|
| |
|
|
Properties of damping couple at very high frequencies
Půst, Ladislav ; Pešek, Luděk ; Košina, Jan ; Radolfová, Alena
The contribution deals with the application of dry friction couples for noise and vibration damping at high frequency of several kHz what brings new problems connected with the small amplitudes of relative slipping motion of contact surfaces. The most important information from the of experimental results is knowledge that the value of evaluated friction coefficient can have different physical sense according to the magnitude of excitation force and to the frequency of applied vibrations. If amplitudes of motion are very small, then the external harmonic force produces only elastic micro-deformations of contacting bodies, where no slip occurs and then the traction contact force is proportional only to elastic deformation of the sample.
|
|
| |
|
|
Records-distortion at discontinuous forces measurements
Půst, Ladislav ; Pešek, Luděk ; Radolfová, Alena
Our paper in the last “Interaction and feedback 2012” conference has been oriented on the influence of force transducer’s mounting on its signal. The presented paper links on the previous contribution and concentrates on the problem of recording time histories of discontinuous periodic forces. The frequency spectrum of sudden jumps in force courses contain many high components, some of them can be laying near to some of the system’s eigenfrequencies. The excitation of these higher oscillations can essentially distort records of force jumps. Unfortunately, the application of low pas filter cannot be used, as it deletes both distorted frequencies as well as these same frequencies in the jumps signal and distorted it again. One of the possibilities how to solve this problem is using special evaluation procedure that enables to estimate (at least approximately) the real measured force. This evaluation method can be used successfully at measurement of dry friction forces arising during vibration’s tangential contact.
|
|
| |
|
|
Parametric "anti-resonance" for two-mass reverse pendulum system
Tondl, A. ; Pešek, Luděk
This contribution deals with further utilization of the parametric anti-resonance phenomenon based on additional parametric excitation fulfilling special conditions having the damping effect. The anti-resonance be used not only for suppressing self-excited vibrations or parametric resonance or decreasing externally excited resonance vibration of the equilibrium position of the not directly excited sub-system of the autoparametric system when the vibrations of the mentioned sub-system is not desired, e.g. rotating machine with vertical shift or the box with sensitive apparatuses situated on the vibrating floor.
|
|
|
Vibration damping by dry friction with microslips
Půst, Ladislav ; Pešek, Luděk
An experimental set for measurement of dry friction characteristics at vibration relative motion has been developed and used for evaluation of time histories of friction forces at motion with given amplitudes, frequencies and loading normal forces. The dry friction coefficient and contact tangential stiffness of elastic micro-deformation were ascertained by means of new evaluation method with particular orientation to the very small amplitudes of relative motions in contact surfaces, when the friction coefficient goes to the zero and the corresponding hysteretic curve degenerates into a oblique line. All displacements are then elastic micro-deformations without any friction.
|
|
|
Model of turbine blades bundles
Půst, Ladislav ; Pešek, Luděk
A detail analysis of dynamical properties of five-blades-bundle mathematical model was carried out with the aim to investigate how the damping elements made of special rubber inserted into slots between blades heads influence the response curves at different distribution of exciting harmonic forces. Viscous-elastic linear Voigt–Kelvin model was used for modeling the rheological properties of damping elements. Constant values of stiffness and damping parameters were supposed at analysis, but the frequency dependent parameters are mentioned as well. The effect of complicated form of higher modes of vibration on blades bundle amplitude resonance level is shown. The importance of orthogonality of excitation forces distribution to the other eigenmodes of blades bundle is discovered at isolating selected resonance.
|
|
| |
|
|
Vliv uložení snímače sil na zkreslení signálu
Půst, Ladislav ; Pešek, Luděk
Některé záznamy měření třecích charakteristik při vibračním relativním pohybu byly zkresleny vlivem vyšších harmonických složek. Numerické řešení jednoduchého modelu experimentálního zařízení ukázalo, že toto zkreslení je způsobeno dynamickými vlastnostmi opěrky snímače síly. Když nějaká harmonická buzení třecí silou souhlasí s vlastní frekvencí opěrky, rušivý signál se zesiluje. Zvýšením tuhosti podpěry se toto zkreslení odstraní.
|
host ::
RSS.