Počet nalezených dokumentů: 2991
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Large Scale Motions in Turbulent Flows
Kellnerová, Radka; Jurčáková, Klára; Procházka, Pavel P.
2019 - anglický
Quadrant analysis based on the Reynolds decomposition was performed on the data from turbulent boundary layer flows above variously rough surfaces. An estimation of a convective velocity for events significant in terms of momentum flux, and the statistics of a length and amplitude of the individual events, together with their spectral analysis, was performed. Based on the analyses, we were able to detect a few individual sweep and ejection events with a length longer than 6δ, which could be considered as very large scale motions (VLSM). We also identified number of events with a longitudinal dimension equal to approximately 3δ labelled as large scale motions (LSM). The analyses were executed for various Reynolds numbers. The number of detected structures increases with the momentum of the flow. Klíčová slova: wind tunnel; large scale motion; quadrant analysis Dokument je dostupný na externích webových stránkách.
Large Scale Motions in Turbulent Flows

Quadrant analysis based on the Reynolds decomposition was performed on the data from turbulent boundary layer flows above variously rough surfaces. An estimation of a convective velocity for events ...

Kellnerová, Radka; Jurčáková, Klára; Procházka, Pavel P.
Ústav termomechaniky, 2019

Assessing Quality of Boundary Layer Flows With the Diagnostic Plot
Jurčáková, Klára; Procházka, Pavel P.; Kellnerová, Radka
2019 - anglický
We experimentally investigated turbulent boundary layers over 4 rough surfaces and 1 smooth surface by particle image velocimetry for a range a free stream velocities. The obtained mean velocity vertical profiles were universally scaled by roughness length z₀ and friction velocity u*, but both parameters have to be obtained from the fit of the logarithmic or composite velocity pro le to the experimental data. Diagnostic plot, which relates turbulence intensity with the mean velocity showed good collapse of different free stream velocities for each surface. It became fully universal in its modified version when the roughness function was taken into an account. We found that turbulence intensities over our surfaces are higher than any published one and that they dependent on roughness length z₀*. Klíčová slova: wind tunnel; turbulence intensity; rough-wall; friction velocity Dokument je dostupný na externích webových stránkách.
Assessing Quality of Boundary Layer Flows With the Diagnostic Plot

We experimentally investigated turbulent boundary layers over 4 rough surfaces and 1 smooth surface by particle image velocimetry for a range a free stream velocities. The obtained mean velocity ...

Jurčáková, Klára; Procházka, Pavel P.; Kellnerová, Radka
Ústav termomechaniky, 2019

Vyšetřování proudění uvnitř přirozeně větraného kravína: předběžné výsledky z experimentů v aerodynamickém tunelu
Nosek, Štěpán; Kluková, Zuzana; Kellnerová, Radka; Jakubcová, Michala; Jaňour, Zbyněk
2019 - český
V této studii byly kvalitativně porovnány střední vektorové (složky podélné a vertikální rychlosti) a skalární pole (intenzita turbulence) v měřítkovém (1:50) modelu přirozeně větraného kravína. Tato kvalitativní srovnání jasně poukazují na účinek simulované mezní vrstvy atmosféry (MVA) a konfiguraci otvorů na proudové charakteristiky uvnitř kravína. MVA mírně drsného terénu vytváří vyšší rychlosti jak u vstupních a výstupních otvorů, tak uvnitř kravina, než MVA velmi drsného terénu. Intenzita turbulence je však více závislá na konfiguraci otvoru. Například, ačkoli MVA byla velmi drsná, a tedy turbulentnější, byly v případě středních otvorů pozorovány nižší intenzity turbulence než u středně drsné MVA. The mean vector (longitudinal and vertical velocity components) and scalar (turbulence intensity) fields within a scale (1:50) model of naturally ventilated cattle barn were qualitatively compared in this study. These qualitative comparisons clearly show the effect of the simulated atmospheric boundary layer (ABL) and the opening configuration on the flow characteristics within the barn. ABL of moderately rough terrain produces higher velocities at both the inlet and the outlet openings and inside the barn than that ABL of very rough terrain. However, the intensity of the turbulence is more dependent on the configuration of the opening. For instance, although ABL was very rough and therefore more turbulent, lower turbulence intensities were observed for that ABL than for the moderately rough ABL in the case of middle openings. Klíčová slova: atmospheric boundary layer; livestock building; natural ventilation; wind-tunnel Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Vyšetřování proudění uvnitř přirozeně větraného kravína: předběžné výsledky z experimentů v aerodynamickém tunelu

V této studii byly kvalitativně porovnány střední vektorové (složky podélné a vertikální rychlosti) a skalární pole (intenzita turbulence) v měřítkovém (1:50) modelu přirozeně větraného kravína. Tato ...

Nosek, Štěpán; Kluková, Zuzana; Kellnerová, Radka; Jakubcová, Michala; Jaňour, Zbyněk
Ústav termomechaniky, 2019

Excitation of wheel blades by axial electromagnet at different regimes
Voronova, Evgeniya; Maturkanič, Dušan
2019 - anglický
The paper describes the natural frequency identification experiment and results of measuring of blade vibration characteristics excitate by one axial electromagnet at different regimes. The measurements were performed in the laboratory of the rotational laser vibrometry originated at the Institute of Thermomechanics AS CR, v.v.i. Klíčová slova: vibration; blade; magnet; frequency Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Excitation of wheel blades by axial electromagnet at different regimes

The paper describes the natural frequency identification experiment and results of measuring of blade vibration characteristics excitate by one axial electromagnet at different regimes. The ...

Voronova, Evgeniya; Maturkanič, Dušan
Ústav termomechaniky, 2019

Příčina mechanického chvění těžních synchronních motorů Palašer a jeho odstranění
Pavelka, J.; Šimek, J.; Kobrle, P.; Kokeš, Petr
2019 - český
Příspěvek popisuje postup a výsledek analýzy mechanického rozkmitávání těžních strojů na dole Palašer v Ruské federaci. Jako příčina byla určena změna velikosti magnetického toku ve vzduchové mezeře vlivem drážkování statorů. Provedené simulace prokázaly možnost odstranění změny magnetického toku injektáží vhodných napětí statorového vinutí. V dalším je popsána realizace této injektáže pomocí přímovazební kompenzace střídavé složky momentu. Na závěr jsou uvedeny oscilografické záznamy před a po injektáži. The paper describes the procedure and the result of analysis of mechanical vibrations of mining machines at the Palašer mine in the Russian Federation. The cause of these vibrations was the change in the magnitude of the magnetic flux in the air gap. The simulations showed the possibility of eliminating these changes in\nmagnetic flux by injecting suitable voltages into the stator windings. The implementation of this injection is further described by torque variable component feed-direct compensation. Finally, oscillography records are presented before and after injection. Klíčová slova: mining machine; synchronous motor; indirect frequency converter; Maxwell force; resonant frequency; feed-direct compensation; injected voltage Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Příčina mechanického chvění těžních synchronních motorů Palašer a jeho odstranění

Příspěvek popisuje postup a výsledek analýzy mechanického rozkmitávání těžních strojů na dole Palašer v Ruské federaci. Jako příčina byla určena změna velikosti magnetického toku ve vzduchové mezeře ...

Pavelka, J.; Šimek, J.; Kobrle, P.; Kokeš, Petr
Ústav termomechaniky, 2019

On Yield Surface Detection, Experiments by Finite Element Method
Klepač, Vilém; Liu, Li-Wei
2019 - anglický
In the submitted report it is described, how experiments by FEM are designed for\nmore precise detection of yield point. Content of report can be devided to these\nareas:\n- Intership travel report\n- Idea of research topic\n- Develop software tools Klíčová slova: FEM; yield surface; plasticity Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
On Yield Surface Detection, Experiments by Finite Element Method

In the submitted report it is described, how experiments by FEM are designed for\nmore precise detection of yield point. Content of report can be devided to these\nareas:\n- Intership travel ...

Klepač, Vilém; Liu, Li-Wei
Ústav termomechaniky, 2019

Utilization of Convolution Neural Network Based Road Detection in Mobile Robot Localization
Krejsa, Jiří; Věchet, Stanislav
2019 - anglický
Mobile robot on-road navigation requires fusion of both global and local sensory information with an emphasis on the road detection processing. The paper deals with the road detection based on convolution neural networks (CNN) using commonly available tools such as TensorFlow and Keras. The road is defined by its linear boundaries. Network output is formed by the road definition together with classification parameters and serves as a local sensor in Kalman filter based localization. CNN based road detection is currently capable to successfully detect about 90% of images. Klíčová slova: convolution neural network; localization; road detection Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Utilization of Convolution Neural Network Based Road Detection in Mobile Robot Localization

Mobile robot on-road navigation requires fusion of both global and local sensory information with an emphasis on the road detection processing. The paper deals with the road detection based on ...

Krejsa, Jiří; Věchet, Stanislav
Ústav termomechaniky, 2019

Real-time diagnostics for ROS running systems based on probabilistic patterns identification
Věchet, Stanislav; Krejsa, Jiří
2019 - anglický
Autonomous mobile robots consists of various software modules to achieve given goal, including solving complex navigation tasks as localization, mapping or path planning. These tasks are highly dependent on the quality of data measured and gathered from hardware subsystems. Using Robot Operating System (ROS) as integration basis reduces the development effort and time to market. While ROS framework itself is considered as reliable and stable to run even soft real-time tasks, in case of any internal failures on data misreadings can be problematic to debug or even identify the problem for common user. Due to this unpleasant situations we develop a virtual assistant, internally represented as diagnostic expert system, to help users to identify and possibly fix the problem. Klíčová slova: diagnostic expert system; bayesian network; system diagnostic Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Real-time diagnostics for ROS running systems based on probabilistic patterns identification

Autonomous mobile robots consists of various software modules to achieve given goal, including solving complex navigation tasks as localization, mapping or path planning. These tasks are highly ...

Věchet, Stanislav; Krejsa, Jiří
Ústav termomechaniky, 2019

Finite element implementation of creep constitutive model including transient effects
Gabriel, Dušan; Masák, Jan; Plešek, Jiří; Kloc, Luboš; Dymáček, Petr
2019 - anglický
A complex creep constitutive model including transient effects was implemented in the finite element code PMD (Package for Machine Design). The material model for P-91-type creep-resistant steel together with computer implementation was verified by means of uniaxial stress loadings. Testing bar was discretized by the finite element method (FEM) and loaded with uniaxial stresses and constant temperatures that were used to demonstrate the analytical solutions in original paper. Klíčová slova: creep; transient effects; FEM Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Finite element implementation of creep constitutive model including transient effects

A complex creep constitutive model including transient effects was implemented in the finite element code PMD (Package for Machine Design). The material model for P-91-type creep-resistant steel ...

Gabriel, Dušan; Masák, Jan; Plešek, Jiří; Kloc, Luboš; Dymáček, Petr
Ústav termomechaniky, 2019

Measurements on KR-D-2 Blade Cascade
Šimurda, David; Luxa, Martin; Radnic, Tomáš; Hála, Jindřich
2019 - anglický
This report contains results and evaluation of aerodynamic measurements conducted on second variant of transonic compressor blade cascade. Klíčová slova: transonic compressor blade; aerodynamic measurements; axial compressor Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Measurements on KR-D-2 Blade Cascade

This report contains results and evaluation of aerodynamic measurements conducted on second variant of transonic compressor blade cascade.

Šimurda, David; Luxa, Martin; Radnic, Tomáš; Hála, Jindřich
Ústav termomechaniky, 2019

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