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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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Concepts of reducing the forces transmitted between the rigid rotor and its frame based on magnetorheological damping devices
Zapoměl, Jaroslav ; Ferfecki, Petr ; Kozánek, Jan
A usual technological solution how to reduce forces transmitted between the rotor and its stationary part is to apply a flexible suspension with damping devices placed between the rotor and its casing. Optimum performance of the constraint damping elements can be achieved if their damping effect is controllable. As the control depends only on speed of the rotor rotation that does not vary rapidly the semiactive devices based on utilization of the magnetorheological phenomenon can be used for this purpose. Then the damping force is controlled by the change of electric current generating magnetic flux passing through the layer of the magnetorheological lubricant. Three concepts of their arrangement were studied: magnetorheological dampers with only one layer of the magnetorheological liquid and dampers with two separated layers formed by the normal oil and magnetorheological lubricants in the serial and parallel arrangements.
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The stability investigation of vibrations of flexibly supported rigid rotors damped by hybrid magnetorheological damping elements
Zapoměl, Jaroslav ; Kozánek, Jan ; Ferfecki, Petr
A usual technological solution how to reduce the time varying forces transmitted between the rotor and its casing consists in application of a flexible suspension and in adding the damping devices to the constraint elements. To achieve their optimum performance their damping effect must be controllable. For this purpose a concept of a hybrid damping device working on the principle of squeezing the layers of normal and magnetorheological oils have been developed. Here in this paper, there is investigated influence of the proposed damping element on stability of the rotor vibrations induced by its imbalance during the steady state operating regimes. The stability is evaluated by two approaches: by utilization of a transition matrix and the Floquet theorem and by the evolutive method. The former determines the stability by means of magnitude of the largest eigenvalue of the transition matrix set up over the span of time of one period, the later by time evaluation of eigenvalues of the system linearized in a small neighbourhood of the steady state phase trajectory of the rotor during one period and calculation of the corresponding damping ratio or logarithmic decrement.
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Judgement of Possibilities of Decrease of Vibration Magnitude of Forced Response by Actuating Kinematic Excitation Effect
Markopoulos, A. ; Ondrouch, Jan ; Ferfecki, Petr
Summary: The task is to determine time history of a kinematic excitation so that after the initial transient component dies out, the magnitude of displacement a kinematicaly excited system has been lower than the magnitude of the system without kinematic excitation. The best solution of the investigated problem can be calculated by means of a procedure using minimization of the functional. However, numerical simulations shows that due to complexity of analysis proposed approach is not useful for solving systems with more than one of degree of freedom. They also tell that the best approaches to decrease a vibration magnitude of a rotor system supported by hydrodynamic bearings are methods using linearization equation of motion.
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Numerical Simulation of a Two-Crack Rotor System Supported by Radial Active Magnetic Bearings
Ferfecki, Petr ; Ondrouch, Jan
In this work a computational simulation is utilized to investigate the steady-state response of a two-crack rotor system supported by radial active magnetic bearings on an excitation by centrifugal forces of discs unbalances. The static deflection of a shaft is considered larger than vibration amplitude of a shaft and therefore a so-called breathing behaviour of cracks is introduced. Parametric study has been carried out in order to investigate influence of different values of the angle between cracks on the steady-state response of a rotor system. The results presented in this work can therefore help with detection of cracks in the shaft.
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Stability Investigation of a Rotor System RK 4 (Rotor Kit 4) with Shaft Containing a Notch
Ferfecki, Petr ; Lukas, T.
Transverse crack is a very often type of damage of a rotor system, which can cause, if undetected, a very serious failure. The computational procedures for investigation of lateral vibration of a rotor system with an open crack are developed and these procedures are applied on a rotor kit RK 4 with a shaft containing a notch. In this work the response of the rotor system RK 4 was computed by means of Newmark method, fourth order Runge-Kutta method and trigonometric collocation method. The stability of lateral vibration of rotor kit RK 4 was investigated by means of Floquet theory.
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