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电磁场数值模拟的背景场/异常场算法是三维正演的有效策略之一,优点为采用解析法计算电磁场背景场代替场源项、克服了场源奇异性,缺点为不适用于发射源布置于起伏地表或背景模型复杂的情形.总场算法是直接对电磁场总场开展数值模拟,其难点是有效加载场源、保证近区与过渡区数值解精度.本文以水平电偶源形式分段加载接地长导线源,并以电场总场Helmholtz方程为矢量有限元法控制方程,实现了基于非结构化四面体网格剖分的接地长导线源频率域电磁法三维正演.通过与均匀全空间中水平电偶源产生的电场解析解对比,验证了本文算法的正确性,并分析了四面体外接圆半径与其最短棱边的最大比值和四面体二面角最小值对数值解精度的影响规律.通过与块状高导体地电模型的积分方程法、有限体积法和基于磁矢量势Helmholtz方程的有限元法数值解对比,进一步验证了本文算法正确性,同时说明了非结构化四面体网格能够更加精细地剖分电性异常体,利于获得精确数值解.
The background field / anomaly field algorithm of electromagnetic field numerical simulation is one of the effective strategies for 3D forward modeling. The advantage of this method is that the background field of the electromagnetic field is replaced by the analytic method to replace the field source item and the field source singularity is overcome. The disadvantage is that it is not suitable for the arrangement of the emitter source Fluctuating ground surface or complex background model.The total field algorithm is a direct numerical simulation of the total field of the electromagnetic field, the difficulty is the effective loading of the field source, to ensure the numerical solution of the near area and the transition area accuracy.In this paper, Grounded long wire source, and the governing equation of Helmholtz equation of the electric field is used as a vector finite element method to realize the three-dimensional forward modeling of the long-wire ground source frequency domain electromagnetic method based on unstructured tetrahedron meshing. By comparing with the uniform full space The analytical solution of the electric field generated by the mid level dipole source verifies the correctness of the proposed algorithm and analyzes the influence of the maximum ratio of the tetrahedron circumscribed circle to its shortest edge and the minimum value of tetrahedron dihedral angle on numerical solution accuracy By comparing with finite element method of finite element method and finite volume method of geoelectric model of massive high conductor and Helmholtz equation based on magnetic vector potential, The validity of the algorithm in this paper is validated in a single step. At the same time, it is demonstrated that the unstructured tetrahedron mesh can segment the electrical anomalous body more finely and help to obtain the exact numerical solution.