|ACTA TECHNICA CSAV|
The paper deals with numerical modelling of the dynamic behaviour of a non-ferromagnetic pulsed induction accelerator (PIA). The task is formulated as a hard-coupled electromagnetic-mechanical problem whose semi-continuous mathematical model is built on the theory of electric circuits. Its discretisation and consequent numerical solution provides various important dynamic characteristics such as time dependencies of the trajectory, velocity, acceleration and also current in the field circuit. The theoretical analysis is supplemented with an illustrative example.
Selected transient phenomena in an induction motor fed from a voltage converter are presented. The following phenomena are in question: Response on i) step change in voltage and frequency, ii) short-term switch-out of all transistors of converter, and iii) short-circuit on the input to a feeding circuit.
The matter waves emitted by electrons in atomic oscillators interfere with one another in interatomic vacuum. Besides generating energy quanta of electromagnetic radiation through interference surges, the matter waves produce also heat energy that appears to be a chaotic by-product of the interference. As a result, the electromagnetic radiation may be considered to be a continuous energy flow of light and heat, where the latter component spreads out at a group velocity of matter waves. Using as a basis the spectrum of the atom of hydrogen, mathematical treatment shows that the two types of energy exhibit ambivalent trends in terms of frequency. Their superposition counterbalances the energy distribution curves, repeating the following standard course in all spectral series of hydrogen: First an increase to a maximum and then a continued decline as the frequency of radiation is increased. This is a similar routine as that of the black body emissivity in Planck's Radiation Law. The maximum values of energy at particular distribution curves (obtained by adding up the quantized and non-quantized energy components) observe the Wien Displacement Law. These results were obtained without using the methods of statistics.
In Part I of the present paper a mixture model of synovial fluid filtration by articular cartilage with a worn-out surface zone in the loaded human ankle joint for steady rolling/sliding and pure sliding motions have been presented. Biphasic models for cartilage and synovial fluid have been used. While the governing equations have been obtained in Part I, numerical results for steady sliding of the talar surface are presented in this part of the paper. For this case and for the physiologic parameters of the ankle joint during walking, a continuous synovial fluid film about 1mm thick is maintained under steady entraining motion according to the classical model without the fluid transport across the articular surface. This might not be the case in the model with filtration of the synovial film by cartilage. On the contrary, the filtration model indicates that synovial fluid is intensively filtrated by articular cartilage with the worn-out surface zone and a synovial gel layer, thick of order 10-7 m, may develop over the majority of the contact. This means that for articular cartilage with a worn-out surface zone boundary lubrication should prevail in the ankle joint under steady sliding motion for the mean values of loading and sliding velocity encountered in walking.
This paper is devoted to the triangular mesh generation on domains with arbitrary geometries. A special approach for the generation of an optimal number of uniformly distributed inner grid points is proposed. The scheme is based on an analogy with the construction of an equilibrium state of a system of a finite number of uniformly charged electrical particles closed in a bounded vessel. The method has minimum geometrical constraints and is therefore suitable also for domains with really complicated geometries. Efficient meshing procedure of the advancing front type is applied to the pre-constructed set of inner grid points and its reliability proved. An object-oriented freeware C++ library XGEN based on the presented method is developed. Advantages of the object-oriented approach are explained and the usage of the meshing tool briefly described. Examples on the mesh generation on various domains are presented.
The paper presents coupled and non-linear electromagnetic and thermokinetic problems occurring during stationary induction heating of flat charges. The possibility of obtaining uniform temperature distribution at two-sided, through heating of charges made of nonmagnetic and ferromagnetic materials is analysed. The following ways of temperature distribution formation in the charge are discussed:
- choice of inductor length (in relation to charge length),
- application of magnetic cores
- gradation of inductor specific electric loading.
Numerous calculations have been presented. Computer programme FLUX2D has been used for the analysis.
Creep behaviour of pure aluminium and two its solid solutions, i.e. Al-13.7Zn and Al-5.5Mg, were investigated extensively using the constant structure creep experiments performed in the steady state creep stage. Results of the investigations of these two solid solutions are summarized here. While the AlZn alloy can be considered a typical alloy exhibiting Class II creep behaviour, the AlMg alloy represents the typical alloy with Class I behaviour. The residual effective stress was chosen as the governing stress variable for the constant structure creep rate. The steady state creep rate is the result of a single dominant dislocation mechanism in both alloys. From an analysis of the constant structure experiments, it was determined that diffusion along high diffusivity paths controls creep in the AlZn alloy. In contradiction with this, creep in the AlMg alloy is controlled by lattice diffusion.