2023-08-06
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Dynamics of a cantilever beam with piezoelectric sensor: Experimental study
Kolman, Radek ; Kylar, Jaromír ; Kotek, Vojtěch ; Cimrman, Robert ; Musil, Ladislav
Online and real-time sensing and monitoring of the health state of complex structures, such as air-craft and critical parts of power stations, is an essential part of the research in dynamics. Several types of sensors are used for sensing dynamic responses and monitoring response changes during the operation of critical parts of complex systems. The piezoelectric (PZ) materials belong to one group of electroactive materials, which transform mechanical deformation into an electrical response. For example, PZ ceramics or PVDF foils are employed for online sensing of the time history of mechanical deformation. Experimentally obtained response of a cantilever beam structure with a glued PZ sensor is the case of interest in this contribution. During the transient problem of the beam loaded by suddenly interrupted load due to the weight of a mass at the end of the beam, the time history of normal velocity at a point on the beam surface has been measured by a laser vibrometer and parallely, the output voltage on the PZ sensor has been measured by an electric device. The experimental data in the case of the first eigen-frequency is in good agreement with the value given by the formulae from the theoretical modeling of free vibration of a linear beam.
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2023-08-06
00:02 |
The connection between the principle of the least action and the thermodynamic condition of stability
Maršík, František ; Trávníček, Zdeněk ; Antošová, Zuzana
The extended principle is formulated for a material point (M.P.) X, which has nonzero mass, temperature, and trajectory x(X,t). The Lagrangian of this variation principle is equal to the kinetic energy from which, the internal energy of the material point (which depends on the entropy) and the additional energy caused by the frictional force are subtracted. The relation between the inertial force and the entropy gradient is found and the gravitational force is completely replaced by the entropy gradient. Thanks to the mentioned properties of the total enthalpy, the Thermodynamic criterion of stability of the state of M.P., is formulated.
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2023-08-06
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2023-08-06
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2023-07-23
00:01 |
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2023-07-23
00:01 |
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2023-07-23
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2023-07-23
00:01 |
Dynamics of Machines and Mechanical Systems with Interactions, DYMAMESI 2023
Zolotarev, Igor ; Pešek, Luděk ; Kozień, M. S.
The aim of the DYMAMESI is to facilitate the exchange of up to date information and knowledge among specialists in structural and multibody dynamics, in coupled interacting systems as aero-elasticity, hydro-elasticity, biomechanics, systems with feedbacks and mechatronics. The colloquium DYMAMESI 2021 is cofunded by the Strategy AV21 initiative of the Czech Academy of Sciences of the Czech Republic, and in 2021 will be hosted by Cracow University of Technology, Institute of Applied Mechanics, Section of Dynamics of Systems.
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2023-07-23
00:01 |
Annular Impinging Jets and an Active Control of Hysteretic Effects
Devani, Yogendrasasidhar ; Antošová, Zuzana ; Trávníček, Zdeněk
An annular impinging air jet with and without flow control was studied experimentally using measurements of the wall pressure and flow velocity by the Pitot probe. To investigate flow control swirling effects, eight synthetic jets were generated from the nozzle center body. The experiments cover Reynolds numbers 4000–10,000 (evaluated from the outer exit diameter of the annular nozzle). For Re<9000, the bistability and hysteresis were identified and two different flow field patterns (A, B) were found under the same boundary conditions. For higher Re>9000, the hysteresis were not found.
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2023-04-24
23:56 |
Srovnání hodnocení přípustnosti trhlin podle R6, BS 7910, ASME XI a NDT ASI (ZP 92016 a příloha X k sekci IV) v oblastech předpokladů aplikovatelnosti, vstupních dat a charakterizace trhliny pro výpočet
Joch, Jaroslav
Výzkumná zpráva srovnává přístupy čtyř metodik (R6, B6 7910, ASME XI a NTD ASI), které se používají při vyhodnocování přípustnosti defektů, nalezených při odstávce JE pomocí metod NDT. Srovnávání se zaměřuje na charakterizaci trhliny, postulované pro výpočet, a na srovnání přístupů na základě dostupných dat a míry konzervativnosti. Pozornost je věnována jak shodám v přístupu, tak i odlišnostem. Jsou zdůrazněna historická a přístupová východiska jednotlivých metodik.
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