2-D electromagnetic modeling by finite‐element method with a dipole source and topography

Geophysics ◽  
2000 ◽  
Vol 65 (2) ◽  
pp. 465-475 ◽  
Author(s):  
Yuji Mitsuhata
Keyword(s):  
Finite Element ◽  
Delta Function ◽  
Dipole Source ◽  
Electromagnetic Modeling ◽  
Secondary Field ◽  
Controlled Source ◽  
Transient Electromagnetic ◽  
Isoparametric Finite Element ◽  
Anomalous Bodies ◽  
Element Technique

I present a method for calculating frequency‐domain electromagnetic responses caused by a dipole source over a 2-D structure. In modeling controlled‐source electromagnetic data, it is usual to separate the electromagnetic field into a primary (background) and a secondary (scattered) field to avoid a source singularity, and only the secondary field caused by anomalous bodies is computed numerically. However, this conventional scheme is not effective for complex structures lacking a simple background structure. The present modeling method uses a pseudo‐delta function to distribute the dipole source current, and does not need the separation of the primary and the secondary field. In addition, the method employs an isoparametric finite‐element technique to represent realistic topography. Numerical experiments are used to validate the code. Finally, a simulation of a source overprint effect and the response of topography for the long‐offset transient electromagnetic and the controlled‐source magnetotelluric measurements is presented.

The Modeling of TEM Responses Simulated by Multi-Transmitter

2012 ◽  
Vol 450-451 ◽  
pp. 1518-1521
Author(s):  
Xin Gong Tang ◽  
Wen Bao Hu ◽  
Liang Jun Yan
Keyword(s):  
Electric Dipole ◽  
Field Survey ◽  
Dipole Source ◽  
Good Resolution ◽  
Controlled Source ◽  
Anomalous Body ◽  
Transient Electromagnetic ◽  
Electromagnetic Responses ◽  
Anomalous Bodies ◽  
Dipole Sources

Using one or two electric dipole transmitters in the Controlled source electromgnetic method, this paper calculate the transient electromagnetic responses of one and two 3D conductive anomalous bodies in the layered earth by varying the number and intensity of the dipole sources. The results of the models show that satisfactory resolution can be achieved when only one dipole source is used. The stronger the intensity of the electric dipole source, the better resolution for the anomalous body for the same offset. When two electric dipole transmitters laid each side of one 3D body, it means that the anomalous body locates in the middle of the sources and the resolution to the target becomes poor. The numerical results of the transient electromagnetic responses of two 3D bodies also support the idea that resolution is not good when two transmitters are used in each side of the targets simultaneously. As the conclusion, in order to get good resolution to the target, multi transmitters laid different side of the geological target should not be used the same time in the field survey.

Finite-Element Modeling of Time-Domain Controlled-Source Electromagnetic Survey with Weighted Laguerre Polynomials

Geophysics ◽  
2021 ◽  
pp. 1-43
Author(s):  
Qingtao Sun ◽  
Runren Zhang ◽  
Yunyun Hu
Keyword(s):  
Finite Element ◽  
Time Domain ◽  
Laguerre Polynomials ◽  
Time Integration ◽  
Sampling Interval ◽  
Controlled Source ◽  
Time Integration Method ◽  
Transient Electromagnetic ◽  
Backward Euler ◽  
Land Survey

To facilitate the modeling of time-domain controlled-source electromagnetic survey, we propose an efficient finite-element method with weighted Laguerre polynomials, which shows a much lower computational complexity than conventional time integration methods. The proposed method allows sampling the field at arbitrary time steps and also its accuracy is determined by the number of polynomials, instead of the time sampling interval. Analysis is given regarding the optimization of the polynomial number to be used and the criterion of selecting the time scale factor. Two numerical examples in marine and land survey environments are included to demonstrate the superiority of the proposed method over the existing backward Euler time integration method. The proposed method is expected to facilitate the modeling of transient electromagnetic surveys in the geophysical regime.

2D marine controlled-source electromagnetic modeling: Part 2 — The effect of bathymetry

Geophysics ◽  
2007 ◽  
Vol 72 (2) ◽  
pp. WA63-WA71 ◽  
Author(s):  
Yuguo Li ◽  
Steven Constable
Keyword(s):  
Finite Element ◽  
Numerical Modeling ◽  
Data Sets ◽  
Electromagnetic Modeling ◽  
Seafloor Topography ◽  
Transmission Frequency ◽  
Controlled Source ◽  
Magnetic Components ◽  
Marine Csem ◽  
Conductivity Contrast

Marine controlled-source electromagnetic (CSEM) data are strongly affected by bathymetry because of the conductivity contrast between seawater and the crust below the seafloor. We simulate the marine CSEM response to 2D bathymetry using our new finite element (FE) code, and our numerical modeling shows that all electric and magnetic components are influenced by bathymery, but to different extents. Bathymetry effects depend upon transmission frequency, seabed conductivity, seawater depth, transmitter-receiver geometry, and roughness of the seafloor topography. Bathymetry effects clearly have to be take into account to avoid the misinterpretation of marine CSEM data sets.

A hybrid three‐dimensional electromagnetic modeling scheme

Geophysics ◽  
1981 ◽  
Vol 46 (5) ◽  
pp. 796-805 ◽  
Author(s):  
K. H. Lee ◽  
D. F. Pridmore ◽  
H. F. Morrison
Keyword(s):  
Finite Element ◽  
Electric Fields ◽  
Three Dimensional ◽  
Mathematical Expression ◽  
Finite Element Mesh ◽  
Electromagnetic Modeling ◽  
Variational Integral ◽  
Element Mesh ◽  
Element Technique ◽  
Scattered Fields

We present an efficient numerical method for computing electromagnetic (EM) scattering of arbitrary three‐dimensional (3-D) local inhomogeneities buried in a uniform or two‐layered earth. In this scheme the inhomogeneity is enclosed by a volume whose conductivity is discretized by a finite‐element mesh and whose boundary is only a slight distance away from the inhomogeneity. The scheme uses two sets of independent equations. The first is a set of finite‐element equations derived from a variational integral, and the second is a mathematical expression for the fields at the boundany in terms of electric fields inside the boundary. The Green’s function is used to derive the second set of equations. An iterative algorithm has been developed to solve these two sets of equations. The solutions are the electric fields at nodes inside the finite‐element mesh. The scattered fields anywhere may then be obtained by performing volume integrations over the inhomogeneous region. The scheme is used for modeling 3-D inhomogeneities with plane‐wave and magnetic dipole sources. The results agree with earlier model analyses using the finite‐element technique.

scholarly journals custEM: Customizable finite-element simulation of complex controlled-source electromagnetic data

Geophysics ◽  
2019 ◽  
Vol 84 (2) ◽  
pp. F17-F33 ◽  
Author(s):  
Raphael Rochlitz ◽  
Nico Skibbe ◽  
Thomas Günther
Keyword(s):  
Finite Element ◽  
Open Source ◽  
Mesh Generation ◽  
Analytic Solutions ◽  
Superior Performance ◽  
Electromagnetic Modeling ◽  
Matrix Assembly ◽  
Controlled Source ◽  
Time Harmonic ◽  
Element Simulation

We have developed the open-source toolbox custEM (customizable electromagnetic modeling) for the simulation of complex 3D controlled-source electromagnetic (CSEM) problems. It is based on the open-source finite-element library FEniCS, which supports tetrahedral meshes, multiprocessing, higher order polynomials, and anisotropy. We use multiple finite-element approaches to solve the time-harmonic Maxwell equations, which are based on total or secondary electric field and gauged potential formulations. In addition, we develop a secondary magnetic field formulation, showing superior performance if only magnetic fields are required. Using Nédélec basis functions, we robustly incorporate the current density on the edges of the mesh for the total field formulations. The latter enable modeling of CSEM problems taking topography into account. We evaluate semianalytical 1D layered-earth solutions with the pyhed library, supporting arbitrary configurations of dipole or loop sources for secondary field calculations. All system matrices have been modified to be symmetric and solved in parallel with the direct solver MUMPS. Aside from the finite-element kernel, mesh generation, interpolation, and visualization modules have been implemented to simplify and automate the modeling workflow. We prove the capability of custEM, including validation against analytic-solutions, crossvalidation of all implemented approaches, and results for a model with 3D topography with four examples. The object-oriented implementation allows for customizable modifications and additions or to use only submodules designed for special tasks, such as mesh generation or matrix assembly. Therefore, the toolbox is suitable for crossvalidation with other codes and as the basis for developing 3D inversion routines.

scholarly journals Reduction of Electromagnetic Reflections in 3D Airborne Transient Electromagnetic Modeling: Application of the CFS-PML in Source-Free Media

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Yanju Ji ◽  
Xuejiao Zhao ◽  
Jiayue Gu ◽  
Dongsheng Li ◽  
Shanshan Guan
Keyword(s):  
Recursive Formula ◽  
Electromagnetic Response ◽  
Complex Frequency ◽  
Electromagnetic Modeling ◽  
Free Medium ◽  
Time Step ◽  
Homogeneous Half Space ◽  
Transient Electromagnetic ◽  
Anomalous Bodies ◽  
Relative Errors

To solve the problem of electromagnetic reflections caused by the termination of finite-difference time-domain (FDTD) grids, we apply the complex frequency-shifted perfectly matched layer (CFS-PML) to airborne transient electromagnetic (ATEM) modeling in a source-free medium. To implement the CFS-PML, two important aspects are improved. First, our method adopts the source-free Maxwell’s equations as the governing equations and introduces the divergence condition, consequently, the discrete form of Maxwell’s third equation is derived with regard to the CFS-PML form. Second, because our method adopts an inhomogeneous time-step, a recursive formula composed of convolution items based on a nonuniform time-step is proposed. The proposed approach is verified via a calculation of the electromagnetic response using homogeneous half-space models with different conductivities. The results show that the CFS-PML can reduce a 60 dB relative errors in late times. Moreover, this approach is also applied to 3D anomalous models; the results indicate that the proposed method can reduce reflections and substantially improve the identification of anomalous bodies. Consequently, the CFS-PML has good implications for ATEM modeling in a source-free medium.

Multidisciplinary Computer Simulation of Transient Electromagnetic-Thermal Phenomena in a Turbogenerator Rotor

2014 ◽  
Vol 528 ◽  
pp. 278-284
Author(s):  
Michael G. Pantelyat ◽  
Mykola G. Shulzhenko ◽  
Elena K. Rudenko
Keyword(s):  
Computer Simulation ◽  
Finite Element ◽  
Thermal State ◽  
Short Circuit ◽  
Computer Code ◽  
Transient Electromagnetic ◽  
Turbogenerator Rotor ◽  
Two Phases ◽  
Element Technique ◽  
Thermal Phenomena

A finite element technique and computer code for the numerical analysis of 3D transient electromagnetic fields and temperature distribution due to negative sequence currents in large synchronous turbogenerator rotors are developed. Electromagnetic-thermal phenomena in a 300 MVA class turbogenerator rotor during a line-to-line short circuit on two phases of the machine are numerically investigated. Effect of the various conditions of the rotor cooling on its thermal state is studied. Numerical results obtained can be used for the computer simulation of the thermo-mechanical behaviour of the rotor.

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