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Stress analysis under torsion loading hard rubber for a large deformation and hyperelastic behaviour
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 enhance the theoretical background for experimental evaluation of material behaviour of hard rubbers on our test rig. First the Mooney Rivlin model (MRM) for shear case of loading was developed and then MRM constants were attained by fitting of the MRM to the experimental torsion-deformation curve. Then the tuned MRM cylindrical model was tested under torsion loading for evaluation of stress state. Besides the radial distribution of shear stress and strain the attention was paid for evaluation of axial stresses. It could help to assess the influence of the tension stresses on the tangential deformations of the test sample during large torsion.
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Some NACA0015 profile support variants with self-excited vibration in subsonic fluid flow
Vlček, Václav ; Štěpán, M. ; Zolotarev, Igor ; Kozánek, Jan
One of the important domain of the contemporary aeroelasticity is the self-excited vibration of isolated profiles together with the self-excited vibration of profiles located in blade cascades. The Institute of Thermomechanics of the AS is engaged in group of projects concerning this aeroelastic problem. Results presented here were obtained solving a part of them [1-5].This experiments were realized in the wind tunnel of suction type placed in the laboratory of the Institute in Nový Knín. Profile NACA0015 with two degrees of freedom support was used. Profile was embedded with variable rotational and translational elasticity. The attention of this paper is concentrated on the time records and corresponding spectra of the translational and rotational movement during the self-excited vibration of the profile. Further results related to other parameters of this vibration will be published separately.
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Free vibration of planetary gearing
Půst, Ladislav ; Pešek, Luděk ; Radolfová, Alena
Planetary gear drives have important advantages over parallel axis gears due to theirs compact design an great torque-to-weight ratio, but dynamic properties of such gearings are more complicated and they need deep dynamic analysis. For improving load sharing among planet wings, the application of flexible planetary pins or using free central wheel is needed. Presented paper is oriented on mathematical model design. The plane type of gearings with four planetary subsystems and fixed planet carrier has been selected. Used helical gearing has an essential smaller variation of contact stiffness against the direct spur gearings. Therefore this stiffness variability is not taken into account. Frequency and modal spectrums of such a dynamic mathematical model of planetary gearing set is presented and influences of design parameters are analysed.
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Acoustic resonance characteristics of the human vocal tract with respect to a soft tissue
Radolf, Vojtěch ; Horáček, Jaromír
A mathematical model, which can help to clarify physical background of an influence of the soft tissue of vocal cavities on the formant frequencies, has been extended. Strong acoustic-structural interaction is demonstrated on the vocal tract cavity for vowel /u:/ prolonged by a tube that is used for voice training and therapy purposes. The glottis is closed by a yielding wall, considering a mass, compliance and structural damping. Viscous losses of the acoustic cavities and radiation impedance at the output are assumed. Significant change in the first acoustic resonance frequency caused by the compliance of the soft tissue at the glottis corresponds to the data found experimentally in earlier study.
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Application of pulse excitation for forced vibration of selected eigenmode of blade wheel under rotation
Pešek, Luděk ; Bula, Vítězslav ; Cibulka, Jan
Application of pulse excitation for forced vibration of selected eigenmode of blade wheel under rotation. The paper deals with a solution of multipoint electromagnetic pulse excitation of turbine blade wheel under rotation for analysis of its dynamic behaviour. Since a width of electromagnetic pulses should decrease with revolution speed, magnetomotoric forces acting to the blades decrease, too. So, the application of more “high-speed” electromagnets distributed along a circumference of the wheel that multiply the excitation potential seems to be inevitable for such a stiff structure. It, however, requires accurate synchronization of the electromagnets with wheel revolutions and with a dynamic response of the selected blade. Furthermore impulse excitation causes, in general, transient oscillations of many superposed eigenmodes of the wheel. Therefore an attention, herein, was paid to develop an appropriate control algorithm for the pulse excitation of electromagnets and to find a proper strategy of electromagnet interconnections to gain a multiplepoint excitation for excitation of selected eigenmodes.
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