|ACTA TECHNICA CSAV|
The paper deals with a frictionless contact problem of two congruent rigid spherical surfaces, one encased in the other, coated with a thin elastic transversely isotropic and incompressible bonded layer. A simplifying approximation for the displacement in the coating enables the problem to be formulated using stress and strain averaged through the coating thickness (for the method see M. J. Matthewson, Journal of Mechanics and Physics of Solids 29 (1981), 89-113). Analytical results are obtained for the contact radius and the contact stress distribution. Given this contact stress distribution, an asymptotic analytical solution for the displacement in the coating is then obtained. The results are applied to the human hip joint.
Since the 1970s, magnetic separation has been increasingly used for purification of liquid, such as heavy-metal ion removal from laboratory waste-water, purification of kaolin clay in the paper-coating industry, waste water recycling in the steel industry, and recycling of glass grinding sludge in cathode-ray tube polishing factories. In the 1980s, large superconducting magnets were adopted for the field coils of high-gradient magnetic separation system used for kaolin clay purification. In this paper some practical aspects of the construction of a matrix high-gradient separator equipped with the DC superconducting electromagnet as well as the problems of working conditions of the separator are presented. In the separator, magnetic field will be generated by superconducting windings than low temperature superconductors (LTS) or high temperature superconductors (HTS).
The principle of a non-destructive method (NDT) for testing materials is based on using eddy currents. Following the quasi-stationary theory, a special approach based on NDT-remote field eddy current technique is described. Using an internal probe, the method is particularly advantageous for a full wall inspection, for instance for testing heat exchangers and pressure tubes. This method allows detecting external and internal defects with approximately equal sensitivity. The paper presents some results of finite element method simulation of the remote field principles in a conductive tube. We compared the voltage induced in the pickup coil (during the period when the probe was moving over a defect) in two cases; when the pickup coil was set in near field and then in far (remote) field. Measuring was realized and compared for several depths of inner and outer defects. The amplitude and complex plane representation of induced voltage were used to interpret defect indication.
The idea of an isothermal conversion of elastic stress into elastic strain by testing elastic moduli in metals is unrealistic. Recent findings suggest that the forces operating in the interior of metals under elastic strain are non-conservative, causing temperature changes and subsequent thermal dilatations to arise. Despite being imperceptible, the dissipations absorb a significant amount of deformation energy, which makes for the adiabatic nature of the Young moduli. The latent thermodynamics needs respecting in numerical predictions of structures' behaviour, especially if dynamic regimes are simulated.
The most popular microturbine system is the single-shaft type using a permanent magnet synchronous generator (PMSG) with high operating speeds, along with a power converter system and a low pass filter to convert the high frequency voltage of the generator to a suitable three phase voltage for the purpose of supplying local loads and/or operate in parallel with a grid. The developed dynamic model of the microturbine (MT) system for a grid-connected operation was based on the dynamics of its subsystems using Matlab/Simulink software. The dynamics of the overall system are investigated by considering local load demand changes while the desired power output of the MT is commanded to follow these load variations. The main impacts resulting from the connection of the MT system to the grid are assessed through power quality performance indexes, e.g. the voltage variations at the connection bus, and the total harmonic distortion (THD) of the associated voltage and current.
Besides traditional procedures of treatment of various cancer lesions as are cytostatics, x-ray irradiation and surgery, the photodynamics is a relatively new and significant promise of the full cancer treatment, especially in early stage and in connection with the gene therapy. In several world institutions the surprising successful treatment results have been achieved by use of this method, however, much less is done in this field in the Czech Republic. Some recent representative treatment results, including our original contributions, are presented.
The creep behaviour of lentil and oat flakes is investigated using uniaxial (oedometric) loading. The experiments are intended to define the limits of the granular behaviour of soils. The biological material was chosen to test the matter consisting of grains of equal diameter and shape. It was found that the behaviour generally copies the behaviour of granular soils (secondary compression) but a negative creep was found after a longer time periods. This is assumed to be the result of structural metastability in the higher load range when strong parallel arrangement induces a quasioverconsolidation of the material. A physical model to explain this behaviour has been proposed.
The paper deals with the methodology of designing a complete fuzzy model of an electrical drive based on a suitable database of measured input-output values. This methodology covers the entire range of possible drive inputs, without requiring any information about the drive structure and parameters. The presented modeling method is verified by simulation by means of the MATLAB� software package. Obtained simulation results demonstrate that this procedure of designing a complete fuzzy model can be applied to any type of drive.