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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Access status: Open Access ,
A new approach to acoustic distributed field shaping
(Wydawnictwa AGH, 2009) Figwer, Jarosław
In the paper a new approach to acoustic distributed field shaping is proposed. In the proposed approach the problem of acoustic distributed field shaping is decomposed into a set of the corresponding autonomous acoustic local field adaptive synthesis and generation problems that are coordinated. These acoustic local fields are synthesized and generated using a recursive synthesis and simulation of power spectral density defined multisine random time-series with the multisine transformation that is additionally aided by an active noise control system.
Access status: Open Access ,
A new concept of a catalyst support for internal combustion engines
(Wydawnictwa AGH, 2007) Worsztynowicz, Barbara
Standard catalysis reactors are characterized by their channel structure. There are several channels per each cm2 of the core's surface. At the same time the length of each channel exceeds 100 times the cross section size. This causes splitting of the incoming to the reactor fumes into thousand pieces. Such a construction is characterized by a Iow mechanical endurance, high flow resistance, high inertia and an inclination for corking of particular channels. The core, according to the new conception, is made of: central partition connected continuously along the whole length of the side wall and a series of side and middle elements situated symmetrically on both sides of the middle partition. The height of the element walls is the height of the side walls and together they form a two side system of a network with crossing passage channels. Those channels are open on the axis inflow-outflow as well as in a direction perpendicular to the mid intersection. Both the middle and the side elements have internal spaces forming respectively middle and side compartments. Those compartments form a common two side open space for each pair of elements situated symmetrically to the middle partition. Each compartment has a connection with the channel network through a particular crack. The catalyser with core of the new construction is characterized by the good flow and mechanical properties. Preliminary experimental tests have shown that the phenomena occurring during the flow through the catalyser are with good agreement with the assumptions.
Access status: Open Access ,
A new vibroacoustic method for shaft crack detection
(Wydawnictwa AGH, 2007) Gosiewski, Zdzisław; Sawicki, Jerzy Teodor
Various excitation techniques have been developed to extract information on dynamic state of rotating machinery. This paper will address the effectiveness of selected excitations and analysed signals towards health monitoring of rotating machines from the shaft crack point of view. The computer simulation study is based on the uncracked and cracked Jeffcott rotor models and the efficiency of the selected approaches is examined. As the excitation we have considered the rotor unbalance, additional harmonic forces, and input conditions. The combined resonances as diagnostic indicators of the cracked shaft are good seen in the total frequency spectrum in the case when we consider the difference between the spectra of cracked and uncracked shaft. We have also introduced a new model of the rotor which allows us to use different method of signal processing for the crack detection and the evaluation of its deep. So more, in such model we can take into account the number of excitation planes and directions of the applied forces, the choice of the analysed signals (e.g. transient, steady-state).
Access status: Open Access ,
Accounting for dry friction influence in oscillatory systems exposed to random excitation
(Wydawnictwa AGH, 2007) Stein, George Juraj; Zahoranský, Radúz
In analysis of translatory oscillatory systems the basis is a simple linear oscillator, whose mathematical treatment is well known. However, an important issue in many practical applications is the friction. This is specifically so for Iow intensity random kinematic excitation in form of acceleration, as is often the case in ground transportation. In the contribution two approaches to friction modelling are described and compared the signum function approach and the physically correct stick-slip approach, together with the commonly used harmonic balance method of Den Hartog. The differences are highlighted, indicating that the physically correct stick-slip approach describes the reality better than the computationally simpler signum approach. These effects are dependent on the relation between the dry friction force value and isolated body driving force, described by Den Hartog's factor K. It will be shown, that depending on the K factor value it is possible to decide which simulation method furnishes better prediction of vibration mitigation properties of an oscillatory system with friction. Moreover, the stick-slip model is of a generic nature and can be widely used for systems modelling. Its application circumvents deeper knowledge of advanced methods of non-linear analysis and enables better exploitation of the commercial simulation software.
Access status: Open Access ,
Acoustic properties of the selected churches in Poland
(Wydawnictwa AGH, 2005) Engel, Zbigniew; Kosała, Krzysztof
The assessment ofthe acoustic properties of interiors of sacral buildings was, for many years, done by means of methods developed primarily for assessing concert halls, opera houses or auditoriums adapted for sacral buildings. Those are Beranek's, Ando's, RASTI and impulse methods. The paper provides short description of those methods as well as their yerification performed by the authors and graduate students of the Chair of Mechanics and Vibroacoustics AGH in several roman catholic churches in Poland. The analysis of those methods proved that - when applied to sacral objects - they are often not complete and must be supplemented. Regardless of numerous papers concerning investigations and creation of acoustic conditions in sacral objects, there is a lach of a uniform, specific method which would allow to assess the acoustic ąuality of such interiors. The new index method, which assesses the acoustic properties of sacral objects by a single-numbered - the global index of acoustic quality - is presented shortly in the paper. This global index is a function of several partial indices, namely: reverberation index, intelligibility of speech index, uniformity of loudness index, external disturbance index and musie sound ąuality index. The index method was applied and yerified in five roman catholic churches in Poland.
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 ,
Active noise and vibration control system design considerations
(Wydawnictwa AGH, 2007) Hansen, Colin H.; Qiu, Xiaojun; Petersen, Cornelis; Howard, Carl Q.; Singh, Sarabjeet
When designing active control systems to reduce noise radiated by vibrating surfaces, there are many variables that need to be optimised to achieve the maximum possible system performance. There are also a number of hardware and software aspects that must be considered and accounted for when a laboratory system is adapted for operation in an industrial or commercial environment. There needs to be some sort of hierarchy in the approach to optimising the many variables which include type, locations and numbers of control sources, quality of the reference signal for feedforward systems, software structure and algorithm considerations and hardware architecture considerations. This paper discuses a number of issues associated with the implementation of active noise and vibration control systems that have been the subject of investigation at The University of Adelaide.
Access status: Open Access ,
Active noise control with moving error microphone
(Wydawnictwa AGH, 2008) Michalczyk, Małgorzata
Electro-acoustic plants controlled by active noise control (ANC) systems in enclosures are usually time-varying. Their changes can be caused by movements of an error microphone, around which zones of quiet are created. Then, the time variations of the electro-acoustic plant can be fast and adaptive ANC algorithms for tracking variations of error microphone position should be used. The preliminary research results showed that the created zone of quiet can move tracking the movement of the error microphone, when filtered-x least mean squares (FX-LMS) algorithm is applied. The paper presents further results of real-world experiments conducted on a special laboratory stand, which enabled to move the error microphone round the circle trajectory with constant rota- tional speed. Two modifications of FX-LMS algorithm were applied in order to accelerate control algorithm convergence and improve tracking properties of the ANC system: normalized FX-LMS and modified FX-LMS algorithm. It was shown, that the zone of quiet can track movement of the error microphone, however, there was no significant difference in control algorithms performance. In all cases the zone of quiet tracked the movement of the error microphone, even for the error microphone velocity as high as 3.7 m/s, and high attenuation was obtained - from 16 dB for the fast microphone movement up to 28 dB for the slowest microphone movement.
Access status: Open Access ,
Advanced control algorithm for stabilization rotational speed in hydrostatic transmission
(Wydawnictwa AGH, 2006) Nawrocka, Agata; Kwaśniewski, Janusz
This study focuses on the adaptive controller to control hydrostatic transmission. A hydrostatic transmission with a variable efficiency pump and a radial engine with constant working absorptivity was chosen. Pump efficiency was controlled using an electrohydraulic control system, comprising a hydraulic cylinder coupled with a pump rotor via a piston rod and a hydraulic servo-valve. As the object is nonlinear and time variant its control is very difjicult. For that reason the adaptive control strategy was chosen and a follow-up control algorithm was designed. This control strategy enables the fine tuning of the fuzzy logie controller's parameters. It can be done online, in each cycle time. Besides, this algorithm is implemented on a PLC controller. This paper outlines the structure of the controller and provides the results of laboratory tests.
Access status: Open Access ,
Analiza cieplno-wytrzymałościowa połączenia walczaka i rury opadowej w warunkach nieustalonych
(Wydawnictwa AGH, 2006) Taler, Jan; Michalczyk, Krzysztof
In this paper the method based on German standard TRD of calculating acceptable speed of heating and cooling power boilers was presented. It was indicated that stresses occurring during heating and cooling according to this standard are much smaller than the acceptable ones. It motivates shortening of starting and shutting-down times and searching for new methods defining acceptable speeds of heating and cooling power boilers.
Access status: Open Access ,
Analiza jakościowa płomienia spalanej aktywowanej magnetycznie mieszanki LPG
(Wydawnictwa AGH, 2005) Worsztynowicz, Barbara
Technical solutions of magnetical activation of the flowing are known, however the obtained results aren't fully repeatable. In this research there have been introduced results of analysis of earth gas and liąuid fuels combustion activated magnetically by suitable magnetizers. They reveal a significant improvement of the energetic and environmental indicators of the activated fuels combustion process. Based on these results, the decision to carry the analysis of combustion of activated LPG mixture has been madę. An improvement of the combustion process has been received, which substantiates the carriage offurther analysis in the quantitative character as well.
Access status: Open Access ,
Analiza przyczyn powstawania pęknięć zmęczeniowych w konstrukcji bębna pędnego maszyny wyciągowej
(Wydawnictwa AGH, 2005) Cichociński, Andrzej; Ładecki, Bogusław
Still in use today there are some hoisting mining machines with motion wheels, the construction of which uses ri-gid 'U' shaped diaphragms to connect side disks. In such wheels periodically, after servicing, fatigue cracks are being found. The authors performed strength analysis done by the finite elements method, and verified its results using appropriate tensammetric measurements. The measurements and analyses performed confirmed that direct cause of the fatigue cracks in the barrels is over-rigidity of the structure due to stiff diaphragms joining the wheel disks. Based on this, recommendations were issued regarding modernization of motion wheels in the discussed ho-isting machines.
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 ,
Analiza współpracy sprężarek recyrkulacyjnych z instalacją syntezy amoniaku
(Wydawnictwa AGH, 2005) Worsztynowicz, Barbara
Analysis of work of high-pressure installation of ammonia synthesis enabled a conclusion about the appearance of unstationary wave courses in the pipes pressing synthesis mixture into the column with catalytic deposit. The phenomena appeared when one of recirculation compressors was turned on. To analyse the system of pipelines and the way of their attachement to basic and recirculation compressors some points were selected to observe synchronic course of rapid changing pressures. The research, in which the wave courses took place, was a ground to identify places of local resonance which were a cause of suction parameters devaluation. It had a negative influence upon the compressor efficiency and also resulted in resonance vibrations of the installation.
Access status: Open Access ,
Analyses of sound isolating attributes for recycling materials
(Wydawnictwa AGH, 2006) Badida, Miroslav; Zvirinský, Vladimír; Lumnitzer, Ervin
All acoustical materials and structures perform better at some freguencies than others. For this reason, a frequency analysis of the noise to be controlled is almost always required for reduction occupational or environmental noise. Recycled rubber structures made from road tyre and car seat can absorb noise thanks porous structure. For mapping needed acoustical descriptors we designed apparatus for measuring the acoustical absorption (?n), acoustical reflection (Ro), acoustical transmitted (Rp) and acoustical isolation (Dnf) coefficients for normally incident sound which define acoustical materials at once. Realized prototype of apparatus based on the impedance tube and standard featuring of a sound level meter was registered as Industry Design No 3679 from 9.10.2003 by Bureau of Slovakia Industrial Property. This paper deal of frequencies analysis basic occupational acoustic characteristics of recycled porous rubber structures.
Access status: Open Access ,
Analysis of positioning accuracy of the effector of a triplanar manipulator
(Wydawnictwa AGH, 2009) Kuźmierowski, Tomasz; Siemieniako, Franciszek
This paper presents an analysis of positioning of the effector of a spatial parallel manipulator of the triplanar type. Computer simulation software for examining positioning accuracy and the simulation results have been described herein. The paper also contains verification of the examination through stand measurements of a manipulator of a selected configuration.
Access status: Open Access ,
Analysis of the dependence between a temperature and working parameters of the MR damper
(Wydawnictwa AGH, 2007) Bajkowski, Jerzy; Bajkowski, Marcin; Grzesikiewicz, Wiesław; Sofonea, Mircea; Shillor, Meir; Zalewski, Robert
In this paper detailed description of temperature influence on MR damper working parameters has been described. Prototype of such a device and its mathematical description taking into considerations a thermal balance, have been proposed. Basing on experimental results, a connection between temperature and operating parameters of tested MR damper has been revealed.
Access status: Open Access ,
Analysis of the thermodynamic losses in the regeneration system of the extraction condensing type power unit at a combined heat and power plant
(Wydawnictwa AGH, 2006) Tokarz, Tadeusz
The paper outlines the method of evaluating thermodynamic losses in the regeneration systems of the extraction condensing type power unit in a combined heat and power plant. The exergy analysis principles were then utilised to compute the thermodynamic losses in heat exchangers of the high-pressure regeneration system in the heating and condensing mode of power unit operation. Finally, the thermodynamic losses are expressed in terms of increased fuel consumption in the boiler, which is of key importance for the calculations of overall costs of power and heat generation in a combined heat and power plant. KEYWORDS: combined heat and power plant, extraction condensing type power unit, regeneration system, thermodynamic losses, energy analysis.
Access status: Open Access ,
Analysis of thermodynamic losses in regeneration systems of the extraction back-pressure power unit in a combined heat and power plant
(Wydawnictwa AGH, 2007) Tokarz, Tadeusz; Karpiel, Tomasz
An algorithm is developed for computing thermodynamic losses in the regeneration systems of the back-pressure power unit in a combined heat and power plant. Thermal measurements taken under the typical working loads were utilised to compute and analyse variability of the thermodynamic losses in heat exchangers of the high-pressure and low-pressure regeneration systems in the heating and pseudo-condensing modes of operation.
Access status: Open Access ,
Application of LQR theory to optimization of vibration isolation of sitting human body
(Wydawnictwa AGH, 2008) Książek, Marek A.; Ziemiański, Daniel
In the paper the linear quadratic regulator (LQR) theory was applied to optimization of vibration isolation system of sitting human operator body subjected to vertical excitations. The optimization approach was applied to system composed of active human body model (AHBM) and passive, linear vibration isolation system (VIS). Synthesis of optimal LQR for the given system was done for two existing, active biodynamical models «back-off» and «»back-on» of sitting human body. Optimization was done for chosen form of vibration isolation criterion. Analytical formula of that form, corresponding to present standards concerning the human body expositions to vibration, was presented. Influence of the LQR on dynamical behavior of the system composed of AHBM and VIS was estimated on the basis of numerical calculations, discussed and graphically presented.