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Awakening of traveling wave of rotor blade wheel by multipoint electro-magnetic excitation
Pešek, Luděk ; Vaněk, František ; Veselý, Jan ; Bula, Vítězslav ; Cibulka, Jan
The analytical expressions for description of traveling waves in rotating blade wheels are presented in the contribution. Both axis-symmetric case of the wheel characterized by multiple eigenvalues and the wheel with imperfection causing the split of this multiplicity are discussed herein. These expressions serve, based on the affinity to the traveling waves, for finding the optimal distribution and time dependences of the excitation forces of the multipoint electromagnetic excitation. The theoretical findings are verified numerically and experimentally on the case of free supported ring in a non-rotating state.
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Damping of turbine blades by means of friction elements
Půst, Ladislav ; Pešek, Luděk ; Veselý, Jan ; Radolfová, Alena
Theoretical analysis of vibrations of double beam system with a friction connection eccentrically situated on beams ends is provided in the first part of contribution. It is shown that the eccentricity of contact changes the type of relative contact motion, increases the damping of entire system, changes forms of beam deformation and increases resonance frequencies. Detuning of beams can also increase efficiency of vibration’s quenching. Experimental verification of this property is described in the second part of contribution.
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Influence of detuning of beams with friction damper on the high of resonance peaks
Půst, Ladislav ; Pešek, Luděk ; Veselý, Jan ; Radolfová, Alena
A system of two parallel beams with excentric friction area and normal contact force produced by spring was investigated in the first part of research report. detuning of beams was realized by additing of permanent magnets always on one of measured beams. This arrangement corresponds to the behaviour of real blades, where the friction contact force is produced by torsion blades. Result of measurement of detuning effect at a pair of blade-models connected by a wedge friction element is described in the second part of report . The measured response curves and the summary diagrams proved that the detuning of blades has positive effect on the decrease of resonance amplitudes.
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Preparation, realization and evaluation of experiment on model test wheel with blades and wedge-shaped friction elements
Pešek, Luděk ; Vaněk, František ; Veselý, Jan ; Bula, Vítězslav ; Procházka, Pavel ; Cibulka, Jan
In the first part of the report the preparation and realization of the experiment on the model test wheel with beam blades having built-in wedge-shaped friction elements. The preparation considered the placement of strain-gauges on the wheel for a deformation measurement, installation of sensors for a friction element displacement observation and the electromagnet for an excitation of resonant vibration at different revolutions. The experiment realization includes both modal analysis of the wheel with and without the friction elements in steady state and analysis of blade vibration at selected revolutions in the range from 60 up to 2100 rpm. Besides the electromagnetic excitation the experiment with the permanent magnet excitation was performed. For evaluation of the friction element influence the comparison method was used when the vibrations of the wheel with the friction elements with the case of the wheel without friction elements at the same test conditions were compare
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New test approach and evaluation of dynamic and thermal parameters of elastomers
Pešek, Luděk ; Vaněk, František ; Procházka, Pavel ; Bula, Vítězslav ; Cibulka, Jan ; Vaněk, Petr
The new test approaches for evaluation of thermo-visco-elastic parameters of elastomers are designed, realized and discussed herein. The main attention is devoted to a kinematic excited rubber beam sample under transient resonant sweep excitation. Mechanical material characteristics, i.e. Young modulus and loss angle, are identified from analytical formulas of FRF function based on measured dynamic loading and response signals. Heat material constants were estimated indirectly by numerical thermo-mechanical FE model and matching numerical and experimental results. The „sweep” regime tests serve for estimation of thermal and mechanical dependences. Long-term tests with cyclic resonant loading enable analysis of material degradation, such as hardening and permanent deformation, due to fatigue. For dynamic tests with pressure pulsation and sudden loading and unloading the high-power electromagnetic pulsater has been developed for damping rubber segments of tram wheels.
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TRAVELLING WAVES IN ROTATIONAL MACHINES
Půst, Ladislav ; Pešek, Luděk
This paper is concerned with vibrations of stationary or rotating disk as a simplified model of real bladed turbine disk. Two types of disks are investigated: perfect rotational disk with the same dynamic properties in all radial directions and imperfect disk having different dynamic properties in two independent modes of vibration. Presented study is first part of theoretical analysis intended as a background for evaluation method used in experimental research of vibrations of bladed disk in real rotational machines or their models.
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Dynamics of Machines 2008
Pešek, Luděk
Traditional national colloquium with international participation is an assembly of research works on mechanics of solids aimed at the dynamics of machines.
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