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It is important to dimension grounding systems properly, because they protect people and devices. Dimensioning of the grounding system is often made using the finite element method, and the properties of the soil are needed for that. Evolutionary methods can be used for the determination of the parameters of a horizontally layered soil model. The basis for the parameter’s determination is Wenner’s method measurements. In this article, the horizontally layered soil model is analyzed using different soil structures. Different evolutionary methods are tested for the presented problem. The aim of the tests is to determine the most appropriate evolutionary method, between those selected, for the presented problem.

The nonlinear analysis of magnetic liquid free surface deformation under the influence of a static vertically oriented magnetic field produced by a pair of Helmholtz coils in a 3D space is presented in the article. The hexagonal pattern of peaks resulting from the Rosensweig or normal instability, occurs when the magnetization of the magnetic liquid exceeds the critical value. To predict the amplitudes and distance between peaks in the pattern, nonlinear analysis should be performed with employed higher order terms in the mean curvature expression of the free surface. The computational strategy presented in the article is divided into two stages. At the first stage, the magnetic field in the 3D space is calculated by the FEM based software Opera Field, while the second stage is devoted to determining the surface profile by minimizing the energy functional using a Differential Evolution algorithm in Matlab. The amplitudes of the central spike and wave number have been computed for the various values of the excitation magnetic field.

Determination of the seven parameters of a Direct Current (DC) motor and drive is presented, based on the speed and current step responses. The method is extended for the motor and drive parameter determination in the case of a controlled drive. The influence of a speed controller on the responses is considered in the motor model with the use of the measured voltage. Current limitation of the supply unit is also considered in the DC motor model. For parameter determination, a motor model is used, which is determined with two coupled differential equations. Euler&rsquo, s first-order and Runge&ndash, Kutta fourth-order methods are used for the motor model simulations. For parameter determination, evolutionary methods are used and compared to each other. Methods used are Genetic Algorithm, Differential Evolutions with two strategies, Teaching&ndash, Learning-Based Optimization, and Artificial Bee Colony. To improve results, deviation of the motor model simulation time is used and Memory Assistance with three different approaches is analyzed to shorten the calculation time. The tests showed that Differential Evolution (DE)/rand/1/exp is the most appropriate for the presented problem. The division of the motor model simulation time improves the results. For the presented problem, short-term memory assistance can be suggested for calculation time reduction.

For precise modeling of electromagnetic devices, we have to model material hysteresis. A Genetic Algorithm, Differential Evolution with three different strategies, teaching&ndash, learning-based optimization and Artificial Bee Colony, were used for testing seven different modified mathematical expressions, and the best combination of mathematical expression and solving method was used for hysteresis modeling. The parameters of the hysteresis model were determined based on the measured major hysteresis loop and first-order reversal curves. The model offers a simple determination of the magnetization procedure in the areas between measured curves, with the only correction of two parameters based on only two known points in the magnetization process. It was tested on two very different magnetic materials, and results show good agreement between the measured and calculated curves. The calculated curves between the measured curves have correct shapes. The main difference between our model and other models is that, in our model, each measured curve, major and reversal, is described with different parameters. The magnetization process between measured curves is described according to the nearest measured curve, and this ensures the best fit for each measured curve. In other models, there is mainly only one curve, a major hysteresis or magnetization curve, used for the determination of the parameters, and all other curves are then dependent on this curve. Results confirm that the evolutionary optimization method offers a reliable procedure for precise determination of the parameters.

Display Omitted Determination of the new analytic expression describing measured magnetization curves.We tested standard and evolutionary methods for the determination of parameters.Used methods are evaluated statistically using average values, cross-validation, CRS4EAs, and the Holm test.We made modification of the best evolutionary method and a new, better approach has been obtained.The presented solution can be used to prepare magnetic material data for any FEM software. Magnetization curves are obtained with measurements and used for the description of magnetic material properties. In the case where the curve is rough problems can appear during the Finite Element Method (FEM) calculations. One of the solutions is the use of an analytically written curve, which fits the measured curve. In this paper different analytical expressions are tested on different measured magnetization curves and compared with each other. Different evolutionary methods are used and tested for the determination of the analytical expressions parameters: The Genetic Algorithm, Differential Evolution with three different strategies, Teaching-Learning Based Optimization and Artificial Bee Colony. To obtain credible and optimal results, we made a statistic evaluation of the results using Cross-validation, CRS4EAs (Chess rating system for evolutionary algorithms), and the Holm test. Based on the tests results we improved the more appropriate evolutionary method, which was Artificial Bee Colony, using the Levenberg-Marquardt algorithm. As a result, two different methods: are presented and tested which combine Artificial Bee Colony and the Levenberg-Marquardt algorithm. An analytical expression is presented which can be used for a wide range of different materials curves and also a stable and efficient method for the determination of the analytical expressions parameters. The presented solution is appropriate to be used together with, or as a part of, FEM calculation software. For preparation of magnetic material data the presented solution can be used as an independent programme for the transformation of the H-B table of values presenting not-smooth measured magnetic material curves (or measured with too few points) into the H-B table of values presenting smooth magnetic material curve which can be used as input data for any FEM software.

This paper introduces measurements using eddy currents and the estimation of hidden crack dimensions. The measurements were made on the defect-free side of the aluminium plate. The dimensions of the excitation coil were investigated with the aim of optimizing the sensitivity of the measurements. Measured values were smoothed properly in order to ease further processing. Furthermore, the estimation of the crack dimensions was made using pre-calculated values obtained with a Finite Element Model. Measurements and tests were made for three different test plates with straight cracks and for one test plate with a crack that was not straight.

This paper shows the use of FEM for a second order time dependent nonlinear electromagnetic field problem, around grounding systems (GS). The applied program solution is suitable for any GS and linear or nonlinear soil properties as well as time-varying fault current. Time integration is conducted with the Newmark algorithm

Magnetic fluid hyperthermia (MFH) is a medical treatment where the temperature in the tissue is increased locally by means of heated magnetic fluid in an alternating magnetic field. In recent years, it has been the subject of a lot of research in the field of Materials, as well as in the field of clinical testing on mice and rats. Magnetic fluid manufacturers aim to achieve three objectives, high heating capacity, biocompatibility and self-regulatory temperature effect. High heating power presents the conversion of magnetic field energy into temperature increase where it is challenging to achieve the desired therapeutic effects in terms of elevated temperature with the smallest possible amount of used material. In order to carry out the therapy, it is primarily necessary to create a fluid and perform calorimetric measurement for determining the Specific Absorption Rate (SAR) or heating power for given parameters of the magnetic field. The article presents a model based on a linear response theory for the calculation of magnetic losses and, consequently, the SAR parameters are based on the physical parameters of the liquid. The calculation model is also validated by calorimetric measurements for various amplitudes, frequencies and shapes of the magnetic field. Such a model can serve to help magnetic fluid developers in the development phase for an approximate assessment of the heating power.

Grounding systems are an important part of protection systems, which protect people and devices in case of lightning strikes and defects in electro energetic systems. Grounding systems are often dimensioned using numerical models, among other numerical methods, also the Finite Element Method. Data about the soil in the surroundings of the grounding system are obtained using measurements. Soil parameters can be determined using analytical soil models. The determination of the soil models’ parameters is an optimisation problem which is based on the measured data. In this paper, different soil models are tested on different data, and compared with each other. Test data are also obtained using finite element models of different soil structures, which offer better analysis of the soil models because the soil structure is known. The horizontally, vertically layered soil and inhomogeneity in the soil are modelled. Different metaheuristics are used and tested for the determination of soil parameters: A Genetic Algorithm, Differential Evolution with two different strategies, Artificial Bee Colony, Teaching-Learning Based Optimisation and a combination of Artificial Bee Colony and Teaching-Learning Based Optimisation. Analysis of the models and solving methods are made based on the test results. As a result, the appropriate soil models among those tested are selected, which are 4, 5 and 6 layered models, and appropriate methods for parameters‘ determination are presented, which are Artificial Bee Colony and a combination of Artificial Bee Colony and Teaching-Learning Based Optimisation. Also, analysis is made of the usefulness of the horizontally multi-layered model for differently structured soils.

Recently, a numerical evaluation has been reported of the magnetic field distribution above a hexagonally distributed spikes pattern of a magnetic liquid free surface. To support the theoretical predictions, as well as numerically obtained results, the measured values of the magnetic field above the magnetic liquid free surface are disclosed in the article. The measurement technique is performed by scanning a magnetic field induction with a Hall sensor at a close distance above the free surface (spikes). The results show that the experimentally obtained magnetic field is distributed in a similar way as a free surface, thus, a quality image of spikes can be reproduced by the magnetically-based technique introduced in the article.

Magnetic fluids are superparamagnetic materials that have recently been the subject of extensive research because of their unique properties. Among them is the heating effect when exposed to an alternating magnetic field, wherein the objective is to use this property in medicine as an alternative method for the treatment of tumors in the body. The heating effect characterization for the alternating magnetic field (AMF) has been studied widely, whilst for the rotational magnetic field (RMF), no systematic study has been done yet. In this article, we present the characterization of the heating power of magnetic fluids in a high-frequency rotational magnetic field. The results show similar behavior of heating power or specific absorption rate characteristics as in AMF.

Purpose – The purpose of this paper is to find the geometry of a crack within a conductive plate and its parameters, on the basis of non-destructive testing, using eddy currents. The input data represents the measured values of magnetic flux density within the centre of the excitation coil. Design/methodology/approach – The position of a crack can be determined by taking into consideration any change in the magnetic flux density between the measured points. The depth and width are determined through the use of a finite element model. Findings – These calculations are the basis for determining a function that explains how magnetic flux density changes if the depth or width has changed. Jacobi's matrix is calculated using the determined functions’ analytical derivatives. Originality/value – After wards, through the Newton-Raphson iterative procedure using the finite element method calculation results, the crack-depth and width can be obtained, this being one of the objectives in this paper. The suitability of the presented method was verified by the experimental example.

Magnetic fluids are distinct magnetic materials that have recently been the subject of extensive research precisely because of their unique properties. One of them is the heating effect when exposed to alternating magnetic fields, wherein the objective is to use this property in medicine as an alternative method for the treatment of tumors in the body. In this paper, we focus on two methods of magnetizing magnetic fluids, firstly using the alternating magnetic field (AMF), and secondly with the rotational magnetic field (RMF). The effects of the first are scientifically well-established, whilst the impact of RMF has not as yet been investigated as presented in this article. So far the effects of RMF have only been studied at low frequencies and high amplitudes, or vice versa. This article presents the results of heating at high frequencies and high magnetic field amplitudes, and the results compared with AMF. This paper presents the construction and implementation of a measuring system which is suitable both types of magnetic field.

This paper introduces a measurement device for identifying a crack's dimensions using eddy current measurement. Measurements of magnetic flux density are conducted for the purpose of finding a crack within a conductive plate. This is done on the basis of nondestructive testing using eddy currents. The absolute value of the magnetic flux density z-component is measured along an axle at the bottom of an excitation coil supplied with an alternating current. The measured B z is exemplified by a surface, whose shape depends on the crack's position and parameters. The received measured values then serve as the basis for the crack's identification and for determining its parameters.

This paper firstly presents a measurement system for determining the magnetic properties of magnetic fluids, based on three pickup coils. The accuracy of the system was tested on known samples and then used for the characterization of magnetic losses (heating power P) on the magnetic fluid sample using two different methods. The first method is based on determining the hysteresis loop area and the second on determining the complex susceptibility; and showed that both methods are equivalent. The aim of this paper was to identify the heating power of the liquid at a known value for the magnetic field, and the arbitrary temperature. Thus, we explored the actual reduction in the heating power due to the heating of the sample, which cannot be achieved without the temperature regulated heat bath using established calorimetric methods.

This paper shows the use of FEM for a second order time dependent electromagnetic field problem, around grounding systems (GS). Twenty-node isoparametric quadratic 3D finite element, three-node quadratic 1D finite element and a spatial transformation of the “infinite space” into the finite space are all applied to achieve better accuracy. Time integration is conducted with the Newmark algorithm. The applied program solution is suitable for any GS and isotropic/anisotropic soil properties as well as time-varying fault current.

This paper deals with the calculation of the electric field in the vicinity of a high-voltage overhead transmission line (TL). Since analytical formulas cannot be used to calculate the electric field in cases when the ground surface under a TL is not flat or when conducting bodies are located under it, we present the use of finite element method (FEM) for this purpose. The electric field distribution has been analyzed for two characteristic high-voltage TLs. A graphical comparison of the electric field strength E 1 m above ground surface is included.

The paper presents a finite-element method-based design and analysis of interior permanent magnet synchronous motor with flux barriers (IPMSMFB). Various parameters of IPMSMFB rotor structure were taken into account at determination of a suitable rotor construction. On the basis of FEM analysis the rotor of IPMSMFB with three-flux barriers was built. Output torque capability and flux weakening performance of IPMSMFB were compared with performances of conventional interior permanent magnet synchronous motor (IPMSM), having the same rotor geometrical dimensions and the same stator construction. The predicted performance of conventional IPMSM and IPMSMFB was confirmed with the measurements over a wide-speed range of constant output power operation.

The calculation of magnetic fields is and important part of the electromagnetic device design process. The numerical approach to the consideration of the material hysteresis is shown in the paper. Some problems with shapes of the new magnetization curves are pointed out. The results of the calculation are compared with the measurement results made on the magnetization setup for the characterization of semi- and hard-magnetic materials.

The paper presents a comparison of torque capability and flux-weakening performance of three-phase flux reversal permanent magnet motors with surface and inset permanent magnets. Finite element analysis is employed to determine the performance of each motor in BLDC and BLAC operation mode. It is shown that the torque capability and flux-weakening performance of surface or inset permanent magnet configuration is strongly dependent on the stator teeth number/rotor pole number combination.

The paper presents a comparison of torque capability of three-phase permanent magnet synchronous motors with different permanent magnet arrangement. Motors with the following permanent magnet topologies were accounted for in the comparison: the surface-mounted permanent magnet synchronous motor (SMPMSM), the interior permanent magnet synchronous motor (IPMSM), the permanent magnet-assisted synchronous reluctance motor (PMASRM) and the flux reversal permanent magnet motor (FRPMM). Finite element method analysis is employed to determine the performance of each motor. Calculated performance of four-pole IPMSM determined by finite element method calculation is confirmed with the measurements at nearly constant nominal output power in the range of speed 3000–10,000 rpm.

PurposeThe paper aims to present the comparison between the performances of the exterior‐rotor permanent magnet synchronous motors with distributed windings and the performances of the exterior‐rotor permanent magnet synchronous motors with concentrated windings.Design/methodology/approachFinite element method is used for motors performance determination. The BLDC operation mode for the motors with different slot and pole number combination and concentrated windings was accounted for in the comparison.FindingsIn the BLDC operation mode motor structures with concentrated windings with similar slot and pole numbers exhibit at the same current density similar or even higher torque capability and lower electromagnetic torque ripple in comparison to the motor structure with distributed windings. Motor structures with 9‐slot/8‐pole, 9‐slot/10‐pole, 12‐slot/10‐pole slot and pole number combinations are the most appropriate for the BLDC operation.Originality/valueThe paper shows which motor structures with distributed or concentrated windings in the BLDC operation mode produce lower torque ripple and higher average torque per ampere.

In the paper, transient finite-element calculation of the rotational magnetic field is shown. For isotropic material, nonlinear magnetic characteristics of the material are described with magnetization curve. For anisotropic material, nonlinear magnetic characteristics of the material are described with magnetization curves for different magnetization directions. For verification, some results of the calculation are compared with the measurement

A simulation model based on finite-element method is presented to simulate the soil ionization phenomenon around the grounding system. The advantage of the methodology proposed in this study against analytical methods is that both simple and complex grounding systems buried in homogeneous or nonhomogeneous soil taking into account soil breakdown process can be modeled. The suggested modeling is validated by comparison of the calculated results, which are laid out for grounding rod and grounding grid, with experimental tests results and simulations results found in literature. The performance of grounding system, considering the soil ionization effect at high-magnitude current, is also compared with the one not considering the soil ionization effect

Electromagnetic theory presents difficult task for the student. The essence of the problem is not the pretentious mathematical treating of the field, but in the field presentation and understanding of field interaction with the material. The paper presents our program tools (FIELD_EDU) for teaching of electromagnetic field, based on the finite element method (FEM). The program concept enables the student to build in the very simple way an arbitrary problem, without being burdened with specific demands of FEM at field analysis. When doing this, the students can help themselves with the library of simple geometrical objects, which have already predefined material properties and boundary conditions. The program tools enable a complete graphical and numerical analysis of one or more examples at the same time

For anisotropic magnetic material, nonlinear magnetic characteristics of the material are described with magnetization curves for different magnetization directions. The paper presents transient finite element calculation of the magnetic field in the anisotropic magnetic material based on the measured magnetization curves for different magnetization directions. For the verification of the calculation method some results of the calculation are compared with the measurement.

This paper presents a measurement of grain-oriented electrical steel under pure alternating magnetic flux condition at inclination angles from −90° to 90° with respect to the rolling direction (RD). The measurement was carried out using a round rotational single sheet tester. The results show a strong asymmetry of alternating power loss and magnetic field strength with respect to the RD. The alternating power loss depends on the side of the band where the specimen was cut off.

Presents the use of the dual reciprocity method (DRM) for solving inverse problems described by Poisson's equation. DRM provides a technique for taking the domain integrals associated with the inhomogeneous term to the boundary. For that reason, the DRM is supposed to be ideal for solving inverse problems. Solving inverse problems, a linear system is produced which is usually predetermined and ill‐posed. To solve that kind of problem, implements the Tikhonov algorithm and compares it with the analytical solution. In the end, tests the whole algorithm on different problems with analytical solutions.

Arthritis, the illness of the bones, is one of the diseases which especially attack the knee joint. Magnetic stimulation is a very promising treatment, although not very clear as to its physical background. Deals with the mathematical simulation of the therapeutical technique, i.e. the magnetic stimulation method. Considers the low‐frequency magnetic field. To consider eddy currents one uses the pair of potentials: electric vector potential T→ and magnetic scalar potential Ω . Since the problem is of low frequency and the electric conductivity of biological tissues is very small, consideration of electric vector potential only is quite satisfactory.

This paper presents the evaluation of saturation and cross-magnetization effects in an interior permanent magnet synchronous motor (IPMSM) over the entire range of direct- and quadrature-axis excitations. The conventional two-axis machine model is modified in order to include the influence of saturation and cross-coupling effects on the variation of self- and cross-coupling inductances in the direct and the quadrature axis. The two-axis machine model parameters are evaluated by experiments performed on an IPMSM using a controlled voltage-source inverter and are compared with parameter values evaluated by the finite-element method. The evaluation of two-axis machine model parameters reveals significant saturation and cross-magnetization effects in both axes, especially in the flux-weakening regime.

This paper shows the use of the hybrid finite-boundary element method (HM) in the analysis of complex grounding systems (GS) designed for protection of power and industrial systems. In the field calculation a three-dimensional (3-D) linear finite element and a 3-D mixed boundary element were applied. The program solution used is suitable for any GS and for isotropic or anisotropic soil properties.

A rotational single sheet tester with square sample (SRSST) is used for the measurement of magnetic properties in rotational and alternating magnetic fields. Two perpendicular measuring coils are coiled up, in the middle of the sample, through the holes in the sample. To obtain the proper size of the measuring coils, the homogeneity of the magnetic field and the influence of eddy currents on the homogeneity of the magnetic field distribution in the sample are investigated.

We present details of the modeling, design, and evaluation of single-channel implantable system with a half cuff for monopolar selective stimulation of the common peroneal nerve in hemiplegia. For this purpose, an activating and total equivalent driving function for 12 /spl mu/m nerve fibers located at six positions within the nerve were calculated by the finite element method (FEM).

This work deals with the application of the scalar product model to different ferromagnetic materials. Different hysteresis curves and minor loops are measured to examine the behavior of the magnetization and to compare it with theoretical calculated curves.

The paper presents a finite element method (FEM) based analysis of interior permanent magnet synchronous motor, designed for flux-weakening operation. Flux-weakening performance determined from the FEM analysis on the proposed permanent magnet motor structure is presented in order to verify the suitability of the design concept for flux-weakening operation. The influence of iron losses on the output power capability is included in the analysis by posterior iron loss calculation. The presented interior permanent magnet motor shows an extremely wide constant-power speed range which exceeds 5:1.

The paper presents the use of the dual reciprocity boundary element method (DRM) for the solution of the inverse problem described with Poisson's equation. The DRM approach has been chosen because it is ideal for the treatment of the nonhomogeneous part of Poisson's equation that determines the source distribution of the inverse problem. The mixed "0-1" order boundary elements were used to discretize the problem. The overdetermined system, obtained with the inverse problem, has been solved using the least square method, Powell's method and Fletcher's method. The presented DRM approach to the solution of the inverse problem is demonstrated on a 2D problem that has an analytical solution.

This paper deals with the research of a small single and a double sheet Tester with specimens of size 105 mm/spl times/52 mm. The aim of the research was to discover whether the small single or double sheet tester fulfils the requirement for satisfactory exactness of the magnetic measurements. The finite element method was used for the magnetic field study. The field distribution was calculated inside and outside the sample, and so the error was obtained. The study shows that small testers can be used for magnetic measurements of electrical sheets with acceptable accuracy.

This paper shows the use at the FEM in the analysis of complex grounding systems (GS) used in practice for protection of power and industrial systems. In order to get an accurate field calculation a twenty-node isoparametric quadratic 3D finite element, a three-node quadratic 1D finite element and a spatial transformation of the "semi-infinite space" into the finite space were applied. The program solution used is suitable for any GS and for anisotropic soil properties.

The magnetic properties of two grain-oriented (GO) samples of the same grade were measured under alternating and rotational magnetic flux conditions. Two samples were measured separately and then together in different arrangement to each other. The interaction of magnetic field between two samples were measured by using a coil, which was placed in between. The results show that the H z component influence measured magnetic properties in the x – y plane.