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Kavitace a nukleace bublin ve vodě s příměsemi
Zima, Patrik ; Maršík, František ; Sedlář, M.
The latest advances in modeling of cavitation in water flows and experimental investigation of bubble nucleation in a cavitation nozzle will be presented. The emphasis will be put on presenting the results of the recent measurements with cavitation nozzle and the critical assessment of the applicability of the cavitation nozzle principle for determining the size of critical bubble radii. Some results of numerical modeling of cavitation in pumps will be summarized.
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Termoakustika
Trávníček, Zdeněk
The thermoacoustic energy conversion systems can operate as heat pumps (or refrigerators which are based on the same principle) or prime movers. The design optimization of the thermoacoustic refrigerator was made using two methods, namely the optimization based on the cooling load maximization and on the coefficient of performance (COP) maximization. The highest COP can be achieved with the noble gas mixture helium-xenon (62%-38%) as the working fluid, while the highest cooling load can be achieved with pure helium.
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Syntetizovaný proud
Dančová, P. ; Trávníček, Zdeněk ; Vít, T.
Equipments working on the synthetic jet (SJ) principle can be used in aerospace industry, automotive industry, pumps and ejectors, cooling and heating applications, intensification of mixing in chemical reactors. SJ can be used for jet control and vectoring, flow control in external and internal aerodynamics, intensification of heat transfer. The main advantage of these applications is relative simplicity of SJ equipment. This article summarizes primary SJ world studies, and it shows examples of own experimental results.
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Rosný bod spalin: teoretické modelování a předběžné měření
Krejčí, A. Petr ; Hrubý, Jan ; Ždímal, V. ; Trávníček, Zdeněk
Based on industrial needs, the dew point temperature of flue gases is re-examined, both theoretically and experimentally, with mixture of sulphuric acid and water vapors as a flue gas model. This work is motivated by inconsistency and unsufficient accuracy of previous works, which differ significantly in data on sulphuric acid saturation pressure. Experimental setup based on the Laminar co-flow tube is used to express saturation pressure of sulphuric acid via measurements of binary homogeneous nucleation rate.
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Energeticky konjugované míry napětí a deformace v mechanice kontinua
Hrubý, Zbyněk ; Plešek, Jiří
The energy conjugate measures of stress and strain enter any constitutive relation for the material behaviour description. There are many strain measures in common use, several of them discussed in the text. The main aim of the contribution is to focus on the derivation of a general energy conjugate stress tensor corresponding with a general Lagrangean strain tensor.
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Vazba kmitajícího systému a zdroje energie
Půst, Ladislav
Majority of publications on mechanical vibrations are based on the assumption that the external excitation is produced by an ideal source of power with prescribed frequency. But in reality, the excitation sources are non-ideal with limited power, limited inertia and their frequency fluctuates according the instantaneous state of oscillating system. The paper presents on overview of systems and results gained during the several dozens of years on this interaction problem. The most characteristic properties of systems excited by source of limited power and limited inertia are variation of revolution, distortion of harmonic motion, instability and non-uniform passage through resonance zone.
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Modelování vibračních vlastností lidských hlasivek
Vampola, T. ; Horáček, Jaromír ; Klepáček, I.
A 3D finite element model of the human larynx including the vocal folds was developed. The model enables to take into account phonation position (tinsion and adduction) of the vocal folds by positioning of the arythenoid and thyroid cartilages. Anisotropic properties of the three layers of the vocal fold living tissue (epitel, ligament and muscle) are modelled respecting the material nonlinearities with increasing prolongation of the tissue in longitudinal direction. The motion of the vocal folds is numerically simulated for a prescribed subglottal pressure loading the vocal folds by a periodic function in the time domain. the generated motion of the vocal folds seems to be qualitatively similar to a vibration mode known from clinical measurements.
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Výpočet dynamických vlastností aerostatických ložisek
Skarolek, A. ; Kozánek, Jan
This contribution deals with computation of stiffness and damping coefficients of aerostatic bearings. Model of bearings is based on Reynolds equation for compressible medium supplemented by descrition of mass flow through feeding system. Time-series of displacements and internal forces are obtained by numerical solution. Linear stiffness and damping coefficients are obtained by means of least squares regression.
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