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  • Articles  (64,103)
  • Springer  (35,462)
  • Elsevier  (28,442)
  • Emerald  (199)
  • American Chemical Society
  • 1995-1999  (64,103)
  • Mathematics  (64,103)
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  • Articles  (64,103)
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  • 1
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: An approach to optimize the design of three-phase induction motors for a wide speed range drive is considered. Two operating points in the speed range are taken into consideration. The problem is handled as a constrained optimization problem. An accurate model for the motor in terms of its dimensions has been developed which predicts the motor performance based on about 60 parameters of motor geometry.
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  • 2
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    Compel 17 (1998), S. 36-46 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The purpose of this paper is to examine the current situation in numerical field computation, paying special attention to the role of education in developing new ideas to meet the ever growing demands of industry.
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  • 3
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    Compel 17 (1998), S. 151-154 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The paper presents a procedure for the design of claw pole alternators for small scale wind power applications. The method involves a preliminary design stage by means of the classical magnetic circuit analysis and a detailed design stage involving a 3D finite element model. This technique has been implemented in the design of a multiple generation for a small scale gearless autonomous system. The developed model can be implemented for the optimization of the rotor claw geometry through a minimization algorithm.
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  • 4
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    Compel 17 (1998), S. 49-54 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The Robin iteration procedure is a technique for the FEM computation of electromagnetic scattering fields in unbounded domains. It is based on the iterative improvement of the known term of a non-homogeneous Robin condition on a fictitious boundary enclosing the scatterer. In this paper it is shown that the procedure is equivalent to the application of the Richardson method to a reduced system and that the use of GMRES significantly reduces the computational effort.
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  • 5
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: This paper reports on the development of a repulsive type magnetic bearing system and the importance of permanent magnet (PM) configuration on the attenuation of radial disturbance. A new configuration of the permanent magnet of the bearing system resulting in improved stiffness characteristics in the radial direction has been described. Prototype models have been designed and developed in our laboratory and experiments carried out.
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  • 6
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    Compel 17 (1998), S. 189-195 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: A three-axes synchronous torque motor with permanent magnet excitation and solid stator and rotor yoke is used to adjust an air borne telescope and to eliminate oscillations. Hence the motor is part of a complex mechanical system and has to be included in the structural analysis. For this reason the attempt is made to simulate the nonlinear behavior of the motor by a dynamic model considering the eddy current fields and the magnetization characteristic of the iron.
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  • 7
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    Compel 17 (1998), S. 412-417 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The current pulse magnetizing process of permanent magnets is considered. General conditions for the design of a pulse magnetizer are given for the case when the magnetizing process is effected on the magnet put in free space. The boundary-integral analysis of the magnetic field inside the magnet is presented. It concerns both the state corresponding to the maximum value of the magnetizing current pulse and the magnetized state after the full magnetizing.
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  • 8
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    Compel 17 (1998), S. 302-306 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Heavy current bushings passing through steel cover plates and housing walls of power transformers, generators and other large power equipment are thermally hazardous elements of construction and a source of additional power losses. Safety and reliability of such expensive objects and safety of power delivery often depend on the proper design of these elements. In the paper a computer analysis, based on Maxwell equations and analytical representation of electromagnetic field was carried out. Non-linear permeability of solid steel was considered with the help of analytical approximation. Eddy current losses have been calculated and compared using different methods of calculation and experiments. The method of forecasting possible excessive heating and hot spot with the help of electromagnetic criteria was used. Various constructional means of loss and hot spot reduction were proposed and examined.
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  • 9
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    Compel 17 (1998), S. 357-363 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The Preisach and Jiles models for hysteresis are applied to reconstruct BH loops from measurement data for constructional steel St 37. The distribution function for the Preisach model is determined from all the available, 18, measured BH loops starting from the initial curve. The five unknown parameters in Jiles model are determined by the simulated annealing method to minimize the distance between the largest measured BH loop and the corresponding computed loop. Although Jiles model gives differences from the measured BH loops for low applied fields, it provides results fitted well to the largest measured loop for which the parameters are optimized. The Preisach model gives good fitting over a wide range of the applied field.
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  • 10
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    Compel 17 (1998), S. 369-373 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The paper deals with the calculation and reduction of torque pulsation in synchronous reluctance motors (SRM). The analysis is based on finite element modeling and proposes a method of dynamic torque characteristic calculation. The mutual connection between static and dynamic torque characteristic is also established. Several aspects for reduction of torque pulsation are demonstrated and applied with success.
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  • 11
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    Compel 17 (1998), S. 364-368 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: A prototype of a special electrical machine - double statored switched reluctance motor - has been developed which produces a very high static and dynamic torque. Possible ways of measuring the machine are presented. The basic parameters of the model are described. Results are compared to those obtained by computer design. A difference between computed and measured results is discussed.
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  • 12
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    Compel 17 (1998), S. 374-377 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: This paper aims to determine the electromagnetic forces acting in a power transformer, when a current corresponding to the first peak of a three-phase circuit flows in the windings. The finite element method for the evaluation of the field's values is applied, and the electromagnetic forces acting in a power transformer windings are calculated. Finally the results of a computation test by a personal computer for the exposed method are graphically presented and some conclusions about the behavior of the calculated electromagnetic forces are derived.
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  • 13
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    Compel 17 (1998), S. 389-392 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Induction coil and the extension cable of an induction heating power supply radiate electromagnetic noise and often give disturbance to other equipment and systems closely located. In this paper a method for measuring near-fields radiated by this system is proposed. Related data measured by using near-field probes and spectrum analyzer are processed and a software is developed for calculating antenna factor. The electric field results are given in graphics.
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  • 14
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    Compel 17 (1998), S. 393-397 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: In the paper a new probe for eddy current testing of low conductivity materials is presented. The new probe has been applied for eddy current testing of H2SO4 water solution. Results of measurements are presented.
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  • 15
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The evaluation of the conductivity profile of layered metallic structures is performed via the inversion of the impedance of a circular air cored probe coil of rectangular cross section. The inversion approach is based on the implementation of generalised radial basis function neural networks. The choice of the size of the network and the evaluation of its weights are handled by the orthogonal least squares learning algorithm. The merits of the proposed method are illustrated in the light of two examples concerning non-destructive testing applications.
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  • 16
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    Compel 17 (1998), S. 773-780 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: A sufficient condition for the existence of a node (i.e. an X-point) in lines of a quasi-static magnetic induction field is proved. The theoretical approach is developed for two-dimensional fields. The problem of obtaining an X-point in a magnetic induction field is encountered in toroidal devices (tokamaks) for controlled thermonuclear fusion experiments. The proposed method is capable of identifying possible X-point locations through the knowledge of field variables which are easy to calculate and/or measure.
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  • 17
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    Compel 17 (1998), S. 690-696 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: An improved model for microwave interdigital filters design and analysis is developed by correction of Denig's procedure (1989). This model enables correct modeling multiple-coupled transmission line structures as parallel sections of single coupled lines. Also, it is very suitable for the design and analysis of the filters by means of widely used microwave CAD programs. In this way the design and analysis of the microwave interdigital filters are significantly simplified. The verification of modified Denig's procedure is carried out through the two examples of the microstrip interdigital bandpass filters by means of program package LIBRA.
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  • 18
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    Compel 18 (1999), S. 120-131 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: In this paper a prototype actuator designed for a high bandwidth servo system is modeled and analyzed using finite elements. Natural frequencies and mode shapes of frequencies below 10kHz are extracted using frequency analysis and compared with the results from an experimental model analysis. The effects of key parameters used in the analysis on the natural frequencies are investigated. The frequency response is calculated using the natural frequencies and mode shapes. The calculated frequency response is compared with experimental results. The comparison of results shows that the numerical results are accurate. From the analysis the mechanical dynamics of the actuator can be understood and characterized. The analysis of the actuator shows that dynamic analysis using finite element modeling is accurate and effective and can be applied to other mechatronic systems.
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  • 19
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    Compel 18 (1999), S. 175-186 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: We introduce the drift-diffusion model with appropriate jump conditions at the junction of the MODFET transistor (AlGaAs/GaAs). We propose a quasi-variational inequality (QVI) model for this device. We assume that the electron density is bounded and piecewise constant. These hypotheses imply that the Poisson's equation becomes linear with respect to the electrostatic potential. The QVI model keeps a coupling with the continuity equation. Free boundaries arise in the medium AlGaAs near the Schottky-gate contact and in the high mobility medium (GaAs) under the effect of the electron affinity discontinuity at the junction. Numerical results of the QVI model show their location versus the applied gate voltage V/up〉 and the molar fraction X of the AlXGa(1-X)As medium. The inequality seems to be a reasonable simplification of the non-linear Poisson's equation.
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  • 20
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    Compel 18 (1999), S. 236-249 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Ventricular surface activation time maps are estimated from simulated and measured body surface potential (BSP) maps and extra-corporal magnetic field maps. In a first step the transfer matrix, relating the primary cardiac sources to the measured potential and/or magnetic field data, is calculated applying the boundary element method. Activation times are determined by minimizing a cost function which is based on this transfer matrix. This optimization method is solved by a quasi Newton method. The critical point theorem is used in order to estimate the starting column matrix.
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  • 21
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    Compel 18 (1999), S. 311-323 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The new set of standards ISO 10303 "STEP" makes it possible to give a complete representation of a product, using the description language EXPRESS. A part of STEP is devoted to the finite element analysis. This paper presents a brief overview of the architecture and the methodology of STEP and EXPRESS, with special attention to the part concerning the finite element analysis. The possibility to use it in modelling electromagnetic phenomena will be discussed. An example showing the description of a typical problem in electromagnetism will be implemented using EXPRESS.
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  • 22
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    Compel 18 (1999), S. 469-482 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The paper describes an efficient method to extract the B-H nonlinear characteristic from the experimental flux-current F-I data obtained using a non-uniform magnetic field device. Both functions are monotonically piecewise linear approximated with the same number of breakpoints. The method was successfully applied to characterize the ribbon core material of a fluxset magnetic field sector. In this case the hysteresis loop and the lumped magnetic circuit were extracted. Comparison with experimental results validates the proposed method.
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  • 23
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    Compel 18 (1999), S. 398-409 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: In this paper, a hybrid formulation for solving time harmonic eddy current problems in terms of magnetic field h is considered. In particular, we discuss some properties of the implicit boundary condition on the discrete level and the computation of the integral operator exploited in this context. An iterative technique is confirmed to be efficient in solving the arising, partly dense, complex linear system of equations. Furthermore, some test results, including timings for linear solvers are presented.
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  • 24
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    Compel 18 (1999), S. 436-444 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Fluxset type eddy current probes are used for detecting discontinuities in conducting materials. The measurements obtained by such probes can be used for the reconstruction of the parameters of the detected discontinuity if the output signal of the measurement is uniquely related to the measured field. In this paper a calibration method is presented for the establishment of the relation between the measured magnetic field and the output signal of the probe. The relation is obtained by the optimisation of the parameters of the mapping between the calculated magnetic field distribution and the measured output signal. The magnetic field distribution due to the interaction of the probe and an infinitesimally thin crack located in a conducting plate is calculated numerically by the solution of a boundary integral equation.
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  • 25
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    Compel 15 (1996), S. 4-21 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Proposes a finite element method for numerical simulation of the hydrodynamic model of semiconductor devices. Presents some scaling factors and a variational formulation. Uses the P1 - isoP2 element to discretize this formulation and the GMRES (Generalized Minimum RESidual) algorithm to solve the associated non-linear system. Proposes an artificial viscous term to stabilize the non-linear system. Gives a choice for an initial solution. Presents the numerical solutions for n+ - n - n+ diodes and 0.25µm gate length Si MESFETs. Calculates a shock wave at 300K. Observes velocity overshoot phenomenon and the effect of heat conduction term.
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  • 26
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    Compel 16 (1997), S. 60-70 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Self-inductance calculations are presented for coils of modular construction. Individual modules have a fixed winding density, so that a complete multi-module coil will be characterized by larger inter-turn spacing at its extremities to provide suitable insulation strength under impulse voltage conditions. Gives inductance computations using finite-element analysis, so that empirical correction factors to take account of end-effects and inter-turn spacing are unnecessary. Comparison where possible with established empirical methods shows consistency. Gives an example of oscillatory high-voltage tests.
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  • 27
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    Compel 16 (1997), S. 84-91 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The paper presents the simplified model of the Class E inverter in which the MOSFET transistor is based on the piecewise-linear (PWL) model. The model does not contain inductances. The PWL description makes it possible to obtain the model in the form of general closed formulae. The general formulae have been obtained by means of MATHCAD and verified with the IsSPICE® simulator. The analysis of MOSFET switching performance in the active region at the constant load current is delivered. The work is a successive step in the systematic research of the Class E inverter as a supplying source in high frequency levitation heating/melting systems. The equivalent RL parameters of the load in such systems vary across a relatively wide range.
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  • 28
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: This paper presents the initial stage of a 3D finite element (FE) model of the electromagnetic field in the arc chamber of a current limiting miniature circuit breaker (MCB). The final objective of the model is to compute the magnetic forces on the arc, and predict the position of the arc at a series of discrete time steps. The trajectory of the arc calculated from the model will then be compared with experimental data recorded by a high speed arc imaging system (AIS) on a flexible test apparatus (FTA) designed to simulate the operation of a commercial MCB under laboratory conditions. By comparing the FE model of the arc behaviour with the actual arc images generated from the AIS an insight into the factors governing the motion of the arc can be gained. In particular the relative importance of the average flux density across the arc chamber is compared with the local flux density distribution at the arc roots. An understanding of the influence of the magnetic flux distribution can then be used to improve the magnetic design of the MCB to promote low immobility times and effective current limiting operation.
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  • 29
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    Compel 17 (1998), S. 285-289 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: A three-dimensional analysis of the quasistationary, magnetic leakage field of a one-phase transformer with asymmetrical disk windings is presented. A simplified mathematical model of the transformer based on Maxwell's equations is applied. Computational results of the leakage reactance for asymmetrical disk-type windings are compared with the analytical ones according to Richter's formulae.
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  • 30
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: In this study, a single-phase induction motor with constant v/f, fed by matrix converter, is considered under various frequencies. The modeling of the motor, mechanical load for single phase induction motor and matrix converter have been obtained by using Simulink package program. The performance of the motor under various frequencies is determined. A single-phase induction motor considered in this work has a running capacitor. The analysis and simulation results are presented.
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  • 31
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    Compel 17 (1998), S. 181-185 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Stochastic methods offer a certain robustness quality to optimization process. In this paper, the genetic algorithm, based on the computer simulation of the natural evolution, is used for the shape optimization of an electromagnetic actuator. The framework is modeled by a 2D finite element method allowing the computation of the magnetic force. The aim is to obtain a desired force profile considering the armature movement.
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  • 32
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    Compel 17 (1998), S. 261-266 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: A magnetic study has been linked to an electrical survey to improve a saturated synchronous machine model. The machine is supplied by a sinusoidal voltage source, but the developed model could be extended to a non-sinusoidal case. The last one corresponds to electrical machines supplied by power electronic converters. First, the machine magnetic state is analysed from a numerical calculation based on the finite element method. Saturation laws are established. The results show that some parameters which were considered constant values vary with the saturation level. Second, we introduce the saturation laws in the machine electrical equations. The voltage supplied machine is simulated for an electrical transient state. Finally, the developed model is compared to a reference one which uses experimental constant parameters. The simulation results show that the proposed electromagnetic laws significantly modify the machine currents' waveforms.
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  • 33
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    Compel 18 (1999), S. 458-468 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The implementation of a vector Preisach model for the modelling of anisotropic hysteretic soft magnetic materials is outlined. Some comparisons with measurements on alternate and rotational magnetic field excitations are shown. The hysteresis model is inserted inside a two-dimensional finite element solver formulated in terms of magnetic vector potential and nonlinear solution is handled by means of the fixed point method with H-scheme. Results obtained on a two-dimensional geometry are described and discussed.
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  • 34
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: To circumvent the high computational costs of modelling each lamination to compute the eddy current distribution in three dimensions in conducting laminations, a simple method has been developed. The laminar nature of the eddy currents due to the magnetic leakage field has been considered by applying an anisotropic conductivity with zero or very low value in the direction normal to the laminations. This yields an overall field distribution serving as basis. In a second step, the much smaller eddy current loops caused by the main magnetic flux parallel to the laminations have been taken into consideration by a one-dimensional analytical model. Nonlinearity is neglected.
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  • 35
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    Compel 18 (1999), S. 504-514 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: A new method for the numerical computation of the dynamic behaviour of electro-dynamic loudspeakers is presented. The numerical scheme, based on the finite element method (FEM), allows the simulation of coupled magnetic, mechanical and acoustic fields. The obtained simulation results are in good agreement with measured data.
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  • 36
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    Compel 18 (1999), S. 275-284 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The identification of magnetic field profiles is crucial in many applications where a direct measurement is difficult. We discuss here a technique, based on the injection of charged particles in the region under examination, which promises to be an innovative and effective tool in the analysis of 1-D field profiles in high current plasma discharges. After the decription of the inverse problem related to the field construction, we consider a suitable discrete identification scheme, and analyze some properties of the latter. The field map in the interest region is reconstructed via a minimization procedure, which identifies the coefficient of a well-suited expansion for the field. In particular, we discuss the precision and robustness of the identification procedure, with respect to the chosen optimization scheme, the amount of data, the order in the field expansion, and the influence of noise on the data.
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  • 37
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Finite element discretizations of low-frequency, time-harmonic magnetic problems lead to sparse, complex symmetric systems of linear equations. The question arises which Krylov subspace methods are appropriate to solve such systems. The quasi minimal residual method combines a constant amount of work and storage per iteration step with a smooth convergence history. These advantages are obtained by building a quasi minimal residual approach on top of a Lanczos process to construct the search space. Solving the complex systems by transforming them to equivalent real ones of double dimension has to be avoided as such real systems have spectra that are less favourable for the convergence of Krylov-based methods. Numerical experiments are performed on electromagnetic engineering problems to compare the quasi minimal residual method to the bi-conjugate gradient method and the generalized minimal residual method.
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  • 38
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    Compel 18 (1999), S. 570-586 
    ISSN: 0332-1649
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Deals with the problem of the electromagnetic torque calculation in the case of either nonuniformity of the air-gap or eccentricity of the rotor. The electromagnetic field distributions have been evaluated for drag-cup motors. An analytical model has been introduced for linear motor based on the variation method for magnetic flux density magnitudes. The total torque and its components have been evaluated for the motors chosen. The decrease of the electromagnetic torque and increase of eddy-current losses have been discussed due to either rotor circular asymmetry or its eccentricity.
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  • 39
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    Compel 15 (1996), S. 32-39 
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    Notes: Details an equivalent circuit model used to stimulate voltage surge attenuation within concentric cylindrical transmission systems. The model is frequency independent and accommodates the linear parameters of the current return path. To illustrate the validity of the approach, calculates the theoretical current distribution within an insulated cable and compares it with results obtained using a finite element analysis package. Finds that there is a good correlation between the two methods. Concludes that the model is simple to implement, has short computational times and can be readily adapted into any transient analysis program.
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  • 40
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    Compel 15 (1996), S. 4-18 
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    Notes: Develops a finite element analysis and solution strategy for the augmented drift-diffusion equations in semiconductors device theory using a multilevel scheme. Decouples the drift-diffusion equations using Gummel iteration with incremental continuation in the applied voltage. Includes augmentation of the carrier mobility to address the issue of non-local electric field effects (velocity overshoot) within the framework of the drift-diffusion formulation. Gives comparison results with hydrodynamic and Monte Carlo models and sensitivity studies with respect to the augmentation parameter. Discretizes the equations with a special finite element method using bases of variable polynomial degree. Accomplishes solution of the resulting linear systems with a multilevel method using the basis degree as the grid level. Presents performance results and comparison studies with direct elimination.
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  • 41
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    Notes: Discusses the 2-D minimum free energy (MFE) parameter and spectral estimation method and presents an algorithm for its implementation. Notes a profound lack of results in the literature on 2-D spectral estimation methods and on their comparison. To address this issue and to impart an overall impression of the performance of 2-D MFE, compares results from the Levinson method, a maximum entropy method (MEM), and a hybrid method with 2-D MFE. Points out that 2-D MFE can provide superior spectral estimates to that produced with MEM and that, in general, MFE requires a larger area of correlation support than the hybrid method. Also notes that 2-D MFE can provide superior spectral estimation over the 2-D Levinson algorithm.
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  • 42
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    Compel 15 (1996), S. 19-30 
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    Notes: Notes that Scalar digital plane waves are made of a finite or infinite sequence of discrete pulses which are solutions of a wave equation. Discusses the 1D and 2D wave equations and shows how the 1D and 2D Laplace transforms may be used in connection with digital signals. Gives some examples of digital plane waves and, as an illustration, gives three different applications of this technique.
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  • 43
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    Compel 15 (1996), S. 47-57 
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    Notes: Noise parameters of high electron mobility transistors (HEMT) at microwave frequencies are a subject of active research since the knowledge of their performance is of key importance for the use of these devices for designing low-noise amplifiers. Employs a simple noise model to derive the analytical expressions for the device noise parameters F0, G0 and N in terms of the electrical elements associated with the basic equivalent circuit of an HEMT. Analyses such expressions to establish some fundamental relationships, as well as the expected noise performance of the device when the parasitic elements representing package effects are included.
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  • 44
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    Notes: Inverter-fed asynchronous motors represent today a source of disturbance in electric drives, because they irradiate outside their frames electromagnetic waves with different frequencies. Knowledge of the disturbances generated inside the drive is necessary. In the paper the influence of the sampling time on the distortion between predicted and actual armature current is evaluated on the basis of an analytical calculus procedure, that allows for an easy evaluation of the harmonic contents of the currents. This is the first step towards the evaluation of the causes of environmental electromagnetic disturbances.
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  • 45
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    Compel 17 (1998), S. 324-328 
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    Notes: Non-linear characteristics, as relations between linked fluxes and currents of individual machine coils, are sought for in the so called circuit models of saturated electrical machines. Their determination can be based on the co-energy of the magnetic field only, which is a multivariable function of all coil currents and rotor position angle. The author proposes the calculation of co-energy values at necessary points by the FEM and the interpolation of the results by a suitable multivariable spline function. The functions of linked fluxes are generated as the first derivatives of the spline. This way could be used to separate the circuit calculation from the field calculation when saturated machines are modelled. An example of a wound rotor induction machine is used to show the elementary problems of the calculation of the non-linear characteristics.
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  • 46
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    Compel 17 (1998), S. 427-438 
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    Notes: The paper presents a historical review, the state of the art and recent advances in the field of computational electromagnetics at leading universities and research institutes in Poland. Contributions made by Polish scientists to the development of fundamental electromagnetism, as well as to computational methods, are emphasized, and some conclusions are drawn regarding expected future developments.
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  • 47
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    Compel 17 (1998), S. 460-474 
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    Notes: Two approaches to 3-D magnetic field calculations for low-power special transformers are presented in the paper. The application of fast calculation procedures based on the finite difference method, to direct solving of the Poisson and Laplace equations is given. The calculated example deals with the three-phase leakage transformer. On the other hand, the iterative solution of regularized integral equations used for calculation of 3-D field distribution and integral parameters of leakage field in current transformer is also presented. The software packages developed by the authors are useful for computer-aided design of low-power special transformers.
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  • 48
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    Compel 17 (1998), S. 489-505 
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    Notes: Recent progress in the development of electromagnetic field theory and sophisticated software for solution of complicated, non-linear, 3-D structures is not always accompanied with relatively cheap and simply presented engineering instructions, easy to use for regular industrial design. In the paper some theoretical and practical examples are given as to how one can get over a excessive calculating difficulties to obtain quickly simple design directions and reduce complicated theory to simple practical conclusions. The fast and cheap package RNM-3D is validated by comparison with industrial test data and with the interactive graphics system is the final illustration of the effectiveness of such an approach. RNM-3D is used successfully in many transformer works the world over.
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  • 49
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    Compel 17 (1998), S. 620-627 
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    Notes: In this paper are summarized our research activities dealing with the theoretical and experimental analysis of high voltage direct current (HVDC) ionizers. We present here the basic principle of a hybrid charge simulation-finite difference method, that has been used to simulate the electric behaviour of these devices, by computing the electric field strength and the ionic current density distribution, therefore the efficiency of emission. We have realized an experimental ion counter and we have used it to verify the values predicted by means of this numerical technique.
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  • 50
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    Notes: During recent years, higher order statistics (HOS) have found a wide applicability in many diverse fields, e.g. biomedicine, harmonic retrieval and adaptive filtering. In power spectrum estimation, the signal under consideration is processed in such a way that the distribution of power among its frequency is estimated and phase relations between the frequency components are suppressed. Higher order statistics and their associated Fourier transforms reveal not only amplitude information about a signal, but also phase information. If a non-Gaussian signal is received along with additive Gaussian noise, a transformation to higher order cumulant domain eliminates the noise. These are some methods for estimation of signal components, based on HOS. In the paper we apply the MUSIC method both for the correlation and the fourth order cumulant, to investigate the state of asynchronous running of synchronous machines and the fault operation of inverter-fed induction motors. When the investigated signal is distorted by a coloured noise, more exact results can be achieved by applying cumulants.
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  • 51
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    Compel 17 (1998), S. 407-411 
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    Notes: The mathematical model of thin cylindrical conducting shell deformation under a current surge was elaborated. The shell deformation influence on the electromagnetic and thermal field distribution has been calculated. The perturbation analysis of the vibration of a thin cylindrical shell under heavy current surge was given. The critical wave number and mode was found and the most probable instability was calculated.
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  • 52
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    Compel 17 (1998), S. 307-312 
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    Notes: This paper presents the results of silicon micromotor static and dynamic simulations by means of finite element method and the Moulton-Adams algorithm as well. Capacitance and torque curves calculation. The virtual work principle has been applied. The dynamic states of the motor are described by the non-linear and non-stationary system of ordinary difference equations solved numerically. Some results of computer simulation of dynamic states are presented and discussed.
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    Compel 17 (1998), S. 402-406 
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    Notes: Temperature dependence of magnetic susceptibility has been approximated by the extension of Curie-Weiss law to ferromagnetic states. Application of similar relations to other properties and corresponding model parameters of magnetic materials would enable thermal analysis of circuits containing ferromagnetic cores.
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  • 54
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    Compel 17 (1998), S. 717-725 
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    Notes: By using complementarity (solving for both potentials, scalar and vector), one often can provide bilateral bounds for some quantities of interest, like for instance the reluctance of a circuit. However, the vector potential method is expensive, and does not make use of information acquired in the first phase of solving for the scalar potetential. We show how to improve on this by a "local correction" process which, starting from h = grad ?, yields a divergence-free b, close to µh, by a series of local and independent (parallel) problems.
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    Compel 17 (1998), S. 708-716 
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    Notes: Many practical applications of neural networks require the identification of non-linear deterministic systems or chaotic systems. In these cases the use of a network architecture known as locally recurrent neural network (LRNN) is often preferable in place of standard feedforward multi-layer perceptron (MLP) networks, or of globally recurrent neural network. In this paper locally recurrent networks are used to simulate the behaviour of the Chua's circuit that can be considered a paradigm for studying chaos. It is shown that such networks are able to identify the underlying link among the state variables of the Chua's circuit. Moreover, they are able to behave like an autonomous Chua's double scroll, showing a chaotic behaviour of the state variables obtainable through a suitable circuit elements choice.
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    Compel 17 (1998), S. 749-756 
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    Notes: The paper reports on a development of an automated CAD optimization system which interfaces an external design routine with a general purpose finite element software. The magnetic analysis is performed using a parameterized model and the process is controlled from within procedures written in MATLAB programming environment. Results are shown for a permanent magnet brushless DC motor.
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  • 57
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    Compel 18 (1999), S. 43-60 
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    Notes: In this paper we present a new autoregressive (AR) method for bispectrum estimation defined in terms of its third-moment sequence. The method is based on the segmentation of data into coupled records, and can be considered to be a modification of the "third order recursion method"(TOR). Its foundation resides in considering the data of the process at the left and the right of each record (needed for the calculation of third moment sequence) as not null and taking them as the data corresponding to the preceding and succeeding record respectively. Several simulated examples show that this method allows model parameters to be obtained with greater precision, most of all when only few data are available per record. The influence of factors such as number of data and records, model order, and added white and coloured Gaussian noise on the parameters' estimation is also considered.
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    Compel 18 (1999), S. 103-119 
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    Notes: There are two conflicting views about electromagnetic phenomena. The first is based on the action between stationary and moving particles of electric charge and the second on energy distributions in electric and magnetic fields. The difference between these approaches is seen most clearly in the roles assigned to the potentials. According to the particle view the potentials convey the force from one particle to another, whereas in the field approach the potentials are system parameters related to the field energy. The article compares the two views and concludes that the particle view faces impossible difficulties because it ascribes local significance to quantities which are unobservable and conflicts with the quantum-mechanical understanding of charge as a statistical distribution.
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    Compel 18 (1999), S. 165-174 
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    Notes: Some improvements are made for Fast Boundary Tracking algorithm according to the practice of the electric machine design in the paper. As discrete variables play a dominant role in determining the values of the objective function and the constraint functions in the motor optimal design, the algorithm is improved in the paper. From the algorithm, a software is developed and used for the optimal design of the induction motors of Y series. The results show that the algorithm is reliable and efficient.
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    Compel 18 (1999), S. 204-214 
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    Notes: In this paper an outline of the development of methods for the analysis of non-linear circuits is presented. Non-inert and inert elements have been discerned and an inertia measure has been proposed. For this purpose, an exponential function with time constant T equal to TR, TL, or TC is formulated for an element of type R, L, or C, respectively. In circuits with the imposed cause, which varies sinusoidally in time with period Te, the following situations are distinguished and considered: Te » T; Te « T; and Te ˜ T. In the first case, the effect changes in time according to the non-linear characteristic of the element. In the second case, the respective circuit is referred to as the "quasi-linear", because for the sinusoidal cause the effect is also sinusoidal. In the third case, the hysteresis occurs and the effect is a two-valued function. The hysteresis effect occurs also in resistive elements.
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    Compel 18 (1999), S. 61-76 
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    Notes: A stationary 3D energy-transport model valid for semiconductor heterostructure devices is derived from a semiclassical Boltznmann equation by the moment method. In addition to the well-known conservation equations, we obtain original interface conditions, which are essential to have a mathematically well-posed problem. An appropriate modelling of the physical parameters appearing in the system of equations is proposed for gallium arsenide. The model being written and its particularities mentioned, we present a novel numerical algorithm to solve it. The discretization of the equations is achieved by means of standard and mixed finite element methods. We apply the model and numerical algorithm to simulate a 2D AlGaAs/GaAs MODFET. Comparisons between expenrimental measurements and calculations are carried out. The influence of the modelling of the physical parameters, especially the electron mobility and the energy relaxation time, is noted. The results show the satisfactory behaviour of our model and numerical algorithm when applied to GaAs heterostructure devices.
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  • 62
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    Notes: Vector potential formulations of Maxwell's equations need to be gauged, otherwise nodally based finite element approximations lead to an ill conditioned linear system. In this paper alternative Lorentz gauge formulations will be analysed. Particular attention will be paid to the conditions to be applied at material interfaces, bearing in mind ease of implementation in a finite element code and efficiency of solution. The methods discussed are designed to cope with the most challenging physical situations, namely, multiply connected abutting conductors made of different materials.
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    Compel 18 (1999), S. 6-37 
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    Notes: A mathematical gas dynamic model for semiconductor devices is numerically analysed. The well-known ballistic diode problem is taken as an example.
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    Compel 18 (1999), S. 77-83 
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    Notes: The divergence equations in Maxwell's theory are Gauss law and the statement that magnetic monopoles do not exist; from this point of view these two equations are fundamental. However, from a practical point of view, it is generally believed that Maxwell's divergence equations are redundant and may be ignored provided that they are satisfied at some time t-0. It has been proved recently that this idea is not correct for boundary-initial value problems. To make mathematical arguments more accessible, we analyse here the role of the divergence equations in the framework of 2D-electromagnetism.
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    Compel 18 (1999), S. 132-142 
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    Notes: For each natural n let Fn denote the collection of mappings of Rn onto itself defined by: F ?Fn if and only if there exist n strictly monotone increasing functions fk mapping R onto itself such that for each x =[x1, ..., xn]T ? Rn, F(x) = [f1(x1), ..., fn(xn)]T. The following new property of the class P0 of matices is proved: a real n × n matrix A belongs to P0 if and only if for every G, H ? Fn the set S0 = { x ? Rn : - G(x) =Ax = - H(x) } is bounded. As an illustration of this property a method of estimating the unique solution of the nonlinear equation F(x) + A(x) =b describing the large class of DC transistor circuits is developed. This can improve the efficiency of known computation algorithms. Numerical examples of transistor circuits illustrate in detail how the method works in practice.
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    Compel 18 (1999), S. 187-203 
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    Notes: Computer simulations were done extensively in order to study non-linear dynamics of laser-plasma interaction in InSb semiconductor. We constructed the modified Duffing kind of non-linear semiconductor plasma oscillator equation. Collision frequency is found to be dominant parameter to influence the bifurcation, chaos, hysteresis and bistable effects of plasma wave. Small windows of higher period cascade above the critical value of laser parameter (a1a2) in the chaos region are observed. Laser-plasma exhibits too much chaotic regime at lower value of laser driving frequency (d). Hysteresis and bistable regions of plasma wave are presented and the conditions for their occurence are identified. The unstable regions completely merge at higher value of effective collision frequency (?).
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    Notes: A boundary element method in terms of the field variables is applied to three-dimensional electromagnetic scattering problems. Especially, the influence of a dipole excited field on low conducting materials situated very close to the antenna will be discussed. We use higher order edge elements of quadilateral shape for the field approximation on curved surfaces. The tangential components of the unknown field variables are interpolated by vector element functions. The Galerkin method is implemented to obtain a set of linear equations. The applicability of the proposed edge element is investigated by the comparison of different BEM-formulations and FEM-results.
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    Compel 18 (1999), S. 515-527 
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    Notes: The paper presents an efficient modeling technique for the fluxset magnetic field sensor. Using separate numerical solutions for the electric and magnetic fields, an equivalent SPICE circuit is extracted in the postprocessing phase. The main contribution of the paper is the technique used to model the distributed capacitive effects in insulation between coils, by concentrating them in an "Extended II scheme", an infinite circuit which is optimally reduced to a finite one. The results are in qualitative agreement with the experimental ones.
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    Compel 18 (1999), S. 611-622 
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    Notes: The paper deals with a coupled field-circuit simulation of transient and dynamic states in a non-linear axisymmetrical electromagnetic device. The mathematical model of the dynamic phenomena includes: an equation of transient electromagnetic field in a non-linear conducting and moving medium, equations of the converter electric circuits and the equation of mechanical motion. The numerical implementation of the algorithm is based on the finite element method. The Crank-Nicholson scheme for time discretization has been applied. In order to include nonlinearity, the Newton-Raphson process has been adopted. The influence of the saturation effect on the dynamic characteristics of the device has been investigated.
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    Notes: Proposes to compare two models - finite element method and "magnetic" equivalent scheme - for numerical modelling of electromagnetic systems. Both these approaches coupled with electric circuit equations take into account saturation effects. Uses a machine of 5.5kW as a model to show the validity of these approaches. Compares the results obtained from numerical calculation with experimental ones.
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    Compel 15 (1996), S. 88-95 
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    Notes: Presents a method for the finite element (FE) analysis of saturation effects in a squirrel- cage electrical machine. The proposed mathematical model includes the FE equations of the electromagnetic field, the equations which define the connection of windings, and the mechanical equation. Applies an approach based on a simultaneous solution of these equations, paying special attention to the movement simulation. Applies the time-stepping method with a fixed grid, independent of the rotar position. In the method the motional effects are simulated by trigonometric interpolation of the results for the previous time step.
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    Compel 15 (1996), S. 36-47 
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    Notes: Shows how a strongly non-linear semiconductor equation can be solved via homotopy deformation methods combined with the arclength continuation procedures. The fundamental goal of these methods is to overcome the instabilities or the failure of the classical Newton-Raphson's schemes which appear when the non-linearity is strong or near limit or bifurcation points. The system, in its artificial transient form, is discretized by the non-linear implicit scheme with local time steps. Uses the mixed finite element (MFE) approach. Presents numerical results, in two dimension, for a realistic device: an Abrupt Heterojunction Bipolar Transistor working as an amplifier.
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    Notes: Investigates the global stability of the zero solution of an impulsive system of differential-difference equations with variable impulsive perturbations. By means of piecewise continuous functions which are analogues of Lyapunov's functions, and of the comparison principle, sufficient conditions for global stability of the zero solution of the systems considered are found.
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    Compel 16 (1997), S. 17-30 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Presents a fast numerical method for computing the lowest degree moments of the exponential function for a segment, square or cubic domain. An exponential function with the argument a multivariate polynomial with a maximum degree of one in each single variable is considered. These kinds of integral are encountered in exponential-fitting finite element methods. For the 1D and 2D cases, a fast method based on the direct evaluation of the moments is used, whereas for the 3D case, a quadrature of 2D moments is considered together with some schemes based on the knowledge of the integrand function in order to improve the computational efficiency.
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  • 75
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    Compel 16 (1997), S. 31-37 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Develops the algorithms for numerical analysis of current density distribution in squirrel-cage rotor bar of arbitrary shape, taking the non-uniform resistivity into account. Gives the structure of a computer program for this strong non-linear problem. Presents, as an example, the results of investigations of wedge-shaped bar.
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  • 76
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    Compel 16 (1997), S. 49-55 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Presents the implicit Runge-Kutta methods as an interesting alternative to Crank-Nicolson and backward Euler methods to solve differential algebraic systems arising in nonlinear transient magnetodynamic problems. An algorithm for diagonally implicit Runge-Kutta methods is proposed that requires minor modifications of existing codes.
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  • 77
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    Compel 16 (1997), S. 38-48 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Examines some basic aspects of hybrid filters, operating effectively when current pulsations of a non-linear variable load occur. The operation of two hybrid filter systems, each equipped with an active power filter, working as: a) a controlled additional current source, b) a controlled additional voltage source, recognized by the authors in previous publications as the most advantageous solution has been examined. For both systems, vectorial equations in a,ß co-ordinates, describing their operation, have been presented. On the basis of these equations a common frequency model of three-phase three-wire hybrid filters has been elaborated. This model has been used for the evaluation of the filtration efficiency of line current harmonics, taking into consideration the applied methods and algorithms to separate filtered harmonics, above all at a pulsating load current. Some conclusions from the theoretical analysis have been verified by simulation of a line loaded by converter with an output current pulsating at frequencies 10 and 20Hz.
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  • 78
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    Compel 16 (1997), S. 71-83 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The article deals with the search for the signals of the real source current or the real source voltage with the help of the ||i - i0|| or ||u0 - u||? min criteria. At the same time there, one must know the power flux between the source and the receiver. The problem is solved by means of a certain Hilbert space where a special square functional is minimized. Both the inner impedance operator of the source and the receiver operator are non-linear. The article presents a simple computational algorithm for a two-terminal circuit, in particular for the circuit consisting of a saturated choking coil and a diode element. This algorithm can be applied to a special class of two-terminal circuits, i.e. the circuits recognized as linear in case of small signal increase. The optimal current is calculated until it is fixed. This way, one gets a periodic steady state. The algorithm in question is always locally convergent, but the global convergence is difficult to prove. However, many numerical experiments indicate the global convergence. Presents the results in the form of computer plots.
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  • 79
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    Compel 16 (1997), S. 92-107 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Building on the Rayleigh-Stevenson approach fictitious internal source distributions responsible for the leading near-field contribution of the long wavelength scattering by a non-dissipative dielectric prolate spheroid are derived. The equivalent multiline sources arising from every polarization of the incoming field on the segment between the foci can be regarded as the result of an ultimate contraction of the volume polarization in the spheroid, or plainly as prolonged multipoles. In the low-frequency asymptotic solution of the first-order in terms of ? the solutions involve line and strip currents, and biline and quadriline charges, the density distributions of which obey simple polynomial laws. Numerical examples are provided, demonstrating their significance in the calculation of near-zone fields in comparison with the direct radiation of elementary sets of point sources approximating the multiline distributions. The range of validity of the low-frequency expansion is estimated by comparing with results obtained using the T-matrix method.
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  • 80
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    Compel 16 (1997), S. 108-122 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The electromagnetic properties of microwave transmission lines can be described using Maxwell's equations in the frequency domain. Applying a finite-volume scheme results in an algebraic eigenvalue problem. In this paper an improved numerical computation of the eigenmodes is presented. Avoids the time- and memory-consuming computation of all eigenvalues in order to calculate a selected set of propagation constants using an iterative method that is carried out twice. The numerical effort and the storage requirements can be reduced considerably.
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  • 81
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    Compel 17 (1998), S. 106-110 
    ISSN: 0332-1649
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: A spherical motor is a novel electromechanical device that has obtained worldwide attention for its attractive advantages. A general analysis of electromagnetic torque in double excited spherical motor has been completed on the calculation of its 3D electromagnetic field distributions. The analysis accounts for the effect of open-end region in the stator. Double scalar magnetic potentials method has been used in the FEM numerical analysis. On the computation results, the other electromagnetic parameters can be calculated, which will be very significant in the design and performance prediction of the spherical motor. The calculation results indicate that the device is capable of continuous speed control and efficient torque production.
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  • 82
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    Notes: The recent achievements in electronic control as well as the higher performance of advanced permanent magnets have brought about a change in the general strategy for design and development of new types of small electrical machines. A special application of permanent magnets (PM) is represented by hybrid stepping motors (HSM). The latter are a sort of combination of variable reluctance-motors and permanent magnet-motors. The influence of various PM inserts into the magnetic circuits of electromechanical converters on field and force distribution has been already investigated by the authors (1996). Promising results for HSM have been reported, especially when rare-earth PMs are used. The main aim of PM inserting, when they are put into slots of slotted pole shoes with radial N-S polarization, is to focus magnetic field lines in the corresponding teeth. As a result, the reluctance stepping torque can be increased depending on the material used. Now a further step is made by extending the analysis from the case of linear to that of non-linear demagnetization curves of permanent magnets.
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  • 83
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    Compel 17 (1998), S. 342-346 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: All the algorithms introduced by the authors in their finite-element computational program for studying fields easily and quickly are described in the paper. Moreover, an application of the analysis of the thermal field to a three-phase transformer is proposed. This analysis gives a valid help to designing transformers having to provide services to satisfy some particular needs.
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  • 84
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    Compel 17 (1998), S. 347-351 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: This paper tests the eddy current analysis methods based on TEAM benchmark model, evaluates the engineering effectiveness of the eddy current codes through product-based test models, and proposes an engineering-oriented loss solver to deal with the eddy current loss problems concerning the core tie-plates in large power transformers.
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  • 85
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    Compel 17 (1998), S. 741-748 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Dynamic non-linear circuits driven by DC voltage and current sources are considered in the paper. The problem of identification of asymptotically stable equilibrium states is analyzed. The circuits are studied where there is a one-to-one correspondence between each operating point of a DC model of a dynamic circuit and equilibrium state of the dynamic circuit. A method is developed, based on quantities concerning resistive circuits only, enabling us to select some of the operating points being asymptotically stable equilibrium states. It is shown that these operating points are asymptotically stable equilibrium states of some class of dynamic circuits which differ one from another in characteristics of the capacitors and inductors. The approach is illustrated by a numerical example.
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  • 86
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    Compel 18 (1999), S. 38-42 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: By using the central limit theorem, it is possible to consider the Fourier's transform of a stochastic process with independent increments as a Gaussian random variable of which the mathematical expectation and the variance are respectively integrals of the mean and the variance of this process. One can then use this result to analyze the statistical properties of linear feedback systems in the frequency domain, that is to say in terms of transfer functions. The advantage of this approach is that one can deal with linear systems subject to squared white noises, in a very simple manner.
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  • 87
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    Compel 18 (1999), S. 84-94 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: This paper describes an efficient reduced-order method for the analysis of cylindrical dielectric resonators with an inhomogeneous dielectric medium. The field equations are formulated using the Laplace-domain finite element method and are reduced to lower-order models using the complex frequency hopping (CFH) technique. CFH is a moment matching technique which has been used successfully in the circuit simulation area for the solution of a large set of ordinary differential equations. The proposed technique is faster than the conventional approach by one to three orders of magnitude. The results are compared with those of other numerical methods available in the literature.
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  • 88
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    Notes: Electrical potentials in a junction field transistor can be calculated using a simplified model based on a complete depletion assumption. This gives rise to a free boundary problem. We show here how we can approximate this problem with a quasi-variational inequality technique and the shape optimization method. A detailed analysis of these methods is presented. Using some numerical experiments we compare our results with the solution of the discrete drift-diffusion system, accomplished with a Gummel-like algorithm. The numerical results suggest that the methods proposed here work successfully and that the shape optimization technique provides a reasonably free boundary without excessive iterations.
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  • 89
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    Compel 18 (1999), S. 215-224 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The paper presents an extension to previous work on modelling AC losses in high-temperature superconducting tapes as a highly non-linear diffusion process. Following successful formulation for a bulk superconductor the presence of silver in a tape has now been included, using a "sandwich" model, to represent more realistically the practical arrangement. The results of the extended 1-D model are included and a new 2-D scheme is described using finite difference formulation. Effects of non-linearity are emphasised.
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    Compel 18 (1999), S. 361-371 
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    Notes: Several second order edge elements have been applied to solving magnetostatic problems. The performances of these elements are compared through an example of magnetic circuit. In order to ensure the compatibility of the system equations and hence the convergence, the current density is represented by the curl of a source field. This avoids an explicit gauge condition which is cumbersome in the case of high order elements.
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  • 91
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    Compel 18 (1999), S. 422-435 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: In this paper a method is presented for an efficient solution of the direct problem (find the scattered field for a given thin crack and driving field) in the time domain. This is a fundamental step in any non destructive evaluation problem. Two different approaches, one in the time domain and the other based on Fourier analysis, are used and compared with reference to a configuration for which some experimental results are available. The advantages and drawbacks of the two approaches are briefly discussed.
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  • 92
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    Compel 15 (1996), S. 40-56 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The electric stress profiles of a needle-plane electrode system used in the laboratory for investigation of tree initiation and growth have been studied. Results from analytical solution based on a hyperboloid shaped needle tend to differ from those from experiments. One reason is that in practice it is difficult to produce a needle of such a shape. Moreover, researchers have used various shaped needles for their tests. Presents the effects of these needle parameters on the electric stress profile. To simulate the presence of space charge, examines two models, i.e. spherical and cylindrical regions around the tip. For simplicity, the space charge was assumed to be uniformly distributed in the confined region. Results show that space charges can enhance or reduce the electric stress adjacent to the needle tip depending on the nature of the applied voltage.
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  • 93
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    Compel 15 (1996), S. 73-85 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Discusses an analytical solution for the capacitance of the circular microstrip patch resonator. Shows that the electrostatic problem can be formulated as a system of dual integral equations, which is reduced to a single Fredholm integral equation of the second kind with a continuous kernel. Discusses the solution of this new integral equation in a certain range of the parameters, and derives some useful formulas for the capacitance. Finally, gives plots of the capacitance in a wide range of the relative permittivity.
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    Compel 15 (1996), S. 22-46 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Charge iteration is an iterative procedure for the finite element computation of unbounded electrical fields, created by voltaged conductors. It makes use of a fictitious boundary, enclosing all the conductors, on which the electrical potential is first guessed and then iteratively improved according to the charge lying on the conductor surfaces. Highlights the theoretical foundations of the procedure outside any numerical context. From this useful insight, obtains a model which can aid the user in utilization of the numerical version of the procedure.
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  • 95
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    Compel 17 (1998), S. 116-120 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The calculation results of the 3D magnetic field in a reactor are examined using the computer packages TRACAL3 as well as OPERA3D. The first own package is based on the boundary integral equations (BIE) and the second commercial package is deduced from finite elements method (FEM). As an example, the magnetic flux density components were calculated. For the reactors with large air gaps, the numerical results obtained by BIE and FEM are relatively close.
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  • 96
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    Compel 17 (1998), S. 128-134 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: In the paper, attention is focused on a class of single-phase transformers that are employed when a high-voltage withstand test is required for verifying the quality of the dielectric insulation of a given component. The HV winding of this kind of transformer is made up of several layers, characterized by height that decreases along with the increase of the voltage profile in order to keep the distance between winding and ground within acceptable limits. Therefore, the designer of such devices is mainly concerned with the shaping of the HV winding; starting from a tentative configuration, he has to find the winding shape such that the electric breakdown cannot occur, at the same time keeping the volume of oil and active materials as small as possible. Traditionally, the design is developed by means of a trial-and-error approach based on a sequence of field analyses, varying a design variable at a time; the paper shows how the design problem can be solved more efficiently by optimizing the profile of the winding in an automatic way.
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  • 97
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    Notes: In analysing coupled electromagnetic thermal behaviours in electrical devices one of the main difficulties is related to the uncertainties of thermal parameters. The authors present, in this work, a technique using the method of experimental designs for the identification of thermal parameters necessary for a coupled finite element model analysing the magneto-thermal behaviour of an electromagnetic device.
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    Compel 17 (1998), S. 337-341 
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    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: The heating of flat metal products has an increasing importance in different technical applications. One of the most advanatageous heating methods is induction heating. The heat is generated within the workpiece itself. It provides high power densities and high productivity. For induction heating of flat metal products two methods are applied: the longitudinal and the tranverse magnetic flux heating. In our case we have applied tranverse flux heating. This paper presents certain results of electromagnetic field obtained by means of finite element method and transient thermal field obtained by finite difference method. The analysis is made by simulating the heating phenomenon while the sophisticated software has been employed.
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  • 99
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    Notes: In this paper the influence of the neutral in the thermal performance of a three-phase squirrel cage induction motor fed by asymmetrical supply voltages is studied and analysed. A 2D finite element formulation was used to solve the steady-state heat transfer problem. The eddy currents in the rotor bars were evaluated using a combined 3D finite element approach with analytical expressions. The numerical solutions are compared with measured experimental results obtained in laboratory tests for two load conditions and two unbalanced power supply situations with and without the neutral wire connected.
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  • 100
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    Notes: Experience and exploring the linear AC and DC actuators confirm the necessity of the computation of forces distribution as the step preceding their optimal design. This paper expresses an approach to computations of different forces of low-voltage linear actuators acting on both mechanical and/or electrical parts. The computations are based on magnetic coenergy concept associated with virtual work method and simulated by step displacement of the armature from the total open through total closed position. The magnetic coenergy is numerically computed through the flux-linkage approach, where the magnetic field distribution is obtained by applying the finite element method in 3D-domain.
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