Directly Iterative Finite Element Algorithm and Its Application in Line Current Source Electromagnetic Response Modeling

Abstract

[Abstract] The Directly Iterative Finite Element algorithm (DIFE) is developed to calculate the electromagnetic responses at earth surface excited by a line current source. The directly iterative formulation is deduced first, then iterative method is adopted to solve these FE equations. The compound griding method including re-interpolation scheme at the adjacent points has been realized to denser local grids near the source point, thus the precision of field calculation near the source point is assured. An iterative approach has put forward to obtain the whole range apparent resistivity from the electric field response excited by line current source. This approach has been verified through model calculations of uniform half space, layered earth and two dimensional earth model. For all these models, apparent resistivity curves very similar to magnetotelluric responses are obtained. It shows in theory that the frequency domain sounding at near zone of the line current source is possible and effective. [Key words]Directly iterative finite element algorithm (DIFE), Line current source, Electromagnetic response, Whole range apparent resistivity.

A Study on 2D CSAMT Forward Modeling and Inversion with a Dipole Source and Topography and Its Applications

“…Yan et al [5,6] derived a 2D theoretical forward formula and boundary conditions for line-source frequency sounding, and with approximate resistivities in the far zone calculated. Chen et al [7] fulfilled 2D forward calculation of EM responses for linesource frequency sounding by using the direct iteration finite element method, with transformation of electrical fields excited by vertical long line-source into apparent resistivity on whole zones realized; however the problem related to EM fields by parallel electrical dipole was not touched in the paper. Di et al [8,9] conducted a research on features of EM responses excited by high power long dipole and forward calculation of CSAMT by line-source in the frequency domain by using the finite element method.…”

Forward Modeling of the Electromagnetic Field Due to a Line Source in Frequency Domain Using the Finite Element Method

“…Ref. [2] indicates that when the survey frequency is high, the wave propagating to the boundary from the source can be considered as plane wave; but for low frequency, the plane wave assumption is not right. Therefore, in order to reduce the influence of the plane wave assumption, the first-order absorption boundary condition is used on all of outer boundaries, which makes the predominant field be absorbed at the boundaries according to the wave propagation rule.…”

Essential Structure Finite Element (ESFE) Algorithm and Its Application to MT 1‐D Continuous Medium Forward Modeling

“…Its difference from conventional FE is to form directly an explicit iterative formulation similar to finite difference algorithm which solves the variation problem corresponding to the boundary value problem of differential equations in the course of seeking the extremum of the functional equation. DIFE is effective in electromagnetic (EM) modeling [2,3] . The main bright point of DIFE is that not only elements but also essential structures are considered in the course of constructing the FE equation group.…”