Mechanics
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ISSN 1734-8927
e-ISSN: 2300-7060
Issue Date
2006
Volume
Vol. 25
Number
No. 2
Description
Journal Volume
Mechanics
Vol. 25 (2006)
Projects
Pages
Articles
Second order closure of heat and mass transport equations for shear turbulence
(Wydawnictwa AGH, 2006) Abdibekov, Ualikhan; Ametov, Olzhas; Zhumagulov, Bakytzhan
The paper contains a model of shear turbulent flow closure based on the second moment eguations for velocity, temperature and concentration fields. The model is constructed on approximation of local - equilibrium turbulence. The solution of the obtained equation is represented in two factors, the first one describes homogeneous flow and the second takes into account the influence of Archimedes' forces, which depend on Richardson's numbers. The minimal number of empirical constants taken from theories of homogeneous turbulence is applied in the model.
Identification of physical parameters of rigid rotor in magnetic bearings
(Wydawnictwa AGH, 2006) Gosiewski, Zdzisław; Górmiński, Marek
Identification of physical parameters of unstable system, as magnetic bearing is, is an important problem, for example in the design of its diagnostic system. Most of the identification methods are applied for stable systems, without requiring feedback terms for identification purpose. However, for identification of marginally stable or unstable systems, feedback control is required to ensure the overall system stability. In many cases, a system, although stable, may be operated in the closed-loop, and it is impossible to remove the existing feedback controller for security or for production reasons. In diagnostic systems, there are usually observed trends in changes of physical parameters (e.g., mass, resistance, inductance, and so on). The physical realization is one of the possible system realizations. For any dynamic system, although Markov system parameters are unique, the realized state-space model is not unique. If one needs to compare the identified state-space model with the analytical model, both models have to be in the same coordinates. An identification method of the state-space model resulting from the physics laws is presented in the paper. The method is a modification of the OKID method and it works exactly in the case when the sum of the input number and output number eguals to the dimension of the state vector. There is no always possibility to measure the state vector, so for identification, it is estimated by deadbeat state observer. On the base of the reconstructed model it is possible to extract ARX model of observer/controller. This model is used to obtain the physical state-space model of the open-loop system for voltage controlled magnetic bearings. As a plant we consider a rigid rotor supported by magnetic bearings. The described method in easy way let us to identify physical parameters (e.g., mass, resistance, inductance, and so on) of the plant, which could be used in diagnostic system.
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.
Testing of a spring with controllable stiffness
(Wydawnictwa AGH, 2006) Rączka, Waldemar Stanisław
The paper shows the structure of a mechanical spring with controllable stiffness and outlines the temperature control systems solutions. This spring was developed in the Department of Process Control, AGH University of Science and Technology (AGH-UST). Its main components are bars made from shape memory alloy (SMA). The unique properties of SMA are outlined. Of particular importance are parameters that affect the spring special behaviour. The spring was tested in an experimental set-up and the compiled test results are provided. Chosen results was shown for different excitations and working temperatures. Obtained results show that the spring built using SMA has many interesting features. It is clear that the spring changes its stiffness during changing working temperature. Unfortunately spring stiffness has nonlinear behaviour so that in the paper was proposed a nonlinear mathematical model of the spring. Model was developed having in mind its usage. It was built for designing a controller spring stiffness.
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.