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Vibrational tests and dynamic analysis of friction effect at railway wheel damped by damping ring
Pešek, Luděk ; Půst, Ladislav ; Bula, Vítězslav ; Šnábl, Pavel ; Boháč, T. ; Tašek, H. ; Běhálek, V.
Experimental modal analysis with one (SIMO) and two (MIMO) exciters with the following objectives: (a) to develop a test methodology to evaluate the friction effect of the damping ring on the vibration damping of the wheel, b) to describe changes in the measured dynamic amplitude-frequency and phase-frequency characteristics to the excitation amplitude and to show the non-linear frictional behavior of the circular damping ring in the wheel groove for different natural vibration shapes was carried out in the dynamic laboratory of Bonatrans a.s. on 11-16 June 2019. The proposed methodology and analysis of the measured results in terms of the effect of the friction couplings of the circular wire are described in the report. This work was performed for design of the damping friction ring with variable curvature and optimal distribution of contact pressures in the groove, which is the aim of the DELTA project.\n
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Experimental and computer modelling study of glottal closing velocity during phonation
Horáček, Jaromír ; Radolf, Vojtěch ; Bula, Vítězslav ; Šidlof, P. ; Geneid, A. ; Laukkanen, A. M.
This preliminary study shows that the impact stress between the colliding vocal folds during phonation should not be evaluated from the maximum velocity of the glottal closing because the velocity of the closing diminishes just before the glottal closure. This phenomenon, which can be caused by a pressure cushion effect in the fast narrowing glottal gap, is demonstrated with measurements from high speed camera images recorded from human and on a physical laboratory model for vowel [u:] phonation and on a three-mass computer model employing a Hertz model of impact force. For a more detailed future study of this phenomenon a faster camera has to be used. \n
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Experimental analysis of bladed wheel modelwith tie-boss couplings – steady and rotational states
Pešek, Luděk ; Bula, Vítězslav ; Šnábl, Pavel ; Cibulka, Jan
Experimental modal analysis of the proposed model of bladed wheel with tie-boss couplings was performed for validation of the numerical FE model. The pre-stresses in contacts were set and evaluated indirectly by the magnetic torque sensor. Then dynamical tests of bladed wheel under revolutions were performed. Theelectromagnetic synchronized pulses were used for excitation of forced vibration of the wheel. The Campbell diagram of the wheel with prestressed contacts was created from the measurement under revolutions. From the attenuation of resonant vibration of the wheel the dampingwas evaluated.
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EXPERIMENTAL ANALYSIS OF BLADED WHEEL MODEL WITH TIE-BOSS COUPLINGS – STEADY AND ROTATIONAL STATES
Pešek, Luděk ; Bula, Vítězslav ; Šnábl, Pavel ; Cibulka, Jan
Experimental modal analysis of the proposed model of bladed wheel with tie-boss couplings was performed for validation of thenumerical FE model. The pre-stresses in contacts were set and evaluated indirectly by the magnetic torque sensor. Then dynamical tests of bladed wheel under revolutions were performed. The\nelectromagnetic synchronized pulses were used for excitation of forced vibration of the wheel. The Campbell diagram of the wheel with prestressedcontacts was created from the measurement under revolutions. From the attenuation of resonant vibration of the wheel the dampingwas evaluated.
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Deformation energy of Yeoh hyperelastic model and constant hyperelastic proportional damping
Šulc, Petr ; Pešek, Luděk ; Bula, Vítězslav ; Košina, Jan ; Cibulka, Jan
The paper deals with a proposal of the dissipated energy of hard rubbers as a function of the deformation energy expressed by the Yeoh hyperelastic model. Then the deformation energy may be dependent only on the first invariant of deformation. Based on the experiment, a “hyperelastic proportional damping” (HPD) is proposed for hard rubbers under finite strains. It is analogical to the model of proportional damping in the elastic theory, i.e. the dissipated energy is proportional to the deformation energy multiplied by the frequency of dynamic harmonic loading. The Yeoh model is chosen since the deformation function is dependent only on the first strain invariant for a description of the simple shear of a surface cylinder. The constants are used to an enumeration of the deformation energy of the Yeoh model for the specific cases of tested rubbers. The coefficients of hyperelastic proportional damping are evaluated on the basis of experimental results,too.
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Experimental analysis of flexible planet pins vibration of rotating four-planetary gearbox
Pešek, Luděk ; Bula, Vítězslav ; Cibulka, Jan
The aim of this report is to describe the measurement and analysis of the measurement results of the rotating four-planetary gearbox with flexible pins designed and manufactured by Wikov Gear. Measurement was carried out at a test facility at Wikov Gear in Pilsen on 17.5. and 21.5. 2017. Two variants of the planetary gear box were tested: a) using the standard bearings (17.5.), B) using the floating ring bearings ("fluting bush"). With the use of standard bearings of the planets, a maximum speed of 8500 rpm and with the floating ring bearings a speed of 14500 rpm were achieved. The bending oscillations of the planet pins were measured by strain-gauges. The methodology of measurement was proposed in ÚT AV ČR. The analysis was focused on the evaluation of frequency spectrograms for finding significant resonances of oscillation of planet pins. This knowledge was used to validate the numerical models developed at ÚT AV ČR and to attune their parameters.
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Dissipated energy of hard rubbers at dynamic torsional finite straining
Šulc, Petr ; Pešek, Luděk ; Bula, Vítězslav ; Cibulka, Jan ; Košina, Jan
The paper deals with a stress analysis of hard rubber under large torsion deformations. This study was motivated by effort to find the dependency the dissipated energy on the deformation energy. Based on the results of an experiment, a function of dissipation energy of hard rubbers for finite strains using the theory hyperelasticity was proposed herein analogically as a prportional damping for elastic theory. Samples of hard rubber of different hardness (EPDM, Silcone) were dynamically tested on the developed torsional test-rig at different frequencies, amplitudes. First the Mooney Rivlin model (MRM) for a shear case of loading was analytically developed and then MRM constants were attained by fitting of the MRM to the experimental torsion-deformation curve. These constants were used to obtain the deformation energy of the MRM models. The coefficients of hyperelastic proportional damping relating a dissipated energy to a strain energy were evaluated for tested rubbers on the basis of experimental results.
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Design of low-subsonic blade cascade model for aero-structural dynamic testing
Pešek, Luděk ; Hála, Jindřich ; Šulc, Petr ; Chládek, Štěpán ; Bula, Vítězslav ; Uruba, Václav ; Cibulka, Jan
Low-subsonic blade cascade model for aerodynamic testing was design in the Institute. The aim is to study the flow dynamics and flutter phenomenon in the cascade with moving blade profiles. The numerical calculations of two proposed cascades were performed for analysis of influence of stagger angle, incident angle of flow and inter-blade phase angles of the relative movement of blades. The results of numerical simulations of fluid dynamics of non-stationary flow both as viscid and non-viscid are presented. Futhermore the solution of the physical model of the designed cascade including excitation of profiles, measuring of the profile displacement and aerodynamic forces are described.
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