ALBERT

Notes: Purpose - The aims of the paper are to improve the dynamic response of an induction motor based position servo system and to remove the chattering problem in the sliding mode control theory by using fuzzy logic principles. The obtained results are also compared with conventional sliding mode controller to show its performance. Design/methodology/approach - The main method used for the research is to form a thin boundary layer neighboring the switching surface by using fuzzy logic. The sliding mode control law is inherently discontinuous naturally. Therefore, there are some difficulties such as so many switches occurring between the control bounds, which cannot be carried out by real controllers. Therefore, fuzzy logic is used in the thin boundary layer to determine the control signal current. Thus, the chattering is eliminated. Findings - The results show that the designed controller has superior performance. But, there are also some difficulties. It is difficult to obtain fuzzy rules. The rules can be obtained by using genetic algorithms without expert's knowledge. However, sliding surface slope C can be optimized to increase system's dynamic performance. Originality/value - A new boundary layer consisting of the fuzzy rules in the sliding mode control is formed.

Notes: Purpose - Nonlinear dynamical systems may, under certain conditions, be represented by a bilinear system. The paper is concerned with the construction of the controllability and observability gramians for the corresponding bilinear system. Such gramians form the core of model reduction schemes involving balancing. Design/methodology/approach - The paper examines certain properties of the bilinear system and identifies parameters that capture important information relating to the behaviour of the system. Findings - Novel approaches for the determination of approximate constant gramians for use in balancing-type model reduction techniques are presented. Numerical examples are given which indicate the efficacy of the proposed formulations. Research limitations/implications - The systems under consideration are restricted to the so-called weakly nonlinear systems, i.e. those without strong nonlinearities where the essential type of behaviour of the system is determined by its linear part. Practical implications - The suggested methods lead to an improvement in the accuracy of model reduction. Model reduction is a vital aspect of modern system simulation. Originality/value - The proposed novel approaches for model reduction are particularly beneficial for the design of controllers for nonlinear systems and for the design of radio-frequency integrated circuits.

Notes: Purpose - This paper aims at developing a computational technique to take account of the laminated nature of iron cores when computing their eddy current losses. Design/methodology/approach - A method is presented to compute three-dimensional eddy current distributions in laminated media by means of the finite element method. In a first step, the laminated medium is assumed to have an anisotropic conductivity with zero (or very low) value in the direction normal to the laminations. In a second step, the eddy currents within the laminates are computed by solving the quasistatic electromagnetic field individually in each sheet. In these essentially two-dimensional analyses, the boundary conditions are taken from the three-dimensional field distribution determined in the first step. Findings - Comparisons with results obtained from a finite element model taking account of each laminate prove the validity of the method. Research limitations/implications - The method is presented for linear media only. Taking account of nonlinearity is an important future topic. Originality/value - Taking account of the laminations by treating the magnetic field distribution obtained from a homogenised model is a novelty of potential benefit to researchers developing methods of loss computation in laminated media.

Notes: Purpose - Characterisation and use of dielectric materials with high permittivity are one of the most developed areas of research in microwave circuit simulation. This is mainly because of their various applications in VHF/UHF and microwave frequencies (correlators, instrumentation systems, ...). The primary virtue of high-dielectric substrates for microwave circuits is the reduced size. Since the high dielectric microstrip line also exhibit low loss and useful impedance range, this class of circuits will undoubtedly find wide applications in microwave integrated circuitry. Design/methodology/approach - Owing to the complexity of the electromagnetic problem, numerical methods become an indispensable tool for analysis and modeling of electromagnetic structures. They are the basis to set-up computer-aided design (CAD) packages. These models must be accurate, reliable, easily extracted and need limited computational requirements. Since there was a demand for a model able to describe these parameters accurately, an extension of the spectral domain approach (SDA) is proposed for microstrip lines with high permittivity. The analysis is based on the solution of a system of algebraic equations, which are derived from Galerkin's technique in the spectral domain. Findings - Analytical expressions are deduced by curve-fitting techniques. These expressions can be easily implemented in a CAD simulation tool to design wireless communication components. In this paper, we have developed accurate and suitable general expressions for characteristic parameters for a wide range of ?r between 1 and 500. The computed results were compared to those available in the literature when possible. In order to validate our models for high values of dielectric constant (128?〈??r〈500), neural models were generated for the characteristic impedance and effective permittivity. A very good agreement is demonstrated. Originality/value - The originality of this paper consists on the development of design formulas to characterise the microstrip lines with high dielectric constant substrate. Closed form equations are almost non-existent in the technical literature since the available design formulas have been developed only for dielectric media value ?r not exceed 128.

Notes: Purpose - The investigation of the efficiency of optimisation technique based on approximation of objective function by multiquadric (MQ) function, used for induction heating devices was the aim of the paper. Design/methodology/approach - The optimisation package based on Matlab language and using Flux2D commercial program for calculation of electromagnetic and thermal fields was built. It allows the use of different optimisation techniques for induction heating devices, e.g. based on MQ function approximation. In the paper two algorithms of approximated points generating have been tested. Findings - The efficiency of MQ optimisation method strongly depends on the applied algorithm of approximated point generating. To ensure high efficiency of MQ optimisation method, the stochastic element of the algorithm of approximated point generating should have a significant role. Research limitations/implications - The efficiency of elaborated algorithms of MQ function approximated point generating should be proved in other applications. Practical implications - The efficient optimisation technique of induction heating devices has been proposed. Originality/value - The two new algorithms for generation of MQ function approximated points have been proposed. The paper could be useful for designers of induction heating devices.

Notes: Purpose - To produce a controlled stirring in a low conducting liquid thanks to a new kind of multiphase inductor. Design/methodology/approach - An experimental pilot consisting of a cylindrical salt water pool surrounded by an innovative multiphase inductor configuration, based on the single phase asynchronous motor principle, is setup. The maximum bulk stirring velocities are measured and compared with the estimate by numerical modelling. Findings - Shows the possibility of controlling the stirring of a low conducting liquid thanks to a multiphase inductive system. The corresponding measurement results give a significant bulk velocity of a few centimetres per second. Practical implications - This new kind of multiphase inductor, working with a single phase induction generator, seems a promising way to produce a controlled stirring in low conducting media which cover a large range of induction applications. Originality/value - Such an innovative inductor configuration has already been tested successfully for metal alloys stirring in the middle frequency area. In this paper, an extension of this kind of multiphase inductive system for electromagnetic stirring of low conducting liquids like electrolytes in the high frequency area is presented.

Notes: Purpose - Aims to apply the generalized minimal residual (GMRES) algorithm combined with the fast Fourier transform (FFT) technique to solve dense matrix equations from the mixed potential integral equation (MPIE) when the planar microstrip circuits are analyzed. Design/methodology/approach - To enhance the computational efficiency of the GMRES-FFT algorithm, the multifrontal method is first employed to precondition the matrix equations since their condition numbers can be improved. Findings - The numerical calculations show that the proposed preconditioned GMRES-FFT algorithm can converge nearly 30 times faster than the conventional one for the analysis of microstrip circuits. Some typical microstrip discontinuities are analyzed and the good results demonstrate the validity of the proposed algorithm. Originality/value - In the future, some more efficient preconditioning techniques will be found for the mixed potential integral equation (MPIE) when the planar microstrip circuits are analyzed.

Notes: Purpose - This paper proposes an automatic procedure to characterize discrete source fields. Design/methodology/approach - A technique is developed to characterize curl-conform fields to be used as source fields or non-local basis functions in finite element formulations. A reduced characterization of such fields using curl-conform finite elements is defined. An automatic construction of these curl-conform spaces is proposed. Findings - A reduced characterization of such fields is shown to be convenient for the coupling with complementary reaction fields and for simply and explicitly defining non-local quantities, such as currents in h-conform magnetodynamic formulations. The reduced form rests on the choice of supports for the fields limited to reduced cut spaces associated with cuts making the definition domain simply connected. Originality/value - Develops a procedure to simplify the construction of curl-conform source fields.

Notes: Purpose - To investigate the feasibility of a novel scheme of high-efficiency induction heater for nonmagnetic metal billets which use superconducting coils. Design/methodology/approach - The idea is to force the billet to rotate in a static magnetic field produced by a DC superconducting magnet. Since a static superconducting magnet has no losses, the efficiency of the system is the efficiency of the motor used. In order to evaluate the temperature distribution arising from the field profile produced by a given SC coil configuration, a numerical model, based on an equivalent electric network with temperature-dependent parameters, is developed. Findings - A substantial independence of the shape of the temperature profile on the angular velocity and the value of the uniform magnetic field applied, is observed. A strong temperature gradient is observed in the radial direction in the proximity of the penetration front and in the axial direction at the top and bottom surface of the billet. Small temperature gradient was observed in the central part of the billet. Research limitations/implications - The reported temperature profile is inadequate for an actual extrusion process which is desired to happen at a constant temperature. The appropriate profile along the billet length can be achieved by a suitable axial shaping of the magnetic field, through the optimization of the coil layout, whereas the undesired radial gradient can be reduced by interspacing the rotation with temperature smoothing intervals. Practical implications - The investigation of the profile of applied magnetic field and the heating procedure which allow to achieve the distribution of temperature suitable for the extrusion process can be carried out by using the present model. Originality/value - A high-efficiency induction heater for nonmagnetic metal billets using superconducting coils in a novel scheme is investigated.

Notes: Purpose - On the basis of the maximum entropy principle, seeks to formulate a hydrodynamical model for electron transport in GaAs semiconductors, which is free of any fitting parameter. Design/methodology/approach - The model considers the conduction band to be described by the Kane dispersion relation and includes both G and L valleys. Takes into account electron-non-polar optical phonon, electron-polar optical phonon and electro-acoustic phonon scattering. Findings - The set of balance equation of the model forms a quasilinear hyperbolic system and for its numerical integration a recent high-order shock-capturing central differencing scheme has been employed. Originality/value - Presents the results of simulations of n+?-n-n+ GaAs diode and Gunn oscillator.

Notes: Purpose - Presents a technique based on the development of an artificial neural network (ANN) model for predicting the electromagnetic inference effects on gas pipelines shared right-of-way (ROW) with high voltage transmission lines. Design/methodology/approach - Examines the induced pipeline voltage under different soil resistivity, fault current and separation distance. Findings - The results indicate strong agreement between model prediction and observed values. Originality/value - Demonstrates that the ANN-based model developed can predict the induced voltage with high accuracy. The accuracy of the predicted induced voltage is very important for designing mitigation systems that will increase overall pipeline integrity and make the pipeline and appurtenances safe for operating personnel.

Notes: Purpose - To present a new parallel method for solving differential equations that describe transient states in physical systems. Design/methodology/approach - The proposed speculative method first solves a differential equation with a large integration step to determine initial data for parallel computations in sub-intervals of time, then speculatively computes in parallel solutions in all the sub-intervals with a smaller integration step and finally composes the final solution from the speculatively computed ones. The basic numerical method applied is the well-known Runge-Kutta algorithm. Findings - The speculative method allows important reduction of the computation time of sequential algorithms. The speed-up of the speculative method that we propose, as compared to the sequential execution, depends on the number of sub-intervals that are defined inside the total analysed time interval. The speed-up increases almost linearly with the number of sub-intervals. The good accuracy of computations in the presented example was obtained. Research limitations/implications - The proposed method can be applied to non-linear systems without discontinuity points and to stable systems (i.e. systems insensitive to the selection of initial conditions). Practical implications - The method can be especially applied for long-lasting computations with a slow convergence of state variables values along with the decrease of integration steps. Originality/value - The paper presents an original parallel method for solving differential equations, which significantly speeds up transient states analysis in physical systems.

Notes: Purpose - Developing an efficient second-order integration method of transient analysis of nonlinear dynamic circuits which overcomes the main drawback of the trapezoidal rule. Design/methodology/approach - Dynamic circuits including transistors and operational amplifiers are considered. A new family of two-step, second-order numerical integration algorithms has been developed using a polynomial approximation. Findings - The algorithms have been worked out which are implicit, A-stable and they depend on a parameter which is allowed to be changed during the computation process according to a proposed strategy. Also the variable step-size formula has been derived enabling us to eliminate a restarting procedure. The method has been implemented and tested using several representative circuits. It has been compared, both theoretically and via numerical examples, with the alternative well known algorithms: the trapezoidal rule and the backward differentiation formula of order two. Research limitation/implications - The algorithms developed in the paper are two-step and second-order, consequently the step size cannot be too large and the algorithms are not L-stable. Originality/value - A new family of two-step implicit integration algorithms is developed. It can be useful for the analysis and design of electronic circuits.

Notes: Purpose - To propose a novel method for defect reconstruction in electromagnetic non-destructive testing (NDT). Design/methodology/approach - The inversion method is based on an optimized database that contains the measured signals for some predefined defect prototypes. The database is supported by an anisotropic simplex mesh, which has been generated adaptively in the abstract n-dimensional space, spanned by the model parameters of the defect type. The actual reconstruction reduces to a mesh search and interpolation. The described theory is demonstrated in the paper by a solved NDT test problem. Findings - We have realized that in addition to sole defect reconstruction, the database provides meta-information about the quality of the inversion, the suitability of the chosen defect model parameters, as well as the capabilities of the testing experiment. Research limitations/implications - Defect models having several parameters require a sophisticated mesh generation algorithm, which works in higher dimensions. Originality/value - In the authors' opinion the mesh database approach offers a totally new point of view of a given inverse problem, and may help in the better understanding of its nature.

Notes: Purpose - The definition of a simple model of low frequency magnetic field created by power industrial installations can be approached by using an equivalent source system (ESS). Given a set of measured magnetic field points, the ESS, made by a limited set of current carrying wires or turns, must be placed and supplied in order to fit the measured magnetic field values. An optimisation procedure can be used to define the current values and the location of the ESS which minimize the error between the measured and computed magnetic field values. Design/methodology/approach - A two-step optimal procedure is defined: in the outer step a stochastic optimisation routine is used to drive the geometric control parameters of the ESS while, in the inner step, the current values flowing through the sources are computed to find the minimization of the error with respect to a set of measured magnetic field values. The optimisation procedure is based on an artificial immune system algorithm which focuses on a deep exploration of the search space and gave interesting results both in terms of accuracy and computational efficiency. Findings - The results show that the proposed approach is able to reconstruct the magnetic field created by complex source system and give some accuracy measure on the reconstruction error. The optimisation process carried out also on conductor positions has allowed to find out the location of the real sources in an accurate way, also in presence of measurement errors. Originality/value - The approach proposed uses optimisation procedures to solve the inverse problem of source reconstruction starting by a set of measured magnetic field values. The definition of a simple equivalent source structure, together with an optimisation procedure to set its control parameters, allows to simulate complex magnetic field sources, like power substations or cable systems, in a very efficient and compact way.

Notes: Purpose - The paper highlights the process of electric vehicles optimal design as an inverse problem and presents the global constrained optimization as the best way to solve it. Design/methodology/approach - The electric vehicle optimal design is carried out by a new approach. It consists an electric vehicle design model managed by constrained optimization techniques. It includes sizing models for all drive train components and a vehicle dynamic model build in a new "design way" as an energy-based model using the response surface methodology. The sensitivity of first simple sizing models can be evaluated by the experimental design method, giving information about the most important part of the model that must be improved. Findings - The result shows the superiority of the constrained optimization technique that treats simultaneously the global optimization and the model adjustment. This method of simultaneous resolution is much more powerful than the successive resolution of each subproblem. The proposed "design approach" used for electric vehicle optimal design offer a large potential in the field of the complex systems design. Originality/value - The electric vehicle design process is treated on a vehicle design model based on a design approach. It allows determining the drive train components specifications for imposed vehicle performances, taking into account the dynamic model of the vehicle and all components interactions. Furthermore, considering fine components sizing models, the components can be sized taking into account the whole system behavior in an optimal global design.

Notes: Purpose - Optimisation in electromagnetics, based on finite element models, is often very time-consuming. In this paper, we present the space-mapping (SM) technique which aims at speeding up such procedures by exploiting auxiliary models that are less accurate but much cheaper to compute. Design/methodology/approach - The key element in this technique is the SM function. Its purpose is to relate the two models. The SM function, combined with the low accuracy model, makes a surrogate model that can be optimised more efficiently. Findings - By two examples we show that the SM technique is effective. Further we show how the choice of the low accuracy model can influence the acceleration process. On one hand, taking into account more essential features of the problem helps speeding up the whole procedure. On the other hand, extremely simple auxiliary models can already yield a significant acceleration. Research limitations/implications - Obtaining the low accuracy model is not always straightforward. Some research could be done in this direction. The SM technique can also be applied iteratively, i.e. the auxiliary model is optimised aided by a coarser one. Thus, the generation of hierarchies of models seems to be a promising venue for the SM technique. Originality/value - Optimisation in electromagnetics, based on finite element models, is often very time-consuming. The results given show that the SM technique is effective for speeding up such procedures.

Notes: Purpose - This paper deals with the collaborative design of electromagnetic devices over the internet network. The design is made by both mechanical and electrical engineers. So, the paper tries to show the importance but also constraints to size such a system using a collaborative optimisation process. Design/methodology/approach - The paper compares two approaches in order to size an electromechanical actuator between mechanical and electrical engineers. In the first one, each profession designs its part, and only common constrained are negotiated. This can result in a design process with many iterations. In the second one, electrical and mechanical engineers built together a common model of the structure and a common list of specifications: this allows a global optimisation that is more efficient. Findings - The main result of the paper is that the second approach in which a global model is built between electrical and mechanical engineers is more efficient. Originality/value - The originality of the paper is to explore the problems and difficulties of an optimisation of an electromechanical device between engineers of different culture working together over the internet network.

Notes: Purpose - The purpose of this paper is to obtain a fully analytical model of an eddy current coupler and to use it in a multi-objective optimisation algorithm. Design/methodology/approach - Analytical expressions of device performances are adopted in the objective function and are obtained from a closed solution of the field problem. The optimisation has been carried out by considering both the torque and the momentum of inertia of the object. Two different structures have been considered. Findings - A fully analytical expression of the torque has been obtained for two different geometrical configurations. The optimisation procedure has been used to compare these structures and it is possible to observe that the DSPM performances are better than the SSPM ones. Research limitations/implications - To obtain a closed form of the torque function, the non-linearities of the iron have been neglected. Nevertheless, in the optimisation procedure has been limited the magnetic flux density in the iron core to a feasible value in the linear part of the ferromagnetic characteristic. The thermal effects have been neglected. Pratical implications - In the industry, eddy current couplers can be used as transmission, dampers and brakes. The use of objective functions (OFs) in a closed formulation allows to perform a light optimisation from the point of view of the time computation and to drastically increase the development efficiency. Originality/value - In this paper, a model for computing the electromagnetic behaviour of eddy current couplers is presented. The optimisation of both the torque and the inertia momentum allows to obtain good static and dynamic performances.

Notes: Purpose - The electroencephalography (EEG) source tomography in bio-electromagnetics is to estimate current dipole sources inside the brain from the measured electric potential distribution on the scalp surface. A traditional algorithm is the low-resolution electromagnetic tomography algorithm (LORETA). In order to obtain high-resolution tomography, the LORETA-contracting algorithm is proposed. Design/methodology/approach - The relation between the dipolar current source J at the nodes in source region and the potential U at the observed points on the scalp surface can be expressed as a matrix equation U=KJ after discretization. K is a coefficient matrix. Usually its simultaneous equation is an under-determined system. The LORETA approach is to find out min?BWJ?2, under constraint U=KJ where B is the discrete Laplacian operator matrix, W is a weighting diagonal matrix. Its solution is J=(WBTBW)-1KT{K(WBTBW)-1KT}+U where {}+ denotes the Moore-Penrose pseudo-inverse matrix. The improvement on this approach is to establish an iterative program to repeat LORETA and reduce the number of unknown J quantities in the step i+1 by contracting the source region excluding some extreme little quantities of J given in the step i. The simultaneous equations will gradually turn to a properly determined system or to an over-determined system. Finally, its solution can be obtained by using the least square method. Findings - Repeating to make the low-resolution tomography by contracting the source region, we can get a high-resolution tomography easily. Research limitations/implications - The LORETA-contracting algorithm is based on the assumption that the dipolar current sources inside the brain are sparse and concentrated based on the physiological study of the brain activity. Originality/value - It is new to repeat LORETA combined with the contracting technique. This algorithm can be developed to solve EEG problems of realistic head models.

Notes: Purpose - To design an optimal active shield for the mitigation of the magnetic stray field around an induction heating device. Design/methodology/approach - The active shield consists of several compensation coils in series and generates a counter field opposite to the main field. One extra compensation winding - the "generating compensation winding" (GCW) - is positioned close to the excitation coil and works as the secondary winding of a transformer. The power in this winding is used to drive the other compensation coils (the active shield), which are the load of the transformer. A circuit with passive components is inserted between the GCW and the other compensation coils. The shield is optimal if it achieves a high field reduction, while the energy dissipation is low. By using a genetic algorithm (GA) that minimizes an objective function, the optimization algorithm finds the optimal geometry and the optimal current for the GCW and the other compensation coils. The objective function uses time harmonic and axisymmetric finite element calculations. Findings - The transformer driven active shield reduces the magnetic field effectively. It is cheap and easy to build, but it works well only for one frequency. Research limitations/implications - The shield is sensitive to tuning of the passive circuit and to changes in the frequency of the induction heater. Practical implications - This transformer driven shield is an alternative for the classical active shield with external power supply. Originality/value - An active shield that does not need an external power supply is a cheap solution for the shielding of magnetic fields.

Notes: Purpose - The parameters of axial-field machines are very small compared with the parameters of conventional machines. Different measuring methods are normally used in order to obtain good estimates of the machine parameters. These methods are difficult to perform, costly and time consuming. This paper proposes the use of genetic algorithms to predict the self and mutual inductances of a specific type of axial-field machine, the Torus motor. Design/methodology/approach - The parameter extraction is reformulated as a search and optimization problem in which the only requirement is a set of values of current versus time and an approximate estimate of the parameters. Findings - The predicted machine self and mutual inductances are verified by comparing with several measuring methods and excellent agreement is obtained. Originality/value - Demonstrates that genetic algorithms can predict the self and mutual inductances of the Torus machine automatically with high accuracy.

Notes: Purpose - The purpose of the paper is to present a novel design method for the optimal finite word length (FWL) finite impulse response (FIR) filters. Design/methodology/approach - The design method is based on a parallel tabu search (TS) algorithm which uses the crossover operator of the genetic algorithm. Findings - Three design examples have been presented to show that the proposed method can provide a good solution to the design problem of a FWL FIR filter. In order to show the validity of the proposed method, the performance of the suggested method has been compared to those of widely-used other methods. From the comparison results, it was concluded that the proposed method can be efficiently used for the optimal FWL FIR filter design. Research limitations/implications - The number of examples can be increased and also the performance of the proposed method might be compared to other design methods, apart from those presented in this work, developed for the design of optimal FWL FIR filters. Practical implications - The use of this method produces optimal digital FWL FIR filters with low complexity and therefore provides advantages in the terms of speed and cost. Originality/value - The originality is the application of the parallel TS algorithm described by the authors to the FWL FIR filter design. The work presented in the paper is particularly important for the researchers studying on the design methods for FWL FIR filter design and the applications of these type filters.

Notes: Purpose - To provide a new and simple inverse rotor time constant identification method which can be used to update an indirect rotor field oriented controlled (IRFOC) induction motor algorithm. Design/methodology/approach - Two different equations are used to estimate the rotor flux in the stator reference frame. One of the equations is a function of the rotor time constant, rotor angular velocity and the stator currents. The other equation is a function of measured stator currents and voltages. The equation that uses the voltage and the current signals of the stator serves as reference model, however, the other equation works as an adjustable model with respect to the variation of the rotor time constant. Voltage signals used in the reference model equation are obtained from the measured DC bus voltage and the inverter gating signals. The proposed scheme is verified using a MATLAB/SIMULINK model for two different motors and experimentally using a DSP development tool (MCK 243) supplied by Technosoft S.A. Findings - The proposed estimator was able to successfully track the actual value of the inverse rotor time constant for different load torque and speed operating conditions. Increased oscillations in the estimated inverse rotor time constant appeared at lower speeds (below 10 per cent of rated speed) due to drift in a PI regulator (used at the estimator side), which was tuned under rated operating conditions and using parameters nominal values. Research limitations/implications - This estimation scheme is limited when near zero speed operation is demanded; otherwise it gives a simple and practical solution. A suggested way out of this, is to provide a self-tuning controller that can automatically adjust even for zero speed operation, or to automatically disconnect the estimator and take the most updated value as long as the operating speed is below a predetermined value. Originality/value - This paper presented a new inverse rotor time constant estimator for an IRFOC induction motor application and in conjunction rotor flux was estimated without voltage phase sensors.

Notes: Purpose - This paper presents a novel multiobjective optimal design of three phase induction motor using simulated annealing (SA) technique for minimizing annual material cost and annual loss cost as two objectives. Design/methodology/approach - The design problem of a three-phase induction motor is presented as a nonlinear multicriterion optimization problem on the basis of minimizing the annual cost of the motor. The annual cost referred is the sum of the annual interest and depreciation of motor active material costs, annual cost of active power loss of the motor and the annual energy cost required to supply such power loss. A computer package is built which generates initial values of motor parameters and gives the optimal values of these parameters with more than one objective function and nonviolated constraints. The problem is solved by giving weights which reflect the priority of objective functions. The SA technique is used as a tool to solve the problem. Findings - To verify the validity, the proposed method is applied to a three-phase induction motor design. From the results, it is found that the proposed method is fast and efficient and hence it is useful for multiobjective design of an induction motor. Originality/value - This method is particularly useful in satisfying the needs of motor producer and consumer by prioritizing their needs and finally arriving at a best compromise solution.

Notes: Purpose - To study the magnetic shielding and the losses of non-linear, hysteretic multilayered shields by using fast to evaluate analytical expressions. Design/methodology/approach - In order to evaluate the shield in the frequency domain, the non-linear shield is divided into a sufficient number of piecewise linear sublayers. Each sublayer has a permeability that is constant (space independent) and complex (to model hysteresis). This expression for the permeability is found from the Preisach model by a Fourier transform. Once H is known in the entire shield, analytical expressions calculate the eddy current losses and hysteresis losses in the material. The validity of the analytical expressions is verified by numerical experiments. Findings - In the Rayleigh region, the shielding factor of perfectly linear material is better than the one of non-linear metal sheets, but also the eddy current losses are higher. The results of the optimization show that steel is only a useful shielding material at low frequencies. Research limitations/implications - The analytical method is valid for infinitely long shields and for weak imposed fields in the Rayleigh region. Practical implications - As the analytical expressions can be evaluated very fast (in comparison with slow finite elements models), many magnetic shields can be compared in parametric studies. Originality/value - Analytical expressions exist for the shielding factor and the losses of linear materials. In this paper, the method is extended for non-linear hysteretic materials. The effects of several parameters (material parameters, incident fields parameters) on the shielding and the losses are shown.

Notes: Purpose - To analyze the operating performance of a fuzzy logic control (FLC) based solar energy conversion modular system controlled by a digital signal processor (DSP) microcontroller. Design/methodology/approach - A range of published works relevant to the solar energy conversion modular systems are evaluated and their limitations are indicated in the first section of the paper. The circuit diagram of the panel-boost converter system is described in the second section. In the third section, a neural network model is suggested for the photovoltaic panel and the model is created in the MATLAB/SIMULINK and then combined with other blocks existing in the system. The design of the FLC method is described in section 4. The simulation and experimental results corresponding to the control of the duty-cycle of the converter to set the operating point of the solar panel at the maximum power point (MPP) are given in sections 5 and 6, respectively. Section 7, summarizes the results and conclusions of the study. Findings - The paper suggests a simple dc-dc boost converter controlled by FLC method. The proposed converter model can be used to obtain maximum power from a photovoltaic panel. Research limitations/implications - In preparing this paper, the resources books existing in the library of our university and the resources relative to the solar energy conversion and FLC published in English language and reachable through the internet were researched. Practical implications - The paper suggests a neural network model for a solar panel, which can be used in the simulation of the solar energy panel-boost converter system. The solar energy panel-boost converter system proposed in this study can be used by the researchers who are working in the solar energy conversion area. Originality/value - The suggestion of a neural network model for a solar panel and creation of this model in the MATLAB/SIMULINK environment provides researchers to simulate and to analyze the performance of the solar energy panel-boost converter system using the MATLAB/SIMULINK simulation program. In addition, since the control approach proposed in this paper does not require the information on temperature and solar irradiance that affect the maximum output power, can effectively find the MPP of the solar panel.

Notes: Purpose - Analytical models are often used in the first steps of the design process. They are associated with optimisation methods to find a solution that fulfil the design specifications. In this paper, the analytical model of an electric motor is built and proposed as a benchmark to highlight the optimisation methods the most fitted to analytical models. Design/methodology/approach - This paper studies the optimal design of a brushless DC wheel motor. First, the analytical model is presented. Each equation used for the sizing is described, including the physical phenomenon associated, the hypotheses done, and some precautions to take before computing. All equations are ordered to ease their resolution, due to a specific procedure which is then described. Secondly, three optimisation problems with an increasing number of parameters and constraints are proposed. Finally, the results found by the sequential quadratic method point out the special features of this benchmark. Findings - The constraint optimisation problem proposed is clearly multimodal as shown in the results of one deterministic method. Many starting points were used to initialise the optimisation methods and lead to two very different solutions. Originality/value - First, an analytical model for the optimal design is detailed and each equation is explained. A specific procedure is presented to order all equations in order to ease their resolution. Secondly, a multimodal benchmark is proposed to promote the development of hybrid methods and special heuristics.

Notes: Purpose - To provide a new method and methodology for researches and academic members which can help them to develop scientific work. Design/methodology/approach - The paper presents closed-form expressions for the harmonic components of the space-vector pulsewidth modulated (PWM) waveforms under inverter fault-mode operations. The main method that is used is the Laplace transform and Fourier series expansion theorem. Findings - Provides information about harmonic sources and its influence on the behavior of the induction machine. Practical implications - The calculated harmonics show a very close agreement with measured harmonics from an experimental digital signal processor (DSP) based modulator. It provides a very useful source of theoretical and practical information for scientific and research area. Originality/value - The method is original and has not been published before. The new and original approach is given by the use of the Laplace transform of space-vectors in the complex plane. This will help to understand harmonics which are formed in four-switch voltage source inverter.

Notes: Purpose - To provide an efficient numerical eigenvalue solution for open waveguides with lossy anisotropic materials. Design/methodology/approach - Vector edge elements are used to represent the core of the problem, and an adaptive perfectly matched layer (PML) is used to truncate the surrounding region. The parameters of the PML are allowed to change at each frequency to obtain accurate results using small number of unknowns. Findings - The method is able to solve many configurations, and considerable reduction in mesh size has been reported. In addition, by adapting the solution according to some error criterion, it will be possible to minimize the dependence on human experience and rely more on automated algorithms. Research limitations/implications - There is a need to improve the performance of the adaptive algorithm by building an automatic adaptive procedure that can work without human intervention. Practical implications - A systematic full-wave algorithm for solving practical electromagnetic engineering problems associated with open waveguides, such as planar transmission lines and optical waveguides, using relatively small computer resources. Originality/value - Proposed a new "dimension" of adaptation for PML, besides the classical h-/p-/hp adaptation methods available in literature. Thus, the requirement for smaller computer resources makes this method cost-effective for industry in the design of practical open waveguides.

Notes: Purpose - Focuses on steady state modelling of basic unipolar non-isolated PWM AC line matrix-reactance choppers (MRC). Their single-phase topologies are similar to well-known basic DC/DC converter ones. The MRC are built up through the adaptation of DC/DC converter topologies, which are based on the substitution of self-commutated unidirectional switches by bi-directional ones. Design/methodology/approach - Presents an approach to modelling of the MRC with averaging operator different to the one used in averaged modelling of the DC/DC converters. There is running averaging of each switching period in the proposed approach. Following this, there is a demonstration of the solutions convergence of the state space and averaged state space equations for infinitive switching frequency. Findings - The running averaging of each switching period should be used if averaged state space method is applied to the analysis of presented choppers. A circuit averaged model build-up procedure of the presented choppers is the same as for the DC/DC ones. Originality/value - Presents a quantitative assessment of accuracy for the averaged models of the presented MRC for finite switching frequency.

Notes: Purpose - This paper describes models of micro-turbines and fuel cells, which can be used in stability studies. Design/methodology/approach - The plants models derived are based on the main equations. These models are developed in the Laplace domain and transient simulation is done using a software developed based on the MATLAB package. Findings - The micro-source is capable of providing effective load-following service in the distribution system. However, the results also show that the micro-source is not an uninterruptible power supply and does not protect the load from voltage instability while in grid-connect mode. When a micro-turbine plant is connected to a point where it gives support to a load in fault conditions, the lower the inertia of micro-turbine plant, the greater is the destabilizing tendency for faults in the distribution system. On the other hand, transient stability is enhanced with aid of the SOFC inverter. Originality/value - The effects of these micro-sources on the network performance are shown and a distribution system embedded with the micro-sources is used as an example. Finally, transient stability and voltage stability of the system are investigated.

Notes: Purpose - To introduce a Whitney-element based coupling of the Finite Element Method (FEM) and the Boundary Element Method (BEM); to discuss the algebraic properties of the resulting system and propose solver strategies. Design/methodology/approach - The FEM is interpreted in the framework of the theory of discrete electromagnetism (DEM). The BEM formulation is given in a DEM-compatible notation. This allows for a physical interpretation of the algebraic properties of the resulting BEM-FEM system matrix. To these ends we give a concise introduction to the mathematical concepts of DEM. Findings - Although the BEM-FEM system matrix is not symmetric, its kernel is equivalent to the kernel of its transpose. This surprising finding allows for the use of two solution techniques: regularization or an adapted GMRES solver. Research limitations/implications - The programming of the proposed techniques is a work in progress. The numerical results to support the presented theory are limited to a small number of test cases. Practical implications - The paper will help to improve the understanding of the topological and geometrical implications in the algebraic structure of the BEM-FEM coupling. Originality/value - Several original concepts are presented: a new interpretation of the FEM boundary term leads to an intuitive understanding of the coupling of BEM and FEM. The adapted GMRES solver allows for an accurate solution of a singular, unsymetric system with a right-hand side that is not in the image of the matrix. The issue of a grid-transfer matrix is briefly mentioned.

Notes: Purpose - To provide a validation of a three-dimensional (3D) macroscopic model for superconductors comparing numerical to experimental AC losses of a BSCCO-2223 tape subject to an orthogonal magnetic field and a transport current. Design/methodology/approach - We solve in 3D geometries the eddy current problem in presence of superconductors, represented by a power-law characteristic rewritten into a variational form. An integral formulation of the magneto-quasistatic Maxwell's equations is used. The solution of the problem is found by an unconstrained minimization of a suitable functional. The numerical results on AC losses computation are compared to experimental data. Findings - The agreement between numerical and experimental data is good in a wide range of currents and magnetic fields. Research limitations/implications - The magnetic field is assumed to be orthogonal to the tape. Different incidence angles should be taken into account. Practical implications - It is possible to extend the range of validity of the engineering formulae for AC losses used in the work. Originality/value - The paper provides a validation of a numerical code against experimental results: this is always challenging in the field of applied superconductivity.

Notes: Purpose - The aim of the present work is to find an efficient solution concerning the computational effort of quasi-static electric field (QSEF) problems involving anisotropic conductivity and permittivity in the frequency domain. Design/methodology/approach - Numerical simulations are carried out with tetrahedral nodal finite elements of first- and second-order and with Withney elements. The solution of the boundary value problem with the aid of the electric scalar potential approximated by nodal finite elements is compared with those by the electric current vector potential represented by edge finite elements. Findings - The simulation with an electric current vector potential approximated by the edge elements of first-order prevail over that by the electric scalar potential approximated by nodal elements of second-order concerning the memory requirements and the computation time at comparable accuracy. Originality/value - The application of edge finite elements to solve QSEF problems considering an anisotropic complex conductivity in 3D.

Notes: Purpose - To establish a statistical formulation of robust design optimization and to develop a fast optimization algorithm for the solution of the statistical design problem. Design/methodology/approach - Existing formulations and methods for statistical robust design are reviewed and compared. A consistent problem formulation in terms of statistical parameters of the involved variables is introduced. A novel algorithm for statistical optimization is developed. It is based on the unscented transformation, a fast method for the propagation of random variables through nonlinear functions. The prediction performance of the unscented transformation is demonstrated and compared with other methods by means of an analytical test function. The validity of the proposed approach is shown through the design of the superconducting magnetic energy storage device of the TEAM workshop problem 22. Findings - Provides a consistent formulation of statistical robust design optimization and an efficient and accurate method for the solution of practical problems. Originality/value - The proposed approach can be applied to all kinds of design problems and allows to account for the inevitable effects of tolerances and parameter variations occuring in practical realizations of designed devices.

Notes: Purpose - Proposes a non-negative matrix factorization method. Design/methodology approach - Presents an algorithm for finding a suboptimal basis matrix. This is controlled by data cluster centers which can guarantee that the coefficient is very sparse. This leads to the proposition of an application of non-matrix factorization for blind sparse source separation with less sensors than sources. Findings - Two simulation examples reveal the validity and performance of the algorithm in this paper. Originality/value - Using the approach in this paper, the sparse sources can be recovered even if the sources are overlapped to some degree.

Notes: Purpose - This paper deals with closed-loop control of a switched reluctance generator (SRG). Design/methodology/approach - The control objective when generating is to maintain the dc link voltage at the required value while achieving maximum efficiency. Three possible control schemes are presented and their performance is examined by testing on an experimental 12/8 three-phase SRG. Findings - A very simple control scheme that requires no prior characterisation of the SRG, an approach based on the use of an inverse machine model and finally, a control scheme that is aimed at achieving optimal efficiency are described and experimental results for all three are presented. Research limitations/implications - The inverse machine model control scheme and the optimal efficiency control scheme require operation at a constant voltage reference for accurate operation (although this is the case for many generator applications). Possible future research might include the expansion of these control schemes to operation with a variable voltage reference. Practical implications - The importance of maximising efficiency is emphasised with a clear method of deriving the optimal efficiency firing angles described. Originality/value - This paper provides a good overview of SRG operation through the experimental implementation of three separate closed-loop voltage control schemes, each of which is described in detail.

Notes: Purpose - The interface between two conducting fluids in a magnetic fluid dynamics (MFD) problem was identified by means of external magnetic field measurements. Genetic algorithms (GA) were applied to solve the inverse problem.The principal component analysis (PCA) was used to speed up the process of interface reconstruction. Design/methodology/approach - With respect to the experimental results we have designed a general technique for mode identification and/or interface reconstruction. Two main procedures are available to solve the inverse problem, the full interface reconstruction and the principle component analysis (PCA) mode. In the case of full reconstruction, it can be decided whether an algorithm for fast identification of the dominant modes applying a FFT module should be performed or not. The full interface reconstruction applies stochastic optimization methods ((GA) or evolution strategies (ES)) for the estimation of the interface shape characteristics. The main goal of the PCA mode is to find the dominant mode of the interface shape and its amplitude. The PCA mode is realized by means of stochastic optimization methods (GA, ES) and a simple direct searching (DS) using the golden section technique. Findings - PCA with GA procedure enables the identification of the dominant mode of the interface shape between two conducting fluids with sufficient accuracy for simulated magnetic fields. Time of identification is strongly reduced due to a redefinition of the genotype representations in the PCA mode. Accuracy of reconstruction depends on the noise level, i.e. signal to noise ratio and a geometrical model used in the reconstruction phase. The correlation between the noise level and values of cost function for identified modes has been found if a proper geometry modelling is applied. Originality/value - The paper describes a new, fast technique for solving an inverse field problem of a MFD problem where the interface between two conducting fluids has to be identified using a magnetic field tomography measuring system.

Notes: Purpose - As well known, in the finite element method, the calculation and the location of the elements of the matrix C of the coefficients requires a lot of calculation times and memory employment especially for 3D problems. Besides, once the matrix C is properly filled, the solution of the system of linear equations is computationally expensive. Design/methodology/approach - The paper consists of two parts. In the first part, to quickly calculate and store only the non-null terms of the matrix of the system, a geometrical analysis on three-dimensional domains has been carried out. The second part of the paper deals with the solution of the system of linear equations and proposes a procedure for increasing the solution speed: the traditional method of the conjugate gradient is hybridized with an adequate genetic algorithm (Genetic Conjugate Gradient). Findings - The proposed geometrical procedure allows us to calculate the non-null terms and their location within the matrix C by simple recursive formulas. The results concerning the genetic conjugate gradient show that the convergence to the solution of the linear system is obtained in a much smaller number iterations and the calculation time is also significantly decreased. Originality/value - The approach proposed to analyze the geometrical space has been turned out to be very useful in terms of memory saving and computational cost. The genetic conjugate gradient is an original hybrid method to solve large scale problems quicker than the traditional conjugate gradient. An application of the method has been shown for current fields generated by grounding electrodes.

Notes: Purpose - This paper presents CoreLab, a sizing environment for electrical devices, based on a new software component standard, ICAR, which offers the possibility of multifaceted components. CoreLab supports the different steps of the sizing procedure of an electrical device by using an optimisation algorithm. It is open, which means that modules can be added to perform new functionalities. Design/methodology/approach - The design of an electrical device has to comply with more and more constraints. In order to integrate and to manage all of these constraints during a design step, the paper proposes a sizing methodology based on an constrained optimisation by using analytical models of the device, and by encapsulating them into software components. Added to these services for the calculation of the sizing model, other services can be useful for the designer during the optimization phase, e.g. the geometry display of the device for each optimisation iteration. In this way, the approach proposes a new software component standard, Interfaces for Component Architecture (ICAR). It offers the possibility of multi-facetted components. The paper also proposes an integrated environment to manage these software components, and their interactions: Core-Lab. These components are then plugged to an optimisation component (algorithm), which manages the different constraints specified by the designer and finds the optimal sizing of the device. Findings - The paper presents the ICAR standard and an environment to manage ICAR components: Core-Lab: the creation of the components (from an analytical model or an existing computation); the projection from one component standard to another; and the composition of components to create a more complex one. Originality/value - The use of software component approach is useful for the sizing of devices. The paper proposes a new standard to support the different aspects of the use of software components during the design of a device: ICAR. Complementary, an open integrated environment is proposed to use these components: CoreLab, but any environment being modified to accept ICAR standard can use ICAR component. So, components can be used in several environments, for example for calculation or optimisation. Components of different types can be gathered together to built a complete application for sizing, e.g. by connection of calculation components (for the sizing model), optimisation component and post-processing components.

Notes: Purpose - Seeks to determine the optimal shape design of an induction heating device. Design/methodology/approach - Presents, through a case study, the optimal shape design of a multiple coil inductor for surface heating. Resorts to a procedure of automated optimal design, based on evolutionary optimisation and processing both continuous-valued and discrete-valued variables. Findings - Demonstrates that it is possible to solve the design problem routinely using an optimisation tool (OptiNet) that is built to work seamlessly with a coupled electromagnetic-thermal simulation. Originality/value - Every design criterion that is likely to be of interest to a designer of industrial applications can be described to the system and optimised in a reasonable time frame.

Notes: Purpose - Aims to present recent activities in experimental investigations and numerical modelling of the induction cold crucible installation. Design/methodology/approach - Temperature and velocity measurements using thermocouples and electromagnetic velocity probes were performed in aluminium melt which was used as a model melt. Measured temperature field and flow pattern were compared with transient 3D calculations based on large eddy simulation (LES) turbulence modelling scheme. Numerical results are in good coincidence with the experimental data. Findings - The modelling results show that only 3D transient LES is able to model correctly these heat and mass transfer processes. Originality/value - It is revealed that transient 3D modelling provides a universal tool for simulating convective heat and mass transfer processes in the entire melt influenced by large scale instabilities in the recirculating flows, which contain several main vortexes of the mean flow.

Notes: Purpose - To use an experimentally calibrated turbulent flow model to determine whether two- and three-phase electromagnetic stirrers provide equivalent stirring when continuously casting steel billets and blooms. Design/methodology/approach - The results obtained in this paper were obtained by using a 3D quasistatic electromagnetic model to obtain the Lorentz forces that act on the liquid steel. A computationally efficient method was used to account for the effect of the conducting fluid motion on the forces. A 3D turbulent flow model that incorporated Reynolds stresses and high order upwinding was used to predict the fluid flow. The model has been calibrated using the experimental data. Findings - The paper shows that for square and rectangular cross section casting moulds, having inside dimensions of 140?×?140?mm and 140?×?196?mm, respectively, a two-phase electromagnetic stirrer consistently produces stirring velocities that are 12-15 percent below those produced by an equivalent three-phase design. Research limitations/implications - The impact on the fluid entering the casting mould through the submerged nozzle has been neglected. The model should be further developed to consider this important factor. Practical implications - A two-phase stirrer is much more compact than the equivalent three-phase design, and since space is at a premium in the vicinity of the casting mould, being able to use a compact design is desirable. The two-phase design was long believed to produce inferior stirring due to the negative impact of electromagnetic space harmonics. This paper shows that for the range of mould dimensions considered in the paper, there is a good trade-off between the compact two-phase design and the slightly lower stirring velocities that result. Originality/value - The paper presents the first quantitative comparison between two- and three-phase electromagnetic stirrers that illustrates, in a practical sense, the stirring effectiveness of each approach. The paper will be of value to users of this equipment.

Notes: Purpose - The comparison of large volumes of complex data resulting from numerical modelling in computational electromagnetics is a demanding task, especially when validating the performance of numerical models against experimental results and testing experimental repeatability. "By-eye" comparisons can lead to inconsistencies and inherent subjectivity. This paper establishes a "visual" benchmark by which comparisons can be made and therefore used to assist in the development of an algorithmic approach to data comparison. Design/methodology/approach - This new method presented here is based on the Cooper-Harper Rating Scale, which is a test pilot's evaluation-rating instrument. This has been modified through qualitative research. The assertion that the rating scale will leave the group mean response unaltered but will reduce the variance has been statistically tested. Findings - The proposed rating scale provides a calibration technique by which to benchmark comparisons. The scale also reduces subjectivity by producing an overall quantitative measure of similarity. The paper concludes with an application of the rating scale to assessment of a candidate algorithmic approach against correlation. Research limitations/implications - The research findings are based on small data sets, which is a limit imposed by the industrial environment in which this scale will be used. Practical implications - This paper provides a tool to overcome some of the key substantial difficulties in communicating similarity or difference, namely that "similarity" and "difference" have no stand-alone definition, there is a lack of a shared language for the comparisons and little commonality for a decision-making framework. Originality/value - This paper provides modellers and experimentalists in computational electromagnetics (particularly electromagnetic compatibility) with a structured approach to quantifying the quality of comparative results.

Notes: Purpose - The use of the prominent FDTD method for the time domain solution of electromagnetic wave propagation past devices with small geometrical details can require very fine grids and can lead to very important computational time and storage. The purpose is to develop a numerical method able to handle possibly non-conforming locally refined grids, based on portions of Cartesian grids in order to use existing pre- and post-processing tools. Design/methodology/approach - A Discontinuous Galerkin method is built based on bricks and its stability, accuracy and efficiency are proved. Findings - It is found to be possible to conserve exactly the electromagnetic energy and weakly preserves the divergence of the fields (on conforming grids). For non-conforming grids, the local sets of basis functions are enriched at subgrid interfaces in order to get rid of possible spurious wave reflections. Research limitations/implications - Although the dispersion analysis is incomplete, the numerical results are really encouraging it is shown the proposed numerical method makes it possible to handle devices with extremely small details. Further investigations are possible with different, higher-order discontinuous finite elements. Originality/value - This paper can be of great value for people wanting to migrate from FDTD methods to more up to date time-domain methods, while conserving existing pre- and post-processing tools.

Notes: Purpose - This paper sets out to develop analytical solution to the hysteresis, eddy current and excess losses using the T(x) model. Based on Steinmetz' postulation, the losses, represented by the area enclosed by the hysteresis loop, are individually formulated in analytical form. The model is applied to sinusoidal and triangular excitation wave forms. Design/methodology/approach - The equivalent interaction fields introduced into the model represent the losses individually by applying the separation and superposition principle. Findings - Contrary to the presently used models, this model describes the hysteresis loop with its natural sigmoid shape and describes the losses individually in simpler mathematical formulation. Research limitations/implications - Experimental verification will still be needed as to the accuracy of the model and the applicability to the various magnetic materials. Practical implications - The model presented here gives a more realistic presentation of the hysteresis loop and by using simpler mathematics than other models it is more accessible to the practical user. At the same time with the easy mathematics and its visual presentation it is a great value to people engaged in theoretical research in the field of magnetics. Originality/value - In contrast with present magnetic loss models, using almost exclusively MSPM with "flat power" loop or the elliptical equivalent loop approximations, these calculations based on the T(x) model of hysteresis and uses realistic shape for the hysteresis loop, resulting in a simpler mathematical formulation.

Notes: Purpose - To provide sufficient conditions for existence, uniqueness and finite element approximability of the solution of time-harmonic electromagnetic boundary value problems involving metamaterials. Design/methodology/approach - The objectives are achieved by analysing the most simple conditions under which radiation, scattering and cavity problems are well posed and can be reliably solved by the finite element method. The above "most simple conditions" refer to the hypotheses allowing the exploitation of the simplest mathematical tools dealing with the well posedness of variationally formulated problems, i.e. Lax-Milgram and first Strang lemmas. Findings - The results of interest are found to hold true whenever the effective dielectric permittivity is uniformly positive definite on the regions where no losses are modelled in it and, moreover, the effective magnetic permeability is uniformly negative definite on the regions where no losses are modelled in it. The same good features hold true if "positive" is replaced by "negative" and vice versa in the previous sentence. Research limitations/implications - It is a priori known that more sophisticated mathematical tools, like Fredholm alternative and compactness results, can provide more general results. However this would require a more complicated analysis and could be considered in a future research. Practical implications - The design of practical devices involving metamaterials requires the use of reliable electromagnetic simulators. The finite element method is shown to be reliable even when metamaterials are involved, provided some simple conditions are satisfied. Originality/value - For the first time to the best of authors' knowledge a numerical method is shown to be reliable in problems involving metamaterials.

Notes: Purpose - To investigate the general necessary condition for synthesis of square, real rational matrices of complex frequency as admittance matrices of active multiports with resistors, inductors, capacitors and possibly multiport transformers and to prove that this condition is also sufficient for synthesis of stable, square, real rational matrices of complex frequency as admittance matrices of balanced active multiports having only resistors, capacitors and voltage-amplifiers with sufficiently large amplifications. The main aim of the paper is to provide a new and general method for stable admittance matrices synthesis and to develop strict realization algorithm by active balanced transformerless multiport networks. Design/methodology/approach - The objectives of the paper are achieved by using factorization of regular polynomial matrices in complex frequency with certain degree as products of other regular polynomial matrices with specified degrees. A set of sufficient conditions for such a factorization is presented and derived a pertinent algorithm as the starting point for investigation and solving network synthesis problem and generation of class of equivalent realizations. Findings - Theorem 1 states that sufficient condition for factorization of Pth order, generally regular polynomial matrix P(s) in complex frequency s with degree L, whose determinant has K distinct zeros, in form P(s)=P1(s)·P2(s), where 1=p2=P20=L-1 is degree of polynomial matrix P2(s), reads: K〉(P-1)·L+p2-1. The coefficient-matrices of s, s2,... in P1(s) and P2(s) are real or complex depending on whether distinct zeros of det?P(s) are real or complex, respectively. Theorem 2 states that: (a) for realization of Pth order matrix of real rational functions in complex frequency s (i.e. RRF matrix) as admittance matrix of active balanced RLC P-port network with multiport transformers, or without them, P generalized controlled-sources and P controlling-ports are necessary, in general; and (b) P balanced voltage-controlled voltage-sources (VCVSs) with real and by module greater than unity controlling coefficients ("voltage amplifications") are sufficient for realization of stable admittance RRF matrix by active, balanced, transformerless, RC P-port network. Originality/value - This is a research paper with the following two main contributions (original results). First, a theorem on sufficient conditions for factorization of regular polynomial matrices in complex frequency; and second, a theorem relating to sufficient conditions for synthesis of matrices of real rational functions in complex frequency by active, balanced, transformerless networks. The results may be interesting for network theorists and researchers in the field of electric circuits and systems.

Notes: Purpose - To provide a time domain formulation for reconstruction of transient currents flowing in massive parallel conductors from magnetic data collected in the dielectric space surrounding the conductors. Design/methodology/approach - A boundary integral equation (BIE) formulation involving Mitzner's and Rytov's high order surface impedance boundary conditions (SIBCs) is used. Input data of the inverse problem are the magnetic fields at given locations near the conductors. In order to validate the inversion algorithm, the magnetic field data are computed solving the direct problem with FEM for given current waveforms. Findings - The improvement in reconstruction accuracy of the new time domain BIE formulation employing high order SIBCs has been demonstrated numerically in a simple test case. The range of validity of the technique has been extended to current pulses of longer duration and the computational burden has shown to increase only by a factor of 4. Research limitations/implications - The proposed formulation can be compared with other possible formulations, both in the time and in the frequency domain. Practical implications - Based on this formulation a new current sensing technique is proposed for realization of low cost current sensors based on magnetic sensor arrays. Originality/value - The inverse problem addressed in the paper has been solved for the first time.

Notes: Purpose - The aim of this paper is to compare different methods for multiobjective optimisation with respect to the same benchmark problem. Design/methodology/approach - The following methods are considered: equilibrium of gradients GB, multi-individual multi-objective evolution-strategy MOESTRA, and goal attainment GATT, respectively. They are applied to the shape design of the pole pitch of an electrical machine, with the aim of maximizing the air-gap induction and minimizing the stray field in the winding. Findings - The same initial solution of the benchmark is considered for all methods. The final solution of GB and MOESTRA dominates the initial one because both objectives are improved. GB is the most expensive method and therefore is not suited when several non-dominated solutions should be identified. Accordingly, the trade-off curve was approximated by means of 15 non-dominated solutions, resorting to MOESTRA. Originality/value - A multi-objective multi-individual evolution strategy of lowest order has proven to be cost-effective in identifying a set of non-dominated solutions, so helping the designer to investigate the structure of the objective space. The requirements in terms of timing and facilities appear to be compatible with the resources of an automated design centre of an industrial company.

Notes: Purpose - Inverse problems are usually ill-conditioned, requiring the adoption of regularization techniques to obtain reliable results. The choice of the regularization method and of the related parameters represents a critical issue that must be based on the knowledge of reliable additional information on the problem. In the paper some possibilities and pitfalls for the choice of regularization strategy are presented and compared. Design/methodology/approach - Electromagnetic inverse problems (EIP) are usually formulated starting from a direct problem, based on a direct operator, providing the effects (e.g. fields, fluxes) generated by known sources acting through known systems. The direct operators involved in many real world electromagnetic phenomena, due to their compactness, lead to ill posed inverse problems. Inversion procedures pursue the solution regularity through the adoption of various regularization techniques. Improper use of regularizations may unduly constrain the approximated solution and, consequently, cause significant lack of accuracy. Mathematical tools for an effective choice of the regularization technique are not available for every application, and a number of issues are still open. The paper presents a common mathematical model for most of the regularization techniques, discussing their benefits and limitations. Findings - The paper discusses limits, applicability conditions, and impact on the performance of reconstruction procedures, of some relevant characteristics of the inversion algorithms, with particular reference to robustness against noise and inaccuracies in the system parameters. Originality/value - Some criteria for an effective application of regularization are also discussed, showing in particular how proper choices, founded on a careful analysis of the direct problem, may reveal quite effective in improving the solution quality.

Notes: Purpose - The purpose of this paper is to present a procedure, which determines the magnetic force acting between a soft magnetic cylinder and a coil taking the hysteresis phenomena into account. Design/methodology/approach - The magnetic force is computed replacing the ferromagnetic body with an equivalent magnetic moment distribution. Isotropic vector Preisach model with analytical expressed Everett function describes the magnetic properties of the ferromagnetic material. The magnetization distribution is calculated applying the integral equation method. The Preisach hysteresis model is included in the iteration process based on Picard-Banach scheme. Findings - In the case of integral equation method the unknown quantities are the magnetization and the magnetic field intensity. In this way the Preisach hysteresis model can be included in a convenient way in the iteration procedure. Knowing the magnetization distribution the magnetic force can be determined. The developed algorithms can be applied in tubular linear motor design. Originality/value - The paper presents a new formulation of the Preisach hysteresis model. With the aim of the analytically expressed Everett function a stable and faster algorithm can be realized to determine the magnetic force in arrangements with ferromagnetic parts.

Notes: Purpose - The paper sets out to formulate the intermolecular forces leading to Barkhausen instability. In the approach the known concept of effective field is used within the framework of the T(x) model. The aim is to provide a mathematical tool to theoreticians and applied scientists in magnetism that is easier to use than those of other models. At the same time to demonstrate the easy applicability of the T(x) model to hysteretic phenomena. Design/methodology/approach - With the combination of the effective and the external field the model is applied to hysteresis loops as well as to the anhysteretic state showing in both cases the local development of unstable conditions at beyond a critical point, leading to local hysteresis loops. Findings - The paper formulates the critical conditions for the hysteretic and the anhysteretic process and calculates the susceptibility as the functions of magnetisation and the applied field. Research limitations/implications - Experimental verification will be required to prove the applicability to the various magnetic materials and to the accuracy of the model. Practical implications - The paper provides an easy mathematical and visual method to show the conditions before and after the Barkhausen instability sets in during the magnetisation process. Originality/value - The paper provides an easy mathematical tool for theoreticians and experimental scientists with a visual presentation of processes leading to Barkhausen instability and magnetic behaviour beyond that by using the T(x) model.

Notes: Purpose - The aim of the paper is the formulation of a simple hysteresis model entirely based on generally accepted concepts. Design/methodological/approach - According to this, the modelling of loops has been achieved by the application of the Langevin-Weiss law of magnetization to transformer equivalent circuits. The loops are generated by the change of the phase of current, introduced by the resistance modelling iron loss. Differential circuit equations have been solved with the help of standard Mathcad procedures. Findings - In spite of the simplicity of such approach, the accuracy of hysteresis loops and iron loss approximations is better than in PSpice simulations and the model can be easily extended to dynamic loops. Research limitations/implications - The application of the model is limited to lower frequencies, where the rise of frequency leads to the widening of the loops without the radical change of their shapes. Practical implications - Presented approach may be useful in simplified analysis of low frequency transformer circuits and in the primary explanation of hysteresis phenomena for teaching purposes. What is original/value of paper - Contrary to other models based on saturation curves, the dynamic hysteresis loops presented in this paper are obtained with the use of basic laws and concepts, without the introduction of any additional assumptions and the separate treatment of the lower and upper branches of the loops.

Notes: Purpose - The paper sets out to develop the T(x) model, based on well known principles and using the free energy of the ferromagnetic binary system as a starting point. Design/methodology/approach - With the inclusion of the coercive and the intermolecular forces the model fully describes the hysteretic process for both major and minor loops, with exchange field between adjacent magnetic moments. Findings - The paper formulates the dependence of the hysteretic system's normalised free energy on parameters such as the temperature, coercivity, other magnetic and materials properties of the ferromagnetic medium. Research limitations/implications - Experimental verification will still be needed as to the accuracy of the model and the applicability to the various magnetic materials. Practical implications - The paper provides an easy mathematical and visual method to present the energy state and its variation of the magnetic materials during magnetisation, including non-saturation conditions. It has a great value to people engaged in theoretical research in magnetism. Originality/value - So far free energy calculations were only possible for major hysteresis loops. The T(x) model, as presented here, is applicable to the calculation of the free energy flow of any symmetrical minor loops as well.

Notes: Purpose - The aim of this paper is to obtain an extensive experimental characterization of a DC magnetron sputtering device used for plasma processing of materials. Design/methodology/approach - Models and measurements are combined for an interdisciplinary characterization of a DC magnetron sputtering device. Langmuir probes are used for the plasma characterization; the magnetic field is measured by using Hall probes and the data are used to validate a magnetostatic three-dimensional numerical analysis of the device; precision mechanical measurements are done for the target erosion profile and the results are related to a simple estimation formula; a simple model is proposed for the target heating. Findings - Data on magnetic and electric fields, electron temperature and density, plasma potential and target erosion are provided. An estimation of the target heating is proposed. Finally, an application concerning thin film deposition is reported. Research limitations/implications - Measurement of the target surface temperature for the validation of the proposed target heating estimation has not been done. Originality/value - In the field of the electromagnetic processing of materials, the reported extensive device characterization is a valuable set of information for an optimized utilization of DC magnetron sputtering devices.

Notes: Purpose - Various parallelization strategies are investigated to mainly reduce the computational costs in the context of boundary element methods and a compressed system matrix. Design/methodology/approach - Electrostatic field problems are solved numerically by an indirect boundary element method. The fully dense system matrix is compressed by an application of the fast multipole method. Various parallelization techniques such as vectorization, multiple threads, and multiple processes are applied to reduce the computational costs. Findings - It is shown that in total a good speedup is achieved by a parallelization approach which is relatively easy to implement. Furthermore, a detailed discussion on the influence of problem oriented meshes to the different parts of the method is presented. On the one hand the application of problem oriented meshes leads to relatively small linear systems of equations along with a high accuracy of the solution, but on the other hand the efficiency of parallelization itself is diminished. Research limitations/implications - The presented parallelization approach has been tested on a small PC cluster only. Additionally, the main focus has been laid on a reduction of computing time. Practical implications - Typical properties of general static field problems are comprised in the investigated numerical example. Hence, the results and conclusions are rather general. Originality/value - Implementation details of a parallelization of existing fast and efficient boundary element method solvers are discussed. The presented approach is relatively easy to implement and takes special properties of fast methods in combination with parallelization into account.

Notes: Purpose - To develop new and existing coupled thermal and mechanical models of electromagnetic solids for the simulation of coupled field problems based on a consistent theoretical and computational framework. Design/methodology/approach - The finite element computational models we describe involve the combination of classical electrodynamics, continuum mechanics, and thermodynamics. In order to create consistent coupled models, we employ the fundamental principles of thermodynamics as a common framework. Findings - Our procedure requires the necessary thermodynamical considerations for building consistent multiphysics models and develops some novel implementation issues that are important from the designers' point of view. Additionally, efficient numerical algorithms for solving the arising static and dynamic nonlinearities are discussed. Research limitations/implications - The paper targets the simulation of coupled problems in macroscopic electromagnetic continua. Practical implication - The application areas of the coupled field models are identified and illustrated by the solution of complex industrial problems. Originality/value - We introduce new computational models and techniques for the solution of some coupled field problems in electromagnetic solids. While some elements of these computational models and techniques have been used for decades, the complete theoretical and computational framework is presented for the first time here.

Notes: Purpose - To analyze effectively magnetic shielding effects by shields with fine structure. Design/methodology/approach - Simplification of the fine structure makes it possible to analyze them efficiently. The authors have introduced a homogenization method to estimate effective permeability of magnetic composite structure for the static field. The homogenization method is applied to the analysis of magnetic shields composed of steel plates and steel rods against DC power lines to test its feasibility. Findings - The properties of the magnetic shielding are analyzed by using the homogenization method. The errors of the magnetic fields increase in case of very few layers. Originality/value - The simplification of the magnetic shields with fine structure by using the homogenization method makes it possible to analyze efficiently magnetic shielding effects, although the accuracy becomes worse in case of very few layers.

Notes: Purpose - This paper presents an efficient procedure for reconstructing the aged region of ferromagnetic material. Design/methodology/approach - The aging of the ferromagnetic material leads to changes of B?-H relationship. This property may be used for detection of the degraded parts of ferromagnetic pieces. In numerical procedures the region with a possible aged zone is described by a finite number of subdomains where the flaw vector is defined with binary entries. Findings - Because of the small B?-H changes, the magnetic field modifications linearly depend (matrix T) by the flaw vectors. Using a double Gauss pivotation scheme, an enough well conditioned and invertible submatrix is extracted from the matrix T. The unknowns associated with this submatrix (called main unknowns) can be easily obtained by a linear relationship from the rest of the unknowns (called minor). In the set of the minor unknowns we search for that vector which gives the smallest error of the principal unknowns in comparison with the values 0 or 1. Originality/value - This procedure leads to a spectacular increasing of the efficiency in comparison with the known procedures.

Notes: Purpose - To provide information on magnetic lens design principles for neutron beam focussing and to characterize the efficiency of these devices. Design/methodology/approach - Magnetostatic and neutron optical computations are presented for permanent magnet and electromagnetic hexapole lenses for neutron beam focusing. The numerical results are verified by magnetic and neutron beam measurements. Findings - Neutron lenses built from brick-shaped permanent magnets approximating the six-pole Halbach structure yield relatively high field constant for a relatively small useful diameter. Electromagnets are weaker, but allow field constant adjustment. Research limitations/implications - The main limitation of both presented solutions resides in the difficulty of obtaining high magnetic flux densities. Superconducting coils in hexapole configuration can overcome this limitation. Practical implications - The magnetic lenses can be used for beam focusing in scattering neutron instruments. The focused beam is also polarized. Originality/value - Analytical formulae are supplied for the neutron path calculation in a six-pole magnetic field. An electromagnet design with permanent magnet flux enforcement is provided.

Notes: Purpose - A family of preconditioned dual-primal FETI iterative algorithms for the solution of algebraic systems arising from edge element approximations in two dimensions is presented. Design/methodology/approach - The primal constraints, which determine the size of the coarse problem to be solved at each iteration step, are here suitable averages over subdomain edges. The condition number of the corresponding methods is independent of the number of subdomains and possibly large jumps of the coefficients. Findings - For h finite elements, it grows only polylogarithmically with the number of unknowns associated with individual substructures, while for hp approximations on geometrically refined meshes, it is independent of arbitrarily large aspect ratios. Originality/value - Proposes an algorithm with a rate of convergence that is independent of possibly large jumps of the coefficients and mesh aspect ratios.

Notes: Purpose - To present a robust optimal design technique in the presence of system parameters uncertainties. Design/methodology/approach - The properties of normally distributed random variables are exploited, together with surface response fitting techniques, with the aim to reduce the computational cost in assessing the effect of uncertainties. Findings - A fast approximate method for computing statistical average is presented together with its implementation for the design of magnets for magnetic resonance imaging. Research limitations/implications - Future research will be focused to multi-dimensional problems and to the best choose of closed form expressions to evaluate statistical moments fitting. Practical implications - Robust optimal design methodologies are receiving an increasing interest in both academic and industrial research, due to their capability of coping with construction uncertainties and tolerances. Originality/value - The effectiveness of the simplified method has been demonstrated for an analytical example and on a simplified superconducting magnet design. The proposed strategy is quite general and it can be applied to a wide class of optimal design problems.

Notes: Purpose - This paper presents new approach to the integration of neural classifiers. Typically only the best trained network is chosen, while the rest is discarded. However, combining the trained networks helps to integrate the knowledge acquired by the component classifiers and in this way improves the accuracy of the final classification. The aim of the research is to develop and compare the methods of combining neural classifiers of the heart beat recognition. Design/methodology/approach - Two methods of integration of the results of individual classifiers are proposed. One is based on the statistical reliability of post-processing performance on the trained data and the second uses the least mean square method in adjusting the weights of the weighted voting integrating network. Findings - The experimental results of the recognition of six types of arrhythmias and normal sinus rhythm have shown that the performance of individual classifiers could be improved significantly by the integration proposed in this paper. Practical implications - The presented application should be regarded as the first step in the direction of automatic recognition of the heart rhythms on the basis of the registered ECG waveforms. Originality/value - The results mean that instead of designing one high performance classifier one can build a number of classifiers, each of not superb performance. The appropriate combination of them may produce a performance of much higher quality.

Notes: Purpose - In this paper, a new method for estimating iron loss under a distorted elliptical rotating flux is proposed. Design/methodology/approach - In order to precisely analyze the iron loss of rotating machines, the iron loss under distorted rotating flux should be taken into account. However, reports of precise analysis considering measured iron loss data under rotating flux are few. Findings - The iron loss of surface permanent magnet (SPM) motor model proposed by the investigation committee of IEE of Japan is estimated using the proposed method. The experimental examination is carried out by measuring the iron loss of the motor using a torque meter. Originality/value - Examines an estimation method of iron loss of motors.

Notes: Purpose - To provide a new semi-analytical procedure which is much faster than FEM and for this reason can be applied in a reconstruction of an interface between two conducting fluids (magnetic fluid dynamics problem) by means of magnetic field tomography. Design/methodology/approach - Three approaches are compared: a simple analytical solution (AS1), a modified semi-analytical solution (AS2), and the finite element method solution. The modified semi-analytical approach takes into account an information about azimuthal spatial harmonics received from the Fourier analysis of magnetic flux density distributions calculated by FEM. AS1 and AS2 have been compared for different modes of the interface using FEM solution as a reference. Findings - It is shown that for small perturbations the AS2 in every case provides smaller errors than AS1 although for some modes (14,24) the quality of the solution is still not satisfactory. Originality/value - This paper describes a new technique for the analysis of electromagnetic field which can be also applied in other problems.

Notes: Purpose - The scope of the work is to provide an hybrid numerical technique for the solution of electric field. Design/methodology/approach - In this paper an integral approach for the solution of static electric field based on a dual discretization (DD) and on a surface method of moment (MoM) is presented. The proposed technique is applied to the solution of 3D electric field problems where different perfectly conducting bodies are placed in a homogeneous and isotropic medium. The approach is also extended to the analysis of static current field. In the presented formulation MoM is applied on a surface domain which is discretized according to a baricentrical dual scheme. Findings - The procedure has been applied to several practical cases and it represents an efficient tool for the evaluation of lumped circuit parameters as capacitances of 3D conducting bodies and ground resistance of grounding systems. Research limitations/implications - The formulation presented in the paper is limited to the calculus of electric field in homogeneous media. For future development the authors are working in order to include non-homogeneous media. Practical implications - The proposed approach aids the designer of electrical systems as large scale grounding systems or integrated circuit connections in the calculations of lumped electrical parameters. Originality/value - The originality of the paper lies in the coupling of MoM with finite formulation and DD.

Notes: Purpose - To present a neural network-based approach to the design of electromagnetic devices. Design/methodology/approach - A neural model is created which reproduces the relationship between the design parameters of the device and the performance parameters, typically field values. Findings - The neural model is a single hidden layer MLP network, trained by using a set of cases calculated, for example, by means of a finite element analysis. The design problem can be solved by fixing the performance values at the output of the network and by calculating the corresponding input values. The relationship between the input and the output of the neural network is represented by three equations systems. By means of these three systems, we can forward the domain of the input, and we can back propagate the desired output throughout the network layers. In such a way, both the domain of the design parameters and the domain of the desired performances values can be projected in the same space. Whatever point inside the intersection between the two projected domains corresponds to a solution of the design problem. Originality/value - Presents a procedure which is able to find a point belonging to such an intersection.

Notes: Purpose - This paper presents a method to improve inverse problem resolution. This method focuses on the measurement set and particularly on sensor position. Based on experiment, it aims at finding sensor position criteria to insure the least bad inverse problem solving. Design/methodology/approach - The studied device is a magnetized steel sheet measured by four sensors. Three optimization techniques are compared: condition number, solid angle and signature optimization. Findings - An efficient criterion to compare the inverse problem resolution quality is presented. The comparison of optimization techniques shows that only signature optimization gives accurate results. Research limitations/implications - A relative simple case is studied in this paper: only four sensors are used to measure a steel sheet. Moreover magnetostatic low-field case is supposed. Nevertheless techniques presented could be applied to more complex studies. Condition number and solid angle optimizations techniques should be tested with more sensors to confirm or infirm their inefficiency. Practical implications - This paper presents the first step of a larger study concerning ships for naval application. The aim is to predict magnetic anomaly created by ship to compensate it. This anomaly could be computed through the resolution of an inverse problem based on internal measurements. The signature optimization technique could be used to find the optimal sensor location onboard. Originality/value - Traditional regularization techniques are focusing on adding mathematical or physical information to the system in order to improve it. This paper provides another approach to improve inverse problem resolution through measurement set. It shows that sensor position optimization should be efficient.

Notes: Purpose - Presents a study of a bulk superconductor sphere placed in a uniform magnetic induction field b0(t). Design/methodology/approach - Adapts some macroscopic laws for the numerical simulation of its evolution. This evolution is determinated by the front tracking method (FTM). Findings - The deduction of some consequences concerning hysteresis losses, and comparison to a direct method are done. Originality/value - Helps to solve some complex three-dimensional eddy current problems in industrial devices.

Notes: Purpose - This paper seeks to propose a systematic method to design multi fuzzy FACTS based stabilizers in a multi-machine power system. Design/methodology/approach - Conventional FACTS based stabilizers are decentralized controllers that adopt local measurements and operate in closed loop. To improve overall system dynamic performance, a coordinating application of FACTS based stabilizer is essential. Although, numerous researches have indicated the effectiveness and superiority of fuzzy logic controllers in comparison with the conventional linear controllers in power system application but researchers have not adequately investigated coordination of multi fuzzy controllers in multi-machine power systems to provide optimal performance. Genetic algorithm is used to determine optimum values of controllers' parameters. Findings - The search space of the optimisation procedure is decreased to a smaller one, design and computation time can be reduced significantly and the design process becomes more systematic. Originality/value - A systematic method is introduced to coordinate multi fuzzy FACTS based stabilizers in multi-machine power systems.

Notes: Purpose - As far as the authors know, no sufficiently complete model of continual induction hardening was developed and solved so far. The paper presents both mathematical model of the process and algorithm of its solution in the quasi-coupled formulation. Design/methodology/approach - Computation of electromagnetic and temperature fields is based on the finite element method, while time variable boundary conditions are determined by means of an original theoretically-empirical procedure. Findings - Substantial are backgrounds for design of the inductor and parameters of the field current as well as parameters of the cooling medium. Research/limitations/implications - The model reached a good level of accuracy validated by suitable experiments. Nevertheless, next work in the field will also have to respect history of the heating before cooling itself (the austenitizing temperature is a function of the velocity of heating). Very important is also appropriate meshing of the investigated region to suppress numerical instabilities appearing during the computation process. Finally, acceleration of numerical schemes is a must, because modelling of one common task (on very fast PCs) takes about 4?h. Practical implications - The results and conclusions may be used for designing devices for continual induction hardening of axisymmetric bodies. Originality/value - Complete mathematical and computer model of the process, original methodology for finding the coefficient of convective heat transfer from the cooled part of the heated workpiece to ambient water spray.

Notes: Purpose - This paper presents a methodology based on Multiobjective Genetic Algorithms (MOGAs) for the design of electrical engineering systems. MOGAs allow one to optimize multiple heterogeneous criteria in complex systems, but also simplify couplings and sensitivity analysis by determining the evolution of design variables along the Pareto-optimal front. Design/methodology/approach - To illustrate the use of MOGAs in electrical engineering, the optimal design of an electromechanical system has been investigated. A rather simplified case study dealing with the optimal dimensioning of an inverter - permanent magnet motor - reducer - load association is carried out to demonstrate the interest of the approach. The purpose is to simultaneously minimize two objectives: the global losses and the mass of the system. The system model is described by analytical model and we use the MOGA called NSGA-II. Findings - From the extraction of Pareto-optimal solutions, MOGAs facilitate the investigation of parametric sensitivity and the analysis of couplings in the system. Through a simple but typical academic problem dealing with the optimal dimensioning of a inverter - permanent magnet motor - reducer - load association, it has been shown that this multiobjective a posteriori approach could offer interesting outlooks in the global optimization and design of complex heterogeneous systems. The final choice between all Pareto-optimal configurations can be a posteriori done in relation to other issues which have not been considered in the optimization process. In this paper, we illustrate this point by considering the cogging torque for the final decision. Originality/value - We have proposed an original quantitative methodology based on correlation coefficients to characterize the system interactions.

Notes: Purpose - To provide an efficient and accurate model for interconnect networks characterised by frequency-domain scattering or admittance parameters. The parameters are derived from measurements or rigorous full-wave simulation. Design/methodology/approach - Initially, Hilbert transform relationships are enforced to ensure causality. A reverse Fourier series representation of the discrete data is then converted to the z-domain and from this a state-space formulation is determined. This enables the application of a judiciously chosen model reduction algorithm to obtain an efficient time-domain representation of the network. Findings - Sample results from both simulated and measured data indicate the efficacy of the proposed modelling strategy. For successful implementation of the strategy, it is necessary to employ the Hilbert transform to ensure that a causal impulse response is obtained. Practical implications - The method is applicable to the interconnect networks for which the analytical models cannot be obtained due to the complexity and inhomogeneity of the geometries involved. Originality/value - The work combines in a novel manner aspects from several existing techniques proposed for network simulation and model reduction. The end result is a highly efficient causal, stable and passive representation of the network in question for implementation in a time-domain circuit simulator.

Notes: Purpose - Propose post processing methods for the edge finite element (FE) method on a tetrahedral mesh. They make it possible to deduce vector values on the vertices from scalar values defined on the edges of the tetrahedra. Design/methodology/approach - The new proposed techniques are based on a least squares formulation leading to a sparse matrix system to be solved. They are compared in terms of accuracy and CPU time on a FEs formulation for open boundary - frequency domain problems. Findings - A significant improvement of vector values accuracy on the vertices of the tetrahedra is obtained compared to a classical approach with a very small additional computation time. Originality/value - This work presents techniques: to obtain the values at the initial nodes of the mesh and not inside the tetrahedra; and to take into account the discontinuity to the interface between two media of different electromagnetic properties.

Notes: Purpose - In this paper, a new application of the Selected Harmonic Elimination Pulse Width Modulation (SHEPWM) technique used in the cascade multilevel inverter topology which is formed by series connections of one-phase bridge type inverters (H-bridge) is introduced. The advantage of the SHEPWM technique is its ability to operate in low switching frequency that makes it suitable for high power applications. Design/methodology/approach - First, the switching angles are calculated using constrained optimization technique. By using these switching angles, the fundamental harmonic can be controlled and the selected harmonics can be eliminated. Then, using these calculated switching angles, a set of equation is formed which calculate the switching angles with respect to the modulation index. The switching angles at any modulation index can be easily obtained by solving the equation set. In this study, this equation set has been solved online using dSPACE DS1103 controller board. Using this technique, three-phase voltages have been obtained from a five-level cascade inverter. These voltages are applied to an induction motor. Findings - The simulation results are verified by the experimental results. The results show that selected harmonics can be eliminated and an ac voltage with variable amplitude and frequency can be obtained using the proposed technique. Originality/value - This paper presents a new application of the (SHEPWM) technique for multilevel inverters.

Notes: Purpose - Improved numerical calculation techniques for low-frequency current density distributions within high-resolution anatomy models caused by ambient electric or magnetic fields or direct contact to potential drops using the finite integration technique (FIT). Design/methodology/approach - The methodology of calculating low-frequency electromagnetic fields within high-resolution anatomy models using the FIT is extended by a local grid refinement scheme using a non-matching-grid formulation domain. Furthermore, distributed computing techniques are presented. Several numerical examples are analyzed using these techniques. Findings - Numerical simulations of low-frequency current density distributions may now be performed with a higher accuracy due to an increased local grid resolution in the areas of interest in the human body voxel models when using the presented techniques. Originality/value - The local subgridding approach is introduced to reduce the number of unknowns in the very large-scale linear algebraic systems of equations that have to be solved and thus to reduce the required computational time and memory resources. The use of distributed computation techniques such as, e.g. the use of a parallel solver package as PETSc follows the same goals.

Notes: Purpose - The paper presents the band gap computation in one- and two-dimensional photonic crystals built up from porous silicon. The frequency dispersion of the dielectric materials is taken into account. Design/methodology/approach - The behavior of the light in a photonic crystal can be well described by the Maxwell equations. The finite difference time domain (FDTD) method is applied to determine the band structure. The frequency dependence of the dielectric constant is taken into account by a sum of second-order Lorenz poles. The material parameters are determined applying a conjugate gradient-based minimization procedure. Passing a light pulse of Gaussian distribution through the photonic crystal and analyzing the transmitted wave can explore the photonic bands. Findings - The realized simulations and visualizations can lead to a much better understanding of the behavior of electromagnetic waves in dispersive photonic crystals, and can make possible to set up experimental conditions properly. The obtained results show again that silicon and porous silicon can be used for the fabrication of photonic crystals. Research limitations/implications - Due to the high computational requirements of the three-dimensional case we plan to work out a parallel version of the presented FDTD algorithm. Originality/value - This paper presents a simple way to take into account the frequency dispersion in the simulation of photonic crystals with the FDTD method.

Notes: Purpose - The aim of the work is to reconstruct the anisotropic complex conductivity distribution with the common Gauss-Newton algorithm. Design/methodology/approach - A cubic region with anisotropic material properties is enclosed by a larger cube with isotropic material properties. Numerical simulations are done with tetrahedral nodal finite elements of second-order. Findings - It can be shown that it is possible to reconstruct anisotropic complex conductivity distribution if the starting values are chosen sufficiently close to the true values of the complex conductivity. Originality/value - In this paper, the anisotropic electric conductivity and the anisotropic permittivity are reconstructed in 3D.

Notes: Purpose - For the spatial reconstruction of a two phase flow, as it might occur in a pipe, the main problem has always been the blurring of the resulting images. Design/methodology/approach - In this paper, we present a method where blurring is implicitly avoided by the use of level sets. The level set method describes the iteratively evolving interface between different materials. The underlying field problem is solved with the boundary element method formulated in the region, where the degrees of freedom are present and the finite element method in all other regions. Findings - Finally reconstruction results of an electrical capacitance tomography sensor are presented to show the validity of the method. Originality/value - Presents a method where blurring is avoided by the use of level sets.

Notes: Purpose - To provide first insight onto the application of hierarchical matrices and adaptive cross approximation (ACA) techniques for electromagnetic scattering problems. Design/methodology/approach - The shielding effectiveness of metallic casings with apertures is analyzed via an electric field integral equation. To reduce the storage needs and the complexity of matrix equation solution, a technique combining the use of hierarchical matrices (H-matrix) in conjunction with the ACA technique is used. Findings - Provides first results for compression of a matrix resulting from a Helmholtz problem by means of hierarchical matrices and ACA techniques. Gives insight into the importance of obtaining a "cheap" preconditioner. Research limitations/implications - The technique resides on the smotheness of kernel functions - which is no longer valid for big wave numbers. Practical implications - Gives means of solving problems of big dimensions in terms of number of unknowns - without the need to tailor the approach for the specific kernel function. The original integration functions used to fill the full matrix can be used here. Originality/value - The paper represents one of the first attempts to use the above-mentioned techniques for the high frequency domain.

Notes: Purpose - The problems presented in the paper concern a three-phase four-wire system with periodical non-sinusoidal voltage sources with inner impedances and asymmetrical linear three-phase loads. Generally, the line currents of the system are asymmetrical. The purpose of the paper is to improve the working conditions of the system by means of symmetrization. Design/methodology/approach - A method of symmetrization of these systems has been proposed. In this paper, the symmetrization problem has been solved by using the symmetrical components theory and compensation of reactive power for each of voltage harmonics under consideration. Findings - After symmetrization currents become symmetrical and their RMS values and active power on source impedances become lower. The realization of symmetrization makes possible: reduction of RMS values of source currents, an assurance of equal loads for individual phases of the system supplied from sources with inner impedances, after symmetrization the voltage source generates and load consumes greater useful active power. Originality/value - The simplified structure of the compensator has been proposed in the paper. The symmetrization has been presented with reference to new structure of the compensator.

Notes: Purpose - This paper discusses the robustness of the algebraic multigrid (AMG) method as well as geometric multigrid (GMG) method against mesh distortion in edge-based finite element analysis. Design/methodology/approach - Analyzes a simple magnetostatic problem, in which the model consists of a cubic iron and the surrounding air region. Prepares three meshes which have same number of elements to evaluate the robustness of multigrid against the distortion of mesh. Findings - The AMG method is shown to be more robust against mesh distortion than the GMG method. Originality/value - Shows that the AMG is more robust than the GMG. This result is of practical interest to the researchers in this field.

Notes: Purpose - The aim of this paper is to use an analytical multi-physical model - electromagnetic, mechanic and acoustic - in order to predict the electromagnetic noise of a permanent magnet synchronous machine. Design/methodology/approach - The aim of this work is to develop and use an analytical multi-physical model - electromagnetic, mechanic and acoustic - of a synchronous machine with permanent magnets. The complete model is coded in order to predict acoustic noise. A study of sensitivity is presented in order to deduce the influential - or significant - factors on the noise. For that, the technique of the experimental designs is used. More particularly, the modeling of the noise will be achieved due to the new "trellis" designs. Findings - Three models are presented: electromagnetic, mechanical of vibration and acoustic. For each of them, comparisons with finite element method and experiments have been made. Several response surfaces are given; they represent the noise according to influential factors, with respect to different speeds of the machine. These surfaces are useful to deduce the parts of the design space to avoid. Originality/value - Different multi-physical aspects are considered: electromagnetic, mechanic and acoustic phenomena are taken into account due to a single analytical model. The experimental design method is the privileged tool used to make the complex relationships between the main variables appear.

Notes: Purpose - To demonstrate the improvement of three-axial magnetic sensors systems for magnetocardiography when using minimum norm solutions (MNS). Design/methodology/approach - The thesis is proved by using figures of merit and by means of repeated numerical simulations, starting from a BEM model for forward calculations. Findings - We found out that both for under-determined and over-determined problems two figures of merit show better performance of a three-axial sensor system when compared with two mono-axial sensor systems. We also showed the positive impact of three component magnetic field data on MNS by means of repeated simulations. Research limitations/implications - The analysis is limited to theoretical sensor systems and can be applied also to realistic measurement set-ups. Noise is considered uncorrelated. The analysis could be carried out with the help of other figures of merit. More refined models for the human body could be adopted. Practical implications - The use of three axial sensor systems is encouraged in the field of magnetocardiography. Originality/value - Numerical analysis of inversion algorithms using three-dimensional magnetic field data in magnetocardiography have been never carried out.

Notes: Purpose - To determine and/or examine overall behaviour of simulation models with large input using as few parameters as possible. To introduce a methodology describing stability of the partitioning of simulation results and the corresponding parameter space. Design/methodology/approach - Partitionings of the parameter space are performed using real-valued mappings called measures of merit. Tools for examining evolution of partitionings and correlations between different partitionings are developed. These tools are applied in two case studies within the field of electrical engineering. Findings - The presented approach provides tools for systematic analysis of parametrised models. Since the classification of results is based on measures of merit, a good choice both simplifies the analysis and improves the stability of partitioning. Included case studies highlight these conclusions. Research limitations/implications - The present form of the methodology is targeted at recursive simulations. Use of more complex partitioning procedures could be the topic of further research. Originality/value - Solid framework for handling and analysing complex parametrised simulations.

Notes: Purpose - The purpose of this paper is to demonstrate how Monte Carlo methods can be applied to the solution of field theory problems. Design/methodology/approach - This objective is achieved by building insight from Laplacian field problems. The point solution of a Laplacian field problem can be viewed as the solid angle average of the Dirichlet potentials from that point. Alternatively it can be viewed as the average of the termination potential of a number of random walks. Poisson and Helmholtz equations add the complexity of collecting a number of packets along this walk, and noting the termination of a random walk at a Dirichlet boundary. Findings - When approached as a Monte Carlo problem, Poisson type problems can be interpreted as collecting and summing source packets representative of current or charge. Helmholtz problems involve the multiplication of packets of information modified by a multiplier reflecting the conductivity of the medium. Practical implications - This method naturally lends itself to parallel processing computers. Originality/value - This is the first paper to explore random walk solutions for all classes of eddy current problems, including those involving velocity. In problems involving velocity, the random walk direction enters depending on the walk direction with respect to the local velocity.

Notes: Purpose - To outline different versions of a novel method for accurate and efficient determining the dielectric properties of arbitrarily shaped materials. Design/methodology/approach - Complex permittivity is found using an artificial neural network procedure designed to control a 3D FDTD computation of S-parameters and to process their measurements. Network architectures are based on multilayer perceptron and radial basis function nets. The one-port solution deals with the simulated and measured frequency responses of the reflection coefficient while the two-port approach exploits the real and imaginary parts of the reflection and transmission coefficients at the frequency of interest. Findings - High accuracy of permittivity reconstruction is demonstrated by numerical and experimental testing for dielectric samples of different configuration. Research limitations/implications - Dielectric constant and the loss factor of the studied material should be within the ranges of corresponding parameters associated with the database used for the network training. The computer model must be highly adequate to the employed experimental fixture. Practical implications - The method is cavity-independent and applicable to the sample/fixture of arbitrary configuration provided that the geometry is adequately represented in the model. The two-port version is capable of handling frequency-dependent media parameters. For materials which can take some predefined form computational cost of the method is very insignificant. Originality/value - A full-wave 3D FDTD modeling tool and the controlling neural network procedure involved in the proposed approach allow for much flexibility in practical implementation of the method.

Notes: Purpose - Analysis and development of a high efficiency, induction heated chemical reactor, medium frequency supplied (1,000-2,000?Hz), able to be equipped with efficient cooling circuits. Design/methodology/approach - The numerical investigations of the technical solutions proposed in this paper are based on 3D finite element models that are experimentally validated. Findings - Solutions to increase the transparency of the cooling envelope of the reactor tank with respect to magnetic field. The positions of envelope regions characterized by high values of power losses are experimentally confirmed by infrared temperature measurements. Practical implications - The numerical analysis and the experimental investigations, show the possibility to implement efficient cooling circuits in chemical reactors without affecting the performances of the induction heating process. By designing properly the metallic envelope of the tank the global efficiencies of the chemical reactors increase at around 90 percent with reduced impact on the working environment and with low costs. Originality - This paper proposes an innovative chemical reactor medium frequency induction heated with efficient cooling circuits and with high global efficiency, higher than the actual induction heated chemical reactors.

Notes: Purpose - The purpose of this research is to develop new techniques for component physical modeling for the dynamic simulation of integrated power systems. Design/methodology/approach - A FE-based phase variable model is proposed so as to achieve fast and accurate simulation. Such a model is established based on the nonlinear transient FE analysis, in order to take into consideration the harmonic effects due to the nonlinear magnetization property, magnetic circuit geometry as well as other design variations. Findings - In the FE-based phase variable model, the inductances are described as functions of the phase angle and the magnitude of winding currents, the rotor position and other operational parameters. They are obtained from the transient FE solutions, stored in tables, and retrieved during the simulation. The FE-based phase variable model is implemented in Simulink in two ways. The first is the equation-based block and the second is the circuit component-based block. The FE-based phase variable models of various electrical components in the power system were studied. This includes various types of rotating machines and transformers. Examination and application examples show the correctness and effectiveness of the proposed operational modeling procedures. Originality/value - The developed FE-based physical phase variable model is as accurate as the full FE model with much faster simulation speed. It will benefit the dynamic simulation of integrated power system. This combination of physical modeling and integrated dynamic simulation is original and represents an added value to the state-of-the-art in this field.

Notes: Purpose - The scope of the work is to provide an identification procedure for an hysteresis model based on nonlinear circuit cells. Design/methodology/approach - An identification procedure for an hysteresis model based on nonlinear circuit cells is presented. The response of elementary cell is equal to a generalized play operator. The procedure allows the identification of the limit symmetric hysteresis loop and of minor loops. The identification procedure is based on the relationship between the circuit parameters and the discretization of the first derivative of the BH curve by means of a staircase function. Findings - The model obtained is employed for the simulation of soft magnetic composite material cores under different supply voltage waveforms. The proposed identification procedure is able to define an accurate model of an hysteretic material with a low number of elemental network cells. The identification algorithm is simple and makes use of the limit hysteresis cycle only. Symmetric minor loops are used to tune "soft" operators for the correct reconstruction of cycles which do not reach saturation. Research limitations/implications - The model is limited to scalar and static hysteresis model. Practical implications - The model obtained can be used in network simulator like SPICE in order to model circuits in which magnetic devices are involved. Originality/value - The circuit hysteresis model has been presented in literature, while its identification is newly proposed by the authors.

Notes: Purpose - The goal of the presented work is the efficient computation of Maxwell boundary and eigenvalue problems using high order H(curl) finite elements. Design/methodology/approach - Discusses a systematic strategy for the realization of arbitrary order hierarchic H(curl)-conforming finite elements for triangular and tetrahedral element geometries. The shape functions are classified as lowest order Nédélec, higher-order edge-based, face-based (only in 3D) and element-based ones. Findings - Our new shape functions provide not only the global complete sequence property but also local complete sequence properties for each edge-, face-, and element-block. This local property allows an arbitrary variable choice of the polynomial degree for each edge, face, and element. A second advantage of this construction is that simple block-diagonal preconditioning gets efficient. Our high order shape functions contain gradient shape functions explicitly. In the case of a magnetostatic boundary value problem, the gradient basis functions can be skipped, which reduces the problem size, and improves the condition number. Originality/value - Successfully applies the new high order elements for a 3D magnetostatic boundary value problem, and a Maxwell eigenvalue problem showing severe edge and corner singularities.

Notes: Purpose - Electrical resistive tomography (ERT) is a non-destructive testing technique based upon the reconstruction of the electrical conductivity profile inside a body from measurement made on its boundary. In the literature about the inverse problems the ERT is considered still challenging being both non-linear, ill-posed and very limited in resolution. Purpose of the paper is to assess the performances of an approach exploiting the circuital behaviour of a particular class of problems, highlighting its advantages in terms of simplicity and reduction of the computer burden. Design/methodology/approach - In this paper, an electrical property of a particular class of problems is pointed out; the same property is used to formulate in terms of a circuital model the ERT problem. The proposed methodology consists basically of combining properly simplified data previously evaluated and collected. The overall procedure is presented with reference to an underground structure diagnostics problem. Findings - The effectiveness of the proposed approach has been evaluated quantitatively by comparing the simplified procedure results with the ones obtained by performing fully 3D FEM analysis. Originality/value - The consistently low errors obtained state the convenience of the method also taking into account that the reconstruction process consists merely in post-processing previously collected data.

Notes: Purpose - Shape and material parameters have major influence on the performance of electromagnetic components. Optimization of these parameters is therefore vital in electromagnetic design. Reduction of the radar cross section (RCS) for aircraft and frequency selective surfaces are two well known examples. Shape and materials optimization is performed for different scatterers in 2D. Design/methodology/approach - Continuum design sensitivities for microwave problems are applied for the gradient-based optimization of scatterers' shape and material parameters. The goal function is chosen to be an average of the monostatic RCS for a sector of incident angles over a frequency band. Numerical tests are presented for 2D scatterers and, specifically, a perfectly electrically conducting scatterer and an absorber on the front edge of an airplane wing are considered. The results are compared with theoretical findings and results in the open literature. Findings - It is demonstrated that a dense frequency sampling of the goal function over a wide frequency band relaxes the requirements on the angular resolution. The broad band requirements on the RCS also avoids corrugations without the resorting to regularization methods and penalty terms added to the goal function. The optimization algorithm refines, in a small number of iterations, the initial geometry of the scatterer to an optimized design with strongly reduced RCS. Originality/value - Shape and material parameters have major influence on the performance of electromagnetic components. Optimization of these parameters for scatterers demonstrates that a densely evaluated goal function over a broad frequency band has the advantages of: lowering the requirements on angular resolution; avoiding corrugations; and regularizing the problem by the broad frequency band requirements which often are naturally included in the performance specification of electromagnetic devices.

Notes: Purpose - The design of electrical machines includes the computation of several requirements and, in general, the improvement of one requirement implies in a degradation of another one: this is a typical multi-objective scenario. The paper focuses on the multi-optimization analysis of a special switched reluctance motor. Design/methodology/approach - Two design requirements were analyzed: the average torque and the ripple torque. The electromagnetic field computation was performed by the finite element method and the torque was computed by the Coulomb's Virtual Work for several positions. This allows us to calculate the average torque and the ripple torque. Three different methods were used to obtain the Pareto set: a min-max approach, the non-dominated sorting genetic algorithm (NSGA) and the strength Pareto evolutionary algorithm (SPEA). In order to save the computation time, the objective functions (the average torque and the ripple torque) were replaced with surrogate functions. Kriging models were used as surrogate functions. Findings - The evolutionary methods (NSGA and SPEA) have a similar performance. The min-max has not the same performance. It could have the same performance only if some unconstrained optimization problems are solved before the multi-objective optimization. The maximum relative deviation between the approximated function (Kriging model) and the same value calculated by the finite element method was equal to 0.8 percent for the average torque and 1.2 percent for the ripple torque. The ripple torque, considered as the difference between the maximum and the minimum values in the 0-90° region, has reduced while its frequency has doubled. This last characteristic provides a better mechanical stability for the driven load because its inertia softens the ripple effects at the double the frequency. The optimized prototype presents higher torques in the region 〈0° and this allows the electronic drive to switch in a broader range rendering the motor operation more flexible. Originality/value - The use of surrogate functions save the computation time with high accuracy. This is very important on the design of electrical machines, a typical multi-objective scenario. Evolutionary methods seem to be well suited to solve this class of problem.

Notes: Purpose - Differential relaying is one of the most widely used techniques for protecting power transformers. The purpose of this paper is to discuss and cover a developed methodology for analyzing the signals obtained from the differential protection of power transformers. Design/methodology/approach - The differential signal obtained from the protective relays of power transformers is analyzed in this paper, in order to establish a relation between time-dependent symmetrical components and space vectors. As a result of the formulation of such a relation, specific patterns are obtained and classified for the plot of the space vector during fault and inrush conditions. Findings - What was found in the course of the work? This will refer to analysis, discussion, or results. It has been found that the discrimination between inrush and fault conditions is possible by observing a characteristic asymmetry in the plots of the space vector. A method for dealing with the said asymmetries based on the absolute value of the space vector as obtained from the differential signal is proposed and discussed. The theoretical approaches given in the paper are further validated through finite element simulations and laboratory tests, which include linear and non-linear loads, in order to account for more severe exploitation conditions. Research limitations/implications - A complete protective algorithm can be developed from the analysis of the methodology proposed, which avoids the spectral analysis, since the methodology is based in pattern analysis rather that in the latter technique. Practical implications - The methodology provides faster identification of the fault during inrush condition, since the spectral analysis is prevented. Originality/value - It may be stated that the major contribution of the paper is the methodology proposed for identifying internal faults in power transformers using pattern characterization of the plot of the space vector.

Notes: Purpose - The paper presents an hybrid optimization technique which couples the artificial immune system (AIS) algorithm with a zeroth order deterministic method. Design/methodology/approach - AIS has been developed to tackle multi-modal optimization problems and it has shown a great ability to explore the objective function space. The algorithm is subdivided into two phases: an outer and an inner cycle. The outer cycle is devoted to the exploration of the space while the inner is a local exploration of the objective function. The new hybrid method proposes to replace the local search by a zeroth order deterministic search to speed up the overall convergence. Findings - Results on two multi-modal analytical objective functions show an increase of speed of the new procedure with respect to the standard AIS. The method is also tested on the TEAM 22 numerical problem and some a posteriori techniques for the analysis of multimodal blind objective functions are discussed. Originality/value - The new Multimodal optimization algorithm has allowed to explore thoroughly feasibility space giving rise to a partition of the whole space, the use of hybrid technique increases the performances of standard AIS increasing the convergence to the optimal points.

Notes: Purpose - To provide a unified analytical tool, based on Park transformation, for the theoretical and practical analysis of a lossy three-phase transmission line. Design/methodology/approach - The results obtained in the study of TEM waves propagation in two-wire line can be extended to a symmetric m-wire line by employing the modal analysis. This approach relates the dynamic of m-wire guided field to the propagation of m modal voltages and currents acting on m single-wire decoupled transverse electromagnetic (TEM) lines. In the symmetric three-phase system case, the modal analysis includes, as a particular case for m=3, the symmetric component theory. In previous papers, the authors applied the Park transformation to study the wave propagation of (TEM) three-phase symmetrical lines. The formulation proposed and tested considers the lossless TEM wave propagation of a three-phase line without consideration to the dissipations phenomena present in the line itself. Taking into account the obtained results, the extension of the developed approach to the lossy three-phase transmission line transient analysis is very useful on both theoretical and practical points of view. Findings - The symmetrical three-phase line Park model for the lossy transmission line transient analysis, regarded as vector formulation of the line modal analysis, has been presented. The proposed examples highlight how, thanks to the Park model, the dynamic analysis of the three-phase line in distorted and unsymmetrical systems becomes an integral part of the more general and well-established power electric system dynamic theory. Originality/value - The three-phase transmission line transient analysis presented in this paper emphasizes the conceptual contents, specific to the Park approach. Furthermore, it gives some results very important for the practical analysis of a lossy three-phase transmission line.

Notes: Purpose - We present a method for the simulation of the dynamical behavior of a coupled magneto-mechanical system given in terms of a conductor moving through an electromagnetic field. Design/methodology/approach - For the magnetic part, we consider a model based on an electric vector and a magnetic scalar potential, whereas the mechanical part is modelled by the equation of a rigid body motion. A weak coupling is employed: at each time step the resulting forces are calculated yielding the new displacement of the conductor. Findings - Numerical results are given for the simulation of an electromagnetic brake with axisymmetric geometry. They indicate that the proposed method is especially well suited for eddy current problems involving moving conductors. Research limitations/implications - Further research should be undertaken toward the application of the proposed method to real 3D problems. Originality/value - The spatial discretization of the problem relies on the use of two independent triangulations to approximate the two involved potentials. Whereas the scalar magnetic potential is discretized by means of nodal H1-conforming finite elements on a grid covering the global computational domain, the vector electric potential is approximated by Hcurl-conforming edge elements on another grid only covering the conductor. The coupling between the two grids is accomplished via the mortar finite element method. At each time step, only the coupling matrix has to be reassembled, all other involved matrices remain the same. Moreover, no remeshing is necessary when the conductor changes its position. The paper should be valuable for any researcher interested in the numerical simulation of eddy current problems.