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Reduction of the energy losses by application of controllable squeeze film dampers
Zapoměl, Jaroslav ; Ferfecki, Petr ; Kozánek, Jan
The unbalance induces lateral oscillations of rotors and forces transmitted to the rotor casing. The squeeze film dampers with integrated rolling element bearings represent a technological solution, which enables to reduce their magnitude, and consequently the resistance against the rotor rotation. To achieve optimum performance of the damping devices, their damping effect must be adapable to the current rotor speed. This paper reports a proposal of a controllable squeeze film damper, the damping effect of which is controlled mechanically by shifting its outer ring in the axial direction. The developed mathematical model of the damper is based on assumptions of the classical theory of lubrication and is completed with implementation of a gas cavitation. The results of the computational simulations show that an appropriate control of the damping force enables to reduce the energy losses in a wide range of operating speeds.
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Parametric identification in mechanical engineering
Kozánek, Jan ; Zapoměl, Jaroslav
This paper deals with parametric identification in mechanical engineering, similarly as in [1]. We assume a linear mathematical model of a vibrating machine in matrix form and in frequency domain, defined by stiffness, viscous damping and mass matrices and by the corresponding resolvent matrix. Parametric identification is understood as the evaluation of the measured data from dynamical experiments and its methods can be divided into indirect (obtaining spectral and modal properties - modal analysis methods) and direct (determination of the coefficient matrices of the mathematical model).
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Stability analysis of the lateral oscillations of a flexibly supported viscoelastic Jeffcott rotor
Ferfecki, P. ; Zapoměl, Jaroslav ; Kozánek, Jan ; Dekýš, V.
Material damping has a significant influence on vibrations of flexible rotors and can induce their self excited oscillations. The squeeze film dampers inserted in the rotor supports are frequently used to suppress occurrence of these undesirable operating conditions. Modelling the shaft by means of a Kelvin- Voigt material can arrive at the overestimation of the effect of internal damping on the rotor movement. This was a motivation to develop a procedure based on utilization of the Zener material (standard solid theoretical material) to represent the shaft of a Jeffcott rotor supported by squeeze film dampers. The development and testing of this procedure, the experimental determination of the appropriate material constants, and learning more on the influence of material damping on the stability and vibration attenuation of flexible rotors are the principal contributions of the presented article.
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Analysis of the lateral vibration of a flexibly supported unbalanced viscoelastic Jeffcott rotor
Ferfecki, P. ; Zapoměl, Jaroslav ; Kozánek, Jan
The behaviour of flexible rotors is significantly influenced by elasticity and damping properties of the shaft. It implies a special attention has to be paid to appropriate choice of a theoretical material to represent the rotors in mathematical models of rotating machines. The procedure developed in this paper concentrates on the investigation of the steady state component of the Jeffcott rotor vibration induced by the disc unbalance and on magnitude of the forces transmitted to the rotor frame. The shaft material is represented by the Zener standard solid material model. The steady state response was determined by application of the trigonometric collocation method. The results of the simulations confirmed the influence of the input oil pressure on the shape of the rotor orbit and on the oscillation amplitude.
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