Ing. Ladislav Musil, Ph.D.

The paper describes the use of a solar concentrator for producing electrical energy. It deals with production of electrical energy using solar radiation. The principle of the device is based on concentration of solar energy into a given area and the use of photoelectric effect for transforming this solar energy into electrical energy. The first goal was to find the amounts of electrical power and waste heat from the solar concentrator. For the chosen design a mathematical model was proposed and solved by Wolfram Mathematica. The following physical quantities and processes were modelled: the total electric power (described by photoelectric phenomenon equations), the flow of oil used as coolant (Bernoulli equation), and heat transfer between the concentrator, the cooling medium and ambient environment (laws of heat transfer by convection, conduction and radiation). The device was built in the laboratory and the numerical model was consequently tested and improved using the measured data. To achieve a relatively optimal level of concentration, an aluminium sheet in the shape of the letter "U" was used. Focused solar rays were used for the electrical energy production in a solar cell located in the lowermost part of the device. Oil flowing through the pipes removes the heat from the solar cell and cooling of the semiconductor layer improves the efficiency of solar-electrical energy conversion. The influence of device positioning (azimuth and elevation angles) was also studied. The authors hope that future experiments will lead to better understanding of the roles of direct and diffusive radiation components.

Kapitola se zaměřuje na elektromagnetická pole a jejich vliv na osoby. Jsou uvedeny příslušné legislativní limity. Jsou ukázány metody výpočtu elektrických a magnetických polí v okolí venkovních vedení vysokého a velmi vysokého napětí za předpokladu znalosti jejich konfigurace a provozního stavu, tj. příslušných napětí a proudů. Rovněž jsou diskutovány nejmodernější a efektivní metody potlačení magnetických a elektrických polí v okolí venkovních vedení.

The paper deals with a mathematical model of electron tubes which is feasible for modern numerical solvers of differential equations. It is described how to measure parameters for the model and how to use these parameters in modeling circuits.

The paper deals with a proposal of a novel computational method of magnetic field distribution in a transformer window. The method decreases demands on computational time and computer memory whereas increasing accuracy of the results. The principle of the method is described and discussed on a simple case of planar 2D arrangement.

It's known that the photovoltaic panel is producing less energy with higher temperature of a panel. The presented results show how we can produce more energy from photovoltaic panels in case of cooling these panels. We look on the panel in elektrothermal analogy and we present the equations solving problem. In paper are discussed possibilities of cooling options like a spontaneous convection or forced convection.

Článek se zabývá kombinovaným chlazením fotovoltaických panelů. Analyzované technologie jsou určeny pro extrémní klimatické podmínky.

The paper deals with a novel method suitable for modelling of surface induction hardening and other tasks, where the problem of discretisation of very thin eddy-currents surface layer is present. The method is based on artificial change of material parameters in the computer model. A methodology is suggested and limitations of its application are thoroughly tested. Odds and merits over other possible methods are also discussed.

The paper deals with Fem based models of surface induction hardening, which are build up with utilization of a suggested method based on artificial change of material parameters. The new modeling method helps with discretisation of very thin surface layer caused by a very low skin depth of the AC electromagnetic field applied on the hardened piece. The added value of the method is studied by means of a comparison with a standard method with very fine discretisation mesh.

The paper deals with methods of optimization of transformer core cross-section. A new library solving the task in a professional computer algebra system of Mathematica was written by authors. The results are shown on an illustrative example.

A new method for an easier discretization of thin surface layers with eddy currents in electrically conductive materials is presented. The basic idea of how to carry out better discretization of a very thin layer is to increase its width by transformation of the material parameters. The suggested transformation increases the skin depth but does not affect the basic integral parameters of the solution, such as the total Joule losses. The accuracy of the method is tested on very simple analytically solvable arrangements and also on two particular examples of industrial induction heating technologies.

The paper deals with tests of a new suggested method for an easier discretisation of thin layers of electromagnetic field penetrating into a conducting material. First the principle of the new method and its derivation is described. Comparison of computation with and without the transformation follows. The comparison is done on several very simple arrangements of induction heating of a ferromagnetic material. The computation were carried out by the FEM based professional code of FEMLAB supplemented with single purpose scripts written by the author in MATLAB and MATHEMATICA.

he paper deals with numerical simulation of the dynamic phenomena in an electromagnetic feeder of molten zinc. Their mathematical model consists of one partial differential equation describing distribution of magnetic fields for various levels of zinc and a system of nonlinear ordinary differential equations for the movement of zinc column caused by the electrodynamic forces acting on melt. Computations are carried out by FEM-based code Femlab and procedures developed and written by the authors in Matlab (particularly Simulink). The methodology is illustrated on an example.

Electromagnetic pumping of liquid metals belongs to rapidly developing industrial technologies that are clean, environmentally friendly and without unfavorable secondary effects. The paper deals with three possible systems applicable for this purpose: a one-phase electrodynamic feeder, a three-phase hydrostatic pump and a magnetohydrodynamic pump. Presented are their mathematical models and schemes used for their numerical solution. The theoretical analysis is illustrated on typical examples from the industrial practice.

The paper deals with a novel method developed for better discretisation of very thin surface layers in which an electromagnetic field of higher frequency is concentrated due to the skin effect. The method was developed to solve problems with thin layers using professional codes with no possibility to use an impedance boundary method. The paper contains full derivation of the proposed method, so that the reader can understand the assumptions and prerequisites necessary for its correct functioning. The errors of the method in particular applications are then investigated.

The paper deals with a suggestion of a method for an easier discretisation of thin layers of electromagnetic field penetrating into a conducting material. The basic idea of how to carry out better discretisation of a very thin layer is to increase its width by transformation of the material parameters. The suggested transformation increases the skin depth but does not affect the basic integral parameters of the solution, such as the total Joule losses. The errors caused by the application of the method on various configurations and the chance of their prediction are examined.

The paper deals with a possible way of computing inductances for circuit models of low-frequency complex devices from the magnetic field distribution. Computations are carried out by the FEM-based professional program FEMLAB supplemented with several single-purpose user procedures in Matlab written by the authors. The principle and results are illustrated on an example of a zinc feeder.

The paper deals with the computation of a thermal dissipation of heat generated in cables bedded in a cable channel. Several disposition of the channel is modelled. The convective part of heat transfer is modelled by computing the air velocities. A model with neglecting of convection is introduced and results compared. The stability due to influence of meshing is discussed. The problem is solved as 2D planar by the professional code of ANSYS supplemented with several single purpose programs written by author.

The paper deals with numerical solution of electromagnetic-thermo-mechanical transient associated with levitation heating of a nonferromagnetic sphere in harmonic electromagnetic field. Investigated is the period during which the body gets from the starting position to the final levitating position in the inductor that is, however, influenced by its next heating. The problem is solved in quasi-coupled formulation. Theoretical considerations are illustrated on an example whose results are discussed.

The paper deals with numerical simulation of the dynamic phenomena in an electromagnetic feeder of molten zinc. Their mathematical model consists of one partial differential equation describing distribution of magnetic fields for various levels of zinc and a system of nonlinear ordinary differential equations for the movement of zinc column caused by the electrodynamic forces acting on melt. Computations are carried out by FEM-based code Femlab and procedures developed and written by the authors in Matlab (particularly Simulink). The methodology is illustrated on an example.

The paper deals with two heavy current applications that works in the field of computer modeling of coupled problems with dominant influence of electromagnetic fields. The first topic is aimed at the possibility of investigation of magnetic fields produced by operation of medium voltage switchgear using the numerical simulation. The paper presents suggested methodology, the main steps of solution in ANSYS environment. The second part of the paper deals with the project whose main goal is to investigate the current loadibility of cables embedded in a cable. The material, from which the channel is made, is produced from recycled PET bottles. The task was to model the heat transfer of resistive heat power from the cable out to the surroundings. The heat flow through the cable insulation, air, channel walls and surrounding soil was modeled for a selected value of resistive heating. The comparision of models with and without inclusion of air flow was also done.

Impedance of long direct massive conductors carrying time-variable currents is a complex function of time. Its evolution is affected not only by the skin effect, but also by the temperature rise. The paper presents a numerical method that allows computing the resistance and internal inductance of a nonferromagnetic conductor of any cross-section from values of the total Joule losses and magnetic energy within the conductor. The theoretical analysis based on the field approach is illustrated on a typical example, whose results are discussed.

A lot of up-to-date industrial technologies associated with treatment of solid and liquid metals are based on thermal and force effects of electromagnetic field. The fundamental process is induction heating of metals that precedes a number of consequent operations such as tempering, drying, melting, stirring, hardening, hot pressing etc. The paper summarizes physical essence of the above processes (that usually represent complex coupled problems) and presents their mathematical and computer models as well as possible methods of their solutions. Theoretical considerations are illustrated on several typical examples solved by the authors.

The paper deals with E-learning with use of Mathematica and webMathematica programs and technologies. It discuses advantages and disadvantages of particular approaches and shows some possibilities of the technologies on the example of teaching text about method of weighted residuals. The possibilities of webMathematica in research area are also discussed.

This paper deals with the use of an information portal in electrical power engineering subjects teaching. Our team has developed an educational portal for computer-aided training. The portal is designed for interactive educational texts hosting. The technology based on webMathematica system from Wolfram Research was used. The system exploits Java Servlet, Java Server Pages (JSP), The Extensible HyperText Markup Language (XHTML) and Mathematical Markup Language (MathML). Teachers can publish texts on internet including interactive examples. Students can than learn about a physical phenomena or mathematical solutions not only by reading texts, but they can also try to get in closer touch with the problem or physical phenomenon etc. by solving prepared examples for different input values, parameters, methods of solutions etc.

The paper presents a numerical method that allows computing the resistance and internal inductance of a nonferromagnetic conductor of any cross-section from values of the total Joule losses and magnetic energy within the conductor. The theoretical analysis based on the field approach is illustrated on several typical examples, whose results are discussed.

Impedance of long direct massive conductors carrying time-variable currents is a complex function of time. Its evolution is affected not only by the skin effect, but also by the temperature rise.

Příspěvek se zabývá modelováním elektromagnetického pole indukčního dávkovače roztaveného zinku. Je modelován režim dávkování i režim přihřívání v prodlevách mezi dávkováním. Je zkoumán a ukázán vliv některých parametrů a možnosti zlepšení účinnosti a výkonu dávkovače.

The paper deals with the optimizing of distribution of weight-uneven vanes along the turbine's rotor circumference. The aim is to find vanes' positions in such a way, that aggregate centre of gravity lies in the minimum distance from the axis of the rotor.

Zpráva shrnující aktuální informace z oblasti nasazení rozptýlených zdrojů ve vazbě na spotřebu elektrické energie.

Článek se zabývá problematikou výpočtu Scottova zapojení transformátoru za pomocí programu Mathematica a převod tohoto výpočtu do programu webMathematica.