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The main objective of this paper is to provide an efficient computational model for fast and accurate calculation of electromagnetically induced vibrations in electrical machines. Although a three-phase permanent-magnet synchronous machine has been used in this paper, the same methodology can be extended to other types of electric machinery. A brief comparison between the different methods for structural analysis in electrical machines is introduced. The method proposed in this paper uses finite-element analysis in order to extract the impulse responses that are used in calculating the vibration. A field reconstruction method is used for the electromagnetic field analysis. [ABSTRACT FROM PUBLISHER]

The nonconformal domain decomposition methods (DDMs) of the hybrid finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) are presented for computing large electromagnetic scattering/radiation problems. The numerical performance of different transmission conditions between finite element method (FEM) subdomains, and FEM and BI domains is studied in this paper. The Dirichlet transmission condition (DTC) employed at the interface between FEM and BI domains has faster convergence than the Robin-type transmission condition, and this finding is different from the conclusions for the FEM DDMs published in the literature. Furthermore, the cement-element (CE)-based dual-primal finite element tearing and interconnecting (FETI-DP) DDM has faster convergence than the Lagrange-multiplier-based FETI-DP method under the FE-BI system, and is also different from that under the system of the FEM with the absorbing boundary condition (FEM-ABC). It shows that the DDMs of FE-BI-MLFMA have some essential differences from those of FEM-ABC. The analysis of these numerical phenomena is presented in this paper. Further comparison between the DDMs of FE-BI-MLFMA and FEM-ABC demonstrates that the DDMs of FE-BI-MLMFA have essential advantages over those of FEM-ABC. Various numerical experiments confirm the accuracy, efficiency, and flexibility of the nonconformal DDM of FE-BI-MLFMA, which is the CE-based FETI-DP DDM with DTC connecting FEM and BI. [ABSTRACT FROM AUTHOR]

Fast design procedures of electrical machines require the use of adapted modeling approaches. This is particularly true for axial flux permanent magnet (AFPM) machines, which have an intrinsic 3-D electromagnetic structure. Indeed, accurate modeling of AFPM machines requires the use of 3-D finite-element analysis (3-D FEA), which is highly time consuming, especially at first design stages. This paper presents a new quasi-3-D analytical model (AM) that allows modeling accurately AFPM machines while saving a huge amount of time as compared with 3-D FEA. This new approach combines a multislice AM, which takes into account a part of the 3-D effects, and considers the end-effects by a simple and effective radial dependence modeling of the magnetic field in AFPM machines. [ABSTRACT FROM AUTHOR]

This paper deals with the magnet pole shape design of permanent magnet machines for the minimization of torque ripple based on electromagnetic field theory. On the basis of a magnetic vector potential and a two-dimensional (2-D) polar system, analytical solutions for flux density due to permanent magnet (PM) and current are obtained. In particular, the analytical solutions for mathematical expressions of magnets with different circumferential thicknesses can be solved by introducing improved magnetization modeling techniques, resulting in accurate calculations of electromagnetic torque. The analytical results are validated extensively by nonlinear finite element method (FEM). Test results such as back-emf measurements are also given to confirm the analyses. Finally, on the basis of derived analytical solutions, a reduction of torque ripple can be achieved. [ABSTRACT FROM AUTHOR]

The aim of this paper is to highlight the capabilities of a new hybrid analytical modeling (HAM) approach for the analysis and design of various electromagnetic structures. After an introduction, where the aim of the development of this modeling approach is presented, the modeling approach is described. The new HAM is based on a strong coupling of the magnetic equivalent circuits method and analytical models (AMs). The AM, based on the formal solution of Maxwell’s equations, is established thanks to the separation of variables method. The HAM is applied to different permanent magnet electric machine structures, and the results are validated extensively by comparison with the finite-element analyses. [ABSTRACT FROM AUTHOR]

An automatic mesh generation method employing a dynamic bubble system can provide a high-quality mesh for electromagnetic finite element analysis. However, it takes a very long time to compute bubbles' movement when a mesh with a large number of elements is generated. The bubbles move according to a force among them, such as the van der Waals force. However, the force received from bubbles of very far distance can be ignored. Therefore, it is unnecessary to calculate the force from all the bubbles. In this paper, we propose a subdivided dynamic bubble system in order to shorten the computation time. The proposed method considers the analysis region to be divided into some tetrahedral subdivisions, and then the bubbles move independently in the tetrahedral subdivisions. As a result, acceleration of the computation time is achieved. [ABSTRACT FROM AUTHOR]

This paper describes a two-dimensional (2-D) analytical model to predict the magnetic field distribution in axial-field magnetic gears by using the sub-domain method. The sub-domain method consists in solving the partial differential equations linked to the Maxwell's equations in each rectangular region (magnets, air gaps, and slots) by the separation of variables method. The proposed model is based on a two-dimensional approximation for the magnetic field distribution (mean radius model) i.e. the problem is solved in 2-D Cartesian coordinates. One of the main contributions of the paper concerns the analytic solution of the magnetic field in a slot open on the two sides (space between the ferromagnetic pole-pieces). Moreover, it is shown that the analytical model and the 3-D finite elements simulations follow the same trends in the determination of the optimum values for the geometrical parameters. As the analytical model takes less computational time than 3-D numerical model, it can be used as an effective tool for the first step of design optimization. [ABSTRACT FROM PUBLISHER]

In this paper, the characteristics of the electromagnetic noise radiated by an external rotor in-wheel motor (IWM) are investigated with the Doppler effect taken into consideration. First, Maxwell stress tensor method is employed to derive electromagnetic forces on the magnet surface. The effect of common current harmonics is also analyzed. Then, a structural model of the rotor is built and modal test is conducted to validate the model. Nodal forces, which are calculated by finite element method, are transferred from the electromagnetic mesh to the structural model for further vibration prediction. Finally, boundary element method is used to calculate the noise radiated by the rotor. In particular, the Doppler effect is considered. The calculated results are validated by the noise test. It is found that the end cap contributes more to the overall noise than the shell, and obvious sound directivity appears in the noise of the IWM. The noise measured perpendicular to the outer end cap is larger than that measured in other directions. In addition, the Doppler effect would induce additional side-frequency components around high-frequency peaks in the external rotor motor. [ABSTRACT FROM PUBLISHER]

This paper deals with the dynamic characteristics of a linear induction motor (LIM) in terms of acceleration times and jerk conditions. We employed Matlab Simulink for conducting simulations of the dynamic modeling of LIM operated by a space vector pulse width modulation inverter. From the simulation results, the maximum load conditions and minimum acceleration times to guarantee passengers' safety were determined. Further, the electromagnetic field theory was employed to derive equivalent circuit parameters, and the results were validated by the finite element method. The analysis model was applied to a magnetic levitation vehicle for providing electromagnetic propulsion force, and its dynamic characteristics were analyzed to predict its operating performance; moreover, experimental results were employed to demonstrate the validity. We believe that the proposed prediction technique for the operating characteristics of LIMs can contribute to improving passengers' safety and riding quality. [ABSTRACT FROM AUTHOR]

Overlapping elements can be used to connect non-conforming meshes in the finite-element method. This approach has been developed with the scalar potential formulation and used to solve magnetostatic problems but not in the case of the vector potential formulation. In this paper, we propose to introduce the overlapping element method in this second formulation. [ABSTRACT FROM PUBLISHER]

The calculation of voltages induced by external electromagnetic fields on multiconductor transmission lines (MTLs) has been the subject of several studies. In this paper, discrete equations for MTLs exposed to incident fields are derived based on the time-domain finite-element method and the backward differentiation formula. Based on these equations, a value-delivery table characterizing the MTLs is presented. Combining this table with modified node analysis formulation, it is convenient for analyzing the responses of transmission lines composed of complex termination networks or complex transmission-lines networks. The validity and efficiency of the proposed algorithm is demonstrated using several examples. Finally, a 1-km 35 kV overhead line above an imperfectly conducting ground is studied, and the influences of ground wire and a metal-oxide arrester to the lightning-induced voltage are both discussed. [ABSTRACT FROM PUBLISHER]

This paper presents copper and iron loss models of a classical switched reluctance motor (SRM) and a mutually coupled switched reluctance motor (MCSRM). The iron losses in different parts of machines are then detailed. Based on the power losses model, a lumped parameter (LP) transient thermal model during driving cycles is performed, the analytical results are validated by the finite-element (FE) transient thermal model. Special attention has been paid to model the salient rotor and a method to transform the salient rotor into a nonsalient one has been proposed. A comparison between the maximum temperatures obtained by using different heat source (average power losses or instantaneous power losses during driving cycles) is given. The experimental tests are also realized to verify the analytical and numerical results. [ABSTRACT FROM PUBLISHER]

This paper involves the computation of 3-D magnetic fields in high-performance, long-lifetime solenoid actuators by finite-element (FE) modeling. Operating at frequencies between 150 and 300 Hz, these actuators are unique in terms of the large force they produce (8–15 N) and their very long lifetime (over five billion continuous duty cycles). Their magnetic circuit typically operates at saturation and, because of the compact dimensions, the 3-D nature of the field distribution needs to be taken into account for their design. Results are presented in terms of the effects of design parameters on saturation and force calculation. [ABSTRACT FROM AUTHOR]

This paper deals with some aspects of formulation and implementation of a broadband algorithm with build-in analysis of some dispersive media. The construction of the finite element method (FEM) based on direct integration of Maxwell's equations and solution of some additional convolution integrals is presented. The broadband, fractional model of permittivity is approximated by a set of some relaxation sub-models. The properties of the 3D time-dependent formulation of the FEM algorithm are determined using a benchmark problem with the Cole-Cole and the Davidson-Cole models. Several issues associated with the implementation and some constraints of the broadband finite element algorithm are presented. [ABSTRACT FROM AUTHOR]

This paper describes iterative methods for the high frequency electromagnetic analysis using the finite element method of Maxwell equations including displacement current. The conjugate orthogonal conjugate gradient method has been widely used to solve a complex symmetric system. However, the conventional method suffers from oscillating convergence histories in large-scale analysis. In this paper, to solve large-scale complex symmetric systems arising from the formulation of the E method, an iterative substructuring method like the minimal residual method is presented, and the performance of the convergence of the method is evaluated by numerical results. As the result, the proposed method shows a stable convergence behavior and a fast convergence rate compared to other iterative methods. [ABSTRACT FROM AUTHOR]

The interaction between an ensemble of cylinders and an inhomogeneous plane wave is introduced and is determined, in the present paper, through a rigorous theoretical approach. Scattered electromagnetic field generated by an indefinite number of infinite circular cylinders is analyzed by the application of the generalized vector cylinder harmonics (VCH) expansion. The exact mathematical model relied upon to represent this scenario considers the so-called complex-angle formalism reaching a superposition of vectorial cylindrical-harmonics and Foldy-Lax Multiple scattering equations (FLMSE) to account for the multi-scattering process between the cylinders. The method was validated by comparing the numerical results obtained with the use of the finite element method and a homemade Matlab code. [ABSTRACT FROM AUTHOR]

The paper describes the formulation and implementation of the broadband finite element time domain algorithm. The presented formalism is valid to analysis of electromagnetic phenomena in linear, frequency selective materials. The complex profile of permittivity of materials is approximated using a set of the Lorentz resonance models. The solution of the integro-differential second order equation is obtained using a singlestep integration scheme and a recursive convolution algorithm. The discussed formulation enables to adopt the structure of the narrowband part as well as the phase of calculation of the convolution equations for the subsequent components. The properties of the algorithm are validated using a finite difference broadband algorithm. [ABSTRACT FROM AUTHOR]

In this paper, a physics-based high-frequency (HF) model of switching power converters including the insulated gate bipolar transistor (IGBT) unit cells, heat sink, and connective printed circuit board (PCB) traces combined in a single electrical circuit is presented. The IGBT model includes the HF stray components superimposed on the well-known Hefner IGBT model. The HF components were calculated using a 3-D quasi-static finite element (3-D FE) analysis. The proposed complex model of the IGBT was verified both numerically and experimentally at different switching frequencies. The computed IGBT model was used in a low–high frequency model of a motor-drive system, and the common mode ground current was experimentally verified showing excellent results. [ABSTRACT FROM AUTHOR]

In the paper, a novel approach to numerical modeling of tube induction welding is proposed. The coupled electromagnetic and thermal model must take into account also the movement of the metal strip: in order to make possible this kind of simulation in reasonable computation time, a simplified approach to the modeling is presented and discussed. [ABSTRACT FROM PUBLISHER]

This paper concerns the modeling of electromagnetic vibration-and-noise sources in permanent-magnet direct current (PMDC) commutator motors. The electromagnetic sources are considered as an electromagnetic field distributed in the air-gap region of a PMDC motor. The latter is then formulated by the two-dimensional field theory in polar coordinates with the consideration of slotting effects and the armature reaction field. Consequently, based on the derived radial electromagnetic field, the radial and tangential magnetic forces acting on the inner surface of the permanent magnets can be expressed as Fourier functions in forms of space and frequency harmonics. The results obtained from the present models agree well with those from the finite-element models. In addition, the measured cogging torque is compared to those calculated by the analytical and finite-element models to validate the formulated electromagnetic field and magnetic forces. Furthermore, experimental investigations are carried out on the electromagnetic vibration-and-noise behavior of a commonly used PMDC commutator motor (such as that in heating, ventilating, and air conditioning (HVAC) systems). By measuring the natural frequencies and the associated mode shapes of the stator, the relationships between the magnetic forces and the measured vibration-and-noise responses are discussed in the frequency domain. [ABSTRACT FROM PUBLISHER]

This paper presents a new neural-network method to describe the electromagnetic (EM) behavior at the interface between the substructures from an internally decomposed EM structure. A set of neural networks is used to represent the EM behavior of the substructure as seen from the interface. This allows EM coupling between substructures to be effectively represented. The method is developed in a finite-element environment. An EM transfer function matrix is formulated to produce training data, allowing neural networks to learn the spatial coupling between EM-field variables at various locations over the interface of the substructure. A new formulation is proposed where trained neural networks are integrated into the finite-element equation for efficient simulation of an overall EM structure. A technique is developed to allow the proposed model to be used with the mesh different from that in neural-network training. Examples show that the proposed method provides better accuracy than conventional neural-network approaches for modeling substructures from an internally decomposed EM problem. Using the proposed model also speeds up finite-element simulation. [ABSTRACT FROM AUTHOR]

In this paper, a new method of electric field design of high voltage vacuum interrupters is proposed. According to the multi-gap insulation effect and the vulnerable breakdown spots theory, the symmetrical voltage shields are proved to be effective. So the initial model of a high voltage vacuum interrupter is designed. Next with finite element methods and optimization theory, a mathematical model of electric field intensity in interrupters is given. What's more, by optimizing this model with finite element software, a more symmetrical electric field in vacuum interrupters is obtained and its peak value appear as in the second auxiliary gaps (the two gaps between the center floating shield and the symmetrical voltage shields). The result shows that with this method, the vacuum interrupters can withstand higher static breakdown. [ABSTRACT FROM AUTHOR]

In order to reduce the influence of axial displacement and/or to ease the assembly, certain capacitive angular sensors use symmetric designs limiting their absolute measuring range to (360°/n) where it is the number of blades. This paper presents a combined sensor that utilizes a Wiegand sensor to obtain ad. ditional information needed to resolve 360°. Since magnetic and electric fields required by the sensing principles do not interfere, one single rotor design can be used for both fields. When the receiver coil on a Wiegand sensor has to drive a current, this current influences the shape and duration of the pulse generated by the sensor. We found that shape and amplitude of the pulse vary depending on the strength of the applied fields and the location of the initial inverse nucleation. Since most of design optimization for capacitive sensors is done by means of simulations, an adequate model of the combined sensor is needed. For the capacitive part, numerical approches such as the finite element method are available. For the pulse wire part, an extended king model has been developed; results of measurements and numerical simulations are reported. [ABSTRACT FROM AUTHOR]

We have investigated and calculated the distribution of electromagnetic fields and forces induced by a three- phase axially-symmetric system of electric current with six electrodes in a cylinder of a finite length [1, 3]. In this paper the alternating current is fed to each of nine discrete circular conductors-electrodes, which are placed on the internal wall of the cylinder. This new mathematical model describes a real device [7], which transforms electric energy into heat. The viscous incompressible flow of weakly electroconductive liquid-electrolyte is obtained by the finite-difference method, using the monotonous vector finite difference schemes. The average axially-symmetric motion of electrolyte and vortex distribution in a cylinder has been considered. The dependence of electromagnetic forces and velocity distribution at the inlet of the cylinder is investigated in the case of: 1) the vortex formation from the Lorentz force inside the cylinder by the electrode, 2) the vortex-breakdown from the swirl velocity at the inlet of the cylinder. [ABSTRACT FROM AUTHOR]

A new discontinuous Galerkin time-domain (DGTD) method based on generalized sheet transition conditions (GSTCs) for analyzing the transient response of electromagnetic metasurfaces is presented. The discontinuities in electromagnetic fields around the vicinity of the metasurface are modeled by placing virtual edges on both sides of the metasurface. The GSTCs are incorporated in the updating equations of the standard DGTD algorithm by integrating the time-domain GSTCs formula with Galerkin’ s-weighted residual method. The DGTD-GSTC formulation can also simulate a bf piecewise linear approximation of a curved metasurfaces due to the unstructured mesh. This is the first time that DGTD is applied to the simulation of GSTCs. The implementation of this new method is verified by numerical cases. [ABSTRACT FROM AUTHOR]

Introduction. The complexity of the theoretical description of the magnetic pulse treatment of the material is in the mutual coupled processes of electromagnetic and thermal fields with plastic deformation of the material and processes in an electrical circuit. The paper deals with the combined transient mathematical model of the system of equations of the electromagnetic field, theory of elasticity, thermal conductivity and electrical circuit. Purpose. Research and testing of the developed mathematical model and assess the impact of various parameters on the process of deformation of the work piece. Methodology. Investigation of nonlinear mathematical model is carried out by the finite element method using a special software package. Results. The resulting solution of the transient mathematical model allows studying the influence of parameters of the circuit, the speed and the characteristics of the material to plastic deformation and heating of the work piece, which allows to select the optimum process parameters. Originality. This is an integrated approach to the development of a mathematical model, which includes the electromagnetic field equations, the theory of elasticity, thermal conductivity and electrical circuit equations with a storage capacitor. Conclusions. A comprehensive mathematical model and its solution are obtained. It is established a small effect of heating temperature on the amount of strain. Currents caused by movement of the work piece must be taken into account in the calculations. Inertial forces significantly affect the nature of the deformation. During the deformation it is necessary to consider the nonlinearity of elasticity modulus. Thermal deformation of the work piece is much less mechanical strain and opposite in sign to them, but the surface temperature stresses due to the high temperature gradient equal to 20 % of the yield strength of the work piece. [ABSTRACT FROM AUTHOR]

We present a performance analysis of a parallel implementation of preconditioned conjugate gradient solvers using graphic processing units with compute unified device architecture programming model. The solvers were optimized for the solution of sparse systems of equations arising from finite-element analysis of electromagnetic phenomena involved in the diffusion of underground currents in both steady state and under time-harmonic current excitation. We used both shifted incomplete Cholesky factorization and incomplete LU factorization as preconditioners. The results show a significant speedup using the graphics processing unit compared with a serial CPU implementation. [ABSTRACT FROM AUTHOR]

Abstract: The enhancements carried out in the tokamak ASDEX Upgrade (AUG) are oriented toward the preparation of the future physics-related activities of ITER and DEMO. To address the main ITER issues, plasma configurations with a wider operational limit (e.g. higher triangularity) are planned for the future experimental campaigns in AUG. To evaluate the mechanical impact on the toroidal field (TF) magnet system a combined electromagnetic and structural finite element model was set up. At first extensive benchmarks of the models are carried out against the AUG reference design configurations with respect to stress [1–3], lateral displacement measurements and poloidal flux pattern. The numerical model was then applied to a set of actual high triangularity (HT) configurations generated by a more favorable poloidal field (PF) current distribution made possible by an extension of the power supply system. The resulting change of the poloidal flux pattern and the lateral force distribution has consequences for the coil shear stress and vault stability. Both aspects are monitored by a safety system measuring the PF flux placed on top and bottom of the outer surface of two TF coils (TFCs) between vault and the TFC supporting structure, so called Turn Over Structure (TOS). The range of the new HT configurations has induced a modification of the flux pattern, so that an adaptation of safety system is required to protect the TFCs system. Following the same criteria of the old safety system [4,5], a new set up of virtual coils will be integrated in the control system of AUG. The motivation of this new set up will be discussed in this paper. [Copyright &y& Elsevier]

Abstract: Electromagnetic forming (EMF) is a high velocity forming technique that reshapes electrically conductive materials by abruptly discharging a bank of capacitors through a coil. The oscillation frequency of the discharge is a key parameter in the design of an EMF system. For a given initial stored energy, there exist a frequency that produces the maximum workpiece deformation. Once we know it, we can set the electrical parameters of the EMF system to make the current intensity oscillate with this optimum frequency. This saves energy and money, preventing also the premature wearing of the coil. The objective of the present paper is to find the optimum frequency of an EMF system. Using the results provided by a finite element model in frequency domain, we are able to obtain the current flowing trough the coil, the Lorentz force acting on the workpiece, a function relating the electrical parameters of the EMF system with frequency and the optimum frequency of the discharge. Our approach can be very useful for coil design and for modeling complex three-dimensional geometries. To validate the method presented here, we apply it to tube compression and tube expansion processes and compare our results with those provided by other authors. [Copyright &y& Elsevier]

Abstract: A finite element model is introduced in this paper to describe the coupling between the welding arc and the weld pool dynamic in pulsed gas tungsten arc welding. The cathode, arc-plasma and melting anode regions are taken into account. The unified time-dependent model describes the heat transfer, fluid flow and electromagnetic fields in the three regions. The originality of the numerical model is its ability to treat the arc and weld pool time evolution under pulsed current welding in a unified formalism, taking into account eddy current in the weld pool. The case of thin plates with fully penetrated weld pools is also handled. To validate the predictions of the model, an Infra-Red camera is used to film the dynamic of the weld pool surface. Then an image processing algorithm permits to get the time evolution of the weld pool width directly from the film. The numerical model is applied to the 304 stainless steel welding, and the computed results show that the predictions are in fair agreement with the experimental results. [Copyright &y& Elsevier]

Provides information on a study which proposed the post-processing procedure for finite-difference time-domain transmission line. Discussion on low-frequency transient problems; Assessment of transient methods in electromagnetic field behavior; Methodology and results.

Focuses on a study which examined the utilization of hybrid finite-element modal expansion method of magic T-junction. Application of modal functions in analyzing electromagnetic fields; Discussion on finite element method and magnetic field components; Methodology and results.

Provides information on a study which summarized the application of generated anisotropic finite-element meshes in electromagnetic field calculation. Development of a model to assess the performance of electromagnetic field system; Utilization of anisotropic meshing in space-time meshing; Methodology and results.

Focuses on a study which presented the application of algebraic multigrid (AMG) method to solve linear system problems in finite element analysis. Discussion on multigrid solvers; Utilization of parallel processing technique and AMG in electromagnetic field analysis; Sample computation of magnetostatic analysis and eddy-current analysis; Methodology and results.

Provides information on a study which examined a method for estimating the back-electromagnetic (emf) field produced in electric machines during operation. Explanation on the computation of back-emf with single finite element (FE) method; Application of single-FE-solution method; Conclusions.

Provides information on a study which examined an extension of the Robin Boundary Condition Iteration method to solve the problem of electromagnetic scattering from three-dimensional cavities embedded in an infinite ground plane. Derivation of equation; Validation of the method; Conclusions.

Copyright of Technical Electrodynamics / Tekhnichna Elektrodynamika is the property of National Academy of Sciences of Ukraine, Institute of Electrodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We propose an approach to solving multisource induction logging problems in multidimensional media. According to the type of induction logging tools, the measurements are performed in the frequency range of 10 kHz to 14 MHz, transmitter-receiver offsets vary in the range of 0.5-8 m or more, and the trajectory length is up to 1 km. For calculating the total field, the primary-secondary field approach is used. The secondary field is calculated with the use of the finite-element method (FEM), irregular non-conforming meshes with local refinements and a direct solver. The approach to constructing basis functions with the continuous tangential components (from Hcurl(Ω) on the non-conforming meshes from the standard shape vector functions is developed. On the basis of this method, the algorithm of generating global matrices and a vector of the finite-element equation system is proposed. We also propose the method of grouping the logging tool positions, which makes it possible to significantly increase the computational effectiveness. This is achieved due to the compromise between the possibility of using the 1-D background medium, which is very similar to the investigated multidimensional medium for a small group, and the decrease in the number of the finite-element matrix factorizations with the increasing number of tool positions in one group. For calculating the primary field, we propose the method based on the use of FEM. This method is highly effective when the 1-D field is required to be calculated at a great number of points. The use of this method significantly increases the effectiveness of the primary-secondary field approach. The proposed approach makes it possible to perform modelling both in the 2.5-D case (i.e. without taking into account a borehole and/or invasion zone effect) and the 3-D case (i.e. for models with a borehole and invasion zone). The accuracy of numerical results obtained with the use of the proposed approach is compared with the one obtained by other codes for 1-D and 3-D anisotropic models. The results of this comparison lend support to the validity of our code. We also present the numerical results proving greater effectiveness of the finite-element approach proposed for calculating the 1-D field in comparison with the known codes implementing the semi-analytical methods for the case in which the field is calculated at a large number of points. Additionally, we present the numerical results which confirm the accuracy advantages of the automatic choice of a background medium for calculating the 1-D field as well as the results of 2.5-D modelling for a geoelectrical model with anisotropic layers, a fault and long tool-movement trajectory with the varying dip angle. [ABSTRACT FROM AUTHOR]

In this study, an accurate and efficient quantum genetic algorithm (QGA) combined with an improved self-adaptive (SA) scheme is proposed to solve electromagnetic optimisation problems. QGA is employed as the main optimisation frame because of its wider search range and higher efficiency than the conventional genetic algorithm. By introducing an improved SA scheme, the population at each generation is divided into two groups for crossover operation according to the magnitudes of individual fitness values. The crossover probability and mutation rate remain unchanged at the early stage of iterative process while the SA scheme will be carried out for the rest of the iterative process. Moreover, the elitist model is introduced to save the optimal father-individuals and abandon the worst ones. All these strategies make the whole population nearly converge to the optimal solution very fast. In two numerical examples of filter design and linear array synthesis, the effectiveness of the author's proposed optimisation algorithm, combined with the finite-difference time-domain method and finite-element method in HFSS, respectively, is verified. [ABSTRACT FROM AUTHOR]

We present an elaborate preconditioning scheme for Krylov subspace methods which has been developed to improve the performance and reduce the execution time of parallel node-based finite-element (FE) solvers for 3-D electromagnetic (EM) numerical modelling in exploration geophysics. This new preconditioner is based on algebraic multigrid (AMG) that uses different basic relaxation methods, such as Jacobi, symmetric successive over-relaxation (SSOR) and Gauss–Seidel, as smoothers and the wave front algorithm to create groups, which are used for a coarse-level generation. We have implemented and tested this new preconditioner within our parallel nodal FE solver for 3-D forward problems in EM induction geophysics. We have performed series of experiments for several models with different conductivity structures and characteristics to test the performance of our AMG preconditioning technique when combined with biconjugate gradient stabilized method. The results have shown that, the more challenging the problem is in terms of conductivity contrasts, ratio between the sizes of grid elements and/or frequency, the more benefit is obtained by using this preconditioner. Compared to other preconditioning schemes, such as diagonal, SSOR and truncated approximate inverse, the AMG preconditioner greatly improves the convergence of the iterative solver for all tested models. Also, when it comes to cases in which other preconditioners succeed to converge to a desired precision, AMG is able to considerably reduce the total execution time of the forward-problem code—up to an order of magnitude. Furthermore, the tests have confirmed that our AMG scheme ensures grid-independent rate of convergence, as well as improvement in convergence regardless of how big local mesh refinements are. In addition, AMG is designed to be a black-box preconditioner, which makes it easy to use and combine with different iterative methods. Finally, it has proved to be very practical and efficient in the parallel context. [ABSTRACT FROM PUBLISHER]

Copyright of Mechanika is the property of Mechanika and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to research the losses and heat of damper bars thoroughly, a multislice moving electromagnetic field-circuit coupling FE model of tubular hydro-generator and a 3D temperature field FE model of the rotor are built respectively. The factors such as rotor motion and non-linearity of the time-varying electromagnetic field, the stator slots skew, the anisotropic heat conduction of the rotor core lamination and different heat dissipation conditions on the windward and lee side of the poles are considered. Furthermore, according to the different operating conditions, different rotor structures and materials, compositive calculations about the losses and temperatures of the damper bars of a 36 MW generator are carried out, and the data are compared with the test. The results show that the computation precision is satisfied and the generator design is reasonable. [ABSTRACT FROM AUTHOR]

In bioelectromagnetics, the structures in which the electromagnetic field is to be computed are sometimes defined by a fine grid of voxels (3-D cells) whose tissue types are obtained by tomography. A novel finite element method is proposed for such cases. A simple, regular mesh of cube elements is constructed, each containing the same, integer number of voxels. There may be several different tissues present within an element, but this is accommodated by computing element basis functions that approximately respect the interface conditions between different tissues. Results are presented for a test model of 128^3 voxels, consisting of nested dielectric cubes, driven by specified charges. The electrostatic potential computed with the new method agrees well with that of a conventional finite element code: the rms difference along the sample line is 1.5% of the highest voltage. Results are also presented for the potential due to a current dipole placed in a brain model of 181 × 217 × 181 voxels, derived from MRI data. The new method gives potentials that are different to those obtained by treating each voxel as an element by 1% of the peak voltage, yet the global finite element matrix has a dimension which is more than 50 times smaller. [ABSTRACT FROM PUBLISHER]

Computation of electromagnetic fields in high resolution computational phantoms requires solving large linear systems. We present an application of Schwarz preconditioners with Krylov subspace methods for computing extremely low frequency induced fields in a phantom issued from the Visible Human. [ABSTRACT FROM PUBLISHER]

A 3-D advanced specialized simulator for designing a microwave-tube slow-wave structure (SWS), called the high-frequency circuit simulator (HFCS), has been developed. It is one module of our recently developed microwave-tube simulator suite. The four major features of the HFCS are as follows: 1) Both the lower and higher order tetrahedral basis functions are applied in the finite-element analysis; 2) two kinds of periodic boundary- condition techniques are proposed, one of which dramatically reduces memory requirements and solution times; 3) the Arnoldi algorithm is modified to more efficiently solve the required generalized eigenmatrix equation; and 4) the postprocessing parameters of the SWS can precisely be computed with the tangential-vector finite-element method. Various numerical examples are solved using HFCS. The accuracy and the performance of the HFCS are compared with commercial software HFSS and CST MWS. It is found that the results from the HFCS agree well with the experimental values as well as the simulated values from the commercial software packages. Moreover, the HFCS takes far lesser solution time and requires lesser memory than the commercial software in the simulation of two examples of SWSs, enabling faster prototyping and more elaborate design optimizations. [ABSTRACT FROM AUTHOR]

Biological data often takes the form of regular grids of samples, e.g., obtained by magnetic resonance imaging (MRI). When the finite-element method is used to predict the electromagnetic fields in volumes specified in this way, the data is first transformed to a geometric model, and then the model is subdivided into finite elements. These steps are expensive and can be unreliable. An alternative is proposed that avoids both steps. A regular mesh of rectangular finite elements is superimposed on the MRI grid. Each element may straddle boundaries between different tissues, but the basis functions are constructed in such a way that they respect the material interfaces. The new method is applied to the forward problem in electroencephalography. A circular head model and a model derived from real MRI data are analyzed with the new method. Sampled potentials at the surface of the scalp compare well with those obtained using the conventional finite-element method. [ABSTRACT FROM AUTHOR]

Presents a finite-element analysis of the electromagnetic field of a BLDC motor considering speed control and mechanical flexibility. Determination of mechanical motion of a rotor; Method of analysis; Analysis of electromechanical characteristics of the spindle system.

Focuses on a study which examined the computation of proximity effect and electromagnetic field mode in gas-insulated lines and bus ducts. Assessment of power density distribution and application of matrix algebra; Sample calculation of finite element method used in electromagnetic models; Methodology and results.