MECHANICS

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Adres wydawniczy: Kraków : Wydawnictwa AGH, 2005-2009
ISSN: 1734-8927 e-ISSN: 2300-7060
Następny tytuł: Mechanics and Control (2010-2016)

Mechanics wydawana w latach 2005-2009. Kontynuowane w latach 2010-2016 pod tytułem Mechanics and Control

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Now showing 1 - 20 of 166

Access status: Open Access ,
Active control of vibrations of a three-axis gyroscopic platform on board of a flying object
(Wydawnictwa AGH, 2005) Koruba, Zbigniew; Styczeń, Jerzy
The work presents an algorithm for active control of vibrations of a three-axis gyroscopic platform during pre-programmed and stabilised operation on board of a flying object. The considerations focus on disturbances resulting from the flying object manoeuvres and short-duration pulses of external forces under the conditions of friction in the bearings and non-linear platform operation range.
Access status: Open Access ,
Techniques of neural networks for signal parameterization used in monitoring systems
(Wydawnictwa AGH, 2008) Wszołek, Wiesław
The paper presents selected aspects of research concerning a new concept in application of computer technology to the analysis of acoustic signal. This new concept assumes, that during the analysis of signal the study is not focused on determining some or other signal parameters, neither it is focused on the signal classification, but it is supposed to lead to an automated understanding of the origins of the deformation, which can be revealed in analyzed signal.
Access status: Open Access ,
Stress analysis in helical springs with closed end coils machined from cylindrical sleeves
(Wydawnictwa AGH, 2006) Salawiński, Józef; Michalczyk, Krzysztof
The review of stress calculation methods in helical springs with rectangular cross-section wire is introduced in this paper. It is demonstrated that methods described in literaturę have various accuracy. Also, the modern construction of helical spring machined from tubular blanks is presented. It is indicated, using Finited Elements Me-thod, that existing for classical springs with opened ends stress calculating methods, are not suitable for springs with capped ends, because the stresses calculated from them are much smaller than the real ones.
Access status: Open Access ,
Hybrid model of the conventional power unit
(Wydawnictwa AGH, 2008) Rusinowski, Henryk; Szapajko, Grzegorz; Stanek, Wojciech
The paper presents the hybrid model of the conventional power unit. The model contains following fragmentary models: model of the boiler, turbine and regenerative heat exchangers. Fragmentary models have been elaborated with the application of the analytical modelling methods, regression and neural networks. Hybrid model of the boiler contains balance model compatible with the German norm DIN and regressive models describing content of the unburnt combustibles in the slag and in the dust and the neural model describing the flue gases temperature at the outlet of the boiler. Model of the turbine contains balance model and theoretical-empirical model of the steam expansion line in the turbine. Models of the heat exchangers contain the balance and empirical models describing the heat transfer. The paper presents the exemplary calculation results and their comparison with the measurements.
Access status: Open Access ,
Calibration of the strip yield model for fatigue crack growth predictions in structural steel
(Wydawnictwa AGH, 2009) Machniewicz, Tomasz
The paper is focused on the calibration of the strip yield (Dugdale) model for crack growth predictions for structural steel. This is achieved by imposing appropriate constraints on yielding the strip elements. To avoid a fortuitous, i.e. physically unjustified choice of the constraint factors, a novel concept for their selection is proposed, namely matching the experimentally observed and predicted by the model cyclic stress-strain behaviour at the crack tip. The approach is shown to yield satisfactory prediction results on crack growth under constant amplitude loading and after application of an overload cycle.
Access status: Open Access ,
Multi-channel virtual-microphone feedback minimum-variance active noise control system
(Wydawnictwa AGH, 2009) Pawełczyk, Marek
Classical active noise control systems are designed to minimise, in a sense, the residual signal at the microphone providing information about acoustic noise and secondary sound interference. The secondary sound operates at the same time on the acoustic noise at other positions including user ears. In the worst case this can result in sound reinforcement at those positions. In many applications placing another microphone directly at the ears is not accepted. It is then justified to make efforts to design a dedicated system. The purpose is to minimise the mean-square value of the noise at the desired location while performing measurements of sound interference results at another location. This can be done by employing the general idea of Vrtual-Microphone Control systems. However, for many active noise control applications the use of a single pair of microphone and loudspeaker does not suffice to obtain satisfactory performance, i.e. generate a zone of quiet of acceptable dimensions. Moreover, for some applications, presence of an obstacle, e.g. the head in an active headrest system, constitutes a barrier for the zone of quiet at one side to propagate to the other side. Therefore, more microphones and loudspeakers are often necessary. In the most general case a coupling between subsequent pairs should be taken into account resulting in a multi-channel system. In previous papers of the author adaptive systems have been designed and analysed. In this paper a fixed parameter multi-channel Virtual-Microphone Control system, optimal in the mean- square sense, is designed. It includes non-minimum phase property of the system channels. Both the case of more inputs than outputs as well as the case of more outputs than inputs are considered. Factorization techniques have been used for the design. The system is verified by successfully controlling noise for the active headrest system.
Mechanics
2006 - Vol. 25 - No. 4
Access status: Open Access ,
Experimental study of vibration control in a two-degree-of-freedom pitch-plane model of a magnetorheological vehicle suspension
(Wydawnictwa AGH, 2007) Martynowicz, Paweł; Sapiński, Bogdan
The paper concerns the vibration control in a two-degree-of-freedom model of vehicle suspension equipped with independently controlled MR dampers in front and rear sections. The suspension model was tested in open-loop and feedback system configurations under harmonic and square base excitations. The experiments were conducted on the specially designed laboratory setup with data acquisition and control system configured in MATLAB/Simulink environment. The obtained results reveal effectiveness of MR dampers in vibration isolation for a wide range of excitation frequencies.
Access status: Open Access ,
Podobieństwa i różnice w zakresie statyki sekcji obudów ścianowych
(Wydawnictwa AGH, 2005) Losiak, Stanisław; Ptak, Jan; Blaschke, Janusz
In the paper schemes of basic group of supports with distribution of loads for three types of units have been presented. It has been demonstrated that schemes with load distribution may be reduced to one collective scheme and a common mathematical description for various types of units may be presented. Application of the common description for testing the characteristics of the units of the same type were discussed. In general, equations for determining the static parameters of the support unit with stretcher cylinder were given. Static-stability characteristics of such a support unit on the basis of exemplary characteristics determined from mathematical description were discussed.
Access status: Open Access ,
Stress analysis in slotted springs
(Wydawnictwa AGH, 2006) Michalczyk, Krzysztof
In this paper the modern construction of slotted springs was presented. It was proven that maximal stresses in such springs under load have higher values than the stresses calculated with previous method. The new model of phenomena and calculating method based on it was proposed. The new method gives results closer to FEM analysis than the previous.
Mechanics
2008 - Vol. 27 - No. 4
Access status: Open Access ,
Analiza techniczna i ekonomiczna rekonstrukcji czerpaków dla koparek kołowych SCHRS 4000 urabiających caliznę w KWB «Bełchatów»
(Wydawnictwa AGH, 2005) Badura, Sławomir; Łopata, Antoni Mieczysław
The paper presents technical and economical analysis of the reconstruction for symmetrical and asymmetrical bucket mounted on the bucket wheel excavators SchRs 4000 in the targets to dredging mineral.
Access status: Open Access ,
Semiactive control strategies for a fully suspended bicycle
(Wydawnictwa AGH, 2005) Plaza, Krzysztof
The purpose of this work is to present methods for designing semiactive vibration systems, which include mathematical models of vibrating structures. Thus aspects of model building, identification and verification are described in the paper as well as determination of the performance indices, choice of the damping technique, shock absorber modeling and algorithm selection. The article presents a semiactive vibration system analysis of a fully suspended bicycle. For all of the simulation experiments and serving as a reference for the identification experiment a phenomenological model of the bicycle was developed in the Simulink environment. The model was confronted with the real time experiments, which were conducted with the help of an electrical system. The necessity of the discussion of the various performance indices is underlined. Simple control strategy is tested on the bicycle.
Access status: Open Access ,
Estimation of the wear in positive-displacement pumps by the time series method
(Wydawnictwa AGH, 2006) Stojek, Jerzy
The article discusses the possibility to assess the wear characteristics in multi-piston positive-displacement pumps operating at constant delivery rate, basing on an analysis of the measured outlet pressure variations. Parameter estimates of the selected parametric models of pressure variations were determined. Comparing the values of parameters, the wear and tear characteristics were determined in the examined pumps.
Access status: Open Access ,
Numerical analysis of the impact of conical diffuser geometry change on velocity distribution in its outlet cross-section
(Wydawnictwa AGH, 2006) Prync-Skotniczny, Krystyna
Paper presents the results of numerical calculations of air flow through a conical diffuser with divergence angle 2alpha = 70 degrees and aspect ratio L/w = 0.82. Constructional changes were introduced into the diffuser in order to obtain a uniform velocity distribution in the outlet cross-section as well as to lower the pressure drop caused by the air flow. The changes consisted in installing two or three coaxial conical flow guides inside the diffuser. Three diffuser inlet velocities were investigated: 5.6 m/s, 6 m/s and 25 m/s. Computer modelling analyses were made using commercial ANSYS software. Calculation results were verified by comparison with laboratory experiment results carried out for the inlet velocity of 5.6 m/s and for two diffuser constructions - without any flow guides and with two conical flow guides installed.
Access status: Open Access ,
Determination of loss coefficient in selected elements of radial fan
(Wydawnictwa AGH, 2005) Fortuna, Stanisław
The article presents a method of measurement and calculation of pressure losses and loss coefficients for inlet cone and inlet chamber of the rotor. Cone coefficients and a total coefficient for a set of elements supplying the radial fan rim are presented and may constitute the base for calculating losses in similar rotors.
Mechanics
Vol. 26 (2007)
Access status: Open Access ,
Professor Wojciech Rubinowicz's contribution to the development of active methods of vibration control
(Wydawnictwa AGH, 2007) Engel, Zbigniew
World known Polish scientist, physicist Professor Wojciech Rubinowicz (1889-1974) contributed immensely to the development of the theory of active methods of noise reduction. Prof. W. Rubinowicz was dealing mainly with optical phenomena, however it should be emphasised, that light waves and acoustic phenomena can be described by similar theoretical equations. Already in 1917 W. Rubinowicz developed the theory of the edge wave, which later on was named the Rubinowicz Edge Wave. He proved the equivalence of Fresnel's and Young's ideas concerning diffraction phenomena. He developed the mathematical description of the Kirchhoff's diffraction theory. Phenomena of mutual interference of light waves incident on screen edge and the effect in the form of wave compensation in certain zones were described. An incident wave on the screen surface (edge) can compensate itself with the wave of the same structure but phase shifted by ? angle, which can cause the total extinction of light. Works of the Polish scientist, which constituted the new approach to the wave phenomena can be considered the starting point in the development of the active method theory.
Access status: Open Access ,
Fatigue resistance of magnesium alloy AZ 91D at high-frequency cyclic loading
(Wydawnictwa AGH, 2005) Bella, Vladimír; Wolny, Stanisław; Dzik, Stanisław
The presented paper brings the results of Mg-alloy AZ 91D fatigue crack propagation and life measured under high frequency cyclic loading (frequency f = 20 kHz, temperature t = 20±10 Celsius degrees, alternating, symmetric tension-pressure, loading cycle asymmetry R = ±1) in the field of high number of cyclic from N = 6·10(5) cycles to N = 1·10(9) cycles.
Mechanics
Vol. 28 (2009)