Research on 3D forward modeling of AEM in frequency domain based on multiscale finite element method
Forward modeling is the basis of Electromagnetic(EM)data inversion,and its computational speed and accuracy have been the two core problems constraining EM inversion.In the 3D EM forward and inversion,the traditional method improves the calculation accuracy by refining the grid or increasing the order of the interpolation basis function,but this also reduces the computational efficiency and restricts the practical application of the 3D EM inversion.Therefore,how to achieve high-precision and fast forward modeling of large-scale models is an urgent problem to be solved in the current 3D EM forward and inversion.In this paper,the multiscale finite element method is applied to the solve Maxwell s equations.We first construct the multiscale basis function that satisfies the local characteristic differential operator on the coarse grid scale,and then solve the original problem on the coarse grid scale.By establishing the field mapping relationship between the two sets of coarse and fine grids,after solving the EM problem on a small number of coarse grids,the EM field response on the fine grid can be obtained by using the field mapping relationship between the two sets of coarse and fine grids,Therefore,the forward modeling response of EM fields at different scales can be quickly obtained under the premise of ensuring the calculation accuracy,and the calculation speed is greatly improved.In addition,this paper further improves the efficiency of 3D forward modeling based on the idea of octree.Finally,we verify the effectiveness of the algorithm by performing multiscale finite element forward modeling on typical geoelectric structures and comparing with the traditional finite element results,we also calculate the EM response for a realistic model—the ovoid zone ore body located at Voisey's Bay,Labrador,Canada,to verify the effectiveness of our algorithm.
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