Number of found documents: 2896
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Generation of Intermittent Jet by Pulse-Modulated Synthetic Jets
Broučková, Zuzana
2018 - English
An axisymmetric air jet was excited using a pair of counter synthetic jets running in opposed direction. First, the control synthetic jets were measured alone. The driving signal was pulse modulated sinusoidal signal. After an adjustment, the primary axisymmetric jet was excited to the bifurcating mode, and its behavior was studied experimentally. For comparison purposes, a reference steady (unforced) jet from the same nozzle was also measured (Reynolds number was approximately 1300). The flow visualization and hot-wire anemometry techniques were used. Keywords: synthetic jet; pulse modulation; flow control Available at various institutes of the ASCR
Generation of Intermittent Jet by Pulse-Modulated Synthetic Jets

An axisymmetric air jet was excited using a pair of counter synthetic jets running in opposed direction. First, the control synthetic jets were measured alone. The driving signal was pulse modulated ...

Broučková, Zuzana
Ústav termomechaniky, 2018

Finite element modeling of the signal propagation in a thin tube and comparison with experimental data
Kruisová, Alena; Kolman, Radek; Trnka, Jan; Mračko, Michal
2018 - English
In finite element modeling of wave propagation problems, both the spatial and temporal discretization lead to dispersion errors. It means that the phase velocity of propagated wave is related to its frequency. In framework of temporal-spatial dispersion analysis, the time step size for implicit time integration method based on the Newmark method is proposed for linear and quadratic serendipity plane finite elements. In this paper, we verify the theoretical dispersion analysis by elastic wave propagation in thin tube, where experimental results are known. Such time step size was used in finite element modeling of the stress wave propagating in this thin steel tube, the results of simulations were compared with experimental results. Keywords: wave propagation; finite element method; dispersion errors Available at various institutes of the ASCR
Finite element modeling of the signal propagation in a thin tube and comparison with experimental data

In finite element modeling of wave propagation problems, both the spatial and temporal discretization lead to dispersion errors. It means that the phase velocity of propagated wave is related to its ...

Kruisová, Alena; Kolman, Radek; Trnka, Jan; Mračko, Michal
Ústav termomechaniky, 2018

Experimental investigation of fault tolerant converter connected to unbalanced grid
Valouch, Viktor; Šimek, Petr; Škramlík, Jiří
2018 - English
A model of the three-phase voltage converter for simulation of its modes of operation in standard as wellas fault states is presented. The presented model can be used to simulate steady-states and also transients at dc and ac side of the grid-connected converter. Based on simulation, an algorithm was designed to identify and localize a fault in some phase of the three-phase converter. Rules how to modify hardware, and control and modulation strategies to hold the converter in operation after the fault are presented and tested. the algorithm was experimentally verified. Keywords: grid-connected converter; fault identification and localization; reconfiguration Available at various institutes of the ASCR
Experimental investigation of fault tolerant converter connected to unbalanced grid

A model of the three-phase voltage converter for simulation of its modes of operation in standard as wellas fault states is presented. The presented model can be used to simulate steady-states and ...

Valouch, Viktor; Šimek, Petr; Škramlík, Jiří
Ústav termomechaniky, 2018

Influence of excitation frequency and pulse width on blade vibration
Voronova, Evgeniya; Maturkanič, Dušan
2018 - English
The paper describes results of measuring of blade vibration characteristics excitation by one electromagnet at harmonic regime.The measurements were performed in the laboratory of rotational laser vibrometry originated at the Institute of Thermomechanics AS CR, v.v.i.\n Keywords: vibration; blade; laser; turbine Available at various institutes of the ASCR
Influence of excitation frequency and pulse width on blade vibration

The paper describes results of measuring of blade vibration characteristics excitation by one electromagnet at harmonic regime.The measurements were performed in the laboratory of rotational laser ...

Voronova, Evgeniya; Maturkanič, Dušan
Ústav termomechaniky, 2018

The Influence of Different Geometries of Human Vocal Tract Model on Resonant Frequencies
Valášek, Jan; Sváček, Petr; Horáček, Jaromír
2018 - English
This paper presents the transfer function approach in order to determine the acoustic resonant frequencies of a human vocal tract model. The transfer function is introduced here as an acoustic pressure ratio between input amplitude at glottis position and output amplitude at mouth opening given by the solution of Helmholtz equation. This equation is numerically approximated by finite element method. The influence of different boundary conditions are studied and also different locations of excitation and microphone. \nFour different vocal tract geometries motivated by vocal tract geometry for vowel [u:] are investigated. Its acoustic resonance frequencies in range 100 - 2500 Hz are computed and compared with published results.\nFurther, the transient acoustic computation with different acoustic analogies are performed. The frequency spectra of Lighthill analogy, acoustic wave equation and perturbed convective wave equation are compared, where the vocal tract model with best frequency agreement with published results was chosen. The dominant frequencies correspond with predicted frequencies of transfer function approach.\n Keywords: wave equation; transfer function; aeroacoustic analogies; perfectly matched layer Available at various institutes of the ASCR
The Influence of Different Geometries of Human Vocal Tract Model on Resonant Frequencies

This paper presents the transfer function approach in order to determine the acoustic resonant frequencies of a human vocal tract model. The transfer function is introduced here as an acoustic ...

Valášek, Jan; Sváček, Petr; Horáček, Jaromír
Ústav termomechaniky, 2018

Numerical investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities
Vampola, T.; Štorkán, J.; Horáček, Jaromír; Radolf, Vojtěch
2018 - English
Acoustic resonance characteristics of 3D human vocal tract model without and with nasal and\nparanasal cavities were computed. Nasal cavities (NC) form the side branches of the human vocal tract and exhibit antiresonance and resonance properties which influence the produced voice quality. Developed FE models of acoustic spaces of nasal and vocal tract for vowel /a:/ are used to study the influence of (NC) on phonation. Acoustics frequency-modal characteristics are studied by modal analysis and numerical simulation of acoustic signals in time domain is performed by transient analysis of the FE models. Keywords: formant frequencies; modelling of phonation; biomechanics of voice Available at various institutes of the ASCR
Numerical investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities

Acoustic resonance characteristics of 3D human vocal tract model without and with nasal and\nparanasal cavities were computed. Nasal cavities (NC) form the side branches of the human vocal tract and ...

Vampola, T.; Štorkán, J.; Horáček, Jaromír; Radolf, Vojtěch
Ústav termomechaniky, 2018

Acoustic characteristics of 3D human vocal tract model with nasal cavities – preliminary experimental results
Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan; Vampola, T.
2018 - English
Acoustic resonance characteristics of 3D human vocal tract model with nasal and paranasal cavities were measured in three different ways: The excitation was realized by (1) self-oscillating vocal folds replica, (2) by a swept harmonic signal from an earphone placed instead of the vocal folds and (3) by a white noise signal from a loudspeaker located in front of the open mouth of the model. Resulting resonance frequencies are comparable for all excitation signals. These experiments were carried out to verify a complex mathematical model. Keywords: formant frequencies; transfer function; biomechanics of voice Available at various institutes of the ASCR
Acoustic characteristics of 3D human vocal tract model with nasal cavities – preliminary experimental results

Acoustic resonance characteristics of 3D human vocal tract model with nasal and paranasal cavities were measured in three different ways: The excitation was realized by (1) self-oscillating vocal ...

Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan; Vampola, T.
Ústav termomechaniky, 2018

Self-excited oscillation properties of the profile NACA0015 in subsonic flow
Zolotarev, Igor; Vlček, Václav; Kozánek, Jan
2018 - English
Self-excited oscillations of the profile NACA0015 in subsonic flow were realized in the wind tunnel. The plunge support had the same elasticity for all experiments, the pitch support had seven different elasticity parameters. During our experiments different types of selfexcited vibration (flutter, stall flutter) were observed. Range of Mach numbers was M = 0.08–0.45, corresponding range of Reynolds numbers is Re = (1–5)·105, when the chord length is used as the characteristic dimension of the profile.\n Keywords: airfoil; aeroelasticity; stall flutter; dynamic stall; limit cycle oscillation; self-excited vibration Available at various institutes of the ASCR
Self-excited oscillation properties of the profile NACA0015 in subsonic flow

Self-excited oscillations of the profile NACA0015 in subsonic flow were realized in the wind tunnel. The plunge support had the same elasticity for all experiments, the pitch support had seven ...

Zolotarev, Igor; Vlček, Václav; Kozánek, Jan
Ústav termomechaniky, 2018

Vibration stability of a vertical flywheel lifted by permanent magnetic rings
Zapoměl, Jaroslav; Ferfecki, P.; Sudhakar, A.; Kozánek, Jan
2018 - English
Lifting the vertical flywheels by permanent magnets is used to reduce energy losses in the support elements. Unstable equilibrium position of pairs of magnetic rings, material damping of the shaft, and nonlinear properties of the support elements can arrive at the flywheel unstable oscillations. Therefore, evaluation of the vibration stability is the essential part of the design process of flywheel devices. In the developed computational procedure the flywheel is represented by a beam-like body, to which an absolutely rigid disc (the actual flywheel) is attached. The determination of the force action between the magnetic rings is based on mutual interaction between two magnetic dipoles. The steady state response of the flywheel on the unbalance excitation is calculated by means of the trigonometric collocation method and its stability is evaluated by application of the Floquet theorem. The developed computational procedures and learning more on behaviour of flywheels lifted by magnetic rings are the main contributions of the carried out research.\n Keywords: vertical flywheels; permanent magnets; vibration stability Available at various institutes of the ASCR
Vibration stability of a vertical flywheel lifted by permanent magnetic rings

Lifting the vertical flywheels by permanent magnets is used to reduce energy losses in the support elements. Unstable equilibrium position of pairs of magnetic rings, material damping of the shaft, ...

Zapoměl, Jaroslav; Ferfecki, P.; Sudhakar, A.; Kozánek, Jan
Ústav termomechaniky, 2018

Synthetic Jet Characteristic Velocity Estimated nn The Basis of Momentum Flux Measurement
Kordík, Jozef; Trávníček, Zdeněk
2018 - English
The paper compares two methods of evaluation of synthetic jet characteristic velocity. The first method of the characteristic velocity estimation is based on a simple measurement of the synthetic jet momentum flux (the jet thrust) by means of precision scales. The second method is a standard one, it is based on spatial-temporal integration of the velocity profile at the synthetic jet actuator nozzle exit. The velocity profile was obtained here using hotwire measurements in air. Comparison of the methods is based on dimensionless stroke length of the synthetic jet. It is confirmed that the results of both methods are nearly the same for higher dimensionless stroke length. On the other hand, if the jet regime approaches to the synthetic jet criterion threshold (i.e. to the dimensionless stroke length of 0.5) the results of both methods diverge. Using the current results a correction is suggested for the momentum-flux-based method to match the standard one. Keywords: synthetic jet; synthetic jet actuator; momentum flux Available at various institutes of the ASCR
Synthetic Jet Characteristic Velocity Estimated nn The Basis of Momentum Flux Measurement

The paper compares two methods of evaluation of synthetic jet characteristic velocity. The first method of the characteristic velocity estimation is based on a simple measurement of the synthetic jet ...

Kordík, Jozef; Trávníček, Zdeněk
Ústav termomechaniky, 2018

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