No. 1, 2000


Pavel Solin: On a model of polluted gas flow, 1–20

This paper is devoted to the numerical simulation of motion of a compressible inviscid fluid polluted by small particles of mass. We assume that the particles are so small that they do not influence the fluid flow. The compressible Euler equations are semi-discretized in space by the Finite Volume Method and transformed into a system of first-order ordinary differential equations. This system is coupled with a system of second-order ordinary differential equations describing the motion of particles within the fluid. Resulting system of ordinary differential equations is solved by suitable implicit and explicit solvers for systems of ordinary differential equations. Two and three-dimensional numerical examples are presented.

Viktor Valouch: Performance criteria of hybrid power filters, 21–43

A general circuit diagram involving main viable configurations of hybrid filters is presented. Assuming that the harmonic detection control strategy is applied, general transfer functions are determined and analysed. An easy to survey table summarizes the basic properties of all main configurations on the assumption of infinite feedback gains of the control strategy. The data in the table are supported by results of simulation, taking realistic values of gains and time delays into consideration. The results presented explain the basic characteristics of the hybrid filters in their wider mutual aspects, so the effectiveness and demanded rating of active parts of the hybrid filters may be evaluated.

Jaroslav Kucera, Pavel Broz, Kryzstof Adamaszek: Decarburization and hardness changes in carbon steels caused by high-temperature surface oxidation in ambient air, 45–64

In the given paper the results of investigation of decarburization and hardness changes caused by oxidation in ambient air in the Fe-C-Cr-Mn-Si steels are reported. The oxidation anneals were carried out at temperatures 900C up to 1200C. The measured values of carbon concentration N(C,x,t) and of hardness HV(x,t) yielded the possibility to calculate carbon diffusion coefficients D(C) and D(HV). The obtained values D(HV) agree with the values D(C) in the frames of experimental errors in the case when the hardness HV(x,t) is directly proportional to the carbon concentration N(C,x,t). Both the diffusivities D(C) and D(HV) depend on temperature T and on chemical composition of the steels. This last dependence can be described by the use of diffusion interaction coefficients bCi and concentrations values Ni of the individual alloying elements -i-.

Ladislav Pust: Vibrations of mechanical system with two piecewise linear characteristics, 65–77

Simplified mathematical model of the active magnetic bearing with stiff rotor is derived and analysed. This magnetic bearing contains two strong nonlinearities; stiff stop of the emergency retainer bearing in mechanical subsystem and current limitation in power amplifier of electrical control subsystem. The influence of each one of these nonlinearities on the behaviour of the whole system in studied. Effects of simultaneous acts of both nonlinearities on the form of oscillations, response curves and on stability of motion are investigated as well.

Czeslaw Sajdak, Krzysztof Kurek, Roman Przylucki: Induction melting and preheating of non-ferrous metals in tanks with conductive walls, 79–89

The paper presents the results of computer simulation for induction melting and preheating of non-ferrous metals in rectangular tanks with conductive walls (metal or graphite). The real heating device was replaced by a flat two-dimensional model with inductor, heat-insulating materials and a tank with melted or preheated metal. Computer programme FLUX2D was used for the calculation of coupled non-linear fields: electromagnetic and temperature ones. Temperature in the walls and in metal as well as basic electric parameters of the heating device were determined.

Ales Tondl, Radoslav Nabergoj: The effect of dynamic absorbers for a parametrically excited pendulum type system: numerical results, 91–108

This paper supplements the previous paper which has dealt with two systems consisting of a basic elastically mounted pendulum system to which an absorber subsystem is attached. Two absorbers are considered: System I whose motion is perpendicular to the pendulum axis and System II whose motion takes place along the pendulum axis. The pendulum basic system is excited parametrically due to the vertical harmonic motion of its suspension point. Beside some further analytical considerations for System I especially numerical results for both systems are presented in this contribution. Numerical results confirm the analytical ones.