Seyedmasoud Ansari

3D finite-element simulation of electromagnetic data for inductive and galvanic components

SUMMARY A finite-element method is presented for modelling geophysical electromagnetic (EM) data. The electric field is decomposed into terms involving vector and scalar potentials. Edge element and nodal basis functions are used to approximate the vector and scalar potentials respectively. The solution is implemented on both rectilinear grids and tetrahedral grids. The particular desire is to investigate the relative importance of the vector and scalar potential terms, and hence the inductive and galvanic parts of the EM response.

Towards Real Earth Models - Computational Geophysics on Unstructured Tetrahedral Meshes?

Using unstructured tetrahedral meshes to specify 3D geophysical Earth models has a numer of advantages. Such meshes can conform exactly to the triangularly tessellated wireframe surfaces in the 3D Earth models used by geologists. This offers up the possibility of both geophysicists and geologists working with a single unified Earth model. Unstructured tetrahedral meshes are extremely flexible, and so can accurately mimic arbitrarily complicated subsurface structures and topography. Also, in the context of electromagnetic methods, unstructured tetrahedral meshes can be very finely discretized around sources and yet can transition to a coarse discretization in the extremities of the solution domain without, in principle, affecting the quality of the mesh. However, using unstructured tetrahedral meshes for geophysical Earth models has its challenges. The tessellated surfaces in wireframe geological models are often not immediately suitable for computational techniques as they can contain intersecting facets and facets with extreme aspect ratios. Generating tetrahedral meshes that are of sufficient quality from real wireframe geological models can therefore be difficult. This presentation will aim to discuss the pros and cons of using unstructured tetrahedral meshes for geophysical Earth models, keeping in mind the complexities of the real subsurface that we are ultimately trying to represent.

A Potential Method for Three-dimensional Numerical Modeling of Geophysical Electromagnetic Problems

A finite-element solution to the three-dimensional geophysical electromagnetic problems is presented. We decomposed the electric field into vector and scalar potentials, in the both Helmholtz equation and equation of conservation of charge. The computational domain is subdivided into unstructured tetrahedral meshes. Both edge and nodal basis functions are used to find approximate solutions for the potentials. The purpose of this study is to efficiently solve the system of equations, and also investigate how vector and scalar potentials, and therefore inductive and galvanic components, contribute to the resulting electric field.