Mechanics
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ISSN 1734-8927
e-ISSN: 2300-7060
Issue Date
2008
Volume
Vol. 27
Number
No. 1
Description
Journal Volume
Mechanics
Vol. 27 (2008)
Projects
Pages
Articles
Statistical characteristics of vibrations of a string forced by stochastic forces
(Wydawnictwa AGH, 2008) Jabłoński, Marian; Ozga, Agnieszka
Our theoretical study aims at finding the statistical parameters characterizing the vibrations of a string without damping and forced by stochastic impulses when the places and moments of actions are random. We derive the dependence of these parameters from the parameters of the string as well as from the stochastic distributions of the impulse magnitude, and of the place of the action. We also carry out a numerical simulation verifying the derived mathematical model and interpret the differences between the results obtained in the simulation and the mathematical calculations. This study is the third stage of research aimed at designing and calibrating a probe that will facilitate measuring of parameters determining the quality of a technological process.
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.
Vibration control of a fluid-loaded circular plate via pole placement
(Wydawnictwa AGH, 2008) Leniowska, Lucyna
This paper presents the application of active control system to reduce the vibration and the sound radiation of a circular plate which is fluid-loaded and clamped at a finite baffle. The plate is driven by a uniform harmonic primary force and controlled by a distributed secondary force generated by the piezodisks. The aim of the paper is to design a controller to modify the response of the plant in some desired fashion. The mathematical model of the system includes the influence the acoustic wave radiated by the plate, Kelvin-Voigt damping in the plate material and viscous fluid damping. For the considered system the transfer function of controller of 4th order, satisfying the polynomial Diofantine equation, is derived. The influence of the fluid-loading and damping effects on the system response are presented graphically and discussed. The results show that plate modes have been reduced very well by obtained controller for a few assumed values of damping coefficients.
The thermodynamical theory of elasto-viscoplasticity accounting for microshear banding and induced anisotropy effects
(Wydawnictwa AGH, 2008) Perzyna, Piotr
The main objective of the present paper is the development of thermo-elasto-viscoplastic constitutive model of a material which takes into consideration induced anisotropy effects as well as observed contribution to strain rate effects generated by microshear banding. Physical foundations and experimental motivations for both induced anisotropy and microshear banding effects have been presented. The model is developed within the thermodynamic framework of the rate type covariance constitutive structure with a finite set of the internal state variables. A set of internal state variables consists of one scalar and two tensors, namely the equivalent inelastic deformation e/p the second order microdamage tensor [symbol] with the physical interpretation that ([formula]) defines the volume fraction porosity and the residual stress tensor (the backstress) alpha. The equivalent inelastic deformation [symbol] describes the dissipation effects generated by viscoplastic flow phenomena, the microdamage tensor [symbol] takes into account the anisotropic intrinsic microdamage mechanisms on internal dissipation and the back stress tensor alpha aims at the description of dissipation effects caused by the kinematic hardening. To describe suitably the influence of both induced anisotropy effects and the stress triaxiality observed experimentally the new kinetic equations for the microdamage tensor [symbol] and for the back stress tensor alpha are proposed. The relaxation time Tm is used as a regularization parameter. To describe the contribution to strain rate effects generated by microshear banding we propose to introduce certain scalar function which affects the relaxation time Tm in the viscoplastic flow rule. Fracture criterion based on the evolution of the anisotropic intrinsic microdamege is formulated. The fundamental features of the proposed constitutive theory have been carefully discussed. The purpose of the development of this theory is in future applications for the description of important problems in modem manufacturing processes, and particularly for meso-, micro-, and nano-mechanical issues. This description is needed for the investigation by using the numerical methods how to avoid unexpected plastic strain localization and localized fracture phenomena in new manufacturing technology.
Application of selected balance methods to the evaluation of performance parameters of the extraction back-pressure power unit in a combined heat and power plant
(Wydawnictwa AGH, 2008) Tokarz, Tadeusz; Karpiel, Tomasz
Thermal measurements of the extraction back-pressure power unit in the combined heat and power plant for a wide range of working loads were utilised to develop an algorithm for computing performance parameters of the power unit. The calculation procedures use the enthalpy balance method and the entropy balance method. Adequacy of the two methods was compared on the basis of performance characteristics of the investigated power unit.