a difficult and hot issue in related research as it is a key step of pre-processing.Combining Delaunay thinning algorithm,frontier advancing algorithm,mesh optimization technology and prior knowledge,the automatic mesh generation in the pre-processing of numerical calculation and its application in the field of mine engineering are studied in this dissertation.The main works are following:(1)The adaptive planar mesh generation method is proposed.Couple of Delaunay refinement algorithm and advancing front algorithm,the size and quality of initial mesh is improved,the local optimum point is generated first as the two-dimensional advancing front algorithm,then boundary conformity is maintained by Delaunay refinement algorithm,the local mesh will be reconstructed using two-dimensional constrained Delaunay criterion finally.The convergence and complexity of the coupled algorithm are analyzed.A mesh optimization method based on node movement is proposed to improve the quality of mesh.Based on the priori characteristics of the input linear model,a two-dimensional size function calculation method is proposed,which can be used to control the density distribution during mesh generation.(2)The adaptive surface mesh generation method is proposed.The initial sample and the Delaunay tetrahedralization are generated,a special kind of triangle is obtained as the initial surface mesh;the size?topological and quality of surface mesh is improved,one sample point is generated during per iteration,the local mesh will be reconstructed using Delaunay criterion.Based on the priori characteristics of the input surface model,a three-dimensional size function calculation method is proposed,which can be used to control the density distribution during mesh generation.(3)The adaptive volume mesh generation method is proposed.The Delaunay tetrahedralization of sample can be get after the surface mesh generation,the size and quality of initial mesh is improved,the local optimum point is generated first as the three-dimensional advancing front algorithm,then boundary conformity is maintained by Delaunay refinement,the local mesh will be reconstructed using three-dimensional constrained Delaunay criterion finally.A mesh optimization method based on node insertion and node movement is proposed to refine the silver element and improve the quality of mesh.It can be combined with the proposed definition method of three-dimensional size function to generate volume meshes with dense distribution in accordance with the prior characteristics of the input model.(4)The mesh generation methods proposed above are applied to the numerical calculation of mine engineering.The stratigraphic model is established by borehole data,and the water pressure distribution of aquifer is calculated,by the functional relationship between water inrush information,water inrush coefficient and unit water inrush established which is established with the help of data analysis method,the risk of water inrush from floor in the mining process of working face can be predicted.The proposed mesh generation method above is applied to the adaptive numerical calculation by simulating the plane thermal steady state distribution,it shows that the mesh generation method is suitable for the requirements of adaptive numerical calculation.The model optimization technology based on re-meshing is studied,which can improve the efficiency and accuracy of subsequent volume grid generation and numerical calculation.For massive unstructured meshes,an isoline/isosurface construction method based on span space and spatial subdivisions is proposed,which can significantly reduce the count of traversing meshes in the process of equivalent construction.