Xinshan Ma

Simulation of substation grounding grids with unequal-potential

A method of forming the equation system for simulating substation grounding grids with unequal-potential, i.e., the potential drop caused by the interior resistance of conductors is taken into account, is presented, based on a theory of combination of field and circuit. The equation system with the potential at discretization points of the grid as unknowns is formed by the method of node analysis in the circuit theory, and the definition of the mutual-resistance between conductors located in conducting media concerns with the electric current field theory. The method presented is capable of calculating the grids with arbitrary structure and floating electrodes in multiple-layer earth models. Comparison of calculation results of grids by equal and unequal potential models is given.

Calculation of EEG problems with anisotropic conducting media by the finite volume method

A realistic head model with anisotropic conductivity is simulated by the finite volume method, which is based on the integral conservation equation. A new mesh discretization method is presented to simulate the realistic head model with anisotropic conductivity. With the method, it is convenient to calculate anisotropic problems with curved boundary surfaces, and the calculation accuracy can be enhanced. The results are compared with analytical solutions of spherical models. The comparison shows that the finite volume method is of high calculation accuracy.

Magnetic field analysis of iron-core reactor coils by the finite-volume method

An accurate evaluation of the magnetic field of the iron-core reactor coils by the finite-volume method (FVM) is presented. The linear and quadratic interpolation scheme of FVM is developed. The numerical results are compared with those obtained by the finite-element method. Good agreement is obtained. The main advantage of the approach proposed is that the formation of coefficient matrix is very straightforward without needing the complicated mathematical derivation.

BEM calculation for magnetic shielding with steel sheets

The Boundary Element Method (BEM) is adapted to the solution of two-dimensional and axisymmetrical nonlinear shielding problems. The high vector-field accuracy attainable permits studies of extremely uniform nuclear magnetic resonance (NMR) fields to be made as well as less demanding shielding calculations. A technique is described in which nonlinearities are replaced by virtual sources in an explicit iteration scheme. All unknowns are on boundaries only and matrix size is not increased due to interior nonlinearities. An example is given. Suggestions for efficiency improvements are made.

Three-dimensional eddy current calculation by an adaptive three-component boundary element algorithm

An adaptive technique of calculating three-dimensional eddy currents by using the three-component boundary element algorithm is presented. The three-component algorithm is a minimum-order boundary element method in the calculation of three-dimensional eddy currents, which employs only three scalar unknowns on each mesh node, so that about 40% computer memory and 50% computational time can be saved relative to the conventional four-component algorithm that usually employs a scalar and a three-component vector as unknowns. The error estimate of the three-component algorithm and the implementation of the adaptive technique are described. The error estimate is based on the residue of the boundary element equation at the non-collocation mesh nodes. The adaptive technique is able to save computer memory and increase the accuracy of the solution greatly.

Analysis of the thin plate eddy-current problem by finite volume method

The eddy-current distribution in a thin conducting nonmagnetic steel plate is calculated by using the finite volume method. Adopting finite volume methods, the governing equations are enforced along closed paths, and the simultaneous linear system with unknown nodes of current vector potential T can be formed in a very straightforward way. The numerical results show very good agreements with the experimental data of TEAM problem 21.

Source region contracting method for EEG source reconstructions

A new electroencephalogram (EEG) source reconstruction method is presented. The method reduces the number of unknown quantities of the basic EEG equation by contracting the source region iteratively. The simultaneous equation system turns from an underdetermined system to an overdetermined system step by step. At last the least square algorithm is used to get a unique solution. The simulation shows that a high-resolution result can be obtained by using the method proposed.

Calculation of the alternating magnetic field near a metal surface

A medium-addition method and its recent development are recommended for calculating the 2-D alternating magnetic field in the vicinity of a defect. A fictitious medium with negative conductivity is suggested to simulate the defect. The prominent advantages of this method are that it requires much less computer capacity and is time saving. It is concluded that a medium-addition method can be used to solve certain electromagnetic field problems in nondestructive testing if the media are linear and the defect is a tiny crack or a small hole. >

Study on EEG inverse problems based on the finite volume method

Summary form only given. The Layered Recursive Algorithm (LRA) based on the Finite Volume Method (FVM) was developed to calculate the high-resolution electroencephalogram (HREEG). It is then extended to solve the dipole localization problem by using the LRA-BEM (Boundary Element Method) combined approach. The results show that FVM is a powerful numerical tool for the numerical calculation of inverse problems of EEG.

Dipole localization method based on the high-resolution EEG

The dipole localization method (DLM) of the electroencephalogram (EEG) is investigated based on the high-resolution EEG. The finite volume method (FVM)-boundary element method (BEM) coupled method is used for DLM. For FVM, a novel mesh generation method is presented to overcome the geometric singularity. This method can be employed to calculate EEG forward problems and extended to calculate the high-resolution EEG (HREEG). Because of the high spatial resolution of HREEG, as well as the merits of FVM and BEM, we can expect that the FVM-BEM coupled method is more accurate than the conventional DLM.