No. 3, 2006


Vratislav Kafka : Mesomechanical model of the effect of plastic prestrain on creep, pp.213-235

The author's general concept of mesomechanical constitutive modeling is applied to a relatively complicated problem-modeling the combination of plastic deformation and creep. These two processes have been studied and modeled separately in previous author's works and the main point of the current study is modeling the transition from the state after small plastic prestrain at room temperature to the creep at a substantially higher temperature. The main hypothesis says that residual energy of internal microstresses after plastic deformation and unloading remains preserved after the transition to creep temperature. This hypothesis alone was not sufficient and had to be complemented by another one. The material is described as a composite consisting of two material constituents: of a compliant constituent and of barriers that hinder the inelastic deformation. The relation of the respective two parts of the residual energy comprised in these two constituents is hypothesized to be preserved too. The model based on these two hypotheses is applied to creep preceded by small plastic strain of a concrete material and confronted with the respective experimental findings. The paper is also meant for a new demonstration of the generality of the author's mesomechanical concept.

Petr Drexler, Pavel Fiala : Numerical and experimental analysis of power pulsed microwave generator, pp.237-253

The paper describes the numerical solution of the transient in a helical power pulsed microwave generator. The generator whose assumed peak power Pn = 10 MW is in operation for approximately 10 ms. The function of the structural parts of the generator was investigated by means of a mathematical model written in mixed formulation (the model consists of a set of partial differential equations describing the distribution of the most important physical fields and an ordinary differential equation for the feeding electric circuit). Selected results of the solution were verified by measurements.

Vaclav Bartos, Milos Ryba : Switching process of the double cage asynchronous machine, pp.255-267

The switching process in a double cage asynchronous machine is analysed. The solution is accomplished using the Laplace transform under necessary simplifying conditions-a linear system is assumed. What is detailed is determining the roots of the characteristic equation. The currents and torque are evaluated.

Irena Kovacova, Dobroslav Kovac : EMC of DC electrical drives-inductive coupling, pp.269-278

This paper deals with computer analysis of the inductive coupling part of the electromagnetic compatibility (EMC) problems focused on the area of power electronics and electrical drives and performed by numerical computer simulation. Also the problem of interference between electric motor and surroundings space caused by electromagnetic field radiation is discussed.

Neela Chattoraj, Jibendu Sekhar Roy : The optimization of gain of patch antennas using genetic algorithm, pp. 279-287

The application of Genetic Algorithm (GA) to the optimization of gains of rectangular and circular microstrip patch antennas are reported. In both the cases the fitness functions are developed using cavity method for the analysis of microstrip antenna and the GA code was developed using C++ language. The results are verified by comparison with the results obtained using MATLAB and some results are supported by experimental verification.

Alice Sperova, Pavel Fiala : Finite element analysis of vibrational micro-generator, pp.289-299

The paper presents the numerical results of analysis of a vibrational micro-generator. The work presented in this paper was conducted as a part of a project aimed at powering low-power sensors. The paper deals with the design of a vibrational micro-generator that is used as a power supply for independent electric circuits. This device can be used in various areas, e.g. transport, electronics, special-purpose machines, and robotics. The proposed design employs magnetic damping of the core movement. It was numerically evaluated and proved to provide significantly larger output voltage and output power than in experimental settings used previously.

Zdenka Benesova, Vaclav Kotlan : Propagation of surge waves induced by lightning stroke on interconnected transmission lines, pp.301-316

The paper deals with the modeling of surge phenomena on transmission lines caused by the lightning stroke. The lightning is modeled by a voltage or current wave injected by a source placed at any internal point of the line. Considered is an overhead line or a combination of an overhead line and cable where the overhead line is connected to the cable directly or via a transformer. The load of the line is a circuit with lumped parameters that can involve resistance, capacitance, inductance, or any combination of them. Propagation of the injected wave is solved numerically in the time domain. The efficiency and correctness of the proposed method are demonstrated on several illustrative examples. Investigated is the distribution of induced current and voltage along the whole transmission line, particularly at the place of connection of both lines.