
Modelling and simulation of selfbalanced vertical rigid rotors
Zapoměl, Jaroslav ; Kozánek, Jan ; Košina, Jan ; Cibulka, Jan
Unbalance of rotors of rotating machines is mostly caused by the manufacturing and assembling inaccuracies. In some cases it can be induced by the rotor operation or can be variable during the rotor running. In these cases the classical approach based on attaching the balancing weights to the rotor surface is not efficient. The technological solution is offered by application of a selfbalancing device. This paper deals with its design, modelling, and investigation of its functionality in dependence of the rotor operation parameters.

 

Reducing vibration amplitude by means of damping control in support elements of flexible rotors
Zapoměl, Jaroslav ; Pešek, Luděk ; Viet, La Duc ; Savin, L. ; Kozánek, Jan
Damping in the supports of rotors loaded by unbalance has influence on the vibration amplitude and critical speed of rotating machines. To minimize the oscillation amplitude during the rotor acceleration and running over the critical velocity, the damping in the support elements should be reduced. The reduction cannot be sudden but must be distributed in time. This requires to determine the proper moment of time when to start this manipulation and the time of its duration. This paper deals with investigation of the possibility of utilization of controllable squeeze film dampers lubricated by magnetorheological oil to accomplish this manipulation.


Preliminary identification of damping properties of tonewood
Povolný, J. ; Kozánek, Jan ; Zapoměl, Jaroslav
Besides elasticity parameters, damping of the material is the crucial parameter of the function of a violin and also of other stringed instruments with a wooden soundboard. Assuming tonewood as an orthotropic linear elastic continuum, our aim is to contribute to hypothesis, that each orthotropic elastic constant has its appropriate loss factor  partial dampings. Dynamic experiments are based on the impulse excitation and the steady state harmonic response is calculated by Fourier transform of timesampled measured signals (excitation and response). Frequency transfer function fitting identification method can determine complex modal and spectral eigenparameters, mainly eigenfrequencies and eigendampings.


Vibration stability of a vertical flywheel lifted by permanent magnetic rings
Zapoměl, Jaroslav ; Ferfecki, P. ; Sudhakar, A. ; Kozánek, Jan
Lifting the vertical flywheels by permanent magnets is used to reduce energy losses in the support elements. Unstable equilibrium position of pairs of magnetic rings, material damping of the shaft, and nonlinear properties of the support elements can arrive at the flywheel unstable oscillations. Therefore, evaluation of the vibration stability is the essential part of the design process of flywheel devices. In the developed computational procedure the flywheel is represented by a beamlike body, to which an absolutely rigid disc (the actual flywheel) is attached. The determination of the force action between the magnetic rings is based on mutual interaction between two magnetic dipoles. The steady state response of the flywheel on the unbalance excitation is calculated by means of the trigonometric collocation method and its stability is evaluated by application of the Floquet theorem. The developed computational procedures and learning more on behaviour of flywheels lifted by magnetic rings are the main contributions of the carried out research.\n


The influence of permanent magnetic rings on the loss power, vibration and stability of vertical rotors
Zapoměl, Jaroslav ; Ferfecki, P. ; Sudhakar, A. ; Kozánek, Jan
Lifting the vertical rotors by permanent magnets is an advanced technological solution for\nreducing energy losses in the supports. The disadvantage of this design is the instable interaction between the magnetic rings, which may destabilize the rotor oscillations. The performed research was focused on the development of computational procedures for analysis of energy losses in the supports of magnetically lifted vertical rotors mounted in rolling element bearings and on analysis of stability of their vibration in a wide range of operating speeds. The computational simulations proved efficiency of the magnetic suspension.


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.


Aspects of energy storage systems focusing on flywheel technologies
Zapoměl, Jaroslav ; Kozánek, Jan
The energy storage devices are used to reduce variation of the power transmitted in complex technological systems. The individual technologies are based on different physical principles and are applicable in different industrial fields. This paper focuses on aspects of the flywheel storage devices that have a direct impact on their design, technological parametres, and extent of their application.


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).


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.
