Du Zhiye

3-D FEM Simulation of Velocity Effects on Magnetic Flux Leakage Testing Signals

The development of computer-based defect characterization scheme for magnetic flux leakage (MFL) method require adequate mathematical models to describe the complicated interactions of sources, fields, velocity and defects in materials. In this paper, a 3-D transient finite element model based on T-Omega formulation was used to analyse MFL system at high velocity, with regard to eddy currents induced in a steel tube because of the relative movement between the exciters and specimen. The eddy currents change the profile of electromagnetic field, which increases difficulty in MFL signals interpretation and defect identification. Typical 3-D defects were modeled and MFL signals caused by the defects of different sizes were simulated respectively. Eddy currents induced by velocity and their characterization in high velocity MFL testing system were investigated.

Application of a Composite Grid Method in the Analysis of 3-D Eddy Current Field Involving Movement

A composite grid method (CGM) was applied in the analysis of eddy current field involving movement. The region of current source and air including the background of moving conductor was discretized with a global grid. The region of moving conductor was discretized with a local grid. The trouble of remeshing in normal finite element technique based on one set of grid is overcome in CGM. At each time step, instead of mesh regeneration it is only necessary to change the coordinates of local grid nodes. The fields on the two sets of grids are solved independently by finite element method and related by an interpolation matrix. The dynamic characteristics of a 3-D coil gun model were calculated by CGM. As a comparison, a 2-D axisymmetric model was also simulated. Numerical results obtained were compared with experimental data.

Parallel Numerical Computing of Finite Element Model of Conductors and Floating Potentials

In computational electromagnetics, parallel computing is more and more studied to deal with large-scale problems which are not able to execute by single PC. Many parallel computing example for electrostatic had been reported. But for electrostatic problems in which floating conductors exist, the realization of parallel is not reported. In the electrostatic model that contains floating conductors, the surfaces of such conductors represent equipotentials but do not constitute a Dirichlet boundary condition. So the partition of such model is difficult to control. This paper presented a way for the partition of the model containing floating conductors and a method that can be used to solve such problem through parallel system. An example which contained three floating conductors was computed by using the method introduced in this paper, the result was displayed and compared with conventional finite element model, the validity of the method is proved.

Prediction of DC Corona Onset Voltage for Rod-Plane Air Gaps by a Support Vector Machine

This paper proposes a new method to predict the corona onset voltage for a rod-plane air gap, based on the support vector machine (SVM). Because the SVM is not limited by the size, dimension and nonlinearity of the samples, this method can realize accurate prediction with few training data. Only electric field features are chosen as the input; no geometric parameter is included. Therefore, the experiment data of one kind of electrode can be used to predict the corona onset voltages of other electrodes with different sizes. With the experimental data obtained by ozone detection technology, and experimental data provided by the reference, the efficiency of the proposed method is validated. Accurate predicted results with an average relative less than 3% are obtained with only 6 experimental data.

Charge Transport Simulation in Single-Layer Oil-Paper Insulation

This paper proposed a simulation method for the charge transport in single-layer oil-paper insulation. The method of transient upstream finite-element method (FEM) is derived in order to calculate the time variation of charge densities in medium. The numerical simulation of charge transport in the single-layer oil-paper insulation is realized by applying the transient upstream FEM to the transport equations of bipolar charges. With reasonable microparameter, the charge transport in an experimental object is simulated. The simulation results are consistent with the experimental data. A bent model of oil-paper insulation is analyzed to study the charge distribution under the actual condition. This paper provides an exploratory research to the simulation of charge phenomenon in oil-paper, and has guiding significance to the design of oil-paper insulation.

3D MFL of steel pipe computation based on nodal-edge element coupled method

Edge element is more suitable for calculating nonlinear magnetic problem containing iron material due to its degree of freedom tangentially continuous. The magnetic flux leakage (MFL) of defect in steel pipe is simulated by using three dimensional(3D) hybrid finite element method (FEM) which couples nodal and edge element in this paper. According to the actual characteristics of steel pipe tested, the parameters of coils are optimized in order to obtain the optimal signal-to-noise ratio. MFL results are respectively calculated for defects of various shapes and dimensions. A novel meshing method is proposed to achieve convergence solution in adjacent area of very tiny defects. The simulation results agree well with the experimental data. Such a research can be employed for identifying defects in steel pipe, which are inspected using the MFL method of nondestructive testing.