František Dzianik, Štefan Gužela and Eva Puškášová
The paper presents a comparison of the process properties of two types of the heat exchangers designed for the heat removal from a high temperature helium cooling loop with steady natural circulation of helium. The first considered heat exchanger is a shell and tube heat exchanger with U-tubes and the other one is a helical coil heat exchanger. Using the thermal and hydrodynamic process calculations, the thermal performance of the two alternative heat exchangers are determined, as well as the pressure drops of flowing fluids in their workspaces. The calculations have been done for several defined operating conditions of two considered types of heat exchangers. The operating conditions of heat exchangers correspond to the certain helium flow rates.
The problem of active vibration control of weakly damped mechanical structures is potentially unstable modes of vibrations due to the positive feedback for some vibration modes. The paper will discuss the change of positive feedback on the negative one using all-pass discrete-time filters. These filters can be arranged in a cascade to stabilize many potentially unstable modes. The piezoelectric actuator as a source of force is used to damp vibration.
Based on the theory laid down in the Part 1  in this paper we are going to display applications in physics and especially in mechanics. After a short summary on coupled fields in mechanics, we generally analyze the analogies in mechanics. As the most important, the electrical analogy is discussed in details. By the electrical analogy based analytical solution we display the results of the coupled thermo-hygro problem with second sound. Finally, a few experiments are discussed, eg. experiments by electrical analogy, experiment on diffusivities, experiment on relaxation time, experiment on hydroglobe. This latter one leads to the engineering application of the problem.
Traditionally, the Furuta pendulum was used for testing advanced control strategies on a simple nonlinear and underactuated structure. In this paper, we investigate analytically and experimentally the dynamical description of the Furuta pendulum focusing on the effect of dry friction on a special bifurcation behaviour of the downward equilibrium position.
Trebuňa František, Bocko Jozef, Pástor Miroslav, Lengvarský Pavol and Prada Erik
The paper deals with design and computation of precise positioning mechanism. The aim of mechanism is to transfer applied load without any change of position of parts in question. The stabilization of position is assured by elastic elements connected to reductor which is adjusted into correct position by an actuator. The functionality of mechanism and its stiffness and strength characteristics were checked by the finite element method. The computations were accomplished for prescribed displacement of reductor. On the base of this type of loading the behaviour of the structure was evaluated.
Two test stands for determining sound insulation in the frequency range above 5 kHz were made. One consisted of two horizontally adjacent reverberation rooms and a special source of high frequency sounds and ultrasounds. The other test stand consisted of a miniaturized test chamber and a special source of ultrasounds. The paper presents results of the preliminary measurements of sound insulation properties of different barriers in the frequency range above 5 kHz.
The article deals with the contribution of Prof. Ing. Pavol Élesztős, CSc. in the field of engineering. He was born in 1948, studied and subsequently remained at the Faculty of Engineering at the Slovak University of Technology in Bratislava since 1968. Under his leadership 6 dissertation theses were defended in the study program of Applied Mechanics. He is the author of 1 monograph, co-author of 2 monographs, author of 30 reviewed scientific articles in journals, and over 250 original scientific papers published in domestic and foreign conference proceedings. Professor Élesztős is currently a Professor Emeritus and is known as a talented teacher.
This article is a celebration of prof. Ing. Stanislav Žiaran’s, CSc. contribution to the field of engineering. Born in 1948, since 1966 he studied and subsequently continued his academic career at the Faculty of Mechanical Engineering, Slovak University of Technology in Bratislava. He has supervised 2 dissertation and 42 diploma theses, which were successfully defended in the study programs Applied mechanics and Mechatronics. Prof. Žiaran is the author to 5 monographs, 9 textbooks, 13 university textbooks, 6 manuals for the engineering industry and more than 290 original scientific papers published in domestic as well as international journals and conference proceedings. He has translated of 111 ISO and EN standards, 107 research reports for practice and he is the editor of 20 peer-reviewed scientific proceedings Noise and Vibration in Practice. He also presented 16 requested lectures at world congresses abroad. Prof. Žiaran is a gifted teacher of mechanics and his students appreciate his enthusiasm and knowledge he is sharing with them.
Kunz Jan, Čala Martin, Pikula Stanislav and Beneš Petr
The aim of this paper is to design, implement, test and compare several tracking filtration methods for predictive maintenance of a jet engine. Based on literature review multiple possible methods are described. Appropriate ones selected for further implementation are peak filtration, coherent demodulation, Vold-Kalman filtration and order analysis. Methods are tested to meet criteria set by an aircraft manufacturer and compared using simulated signals.
The analytical model of a fluid filled cylindrical shell is used to analyse the wave propagation in the quarter wavelength absorbers. It has been found, that due to the strong fluid-structure interaction, the considerable wave speed reduction can be reached using a compliant shell. Thus via parametric studies, the dimensions of the absorbers are assessed to reach more efficient and compact design. Furthermore, the use of the compliant materials allows treating the fluid to be incompressible, which helps to simplify the calculations.