Mechanics and Control
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ISSN 2083-6759
e-ISSN: 2300-7079
Issue Date
2015
Volume
Vol. 34
Number
No. 2
Description
Journal Volume
Mechanics and Control
Vol. 34 (2015)
Projects
Pages
Articles
Time-variant frequency response function for analysis of time-varying mechanical systems
(Wydawnictwa AGH, 2015) Dziedziech, Kajetan
System Identification is an important and often complex process in many areas of engineering. This process is not easy when the parameters of the analyzed system vary with time. In such cases, classical methods fail to properly identify the parameters. The work demonstrated in this paper deals with the identification of natural frequencies in time-variant systems. The paper presents the application of the Time-Variant Frequency Response Function for this analysis. The calculation procedure requires division of the output spectrum by the input spectrum, which often leads to division by close-to-zero values, this leads to infinite (or undefined) values of the resulting transfer function. Additional processing is required for interpretation. The major focus and challenge relate to the ridge extraction of the above time-frequency characteristics. The methods presented in the paper are illustrated using an experimental multi-degree-of-freedom system. The results show that the proposed method correctly captures the dynamics of the analyzed time-variant systems.
Control system preventing thermal gradient development on foils of foil bearing
(Wydawnictwa AGH, 2015) Lubieniecki, Michał Lucjan; Miodunka, Marek
This article presents attempts at automating a control system to reduce temperature scatter on the foil of a foil bearing. The control system reads the temperatures at six circumferential locations of the bearing's foil and distributes control currents to the thermoelectric modules integrated into the bearing's bushing. Three basic approaches have been proposed and tested: 1) a simple hot-spot tracking algorithm assigning predefined current values to the modules closest to the hot-spot location, 2) a tracking algorithm reducing abrupt changes in the control currents and, in effect, the local heat flux distribution, and 3) a tracking algorithm enhanced with a PID controller. The proposed controller has been implemented and compared to the performance of a temperature controller that does not have tracking capabilities. The implemented control strategies have proven the feasibility of temperature scatter reduction inside the investigated bearing. In most test cases, the instantaneous gradient reduction exceeded 50% (reaching 63% at its best).
On nonlocal modeling in continuum mechanics
(Wydawnictwa AGH, 2015) Martowicz, Adam
The objective of the paper is to provide an overview of nonlocal formulations for models of elastic solids. The author presents the physical foundations for nonlocal theories of continuum mechanics, followed by various analytical and numerical techniques. The characteristics and range of practical applications for the presented approaches are discussed. The results of numerical simulations for the selected case studies are provided to demonstrate the properties of the described methods. The paper is illustrated with outcomes from peridynamic analyses. Fatigue and axial stretching were simulated to show the capabilities of the developed numerical tools.