Mechanics
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ISSN 1734-8927
e-ISSN: 2300-7060
Issue Date
2005
Volume
Vol. 24
Number
No. 2
Description
Journal Volume
Mechanics
Vol. 24 (2005)
Projects
Pages
Articles
Simplified model of the dynamics of magneto-rheological dampers
(Wydawnictwa AGH, 2005) Alexandridis, Alexander A.; Gołdasz, Janusz P.
It has been long recognized that the inertia and compressibility of the fluid have a significant effect on the dynamic behavior of Magneto-Rheological (MR) dampers. Previous studies have revealed the nature of the effect through the analysis of a comprehensive, albeit fairly complex, state-space model of the MR monotube damper hydraulies. The present paper outlines a simpler model of the damper and presents simple analytical expressions for the transfer function between the input velocity (or stroke) and the output force. Pistons with single and dual flow passages are analyzed. In addition, simple expressions for the damper natural frequency and damping ratio are given. Finally the transfer functions are presented analytically as well as in the form of Bode plots of the amplitude and the phase angle of the transfer functions vs. the normalized frequency.
Diagnosing elements of propulsion plant of naval vessels by means of vibration measurement
(Wydawnictwa AGH, 2005) Charchalis, Adam; Ćwilewicz, Romuald; Grządziela, Andrzej
The application of vibro-acoustic analysis methods in naval technology has been presented in the paper. This element of Base Diagnosing System (BDS) is accepted and used in the ships, which are powered by the COGAG power plant. The paper presents investigations of permissible in-service unbalance and appropriate assemblage of turbine rotors on the basis of selected vibroacoustic parameters, and finally determination of their permissible operation time resources. Another element of BDS is vibration control of misalignment of propulsion shafts. The described conception concerns evaluative process of the centring state in a transmission shafts within powered, marine gas turbine system as a function of ships displacement. Some structural components of the gas turbine unit and reduction gearbox have been selected for the analysis. Some results of the vibro-tests have been presented as well. All tests had been worked out during sea trials. This described idea is based on the researches of the corvettes' 1241 type power plants.
Identification of flexible structure model for piezoelectric vibration control
(Wydawnictwa AGH, 2005) Gosiewski, Zdzisław
Modern structures are light and compliance. Therefore, they are strongly influenced by external and internal perturbations. To reduce the structure vibrations the active vibration controls systems are designed. When active control of flexible structures is sought, three items must be individually and simultaneously considered. 1) The creation of reduced-order models. 2) Placement of sensors and actuators. 3) Countermeasures for spillover. All these problems are particularly important in the case of active system with parameter-distributed piezoelectric sensors and actuators. The glued piezoelectrics and their amplifiers change the structure parameters and should be taken into account in the model of the open-loop system. In the paper we consider an identification method which leads directly to the reduced-order model of the open-loop system. Analytical and experimental investigations were carried out for flexible beam with fixed one end and with opposite free end. Piezoelectric strips were glued on both sides of the beam: one works as a sensor and second one as an actuator. It means that we have designed single input single output system. It is appeared that used amplifier works as a low-pass filter which cuts-off the high-frequency dynamic effects. The frequency response function (FRF) was recorded and model of open-loop system was adjusted to experimental results. Taking into account the theory of reduced-order model of flexible structures we can state that resonances are connected with poles while anti-resonances with zeros of system transfer function. The resonance and anti-resonance frequencies were used directly in the model while damping coefficients were calculated by using of the least-square sum method. In the next step some control laws were used to damp the vibration of the beam. The proper control law was chosen with help of computer simulations. The active control loop rapidly accelerates the vanishing of the impulse-excited transient vibrations of the structure. Experimental results confirmed the analytical considerations.
Sliding mode control for active magnetic bearing system
(Wydawnictwa AGH, 2005) Gosiewski, Zdzisław; Żokowski, Mariusz
Sliding mode control of a single-axis type bang-bang megnetic bearing actuator is reported in this paper. The two electromagnets are driven by switching between a positive and a negative constant voltage. Sliding mode control using these switching surfaces in turn is shown to be possible. The sliding mode turns out to take place in a subregion of state space defined by s1(x)s2(x) lessim 0 rather than on a surface defined by s(x) = 0 as in most standard cases.
Model identification for active noise control in the presence of primary noise
(Wydawnictwa AGH, 2005) Kasprzyk, Jerzy
A problem of electro-acoustic plant identification for active noise control is discussed. It is assumed that data from identification experiment are contaminated by a primary noise that should be attenuated later. Three examples of such a noise are considered: sine (discrete spectrum), noise generated by a motor (narrowband time-varying spectrum) and broadband noise (pseudorandom). It is shown that thanks to preprocessing the data by disturbance adjusting filtration (DAF) it is possible to improve the results significantly when the data are contaminated by a narrowband primary noise. DAF is the procedure of selective filtration in frequency domain consisting in removing from the spectra all lines for frequencies corresponding to the noise. The results of real-world experiments carried on in a laboratory enclosure show the accuracy of estimated frequency responses obtained in the proposed approach. The procedure is efficient when multisine signals are used to excite the plant.