Národní úložiště šedé literatury Nalezeno 35 záznamů.  začátekpředchozí21 - 30další  přejít na záznam: Hledání trvalo 0.00 vteřin. 
Verification of our deformation member for measuring axial force under torsional dynamic load
Šulc, Petr ; Pešek, Luděk ; Štěpánek, Ivo ; Šnábl, Pavel ; Bula, Vítězslav
This paper deals with experimental testing of hard rubbers under torsional harmonic loading on an axial torsional servohydraulic testing machine Instron 8852. In evaluating these experiments, we focused on obtaining axial forces and elongation, which is a confirmation of the so-called Poynting effect under torsional loading. An important result from these experiments is a comparison of axial forces from this device with the results from our designed and assembled torsion device with a deformation member for measuring axial forces, which brings us some verification of this device.
Measurement of friction coefficient between damping wire and groove
Šnábl, Pavel ; Pešek, Luděk ; Bula, Vítězslav ; Běhálek, V. ; Boháč, T. ; Tašek, H.
Damping wire is being used on railway wheels for noise suppression. It is inserted into a groove of the wheel and dry friction damping reduces vibrations and thus the noise transmitted by the wheel. For increase of durability of the wire, surface treatment of the groove and the ring must be applied to prevent corrosion. Three combinations of diferent surface treatments were studied during reciprocating motion in a set of measurements with diferent frequencies and normal forces to evaluate friction coeficient. Then, those measurements were repeated after a long-time run to evaluate the change of friction coeficient after the wear of the surfaces.
The new HPC results of 3D FE modelling of dry-friction damping at tie-boss couplings of bladed wheel - 6nd resonant mode
Pešek, Luděk ; Šnábl, Pavel ; Bula, Vítězslav
The paper is a direct continuation of our study published in the last colloquium DYMAMESI. This paper deals with the new results of dry-friction damping calculation of the bladed wheel with tie-boss couplings vibrating at a higher resonant mode, i.e. mode with 6 nodal diameters (ND). The numerical solution of the wheel based on 3D finite element method with surface-to-surface dry friction contact model is applied. Due to dry friction contacts and non-linear solution, it leads to HPC computations and long computation times. Therefore, the earlier proposed computational strategy for damping evaluation where the resonant attenuation is computed directly from the defined resonant initial conditions given by the 6ND mode is used. Comparison of experimental and numerical results of dynamical behaviour of the bladed wheel yields a reasonable agreement for the studied vibration mode.
Identification of dynamic properties of built electrodynamic shaker
Šnábl, Pavel ; Kozánek, Jan ; Pešek, Luděk
Electrodynamic shaker was built in our institute for excitation of vibrating blade in a flow field. The shaker consists of permanent magnet and voice coil, 3D printed body, core and cover, and two at suspension rings laser-cutted from Pertinax. For simulation purposes of the whole system, identfication of shaker dynamic parameters was needed. Several identification methods in time or frequency domain were used, and it was shown that the shaker model must contain nonlinear stiffness in order to describe the real system more accurately.
Analysis of measurement of temperature dependence inside rubber sample under dynamic harmonic load
Šulc, Petr ; Pešek, Luděk ; Bula, Vítězslav ; Šnábl, Pavel ; Cibulka, Jan ; Košina, Jan
This work deals with the preparation and methodology of temperature measurement inside a rubber sample. In this paper, a rubber sample with temperature sensors is described and a description with a temperature measurement scheme under torsional dynamic stress with the possibility of measurement in a temperature chamber is proposed. Large torsional deformations are considered for harmonic torsional loads. The reason for these measurements is to determine the temperature dependence and sensitivity of the heat output parameters.
Dynamic and heat transfer analysis of a container with measuring instruments for space probes
Zolotarev, Igor ; Bula, Vítězslav ; Šnábl, Pavel ; Gabriel, Dušan ; Dobiáš, Jiří ; Masák, Jan ; Snížek, Jan ; Souček, Jan
Rocket boosters and spacecraft are subject to intense acoustic environments during launch, which induce high levels of vibration in structural elements and equipment. In addition, elastic structural interactions with propulsion systems and flight control systems can produce low-frequency, high-deflection flight instabilities. Natural vibration of the container with measuring equipment were studied by numerical and experimental methods in the laboratory of Institute termomechanics CAS. Heat transfer analysis inside the container was made by FEM with respect to the conditions during start of the rocket and work in space.\n
Contribution to HPC FEM calculations of bladed disk dynamics with dry-friction contacts
Pešek, Luděk ; Šnábl, Pavel ; Bula, Vítězslav
The experimental set-up for studying dynamical behaviour of the bladed wheel with pre-stressed dry-friction contacts in tie-bosses was built. The numerical solution of the turbine bladed wheel with tie-bosses based on 3D finite element method with surface to surface dry-friction contact model is proposed. Comparison of experimental and preliminary numerical results of dynamical behaviour and damping estimation of our bladed wheel design yielded a reasonable agreement. Due to dry-friction contacts and non-linear solution of 3D FE model it, however, leads to HPC computations and long computation times. The contribution deals with description of computational strategy for damping evaluation and achieved results, too.
Influence of contact region size between damping wire andand metal ring on overall damping
Šnábl, Pavel ; Pešek, Luděk ; Bula, Vítězslav ; Cibulka, Jan
Damping wire curved to circular shape is inserted into a groove of slightly smaller diameter in damped steel ring. Deformation of circular-shaped wire causes uneven distribution of pressure in the groove and evenno contact between the wire and the groove in some regions. Experimentaimed for nding those regions was performed and the results are shown.Axial pre-stress of the wire was then applied and it was proven that it helps to reduce the regions with no contact. Dynamic test were made to see how larger contact region achieved by axial pre-stress inuences overall damping of damped steel ring.
Contribution to modelling of bladed model disk with dry-friction contacts in tie-bosses
Pešek, Luděk ; Šnábl, Pavel ; Šulc, Petr ; Půst, Ladislav ; Bula, Vítězslav
The experimental set-up for studying dynamical behavior of the bladed wheel with pre-stressed dry-friction contacts in tie-bosses was built. The numerical solution of the turbine bladed wheel with tiebosses based on 3D finite element method with surface to surface dry friction contact model is proposed. Comparison of experimental and preliminary numerical results of dynamical behavior and damping estimation of our bladed wheel design yielded a reasonable agreement. Limitation of the non-linear solution due to dry friction contacts is HPC computations and long computation times. The contribution will deal with the achieved results.\n
Extension of backlash based dry friction model in simulink and comparison with dahl and lugre models on simulations of blade triple
Šnábl, Pavel ; Pešek, Luděk ; Půst, Ladislav
Behaviour of analytical dry friction model based on SIMULINK. Backlash block with Coulomb friction is compared with Dahl model. The Backlash based model is herein extended to contain velocity-dependent friction characteristic and is compared with LuGre model. All models are used on analytical model of blade triple with mistuned blades and vibration attenuations from first resonant mode of this system are compared. Instability of Dahl and LuGre models for large time-step are shown.

Národní úložiště šedé literatury : Nalezeno 35 záznamů.   začátekpředchozí21 - 30další  přejít na záznam:
Chcete být upozorněni, pokud se objeví nové záznamy odpovídající tomuto dotazu?
Přihlásit se k odběru RSS.