Number of found documents: 2882
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Computationally Efficient Model of the Human Vocal Fold
Štorkán, J.; Vampola, T.; Horáček, Jaromír
2017 - English
One mass model of the vocal folds with three degrees of freedom in 2D space was created and used to simulate the movement of the vocal folds. Vocal folds are modeled as a solid mass stored flexibly in 2D. The model is excited by aerodynamic forces. The flow is solved by analytical model incompressible and non-viscous fluid with constant flow. In case of close of the glottis are aerodynamic forces replaced by Hertz model of the contact forces. Movement equations are solved by numerical method. The model allows to solve the movement of the vocal folds in the time domain, pressure field acting on the vocal folds or contact pressures. Keywords: simulation of vocal folds; ideal fluid flow; nonlinear vibration; self-exciting vibration Available at various institutes of the ASCR
Computationally Efficient Model of the Human Vocal Fold

One mass model of the vocal folds with three degrees of freedom in 2D space was created and used to simulate the movement of the vocal folds. Vocal folds are modeled as a solid mass stored flexibly in ...

Štorkán, J.; Vampola, T.; Horáček, Jaromír
Ústav termomechaniky, 2017

Design of low-subsonic blade cascade model for aero-structural dynamic testing
Pešek, Luděk; Hála, Jindřich; Šulc, Petr; Chládek, Štěpán; Bula, Vítězslav; Uruba, Václav; Cibulka, Jan
2017 - English
Low-subsonic blade cascade model for aerodynamic testing was design in the Institute. The aim is to study the flow dynamics and flutter phenomenon in the cascade with moving blade profiles. The numerical calculations of two proposed cascades were performed for analysis of influence of stagger angle, incident angle of flow and inter-blade phase angles of the relative movement of blades. The results of numerical simulations of fluid dynamics of non-stationary flow both as viscid and non-viscid are presented. Futhermore the solution of the physical model of the designed cascade including excitation of profiles, measuring of the profile displacement and aerodynamic forces are described. Keywords: blade cascade; flutter; low-subsonic; experimental research Available at various institutes of the ASCR
Design of low-subsonic blade cascade model for aero-structural dynamic testing

Low-subsonic blade cascade model for aerodynamic testing was design in the Institute. The aim is to study the flow dynamics and flutter phenomenon in the cascade with moving blade profiles. The ...

Pešek, Luděk; Hála, Jindřich; Šulc, Petr; Chládek, Štěpán; Bula, Vítězslav; Uruba, Václav; Cibulka, Jan
Ústav termomechaniky, 2017

Modelling of Flow in Linear Blade Cascade with Thick Trailing Edge at a Lower Reynolds Number
Straka, P.; Příhoda, Jaromír
2017 - English
In the paper there are compared results of numerical simulation of compressible turbulent flow through a low-pressure turbine blade cascade with relatively thick trailing edges for various physical models. Steady, unsteady, fully turbulent, transitional, two-dimensional and three-dimensional models are compared. Results show that: a) steady simulation gives an incorrect prediction of the boundary layer development, b) two-dimensional unsteady simulation leads to inaccurate prediction of the far wake development and c) only three-dimensional unsteady transitional simulation gives sufficiently accurate prediction. Results of numerical simulations are compared with the experimental data. Keywords: linear blade cascade; boundary layer transition; vortex series Available at various institutes of the ASCR
Modelling of Flow in Linear Blade Cascade with Thick Trailing Edge at a Lower Reynolds Number

In the paper there are compared results of numerical simulation of compressible turbulent flow through a low-pressure turbine blade cascade with relatively thick trailing edges for various physical ...

Straka, P.; Příhoda, Jaromír
Ústav termomechaniky, 2017

Posouzení výpočtové dokumentace návrhu opravy heterogenního svárového spoje nátrubku PG technologií Weld Overlay. Dokumentace k výpočtovému modelu MKP pro hodnocení kritické velikosti trhliny.
Pták, Svatopluk; Masák, Jan; Gabriel, Dušan
2017 - Czech
V první cásti zprávy je vypracováno posouzení výpoctové dokumentace návrhu opravy heterogenního svarového spoje nátrubku superhavarijního napájení parogenerátoru v JE Dukovany technologií Weld Overlay (WOL). V druhé cásti zprávy je shrnuta dokumentace k vytvorenému MKP modelu nátrubku s trhlinou, který bude použit k výpoctu kritické velikosti trhliny v nátrubku parogenerátoru. Available at various institutes of the ASCR
Posouzení výpočtové dokumentace návrhu opravy heterogenního svárového spoje nátrubku PG technologií Weld Overlay. Dokumentace k výpočtovému modelu MKP pro hodnocení kritické velikosti trhliny.

V první cásti zprávy je vypracováno posouzení výpoctové dokumentace návrhu opravy heterogenního svarového spoje nátrubku superhavarijního napájení parogenerátoru v JE Dukovany technologií Weld Overlay ...

Pták, Svatopluk; Masák, Jan; Gabriel, Dušan
Ústav termomechaniky, 2017

Optimalizace výběru senzorů pro lokalizaci zdrojů akustické emise
Chlada, Milan; Převorovský, Zdeněk
2017 - Czech
Podobně jako v případě globálního polohového systému (GPS) se v případě lokalizace materiálových defektů metodou akustické emise (AE) setkáváme s efektem tzv. snížení přesnosti vlivem geometrie (GDOP). Kromě možností stávajících přístupů k analýze a porovnání různých konfigurací senzorů z hlediska přesnosti lokalizace přináší nově navržená metoda další výhody při detekci kritických oblastí charakterizovaných velkou citlivostí k chybám určení začátků signálů. Analogicky k parametru GDOP umožňuje výpočet tzv. citlivostních map i pro případy nespojitých těles, či anizotropních materiálů. Vychází z algoritmu hledání nejkratších cest v diskrétně zadaných tělesech, což generuje další náhledy na problematiku skrze podobnostní mapy a schémata nejednoznačností. Similarly to Global Positioning System (GPS), location of material defects by acoustic emission method meets the geometrical dilution of precision (GDOP) phenomena. Besides the several attitudes how to mathematically express its measure and compare particular sensor configurations in accordance with desired location precision, recently proposed method brings extended possibilities for detection of critical regions characterized by strong sensitivity of location results to signal arrival time changes or errors. Analogically to GDOP parameter it yields the sensitivity map available even for non-continuous or anisotropic materials. During the computation it uses the algorithm for finding the shortest ways in discretely defined bodies, which furthermore enables to view the problem through the so-called similarity and ambiguity maps. Keywords: acoustic emission; source location; geometrical dilution of precision Available at various institutes of the ASCR
Optimalizace výběru senzorů pro lokalizaci zdrojů akustické emise

Podobně jako v případě globálního polohového systému (GPS) se v případě lokalizace materiálových defektů metodou akustické emise (AE) setkáváme s efektem tzv. snížení přesnosti vlivem geometrie ...

Chlada, Milan; Převorovský, Zdeněk
Ústav termomechaniky, 2017

Lokalizace zdrojů spojité akustické emise pomocí časové reverzace signálů
Převorovský, Zdeněk; Krofta, Josef; Kober, Jan; Chlada, Milan
2017 - Czech
V příspěvku je navržena nová metoda lokalizace akustické emise (AE) využívající proceduru časové reverzace signálů (TR – Time Reversal) s jedním snímačem pro lokalizaci pulzní AE na šumovém pozadí z jiných zdrojů, resp. se dvěma snímači pro lokalizaci zdrojů spojité AE (úniků média). TR procedura je zde poprvé aplikována na dlouhé signály s charakterem náhodného šumu. Metoda byla ověřována pomocí simulovaných zdrojů AE na ocelové desce a částech potrubí a výsledky potvrdily její robustnost. Určitou nevýhodou je nezbytnost podrobného skenování předem vymezené oblasti v okolí pravděpodobného výskytu zdroje, kterou je však možné eliminovat např. pomocí rozsáhlejších numerických simulací na počítačovém modelu konstrukce. Přesnost lokalizace kvazibodového zdroje (okolo 1 mm) je lepší než vlnová délka či apertura snímačů. A new solution with the help of Time Reversal (TR) signal processing approach is suggested in this paper. It allows planar location of burst AE sources under high background noise using only one transducer, and continuous AE sources with two transducers, both under high background noise from other sources. TR procedure was in this approach applied to long random noise signals for the first time. Suggested method was verified by means of experimentally simulated AE sources on a steel plate and tube. Source location results certified high robustness of suggested approach. Certain disadvantage of the new method is requirement of detailed scanning of region around a presumed source. Scanning may be eliminated if we use numerical simulations with TR signals put into a computer model of the structure. Localization accuracy of suggested procedure (approx. 1 mm) is better than the wavelength and transducers aperture. Keywords: burst and continuous AE on; leakage location; time reversal acoustics Available at various institutes of the ASCR
Lokalizace zdrojů spojité akustické emise pomocí časové reverzace signálů

V příspěvku je navržena nová metoda lokalizace akustické emise (AE) využívající proceduru časové reverzace signálů (TR – Time Reversal) s jedním snímačem pro lokalizaci pulzní AE na šumovém pozadí z ...

Převorovský, Zdeněk; Krofta, Josef; Kober, Jan; Chlada, Milan
Ústav termomechaniky, 2017

Transition Modelling on Separated Flow in Turbine Cascade
Louda, Petr; Příhoda, Jaromír; Kozel, K.
2017 - English
The work deals with numerical simulation of turbulent ow through turbine cascade by RANS model with model of transition to turbulence. Performance of two transition models is compared. First one is gamma-zeta model based on transition criteria, second one algebraic transition model based on the concept of laminar uctuations energy (Kubacki, Dick 2016). The criterion for transition in separated state is re-formulated in order to remove stream-wise non-local formulation. The performance of the transition models is observed on the shock wave - boundary layer interaction on turbine blade. Keywords: turbine cascade; transition model; separation bubble; shock wave-boundary layer interaction Fulltext is available at external website.
Transition Modelling on Separated Flow in Turbine Cascade

The work deals with numerical simulation of turbulent ow through turbine cascade by RANS model with model of transition to turbulence. Performance of two transition models is compared. First one is ...

Louda, Petr; Příhoda, Jaromír; Kozel, K.
Ústav termomechaniky, 2017

Modelling of running waves in turbine blades cascade
Půst, Ladislav; Pešek, Luděk
2017 - English
Dynamic properties of blades in the blade cascade excited by steam flow from the stationary bladed disk are investigated with the aim to explain origin and behaviour of running waves. It is shown that one of the most important reasons for existence of running waves is the running periodic forces from steam wakes due to different numbers of blades of stationary and rotating wheels. On a simplified computational model of disk with closed 10-blades bundle are presented resulting velocities, theirs directions and modes of forced running waves. The effect of these forced running waves on the existence of flutter waves will be shortly mentioned as well. Keywords: blade cascade; turbine disk; delay of excitation forces; forward; backward running waves Available at various institutes of the ASCR
Modelling of running waves in turbine blades cascade

Dynamic properties of blades in the blade cascade excited by steam flow from the stationary bladed disk are investigated with the aim to explain origin and behaviour of running waves. It is shown that ...

Půst, Ladislav; Pešek, Luděk
Ústav termomechaniky, 2017

Reduction of the energy losses by application of controllable squeeze film dampers
Zapoměl, Jaroslav; Ferfecki, Petr; Kozánek, Jan
2017 - English
The unbalance induces lateral oscillations of rotors and forces transmitted to the rotor casing. The squeeze film dampers with integrated rolling element bearings represent a technological solution, which enables to reduce their magnitude, and consequently the resistance against the rotor rotation. To achieve optimum performance of the damping devices, their damping effect must be adapable to the current rotor speed. This paper reports a proposal of a controllable squeeze film damper, the damping effect of which is controlled mechanically by shifting its outer ring in the axial direction. The developed mathematical model of the damper is based on assumptions of the classical theory of lubrication and is completed with implementation of a gas cavitation. The results of the computational simulations show that an appropriate control of the damping force enables to reduce the energy losses in a wide range of operating speeds. Keywords: squeeze film damper; controllable damping; friction in bearings; energy losses reduction Available at various institutes of the ASCR
Reduction of the energy losses by application of controllable squeeze film dampers

The unbalance induces lateral oscillations of rotors and forces transmitted to the rotor casing. The squeeze film dampers with integrated rolling element bearings represent a technological solution, ...

Zapoměl, Jaroslav; Ferfecki, Petr; Kozánek, Jan
Ústav termomechaniky, 2017

A short wave limit of the frequency equation for plane-stress nonaxisymmetric disc motions
Červ, Jan; Valeš, František; Adámek, V.
2017 - English
It is proved that the general frequency equation for plane-stress nonaxisymmetric disc motions tends for the first mode of propagation and for wavelengths very short when compared with the disc radius to the secular equation for Rayleigh waves. Keywords: frequency equation; elastic disc; Rayleigh waves Available at various institutes of the ASCR
A short wave limit of the frequency equation for plane-stress nonaxisymmetric disc motions

It is proved that the general frequency equation for plane-stress nonaxisymmetric disc motions tends for the first mode of propagation and for wavelengths very short when compared with the disc radius ...

Červ, Jan; Valeš, František; Adámek, V.
Ústav termomechaniky, 2017

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