Imre Sebestyén

Transient eddy current analysis of pulsed eddy current testing by finite element method

Transient eddy current analysis of pulsed eddy current testing was performed by time-stepping method and Fourier transform method. The characteristics of two methods were evaluated by using a simple model. The accuracy was examined by the comparison of calculated and measured data. The calculated results of the two methods provided good agreement with measured data. However, it was clear that the Fourier transform method provided higher accuracy of amplitude than the time-stepping method. As a three-dimensional problem of pulsed eddy current testing, the TEAM Workshop Problem 27 was analyzed by an edge-element finite element method.

Calculation of losses in laminated ferromagnetic materials

A numerical method for calculation of the power losses of nonlinear laminated ferromagnetic cores is presented. The calculation is made in two subsequent steps. In the first step, the approximate magnetic field distribution in the material is determined assuming a nonlaminated bulk nonlinear ferromagnetic material with anisotropic conductivity. In the second step, the nonlinear ferromagnetic material of the laminated core is replaced to linear material with spatially inhomogeneous permeability. The actual permeability distributions of the lamination are determined based on the magnetic field obtained from the first calculation and the nonlinear B-H curve of the material. In this paper, the outlined method is verified through calculations and measurements made on simple benchmark arrangements. Different methods for assigning the inhomogeneous permeability are also investigated.

Approximate prediction of losses in transformer plates

Three methods are presented for the approximate prediction of losses in laminated transformer cores. The input data of the calculations are the field distribution obtained by a FEM code assuming the laminated core as a homogeneous medium that conductivity is zero in the direction perpendicular to the lamination. These data are processed by the developed methods to obtain an agreeable approximation of the power losses in the transformer plate. For each approach the same benchmark problem is solved to exploit the properties of the approaches. The goal of the presented study is to select the most suitable method that can be used as a postprocessor of a FEM code.

Application of optimally distorted finite elements for field calculation problems of electromagnetism

We applied adaptively generated anisotropic finite-element meshes (i.e., meshes containing intentionally distorted elements) for electromagnetic field calculation. By this method, we achieved significant improvement in computing performance. Moreover, anisotropic meshing proved to be an essential tool in space-time meshing. In this paper, we summarize our experiences.

Magnetic field and force calculation for magnetic-aided machining devices

The paper deals with the magnetic field and force calculation for a device used in magnetic-aided machining (MAM). This novel manufacturing process has a very special characteristic that the working force is generated by a magnetic field. To determine the force acting on the tool due to the magnetic effect is crucial for analyzing the mechanical behavior of the device. The magnetic field calculations are performed by the finite element method. The global magnetic force acting on the tool is determined by the method of integrating Maxwells stresses and using the magnetic dipole model of the magnetized body and are compared to the measured data.

Practical Criteria for the Separability of Eddy-Current Testing Signals on Multiple Defects

Practical quantities have been introduced by the authors to characterize the interaction among multiple defects located in a specimen under eddy-current testing (ECT). If these quantities indicate that the interaction between the pairs of defects is negligible, the signal of an ECT probe for multiple defects can be calculated as the superposition of those signals, which are obtained for each defect as if it would be a single one. Conversely, if the criteria holds, the measured ECT signal can be decomposed into signals associated with the individual defects, which essentially simplifies the solution of the inverse problem of defect reconstruction. As an application of the criteria, the design of a novel barcoding system is presented, which is developed for marking metallic parts by laser treating, and where the applicability of linear signal processing methods for the reading out of the barcode is a requirement.

Optimization for High Voltage Composite Insulators Using Experimental Design Theory

In the paper a method for optimizing parameters of HV composite insulators is presented. The optimal values of design parameters are determined by multivariable optimization procedure using theory of experimental designs. For repetitive calculation of the electric field strength the finite element method is used with domain decomposition. This method gives fast working software with accurate results to examine a very complex geometry without extra high computational effort.

Boundary refinement in n-dimensional Delaunay-meshing

A practical and robust mesh refinement algorithm was developed for simplex meshes based on the point insertion method. The algorithm fully exploits the n-dimensional phenomenon of simplex elements, and focuses on boundary refinement as the most general case. The resulting mesh is a constrained Delaunay-type. The algorithm was successfully tested on 3D and 4D problems. Also a data structure was developed for the efficient implementation of the algorithm.