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Component-wise partitioned finite element method in linear wave propagation problems: benchmark tests
Kolman, Radek ; Cho, S.S. ; Červ, Jan ; Park, K.C.
A novel explicit time scheme for nite element computations of wave propagation problems in solids is presented. The presented algorithm, with the component-wise partition of equations of motion to the longitudinal and shear parts, is designed to more precisely integrate wave propagation in accordance with their dierent propagation wave speeds. The suggested three-time step integrator is fully explicit with the diagonal mass matrix, of second-order accuracy, conditionally stable and it exhibits minimal sensitivity behavior on time step size satisfying the stability limit. We present two numerical tests of wave propagation phenomena to show accuracy and performance of the proposed method.
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Symetric profile experiments with a velocity near the stall-flutter cut-off
Vlček, Václav ; Zolotarev, Igor ; Kozánek, Jan
Aeroelastic experiments with the profile NACA0015 with two degrees of freedom were realized in aerodynamic tunnel of the Institute of Thermomechanics, Czech Academy of Sciences, Prague. Attention was concentrated to the profile behaviour at velocity where the profile is just on the end of the velocity interval, where stall-flutter occurs. The flow field was measured with Mach-Zehnder interferometer, interferograms were registered with the high speed camera. Difference in the profile behaviour in these conditions was registered.
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Running excitation of blades bunches
Půst, Ladislav ; Pešek, Luděk
Application of additional damping elements or friction connection into blades’ shroud very effectively restricts undesirable vibrations of turbine blades vibrations. The previous investigation of dynamic properties of five-blades-model connected either by a rubber element, by direct Coulomb friction contact or by modified Coulomb friction contact showed very positive results. However, only one type of excitation force vector with one harmonic force acting on the first mass has been used in these studies. Proposed paper will be oriented on the response of the same fiveblades- bunch provided again by means of the same types of dry friction damping connections, but excited by running harmonic force. This type of excitation corresponds better to the real excitation in the steam or gas turbine. Influence of friction forces type, running velocity (depends on ratio of stator and rotor blades numbers), amplitudes of excitation forces, etc. will be analysed and presented.
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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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Static, spectral and modal analysis of the support of NACA0015 profile
Chládek, Štěpán ; Kozánek, Jan ; Vlček, Václav ; Zolotarev, Igor
In this paper the static and dynamic properties of the new proposed aerodynamical NACA0015 profile were experimentally investigated. The static stiffness of the angular and longitudinal profile support were determined by optical method. By pulse excitation were measured dynamical characteristics for different stiffness and mass configurations and identified corresponding spectral and modal properties. It will be useful for appropriate tuning of this dynamical system to achieve the flutter vibration in aerodynamical tunnel.
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Acoustic-structural interaction in human vocal tract prolonged by a tube
Radolf, Vojtěch ; Horáček, Jaromír
Phonation into tubes is often used for voice training and therapy. This paper introduces a mathematical model, which can help to clarify physical background of an influence of the soft tissues of vocal cavities on the acoustic resonances (formant frequencies). Substantial change in the first formant frequency caused by the soft tissues in the human vocal tract is in principle in the acoustic-structural interaction of the acoustic cavity semiocluded by the tube, with the yielding wall created for example by the soft tissues in the larynx.
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