Number of found documents: 3132
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Vysokonapěťový pulzní zdroj a řídící jednotka
Gruber, Jan; Janovec, Jiří; Šonský, Jiří; Němec, Tomáš
2022 - Czech
Zpráva obsahuje popis sestavy vysokonapěťového pulzního zdroje (PPSU) a řídící jednotky (SPCU), které jsou využívány v kombinaci s výbojovou komorou a párem elektrod k aerosolové syntéze nanomateriálů. Uvedena jsou schémata zapojení, seznam elektronických i mechanických součástek, jakožto i popis konektorů a zřetězeného propojení více soustav. Zpráva rovněž obsahuje informace o referenčních parametrech výbojů a popis komunikačního protokolu včetně nastavitelných proměnných. The report contains description of Pulsed Power Source Unit (PPSU) and Spark Control Unit (SPCU), which are utilized in combination with Spark Discharge Chamber and pair of electrodes for aerosol synthesis of nanomaterials. The report includes electronic schematics, list of components, description of connectors and way to chain-link and operate more sets of units. The report also includes information about discharge reference parameters and description of communication protocol and its variables. Keywords: electrotechnics; high-voltage; power transformation; pulse generators Available at various institutes of the ASCR
Vysokonapěťový pulzní zdroj a řídící jednotka

Zpráva obsahuje popis sestavy vysokonapěťového pulzního zdroje (PPSU) a řídící jednotky (SPCU), které jsou využívány v kombinaci s výbojovou komorou a párem elektrod k aerosolové syntéze ...

Gruber, Jan; Janovec, Jiří; Šonský, Jiří; Němec, Tomáš
Ústav termomechaniky, 2022

Vibration mode shape extraction of bladed disk
Mekhalfia, Mohammed Lamine; Procházka, Pavel; Tchawou Tchuisseu, Eder Batista; Maturkanič, Dušan; Hodboď, Robert
2022 - English
This research paper deals with the experimental protocol followed to visualize the vibration mode shape of an aero-engine bladed disk. This study is based on a comparison between the numerical results obtained through Finite element methods (FEM) using ANSYS software and experimentally using the laser Doppler vibrometer. Therefore the bladed disk was transformed into a 3D virtual environment and structural analysis was performed. The results demonstrate a match between the numerical and the experimental one, this match offers the possibility for using the model for future studies. Keywords: blade disk; mode shapes; laser doppler vibrometer Available at various institutes of the ASCR
Vibration mode shape extraction of bladed disk

This research paper deals with the experimental protocol followed to visualize the vibration mode shape of an aero-engine bladed disk. This study is based on a comparison between the numerical results ...

Mekhalfia, Mohammed Lamine; Procházka, Pavel; Tchawou Tchuisseu, Eder Batista; Maturkanič, Dušan; Hodboď, Robert
Ústav termomechaniky, 2022

Approaches to dynamical analysis of rotors with parameters of uncertain magnitudes
Zapoměl, Jaroslav; Kozánek, Jan; Košina, Jan; Cibulka, Jan
2022 - English
In many cases, the rotor configuration or loading characteristics are described by parameters of uncertain magnitude. Several procedures were developed to analyse such systems. This paper deals with the approach based on application of the fuzzy numbers. The investigated mechanical system is a rotor supported by hydrodynamic bearings. The parameters of its loading have uncertain values. Keywords: rotors; uncertain parameters; fuzzy numbers approach Available at various institutes of the ASCR
Approaches to dynamical analysis of rotors with parameters of uncertain magnitudes

In many cases, the rotor configuration or loading characteristics are described by parameters of uncertain magnitude. Several procedures were developed to analyse such systems. This paper deals with ...

Zapoměl, Jaroslav; Kozánek, Jan; Košina, Jan; Cibulka, Jan
Ústav termomechaniky, 2022

Turbine blade linkages in reduced modal synthesis model
Pešek, Luděk; Šnábl, Pavel
2022 - English
The paper is the first stage of our modelling turbine blade linkages in reduced modal synthesis model. The modal synthesis method is used for the dynamic behaviour studies of turbine bladed wheels with frictional inter-blade linkages and in case of the microslips the stiffening effect of the linkages play an important role in wheel dynamics. The paper presents the first results of modal analysis of the wheel when springs were used to substitute the linkages in the modal synthesis model. Keywords: bladed wheel; reduced model; tie-boss; shroud; stiffening Available at various institutes of the ASCR
Turbine blade linkages in reduced modal synthesis model

The paper is the first stage of our modelling turbine blade linkages in reduced modal synthesis model. The modal synthesis method is used for the dynamic behaviour studies of turbine bladed wheels ...

Pešek, Luděk; Šnábl, Pavel
Ústav termomechaniky, 2022

Annular impinging jets and an active control of hysteretic effects
Devani, Yogendrasasidhar; Antošová, Zuzana; Trávníček, Zdeněk
2022 - English
An annular air jet with and without flow control was studied experimentally using flow visualization and measurements of the wall pressure and flow velocity by the Pitot and Prandtl probes and the hot-wire anemometer. To investigate flow control swirling effects, eight synthetic jets were generated from the annular nozzle center body.The experiments cover Reynolds numbers 4000–10000 (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 and B) were found under the same boundary conditions. For A pattern, a small recirculation area (bubble) of separated flow is attached to the nozzle center body. For B pattern, a large recirculation area of separated flow bridges entire nozzle-to-wall distance. For higher Re > 9000, the bistability and hysteresis were not found.Flow control swirling effects causes suppression of the hysteresis. Moreover, weak flow control causes that the entire annular jet is forced into a precessing motion. Keywords: annular jet; impinging jet; bistability; hysteresis Available at various institutes of the ASCR
Annular impinging jets and an active control of hysteretic effects

An annular air jet with and without flow control was studied experimentally using flow visualization and measurements of the wall pressure and flow velocity by the Pitot and Prandtl probes and the ...

Devani, Yogendrasasidhar; Antošová, Zuzana; Trávníček, Zdeněk
Ústav termomechaniky, 2022

Aeroacoustic Noise Source Investigation in the Case of the Blade Cascade
Procházka, Pavel P.; Antoš, Pavel; Šnábl, Pavel
2022 - English
The blade cascade consisted of five NACA 0010 profiles is examined in the framework of project dealing with nonlinear dynamic phenomenon related to stall flutter of flexible profiles with pitch degree of freedom in subsonic flow. Various angles of attack (AoA) of the cascade generates different (broadband) aeroacoustic noise. The goal of this article is to describe the existence of possible noise sources using two experimental methods – Particle Image velocimetry (PIV) and hot-wire (HW) anemometry. Keywords: blade cascade; time-resolved PIV; HW anemometry; FFT Available at various institutes of the ASCR
Aeroacoustic Noise Source Investigation in the Case of the Blade Cascade

The blade cascade consisted of five NACA 0010 profiles is examined in the framework of project dealing with nonlinear dynamic phenomenon related to stall flutter of flexible profiles with pitch ...

Procházka, Pavel P.; Antoš, Pavel; Šnábl, Pavel
Ústav termomechaniky, 2022

Temporal, Spatial, and Spatio-temporal correlation of the velocity fluctuations
Jurčáková, Klára
2022 - English
Taylor's hypothesis about frozen turbulence [1] says that if the turbulence intensity is small compared to the mean velocity then the advection of a turbulent flow field past a fixed point can be taken entirely due to the mean flow. This means that in the “frozen turbulent field” spatial and temporal dimensions can be interchanged. Although the main assumption of Taylor's hypothesis is not met in the atmospheric boundary layer (the intensity of turbulence is usually between 10 and 20%) the hypothesis is commonly used to calculate integral length scales of turbulent fields from point measurements. Particle image velocimetry with high temporal resolution (TR-PIV) allows us to analyze both temporal and spatial cross-correlations in the turbulent flow fields and to evaluate obtained results. Keywords: frozen turbulence; wind tunnel; integral length scales; Particle Image Velocimetry Available at various institutes of the ASCR
Temporal, Spatial, and Spatio-temporal correlation of the velocity fluctuations

Taylor's hypothesis about frozen turbulence [1] says that if the turbulence intensity is small compared to the mean velocity then the advection of a turbulent flow field past a fixed point can be ...

Jurčáková, Klára
Ústav termomechaniky, 2022

Damping of human vocal folds vibration
Radolf, Vojtěch; Horáček, Jaromír; Bula, Vítězslav; Geneid, A.; Laukkanen, A. M.
2022 - English
This study investigates the biomechanics of the end-part of phonation, i.e. the so-called phonation offset, experimentally. This information of vocal fold damping is important for testing and further development of mathematical modelling of phonation. The measurements of the damping ratio, based on high-speed videolaryngoscopic registrations, were realized on a male subject phonating on the vowel [o:]. The results show during the phonation offset a remarkable decrease of vibration frequency of the vocal folds and an increased damping ratio limiting to the value D≈ 0.2. The results for vocal folds’ damping are in agreement with previous measurements performed on humans using different methods. Keywords: damping ratio measurement; phonation offset; high-speed videolaryngoscopy Available at various institutes of the ASCR
Damping of human vocal folds vibration

This study investigates the biomechanics of the end-part of phonation, i.e. the so-called phonation offset, experimentally. This information of vocal fold damping is important for testing and further ...

Radolf, Vojtěch; Horáček, Jaromír; Bula, Vítězslav; Geneid, A.; Laukkanen, A. M.
Ústav termomechaniky, 2022

Design of the magnetically sensitive hydrodynamic bearing for the experimental rotor rig
Ferfecki, P.; Zapoměl, Jaroslav; Molčan, M.
2022 - English
In a hydrodynamic bearing, the relative motion between the rotating shaft and stationary housing is separated by a thin film of a lubricant. The magnetically sensitive lubricants with the promise of a semiactive control are able to improve the vibration response of the rotor system supported by the hydrodynamic bearings. A design of the magnetically sensitive hydrodynamic bearing is briefly introduced in this paper. The presented experimental rotor rig is proposed to analyse the large range of load conditions and rotational speeds of the bearing. The designed hydrodynamic bearing is intended to test the ferrofluids, magnetorheological oils, and nano-micro composite magnetic fluids. The apparent viscosity of the magnetically sensitive lubricant is altered by the magnetic field generated by the electric coil and thus the position of the bearing journal is shifted. The experimental measurement results show that the rheological behaviour of the lubrication layer with a magnetorheological fluid is significantly influenced by a magnetic field. The raising magnitude of the current in the electric coil leads to an increase in the bearing's load performance. Keywords: magnetically sentivive fluid; hydrodynamic lubrication; sommerfeld number; experimental measurement; load bearing capacity Available at various institutes of the ASCR
Design of the magnetically sensitive hydrodynamic bearing for the experimental rotor rig

In a hydrodynamic bearing, the relative motion between the rotating shaft and stationary housing is separated by a thin film of a lubricant. The magnetically sensitive lubricants with the promise of a ...

Ferfecki, P.; Zapoměl, Jaroslav; Molčan, M.
Ústav termomechaniky, 2022

Ochranné obvody měničů TF
Hauptmann, R.; Kokeš, Petr
2022 - Czech
Zpráva obsahuje popis a výsledky simulací obvodů, které slouží jako ochrany proti poškození hlavního silového obvodu napájení vinutí TF (Toroidal Field) tokamaku v případě vzniku havarijních stavů. Za normálního provozního stavu ochranné obvody činnost silových obvodů neovlivňují. Ochranné obvody tvoří samostatný systém, který je funkčně nezávislý na obvodech měničů a jejích řízení. Charakter funkce tohoto systému je koncipován jako bezpečnostní obvod – závada ochranného systému vede vždy k bezpečnému odstavení zařízení. Description and results of numerical simulations of circuits, which provide damage protection of the main power supply circuit for tokamak TF (Toroidal Field) coils under emergency conditions, is presented. In case of normal operation the protection circuits do not affect operation of the power supply circuitry. The protection circuits represent a separate system which is functionally independent of circuits and control of power converters. Functinality of this system is designed as a safety circuit - a fault of the protection system always causes safety shut-down of the device. Keywords: tokamak; TF coils; power converter Available at various institutes of the ASCR
Ochranné obvody měničů TF

Zpráva obsahuje popis a výsledky simulací obvodů, které slouží jako ochrany proti poškození hlavního silového obvodu napájení vinutí TF (Toroidal Field) tokamaku v případě vzniku havarijních stavů. Za ...

Hauptmann, R.; Kokeš, Petr
Ústav termomechaniky, 2022

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