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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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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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The test of the time-difference method for the torsion vibration of the rottating shaft
Pešek, Luděk ; Bula, Vítězslav ; Cibulka, Jan
The contribution deals with testing of the time difference method by using the encoder for evaluation of the torsion vibration of the rotating shaft under dynamic torque moment excitation. The testing of accuracy of this method was first performed on the numerical simulations of the pulse signals and then on the real experimental data gained from the encoder. Then the method was implemented into dSPACE control system for on-line processing. The achieved experimental results are in accordance with the numerical assumptions.
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Air-pressure characteristics and visualization of bubbling effect in water resistance therapy
Radolf, Vojtěch ; Horáček, Jaromír ; Bula, Vítězslav ; Laukkanen, A. M.
This study investigates the influence of a widely used method in voice training and therapy, phonation into a resonance tube with the outer end submerged in water (‘water resistance therapy’ with bubbling effect). Acoustic and electroglottographic (EGG) signals and air pressures in the mouth cavity were registered and the formation of bubbles was studied using high speed camera. Bubbling frequency dominates in the spectra of the pressure signal being about 15 dB higher than the amplitude of the first harmonic, which reflects the fundamental frequency of the vocal folds’ vibration. Separation of the bubbles 10 cm under water surface starts when the buoyancy force acting on the bubble is approximately equal to the aerodynamic force in the tube.
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