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.

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.

A Combined Knowledge-Based and Finite Element Approach to Forging Die Design

1991 ◽  
Author(s):  
Imtiaz Haque ◽  
P. D. Dabke ◽  
Chesley Rowe ◽  
John Jackson
Keyword(s):  
Finite Element ◽  
Mesh Generation ◽  
Die Design ◽  
Knowledge Based System ◽  
Knowledge Based ◽  
Element Simulation ◽  
Regeneration Procedure ◽  
Element Approach ◽  
Forging Die ◽  
Simulation Package

Abstract This paper presents the use of a knowledge-based system to provide the link between computer-aided rule-of-thumb procedures and a finite element simulation package for the design of forging dies. The knowledge-based system automates the mesh generation and regeneration procedure that is traditionally the most cumbersome aspect of such a process. The system is programmed in Prolog, C, and Fortran. It is based on parametric mapping approach and generates 2-D quadrilateral meshes. Results are presented to show its effectiveness in reducing the effort and skill required for conducting forging simulations.

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 Comparison of the Performance of Hexahedral and Tetrahedral Elements in Finite Element Models of the Foot

2010 ◽  
Author(s):  
Srinivas C. Tadepalli ◽  
Ahmet Erdemir ◽  
Peter R. Cavanagh
Keyword(s):  
Finite Element ◽  
Mesh Generation ◽  
Complex Structure ◽  
Shear Loading ◽  
Superior Performance ◽  
Hexahedral Mesh ◽  
Tetrahedral Elements ◽  
Heel Pad ◽  
Hexahedral Elements ◽  
Foot Biomechanics

Characterization of the contact pressure patterns under the foot provides significant insight into pathological conditions such as diabetic peripheral neuropathy [1]. The finite element method (FEM) is widely used in foot biomechanics for predictive simulations of plantar pressures in barefoot and shod conditions [2–6]. In the analysis of the foot, mesh generation accounts for most of the labor in model development, due to the complex structure of the foot including highly partitioned, embedded, and branching geometries. In FEM, hexahedral elements are preferred over tetrahedral elements because of their superior performance in terms of convergence and accuracy of the solution [7]. This becomes more apparent as the convergence behavior of the simulations are hindered by large deformation, material incompressibility, and contact with friction, mechanical features which are commonly seen in foot biomechanics. Unfortunately, unlike tetrahedral meshing which is highly automated [8], hexahedral mesh generation is a time consuming process requiring considerable operator intervention. Despite their reputed advantages, the relative performance of tetrahedral meshes in foot models has not been well established; to our knowledge, there has not been a comprehensive study comparing the performance of hexahedral and tetrahedral elements when material and geometric nonlinearity are included combined with material incompressibility and shear force loading conditions. Hence, the objective of the present study was to evaluate various types of meshes that can be used to model the interaction of a bone-soft tissue construct and rigid floor complex under compressive and shear loading in a heel-pad analog model.

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