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Možnosti elektromagnetického čerpání tekutých kovů a jejich numerické modelování
Musil, Ladislav ; Doležel, Ivo ; Karban, P. ; Ulrych, B. ; Barglik, J.
Electromagnetic pumps and feeders of molten metals are widely spread devices used in many branches of industry. Their operation is, however, accompanied by a high consumption of energy. Im-provement of their efficiency and optimization of their design requires detailed knowledge of the relevant electromagnetic (and sometimes also thermo- and hydrodynamic) processes. The paper deals with the principles of operation of such devices, presents their mathematical models and techniques of their numerical solu-tion. The theoretical analysis is illustrated on typical examples providing the fundamental ideas about their operation parameters and characteristics.
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Řešení 3D elektrostatických problémů se singulaturou s použitím adaptivní hp-FEM
Kůs, Pavel ; Šolín, Pavel ; Doležel, Ivo
For most numerical methods, accurate resolution of singularities occurring at sharp re-entrant corners or edges of electrically conductive objects is highly problematic. Finite differences are known for their inability to treat complex geometries, and traditional low-order (piecewise-linear or quadratic) finite element methods (FEM) exhibit extremely poor convergence. Nowadays, the best numerical method for the solution of most singular problems is the adaptive hp-version of the FEM (hp-FEM). This method is based on spatial refinements toward the singularities combined with optimal variation of polynomial degrees on the elements. The hp-FEM has mathematically proven exponential convergence, and also in practical computations typically it is by several orders of magnitudes faster than standard FEM.
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Numerical Analysis of the Magnetic Field of the Trolley Bus
Nečesaný, Jakub ; Škramlík, Jiří
This work is focused on magnetic field modeling and analysis inside and outside the trolley bus 21Tr. Computation is carried out for various working regimes for application of two different power switching semiconductor devices. Influence on environment and near low-current and telecommunication systems is evaluated. Computation of the magnetic field is per-formed by a professional FEM-based program QUICKFIELD. Problems associated with numerical computation are discussed. Local maximum of the magnetic field is also determined.
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3D diagnostika koherentních struktur ve volném proudu plazmatu
Hlína, Jan ; Sekerešová, Zuzana ; Šonský, Jiří
Optical radiation of a thermal plasma jet was recorded by a fast - shutter CCD camera through an optical system providing two perpendicular and simultaneous views of the jet. The measuring system yielded series of plasma jet images containing 8 pictures with exposure times 400 ns and intervals 7 us. The evaluation of the records was based on reconstructing the distribution of plasma optical radiation in planes perpendicular to the plasma jet axis by the inverse Radon transform. A repetitive application of this transform along the axis of the jet yielded the complete 3D distribution of the optical emission in the plasma jet. The differences between the resulting 3D matrices representing the optical intensities derived from adjacent pictures in the recorded series was used for the identification of coherent structures as regions characterized by the temporal increase or decrease of the optical emission.
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Aplikace waveletové analýzy a Fournierovy transformace pro zkoumání časoprostorové dynamiky termického plazmatu
Gruber, Jan
Electric arc plasma generated by the plasma torch (plasmatron) was analyzed. Electric arc and resulting plasma jet were observed from four directions in two parallel planes perpendicular to the jet axis and arc current and voltage were also recorded synchronously. The record lengths and time resolution were sufficient for the application of the FFT yielding a detailed view of the oscillation phenomena in the plasma flow and for comparison with oscillations of voltage and current. Significant oscillations were identified and their planar distributions examined. Wavelet analysis was used for temporal dynamics investigation yielding information about structures dynamics. Different types of structures were identified and their mutual influence is described.
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PWM Strategy for Matrix Converter
Lettl, Jiří ; Flígl, S.
The presented paper deals with matrix converters pulse width modulation strategies design with emphasis on the electromagnetic compatibility. The most of the contemporary modulation strategies are able to provide practically sinusoidal waveforms of the input and output currents with negligible low order harmonics, and to control the input displacement factor. A special digital control system was developed for the realized experimental test bed which makes it possible to achieve greater throughput of the digital control system and its variability.
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The Impact of the Grid Impadance on the HPF Performance
Škramlík, Jiří
For the implementation of Hybrid Power Filters (HPF) into a real environment it is desirable to know the impact of the grid impedance on the HPF performance. The paper evaluates the impact of diffetent components of the grid impedance and a load impedance on the HPF performance criteria by using the Fourier analysis.
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