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Generation of Intermittent Jet by Pulse-Modulated Synthetic Jets
Broučková, Zuzana
2018 - anglický
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. Klíčová slova: synthetic jet; pulse modulation; flow control Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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. Klíčová slova: wave propagation; finite element method; dispersion errors Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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. Klíčová slova: grid-connected converter; fault identification and localization; reconfiguration Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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 Klíčová slova: vibration; blade; laser; turbine Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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

EXPERIMENTAL ANALYSIS OF BLADED WHEEL MODEL WITH TIE-BOSS COUPLINGS – STEADY AND ROTATIONAL STATES
Pešek, Luděk; Bula, Vítězslav; Šnábl, Pavel; Cibulka, Jan
2018 - anglický
Experimental modal analysis of the proposed model of bladed wheel with tie-boss couplings was performed for validation of thenumerical FE model. The pre-stresses in contacts were set and evaluated indirectly by the magnetic torque sensor. Then dynamical tests of bladed wheel under revolutions were performed. The\nelectromagnetic synchronized pulses were used for excitation of forced vibration of the wheel. The Campbell diagram of the wheel with prestressedcontacts was created from the measurement under revolutions. From the attenuation of resonant vibration of the wheel the dampingwas evaluated. Klíčová slova: turbine blade; coupling; dry-friction Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
EXPERIMENTAL ANALYSIS OF BLADED WHEEL MODEL WITH TIE-BOSS COUPLINGS – STEADY AND ROTATIONAL STATES

Experimental modal analysis of the proposed model of bladed wheel with tie-boss couplings was performed for validation of thenumerical FE model. The pre-stresses in contacts were set and evaluated ...

Pešek, Luděk; Bula, Vítězslav; Šnábl, Pavel; Cibulka, Jan
Ústav termomechaniky, 2018

The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids
Kolman, Radek; Berezovski, A.; Kruisová, Alena
2018 - anglický
The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids aims to bring together scientists and engineers with interest in advanced modelling of wave propagation in solids. The Conference on Advanced Modelling of Wave Propagation in Solids will concentrate on topics related to analytical, numerical and experimental studies of linear and non-linear waves in conventional, advanced and modern materials like metamaterials and auxetic materials, to strongly dispersive wave propagation in inhomogeneous solids and to waves in materials with microstructure, etc. Attention will also be devoted to up-to-date formulations of non-linear constitutive equations in the description of material response under thermomechanical loading, dynamic fracture and damage, phase transformations, shock waves, and to dissipative effects. The recent advances and properties of analytical and numerical approaches and strategies should also be discussed. The main purpose of the Conference on Advanced Modelling of Wave Propagation in Solids is to discuss novel and recent methods of wave propagation modelling and to consider expected credibility of results especially in cases when comparison with those of experiment is not available. Theoretical, computational as well as experimental contributions on the wave propagation are welcome. Klíčová slova: wave propagation; advanced materials; numerical methods; experimental methods; dynamic behaviour of materials Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids

The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids aims to bring together scientists and engineers with interest in advanced modelling of wave propagation in solids. ...

Kolman, Radek; Berezovski, A.; Kruisová, Alena
Ústav termomechaniky, 2018

The Influence of Different Geometries of Human Vocal Tract Model on Resonant Frequencies
Valášek, Jan; Sváček, Petr; Horáček, Jaromír
2018 - anglický
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 Klíčová slova: wave equation; transfer function; aeroacoustic analogies; perfectly matched layer Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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. Klíčová slova: formant frequencies; modelling of phonation; biomechanics of voice Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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. Klíčová slova: formant frequencies; transfer function; biomechanics of voice Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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 Klíčová slova: airfoil; aeroelasticity; stall flutter; dynamic stall; limit cycle oscillation; self-excited vibration Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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

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