No. 1, 1997


Daniel Mayer: Contribution to the synthesis of symmetrizing three-phase circuit, 1–12

Unbalances in three-phase networks caused by connecting to them unbalanced three-phase (in particular, one-phase) consumers are dealt with by means of a symmetrizing circuit. The ways of design of the symmetrizing circuit described in literature are based on some restrictive assumptions. A weakening of these assumptions is the aim and the main contribution of the present paper. As a rule, the symmetrizing circuit which also can compensate the power factor of the consumer to the required value, can be in practice realized only in a way which symmetrizes the load only partly. In the paper we introduce quasi-symmetry coefficients, which enable us to assess the function of the symmetrizing circuit.

Josef Adam, Ivo Dolezel: Computation of the open boundary magnetic field of an electromagnet and its comparison with experiments, 13–27

The commercial program OPERA 2D (VECTOR FIELDS, GB) has been tested with the aim to evaluate its applicability for computation of open boundary magnetic fields. The solved arrangement was a cylindrical coil with the open ferromagnetic core. The results (field distribution and other derived quantities) were compared with values obtained experimentally for two positions of the core. The accordance of calculations and measurements was almost perfect not only in the local values, but also in the integral quantities (inductance of the arrangement).

Vaclav Nenicka, Jan Hlina: Identification of basic oscillations in plasma jets, 29–51

The paper contains an information about the FFT spectra describing the dynamics of a plasma jet generated by a cascade plasmatron operated with a tangential inlet of argon in the interval of input gas flow rates from 10 l/min to 200 l/min for electric currents from 100 A to 225 A and discharge chamber lengths from 40 mm to 80 mm. The dependence of the plasma jet dynamics on the gas flow rate is shown. According to the results the influence of the arc current and the discharge chamber length is not decisive for the dynamics before its second stage when the interaction of the both mechanisms controlling the plasma jet dynamics in the first and third stages take place. These two mechanisms are represented by the onset of a shear layer and a global resonance in a plasma jet.

A. Walicka: Pressure distribution in a ferrofluid flow between rotating surfaces of revolution, 53–71

The steady laminar flow of a viscous ferrofluid is considered, through a narrow space between two rotating surfaces of revolution, having a common axis of symmetry. To solve this problem the boundary layer equations are used and expressed for the axially symmetric case in a curvilinear orthogonal coordinate system x, u, y connected with one of the surfaces. The method of integral approaches is used to solve the boundary layer equations. As a result one obtains the formulae expressing such flow parameters as the velocity components vx, vu, vy (without inertia effects) and pressure p (with total inertia).

Jiri Bendl, Ludek Schreier: Solution of selected failure states in power system with asynchronous generator, 73–91

The paper presents analysis of a power system with asynchronous generator which feeds a local load in an autonomous operation. Two types of failure states are investigated: i) a sudden change in the load in some of the phases, implying a dissymmetrical operation, and ii) disconnecting of a part of the battery of capacitors. The negative consequences of the failures are discussed. Especially there appear considerable overvoltages and overcurrents which can damage or destroy electrical appliances and equipment.

Alexander M. Samsonov: How to predict, generate and observe strain solitons in solids, 93–113

Mathematical theory of long nonlinear strain waves in elastic wave guides was developed in order to initiate the successful generation of strain solitons in solids. New nonlinear quasi hyperbolic "double dispersion equation" (DDE) was derived to describe long nonlinear wave evolution in a thin hyperelastic rod. Various exact travelling wave solutions to the DDE were obtained, additional conditions were found, under which the long nonlinear solitary strain waves may exist in nonlinearly elastic materials. Based on the theory, the experiment was proposed and longitudinal strain solitons in nonlinear elastic wave guides were generated successfully, using laser pulse source, and observed by means of holographic interferometry method. The compression strain solitary wave as a whole is shown on pictures. We demonstrate that the strain soliton can be reproduced and observed in a physical lab in ordinary conditions.