No. 1, 2007


Miros Pirner : Aeroelastic models of building structures, pp. 1-14

Critical assessment of aeroelastic models. Influence of non-observation of the Froude number. Demonstration of same on an example.

Jiri Sonsky : Applying fibre optics to plasma jet diagnostics, pp. 15-31

Photodiode arrays can be successfully used in plasma jet diagnostics thanks to their capability of fast response to light signals, allowing high sampling rate, sufficient sensitivity and low noise. The fibre optics coupling can overcome low spatial resolution and yield a unique flexibility. Thanks to using modern integrated circuits and electronic devices, we get a reduced electromagnetic noise. The new experimental layout is suitable for desired experimental conditions and technological applications. Multidirectional observation and applying inverse Radon transform yield reconstructed cuts perpendicular to the plasma jet axis, which are directly unavailable by recent experimental methods. These cuts and their time evolution are suitable for tracking rotational instabilities of the plasma jet axis position, evolution of plasma velocities and velocity profiles, as well as studies of the enthalpy distribution and heat flow vector vorticity that are prepared for next publication.

Pavel Zaskalicky, Maria Zaskalicka : Torque ripple calculation of universal motor supplied by triac converter, pp. 33-43

A universal motor is one of the most used electrical machines in small electrical instruments and home equipments because its speed is easily controlled by the control of supply voltage. The present paper shows analytical calculation of the torque ripple and current waveform of the motor by triac converter supply. The converter output voltage waveform is expressed by the Fourier series. The armature reaction of the motor is included in the calculation. The motor performance is computed, using the circuit parameters determined by measurements. Calculated waveforms are confirmed by the experimental results.

Jiri Klima : Space-vector based PWM strategies with six-fold symmetry for three-phase voltage source inverters, pp. 45-67

The objective of the paper is to present the output waveforms for the known three phase inverters (B4, B6 and B12 voltage source inverters) with six fold space vector PWM symmetry. This modulation strategy ensures synchronization, half wave symmetry and three-phase symmetry. The principles of achieving synchronization and symmetries in terms of space vectors for the two level, three level and four switch inverters are presented. The analytical results are validated by the experiments.

Jaroslav Feda : Creep effect of angularity, pp. 69-79

Some dry granular materials (angular and rounded silica gel, powdered and granulated clay) were loaded in an oedometer and their uniaxial creep analysed. Creep curves were of hyperbolic nature, except the spherical silica gel. Thus the grain shape plays with creep an important role. Creep parameters are mutually related and their relation does not depend on the angularity. Creep is governed by nonlinear directrices.

Jaroslav Timko, Jaroslava Zilkova, Peter Girovsky : Shaft sensorless vector control of an induction motor, pp. 81-91

The present paper deals with design of artificial neural networks and their application to dynamical system modelling. Shaft sensorless control of induction motor drives requires knowing the instantaneous value of rotor speed. This paper considers the problem of speed estimation, based on neural modelling approach, in the shaft sensorless vector control structure with the induction motor. Suggested have been two differing neural estimators; one for observing the magnetizing current and the other one for observing the motor angular speed. Structures of the ANN estimators are based on measurable motor variables: components of stator current and voltage.

R. C. Chaudhary, Arpita Jain : Unsteady free convection flow past an oscillating plate with constant mass flux in the presence of radiation, pp. 93-108

This paper investigates the unsteady viscous incompressible flow past an oscillating plate when mass is supplied to the plate at constant rate in the presence of radiation. The fluid is a Newtonian, gray, absorbing-emitting but non-scattering medium. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The dimensionless governing equations are solved in a closed form by Laplace-transform technique. A parametric study illustrating the influence of various parameters on the velocity, temperature as well as on the skin-friction, rate of heat transfer and the Sherwood number is conducted graphically and the physical aspects of the problem are discussed.