Online ISSN
1751-8830
Print ISSN
1751-8822
IET Science, Measurement & Technology
Volume 1, Issue 1, January 2007
Volumes & issues:
Volume 1, Issue 1
January 2007
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- Author(s): L. Davenport
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, page: 1 –1
- DOI: 10.1049/iet-smt:20079031
- Type: Article
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- Author(s): O. Bíró ; S. Außerhofer ; G. Buchgraber ; K. Preis ; W. Seitlinger
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 2 –5
- DOI: 10.1049/iet-smt:20060031
- Type: Article
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Direct current (DC) flowing through the earthed neutrals of transformer windings causes a DC component in the magnetising current. Owing to non-linearity, the waveform of this current is strongly distorted. A method based on the finite element analysis of a transformer is presented that is capable of predicting the waveform of the magnetising current with the voltage of the winding as well as the magnitude of the DC bias given. The relationship between the flux linkage of the winding and the value of the magnetising current is determined, with static conditions assumed. With the aid of this flux–current curve, the dependence of the waveform and thus of the DC component of the magnetising current upon the bias flux is established. Hence, the flux bias yielding the given DC component is obtained by suitable iterative techniques, arriving at the waveform of the magnetising current with the prescribed DC value. Measurement of the current waveform at various voltages and DC bias has been carried out on a single phase transformer. The computed waveforms agree well with the measured ones. - Author(s): S. Koch ; H. De Gersem ; T. Weiland
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 6 –11
- DOI: 10.1049/iet-smt:20060039
- Type: Article
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In many technical devices such as transformers and electrical machines, large differences in geometric dimensions are observed. As a consequence, the generation of a 3D computational grid for the whole device leads to unacceptably large numbers of elements or can even fail. In addition to the commonly applied cartesian or cylindrical symmetries of the overall geometry, the model can be subdivided into parts featuring translational or cylindrical symmetries. Such parts are discretised separately, accounting for the local symmetry, and are then combined with the surrounding 3D model. Excitations and boundary conditions of the submodels are not necessarily symmetric but are expected to be smooth in the direction of the symmetry. Then, the field distribution at the interface is well approximated by a set of spectral elements along the dimension of symmetry. Coupling between the model parts is carried out by means of Lagrange multipliers. A single-phase transformer with thin insulation sheets is taken as an example to illustrate the proposed hybrid discretisation. The cross-section of the cylindrically symmetric part containing thin sheets, is represented by a fine 2D finite-element mesh so that all the geometrical details can be resolved, and the rest of the structure is discretised by a 3D mesh. Nevertheless, a fully 3D field distribution is calculated in all model parts. Only a small number of harmonic functions is needed to account for the azimuthal field variation at the cylindrical interface. Hence, the number of unknowns in the numerical model is reduced significantly, while a high level of accuracy is maintained. - Author(s): O.A. Mohammed ; S. Liu ; Z. Liu
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 12 –16
- DOI: 10.1049/iet-smt:20060030
- Type: Article
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An FE-based physical phase variable model is proposed for PM machines under stator short-circuit faults. The parameters of the proposed model, inductances and back EMFs are determined using the FE-circuit coupled computation of the machine under the same type of fault. The parameters obtained include information on the fault location and the number of turns involved, in addition to the space harmonics and the effects of stator saturation. The FE-based phase variable model that has been developed is verified through comparison with the FE model. The significance of the work is that it introduces a feasible procedure to build a physically accurate and computationally fast phase variable model for PM machines under stator short-circuit fault conditions. Such a model is useful for the study of fault diagnosis and prognosis. - Author(s): K.R. Geldhof ; T.J. Vyncke ; F.M.L.L. De Belie ; L. Vandevelde ; J.A.A. Melkebeek ; R.K. Boel
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 17 –20
- DOI: 10.1049/iet-smt:20060026
- Type: Article
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The use of embedded Runge–Kutta methods for the time-domain simulation of a dynamic finite element model of a switched reluctance motor is discussed, along with the features of embedded Runge–Kutta methods for the numerical solution of this model. It is shown that step size control and interpolator polynomials can be used to take accurately into account the discrete effects of current control and a pulse width modulated supply on the drive dynamics. - Author(s): T.G.D. Hilgert ; L. Vandevelde ; J.A.A. Melkebeek
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 21 –24
- DOI: 10.1049/iet-smt:20060018
- Type: Article
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A method is proposed to calculate the vibrations of magnetised electrical steel due to magnetic forces and magnetostriction. As an example, calculations have been carried out on two-pole and four-pole induction machines (IMs) with no load. If only the main components of the vibrations are considered, analysis of the results reveals that, in the case of the two-pole IM, the contributions of the magnetic forces and the magnetostriction add up, whereas, in the case of the four-pole IM, the respective contributions are subtracted. It is concluded that it is not justified to assume that magnetostriction in all cases will increase the vibrations of electromechanical devices. - Author(s): R.V. Sabariego and P. Dular
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 25 –29
- DOI: 10.1049/iet-smt:20060028
- Type: Article
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The paper deals with a new finite element scheme for non-destructive eddy-current testing (ECT) problems involving multiply connected test pieces and differential probes. It concerns a perturbation technique applied to the magnetodynamic h−phis formulation. The unperturbed field (in the absence of the flaw) is conventionally computed in the complete domain. The source of the perturbation problem is then determined by the projection of the unperturbed field in a relatively small region around the defect, the optimum size of which depends on the working frequency. The discretisation of this reduced domain is well adapted to the size of the defect and chosen independently of the dimensions of the excitation probe and the specimen under study. At a discrete level, the voltage change is efficiently computed by integration only over the defect and a layer of elements in the reduced domain that touches the defect's boundary. The accuracy of the proposed perturbation model is illustrated by comparison of the results obtained for different dimensions of the reduced domain with those achieved in the conventional way. The considered test case involves a differential probe scanning the outer surface of a metal tube for the detection of through-wall cracks. - Author(s): D.-H. Kim ; J.K. Sykulski ; D.A. Lowther
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 30 –36
- DOI: 10.1049/iet-smt:20060024
- Type: Article
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The paper deals with two types of optimisation problem: optimised source distribution and the shape optimum design, using continuum design sensitivity analysis (CDSA) in combination with standard electromagnetic (EM) software. Fast convergence and compatibility with existing EM software are the distinctive features of the proposed implementation. To verify the advantages and also to facilitate understanding of the method itself, two design optimisation problems have been tested using both 2D and 3D models: the first is an MRI design problem related to finding an optimum permanent magnet distribution, and the second is a pole shape design problem to reduce the cogging torque in a BLDC. - Author(s): G. Hawe and J. Sykulski
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 37 –47
- DOI: 10.1049/iet-smt:20060035
- Type: Article
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The high computational cost of evaluating objective functions in electromagnetic optimum design problems necessitates the use of cost-effective techniques. The paper discusses the use of one popular technique, surrogate modelling, with emphasis placed on the importance of considering both the accuracy of, and uncertainty in, the surrogate model. After a brief review of how such considerations have been made in the single-objective optimisation of electromagnetic devices, their use with kriging surrogate models is investigated. Traditionally, space-filling experimental designs are used to construct the initial kriging model, with the aim of maximising the accuracy of the initial surrogate model, from which the optimisation search will start. Utility functions, which balance the predictions made by this model with its uncertainty, are often used to select the next point to be evaluated. In this paper, the performances of several different utility functions are examined, with experimental designs that yield initial kriging models of varying degrees of accuracy. It is found that no advantage is necessarily achieved through a search for optima using utility functions on initial kriging models of higher accuracy, and that a reduction in the total number of objective function evaluations can be achieved if the iterative optimisation search is started earlier with utility functions on kriging models of lower accuracy. The implications for electromagnetic optimum design are discussed. - Author(s): P. Ingelström ; V. Hill ; R. Dyczij-Edlinger
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 48 –52
- DOI: 10.1049/iet-smt:20060025
- Type: Article
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V-cycle and non-standard W-cycle versions of a multiplicative Schwarz preconditioner based on hierarchical basis functions are presented. It is used together with a Krylov subspace method to efficiently solve the linear system that results from higher-order finite element (FE) discretisations of time-harmonic Maxwell equations. A recently developed hierarchical basis for H(curl)-conforming (vector-valued and tangentially continuous) FE spaces on tetrahedral meshes is also briefly presented. On this basis, a certain amount of orthogonality between basis functions of different orders is obtained through the requirement that the Nédélec interpolation of higher-order basis functions vanishes in lower-order FE spaces. Numerical experiments are used to show the good performance of the presented schemes. In these experiments, the performance obtained with the presented basis is compared with the performance obtained by several other hierarchical bases found in the literature. For third-order elements, it is observed that most bases give very similar performance and that the V-cycle preconditioner typically requires about 30% more computing time than the W-cycle one. For fourth-order elements, the new basis combined with the non-standard W-cycle preconditioner leads to the best performance. The computing times for the other combinations are about 40% longer, at best. - Author(s): B. Doliwa ; H. de Gersem ; T. Weiland ; T. Boonen
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 53 –56
- DOI: 10.1049/iet-smt:20060036
- Type: Article
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An optimised low-frequency solution algorithm is proposed that reduces the electromagnetic wave equation to a small number of scalar potential problems. The latter can be solved using black-box algebraic multigrid solvers. Within the framework of the finite integration technique, the reduction of the wave equation is accomplished by tree/cotree decompositions of primary and dual grids, which allow for highly efficient solutions of Ampere's and Faraday's equations. The example of a ferrite-loaded accelerator component demonstrates that the scheme is much more efficient than the direct approach using Krylov subspace solvers. - Author(s): K.W.A. Van Dongen ; C. Brennan ; W.M.D. Wright
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 57 –62
- DOI: 10.1049/iet-smt:20060023
- Type: Article
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The paper describes a reduced forward operator for solving electromagnetic scattering problems using a volume integral equation in conjunction with a conjugate gradient fast Fourier transform scheme. The reduction is obtained by decoupling of the interaction between the locations in the spatial computational domain at which there is non-zero contrast and those positions at which there is zero contrast. The decoupling is achieved by multiplication of the kernel by a diagonal matrix whose entries reflect the presence or absence of contrast at the associated point. Analysis supported by numerical experiments shows that the conjugate gradient algorithm applied to the reduced system converges more rapidly than when it is applied to the original system. - Author(s): F. Rapetti and A. Bossavit
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 63 –66
- DOI: 10.1049/iet-smt:20060022
- Type: Article
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Low-order Whitney forms are widely used for electromagnetic field problems. Higher-order ones are increasingly applied, but their development is hampered by the complexity of the generation of element basis functions and of the localisation of the corresponding degrees of freedom on the mesh volumes. The paper aims to give a geometrical localisation of the degrees of freedom associated with Whitney forms of a polynomial degree higher than one. A conveniently implementable basis is provided for these elements on simplicial meshes. As for Whitney forms of degree one, the basis is expressed only in terms of the barycentric co-ordinates of the simplex. - Author(s): A. Nicolet and F. Zolla
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 67 –70
- DOI: 10.1049/iet-smt:20060042
- Type: Article
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The purpose of the paper is to propose an efficient method to compute propagation modes in helicoidal waveguides. An helicoidal system of co-ordinates is introduced to define the structure and to set up the problem. These co-ordinates, albeit non-orthogonal, preserve the translational invariance in a way that allows a two-dimensional finite element model similar to that of classical straight waveguides. - Author(s): A.R. Ruddle
- Source: IET Science, Measurement & Technology, Volume 1, Issue 1, p. 71 –75
- DOI: 10.1049/iet-smt:20060013
- Type: Article
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Predicted 3D electromagnetic field distributions from TLM models of two vehicle-mounted antenna installations are compared with 2D measurements for similar systems over four horizontal planes. Sample qualitative (visual) comparisons provide useful insights into the sources of some of the differences between the models and the measurements. Quantitative measures show that these differences are within the measurement uncertainty for more than 83% of the points for a roof-mounted antenna, and for more than 70% for a wing-mounted case. These results are considered to be excellent, given the known disparities between the measured and simulated systems.
Editorial: Selected papers from CEM 2006
Prediction of magnetising current waveform in a single-phase power transformer under DC bias
Hybrid finite-element method for discretising cylindrically symmetric parts in electrotechnical models
FE-based physical phase variable model of PM synchronous machines under stator winding short circuit faults
Embedded Runge–Kutta methods for the integration of a current control loop in an SRM dynamic finite element model
Numerical analysis of the contribution of magnetic forces and magnetostriction to the vibrations in induction machines
Perturbation technique for the finite element modelling of differential probes in non-destructive eddy-current testing
Design optimisation of electromagnetic devices using continuum design sensitivity analysis combined with commercial EM software
Considerations of accuracy and uncertainty with kriging surrogate models in single-objective electromagnetic design optimisation
Comparison of hierarchical basis functions for efficient multilevel solvers
Optimised electromagnetic 3D field solver for frequencies below the first resonance
Reduced forward operator for electromagnetic wave scattering problems
Geometrical localisation of the degrees of freedom for Whitney elements of higher order
Finite element analysis of helicoidal waveguides
Validation of predicted 3D electromagnetic field distributions due to vehicle-mounted antennas against measured 2D external electric field mapping
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