复杂电性结构大地电磁二维响应特征

Magnetotelluric Responses of Two-Dimensional Complex Conductivity Structures

为了改进计算区域离散化问题,本文利用自适应非结构化网格有限单元法求解二维地电结构下大地电磁场满足的加权余量表达式。在有限元求解电磁场的过程中,网格剖分越精细、计算精度越高,计算量也会越大。此外,结构化网格难以适应任意地形以及复杂地质构造。而自适应非结构化网格在电性变化剧烈的区域会自动加密,在电性缓变的区域则生成粗疏的网格,从而优化网格质量与数量。因此,文中引入COMSOL Multiphysics软件,以实现若干地电模型的构建及非结构化自由四边形单元网格化。将网格数据信息导入本文算法,计算大地电磁场响应,并与解析解及数值解对比。结果表明,基于非结构化网格的正演模拟精度高、适应性强,为计算区域网格化提供了新的方法。

To improve the discretization technique,adaptive unstructured quadrilateral grid finite element（FE）procedure is presented for solving weighted residual formulation of magnetotelluric（MT）fields in 2-D conductivity structures.The finer the meshes are,the more accurate the numericalsolutions are.However,this is at the cost of time-consuming and large memory requirement.Adaptive mesh refinement generally provides an optimization of both run time and accuracy since in the method meshes are only refined where the electrical parameters vary intensely,while coarsen in the slow electrical resistivity change region.Due to the fact that regular grids have no potential to incorporate arbitrary topography and complex geologic structures,we introduced COMSOL Multiphysics software package to build arbitrary geometries and subdivide them with free quadrilaterals,then apply meshes information to our algorithm.Comparison with analytical solutions and previous numerical solutions demonstrate a high-accuracy and flexibility of numerical simulations based on unstructured grid,a new technology to discretize the computating domain.