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DYMAMESI 2016 - proceedings
Zolotarev, Igor ; Pešek, Luděk
Proceedings of the Colloquium DYNAMICS OF MACHINES AND MECHANICAL SYSTEMS WITH INTERACTIONS (DYMAMESI), that was held in the Institute of Thermomechanics in Prague, March 1 - 2, 2016 deal with problems structural and multibody dynamics, in coupled interacting systems as aero-elasticity, hydro-elasticity, biomechanics, systems with feedbacks and mechatronics. The published papers was divided into the two parts: Interactions - vibration of dynamic systems coupled with surroundings, mechanical systems with feedbacks, mechatronic active elements, measurement methods and identification in interaction problems, interactions in biomechanics, aero- and hydro-elasticity in rotational engines (bearings, blades, sealings, spaces), analytical and numerical methods in solutions of interactions and Dynamics of Machines - dynamics and vibrations of mechanical systems and solids, non-linear systems - stability, bifurcations, chaos, damping technologies - materials, active elements, methods, identification, vibrodiagnostics, fatigue, computational mechanics and experiments.
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Analysis of the lateral vibration of a flexibly supported unbalanced viscoelastic Jeffcott rotor
Ferfecki, P. ; Zapoměl, Jaroslav ; Kozánek, Jan
The behaviour of flexible rotors is significantly influenced by elasticity and damping properties of the shaft. It implies a special attention has to be paid to appropriate choice of a theoretical material to represent the rotors in mathematical models of rotating machines. The procedure developed in this paper concentrates on the investigation of the steady state component of the Jeffcott rotor vibration induced by the disc unbalance and on magnitude of the forces transmitted to the rotor frame. The shaft material is represented by the Zener standard solid material model. The steady state response was determined by application of the trigonometric collocation method. The results of the simulations confirmed the influence of the input oil pressure on the shape of the rotor orbit and on the oscillation amplitude.
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Additional axial stress of rubber cylinder at torsion deformations and large strains
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 additional axial stresses. It helps to assess the influence of the tension stresses on the tangential deformations of the test sample during large torsion strains.
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Evaluation of aerodynamic damping and natural frequencies from numerical simulations and experiments
Chládek, Štěpán ; Horáček, Jaromír ; Zolotarev, Igor
The paper describes different ways for aerodynamic damping and natural frequencies evaluation in a problem of fluid-structure interaction. It is useful for both numerical simulations and experimental measurements. The Fourier transform is used for the frequency evaluation and the damping is evaluated both in time and frequency domain. Significant influence of the chosen sampling frequency and the length of time record on the accuracy of the results are demonstrated both in the numerical simulation and in the experiment that was performed with the flexibly supported profile NACA 0012 with two degrees of freedom.
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Some atypical flutter characteristics of the NACA0015 profile
Vlček, Václav ; Zolotarev, Igor ; Kozánek, Jan ; Štěpán, M.
The part of the aeroelastic experiments with profile carried out in wind tunnel of the Institute of Thermomechanics, v.v.i. at stream velocity M = 0.15-0.38 in the interval of Reynolds numbers Re = (1.8-5.0)•105 is presented. The results relate to the self-excited vibration of the profile NACA0015, which had two degrees of freedom allowing rotation and transverse displacement of the profile. The elasticity of the two degrees of freedom support has not been, during the experiments, changed. The dependence of Strouhal numbers on the speed of the stream.has been obtained. In one case the excitation of an unstable state occured and during the measurement the jump to a stable state arised. The kinematics of the model during this transition is described.in detail.
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Vibration of blade bunch forced by delayed excitation
Půst, Ladislav ; Pešek, Luděk ; Radolfová, Alena
Response of the five-blade-bunch linked in the shroud by means viscous-elastic damping connections and excited by running harmonic forces is investigated. This type of excitation corresponds to the real excitation in the steam or gas turbine with different number of rotor and stator blades. After ascertaining of phase delay between neighbouring blades, the different dynamic properties of isolated and closed five-blade bunch are shown and analysed in this contribution. Recommendation how apply ascertained results for evaluation of experimentally gained data from dynamic measurements on bladed disk is added.
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