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A short study on self-balancing of vertical rotors mounted in passive contactless bearings
Zapoměl, Jaroslav ; Kozánek, Jan
Energy losses and wear of the support elements of high-speed rotors can be reduced by mounting the rotors in stable passive contactless bearings, the operation of which is based on magnetic levitation. The goal of the conducted research was to investigate applicability of selfbalancing device added to vertical rotors supported by bearings showing low stiffness and damping, which is a specific property of passive magnetic bearings. This paper deals with applicability and efficiency of self-balancing devices added to vertical rotors supported by bearings having very low stiffness and damping, which corresponds to the properties of magnetic frictionless bearings.
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Study of the oscillation of a pendulum in a magnetic field
Zapoměl, Jaroslav ; Kozánek, Jan ; Košina, Jan ; Cibulka, Jan
Realization of some technological processes requires application of rotating machines with a vertical rotor mounted in rolling element bearings. One of the requirements put on their operation is minimization of energy losses in the support elements. The proposed design variant consists in supporting the vertical rotor by one rolling element bearing placed at its upper part and by one axial magnetic bearing mounted in its lower end. The magnetic bearing is composed of an electric coil coupled with the stationary part and of a permanent magnet attached to the rotating part. The magnetic force attracts the permanent magnet, which reduces radial displacement of the lower end of the rotor. The magnetic field between the magnets represents a force coupling between the rotor and the stationary part, which shows some stiffness and affects the system natural frequencies. The controlled change of the stiffness makes it possible to reduce the rotor lateral oscillations in the resonance area. The investigated pendulum is coupled with the frame by a revolute joint at its upper end. The permanent magnet is attached to its lower end. The electric coil is coupled with the stationary part and placed under the pendulum. The system is excited by a moment of harmonic time history, which sets the pendulum into a seesaw motion.\n\n
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Analysis of vibration of rotors with a thick rigid disc on the overhanging end supported by hydrodynamic bearings and loaded by uncertain unbalance effects
Zapoměl, Jaroslav ; Ferfecki, P. ; Molčan, M. ; Kozánek, Jan
Rotors of some rotating machines consist of a shaft and a rigid disc attached to its overhanging end. Because of manufacturing and assembling inaccuracies, the disc is unbalanced. In general case, the disc principal axis of inertia deviates from the shaft axis (both axes are skew lines) and the disc center of gravity is not situated on the shaft center line. Then the disc inertia effects are the source inducing the rotor lateral vibration. As magnitude of parameters specifying the disc unbalance is uncertain, application of an adequate method is required to perform the analysis. In addition, if the rotor is supported by hydrodynamic bearings, their nonlinear properties lead to rising complexity of the system vibration and to reducing its predictability. In the presented paper, the motion equation of a rigid disc has been derived. The shaft was represented by a beam body that was discretized into finite elements. The stiffness and damping parameters of the hydrodynamic bearings were linearized in vicinity of the rotor equilibrium position. Then vibration of the rotor is governed by a set of linearized motion equations. The fuzzy numbers were applied to consider uncertainty of the disc unbalance parameters. The presented procedure provides the approach to computational analysis of rotating machines with the rotor having a disc attached to its overhanging end and the geometrical, mechanical, or technological parameters of which have uncertain values.
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Identification of dynamic properties of built electrodynamic shaker
Šnábl, Pavel ; Kozánek, Jan ; Pešek, Luděk
Electrodynamic shaker was built in our institute for excitation of vibrating blade in a flow field. The shaker consists of permanent magnet and voice coil, 3D printed body, core and cover, and two at suspension rings laser-cutted from Pertinax. For simulation purposes of the whole system, identfication of shaker dynamic parameters was needed. Several identification methods in time or frequency domain were used, and it was shown that the shaker model must contain nonlinear stiffness in order to describe the real system more accurately.
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Modelling and simulation of self-balanced 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 self-balancing device. This paper deals with its design, modelling, and investigation of its functionality in dependence of the rotor operation parameters.
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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.
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