MT有限元模拟中截断边界的影响

利用有限元方法进行大地电磁正演数值模拟时，由于是在有限网格区域上的数值计算，模拟计算时的网格边界为截断边界，而有限元数值模拟时的大地电磁场边界条件需要在足够远处才能够满足，所以截断边界的存在可能会使大地电磁正演模拟的边界条件无法满足，致使对计算结果和计算精度产生影响。利用有限元二维正演程序，在网格边界处加载一维情况下的大地电磁场，然后固定研究区域的网格剖分，并对一维地电模型和二维地电模型在改变有限元网格边界大小的情况下进行计算。在对一维模型进行模拟计算时，截断边界对边界条件没有影响，边界条件自然满足。而对二维模型进行模拟计算时，截断边界的存在对计算结果有较大影响。利用趋肤深度作为有限元网格边界变化的量度，通过改变网格边界大小，对不同的二维地电模型进行计算比较，总结出适合大地电磁有限元正演模拟的参考网格边界。

Influence of Truncated Boundary in FEM Numerical Simulation of MT

Due to the limited calculation space in the magnetotelluric numerical simulation with finite element method(FEM), mesh boundary is generrally truncated. The existence of truncated boundary may make boundary conditions unsatified and thus affect calculated results and precision to some degree. We calculated the responce of one-dimensional and two-dimensional geoelectric models with two-dimension FEM forward program in which the boundaries of researching area are taken as one-dimensional situation with different truncated boundary. There is no effects on calculated results when simulating one-dimension models, because boundary conditions is satisfied naturelly. But to two-dimensional models, the truncated boundary may make boundary conditions unsatisfied and affect the results and precision. With skin depth as measurement of mesh boundary,we calculated and compared the results of some models with different mesh boundary, and at last got the referenced truncated boundary in MT FEM simulation.