No. 1, 2003


Ivo Dolezel, Petr Kloucek, Pavel Solin, Bohus Ulrych : Distribution of electrical charge in a system of finite conductors, pp.1-13

Numerical approximation of the distribution of electrical charge in systems of mutually electrically isolated conductors carrying different electric potentials is in practice extremely difficult by means of standard FE schemes. The main obstacles are represented by lack of the boundary conditions and geometrical incommensurability of various elements present within the investigated domain. The paper reformulates the problem onto a system of the first-kind Fredholm integral equations with a weakly singular kernel that is discretized alternatively to the classical Nystrom method. Solvability and unambiguousness of the continuous mathematical model as well as convergence of the numerical scheme is shown. Quasi-equilibrium approach for the simulation of moving conductors is also discussed. The methodology is illustrated on a typical example.

Daniel Mayer : Basic theory of new maglev system, pp.15-26

The ways of the magnetic levitation have passed through an intensive and financially very expensive development within the last forty years. The research and development works have been recently finished and nowadays first magnetically levitated fast trains HSGT (High Speed Ground Transportation) are introduced into operation. One of them is the German system Transrapid based on the electromagnetic principle, another system MLU of the Japanese provenience is based on the electrodynamic principle with superconducting magnets. Several years ago, one more interesting magnetically levitated transport system was patented in the USA that uses permanent magnets in the Halbach array. Up to now, this system called Inductrack has been experimentally verified only on small models, but the acquired experience indicated that in comparison with existing Maglev systems this new system has a number of remarkable properties. The paper represents the first (as far as the author knows) contribution aimed at building of the corresponding mathematical model.

Ales Materna, Frantisek Kroupa : Bending of beams with nonlinear thermally sprayed coatings, pp.27-48

Young's moduli of thermally sprayed especially ceramic coatings are, due to the presence of microcracks, substantially smaller than those of well sintered materials. However, under high compressive or tensile stresses the behaviour of coatings is strongly nonlinear, which is caused by the elastic decrease or inelastic increase of the microcrack densities.

The bending of beams with nonlinear coatings on the compression or tension face caused by residual stresses or external moments is analyzed theoretically. Examples of the stress distributions are given and the differences between the nonlinear and linear solutions are discussed. The effect of the existing residual stress on the stress distribution under external moment due to nonlinearity is emphasized.

Frantisek Kroupa : Dependence of microcrack densities in thermally sprayed coatings on deformation, pp.49-64

Young's moduli of thermally sprayed coatings, measured at small deformations, are known to be much smaller than those of well sintered materials, due to a high density of microcracks. Moreover, at higher deformations the behaviour of coatings is strongly nonlinear, which may be attributed to changes in microcrack densities with deformation. In this paper, the dependence of the microcrack densities on compressive and tensile deformation is predicted on the basis of two known dependences: theoretically predicted dependence of Young's modulus on microcrack density and the nonlinear stress-strain relation.

Hedaya Al Asooly, Josef Tlusty, Viktor Valouch : Comparison of different methods for optimal control of UPFC for load flow control and voltage flicker elimination and current harmonics elimination, pp.65-75

Recent advances in power system handling capabilities of static switches have made the use of the voltage source inverter (VSI) feasible at both transmission and distribution levels. This paper demonstrates a new optimal control scheme for Unified Power Flow Controller (UPFC) to control power flow as well to improve the system stability and to eliminate current harmonics and voltage flickers Three tracking strategies have been tested: tracking according to steady state behaviour, continuous linear quadratic tracker and tracking with PI controller.

Jindrich Rybar, Milan Krasl : Calculation of losses in windings of superconducting transformer, pp.77-88

The paper deals with numerical computation of the AC losses in windings of a superconducting transformer. The formula used for their evaluation is based on experimental data and depends on geometrical and material parameters of the arrangement. The authors focused their attention on analysis of influence of the magnetic field and the angle under which this field is applied to the superconductors. The methodology is illustrated on an example-a superconducting transformer manufactured in SKODA Research Ltd.

Pavol Fedor, Daniela Perdukova, Jaroslav Timko : Identifying the asynchronous motor inner values, pp.89-97

The paper deals with the identification of asynchronous motor inner values, i.e. with the identification of magnetic rotor flow and motor moment. Proposed identification structure for the asynchronous motor is based on an AM mathematical model, which utilizes commonly attainable measurable motor values, specifically the stator currents and the rotor mechanical speed. This structure allows a quality identifying the motor rotor flows even at unknown rotor resistance. Proposed structure results are verified by modelling basic working states by means of programming package MATLAB.

Ales Tondl, Lubomir Kocanda : Self-excited two-mass system with soft impacts, pp.99-112

To a basic one-mass self-excited system a tuned absorber is attached the motion of which is influenced by soft impacts. The self-excitation is considered as that of the van der Pol type. The stops are symmetrically situated to the absorber mass equilibrium position. The results of numerical simulation are presented in diagrams showing a certain ratio of extreme deflections of the basic system in dependence on the tuning coefficients of the tuned absorber. This ratio of maximal extreme deflections of the basic system to the amplitude of the system without absorber is the measure of the tuned absorber's efficiency. The following effects are investigated: the ratio of the absorber mass to the basic system mass, the distance of the stops, absorber motion damping, and damping in the stops. Generally the stops do not represent a favourable effect.