National Repository of Grey Literature 207 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
Effect of Cylinder Roughness on Strouhal Number
Yanovych, Vitalii ; Duda, D. ; Uruba, Václav ; Procházka, Pavel P. ; Antoš, Pavel
The main goal of this paper is to establish a better understanding of the relationship between a Strouhal number and surface roughness. Hot-wire anemometry was used to evaluations the characteristics of turbulent flow behind circular cylinders with different relative roughness 0% (smooth surface) 0.83%, 1.67%, 3.33%, and 6.67%. At the experimental investigation, the Reynolds number based on the cylinder diameter was 5 × 103 < Red < 2 × 104. The obtained data showed that the Strouhal number decreased with increasing roughness. While, the dissipation rate decreases, and the value of the Kolmogorov and Taylor microscales increases. Also, spectral analysis of streamwise velocity fluctuations allowed us to estimate the location of the vortex-shedding frequency which at growing roughness tends to reduce.
The Design and Aerodynamic Testing of DPIK Probe
Procházka, Pavel P. ; Barraclough, V. ; Skála, Vladislav ; Uruba, Václav
The isokinetic probe used to detect the liquid phase drift from the cooling tower is presented here. The main motivation is costs reduction that arises during standard drift measurements. The probe was developed in the framework of the grant project between private company 4Jtech and Institute of Thermomechanics. The aerodynamic design and optimization of this probe should fulfill one important criterion – to capture the droplets from the drift with maximal efficiency. Kalorimetric principle is then used to evaluate the amount of trapped water. Standard PIV (Particle Image Velocimetry) measurement technique and modified IPI (Interferometric Particle Imaging) methods were used to measure the flow field topology and the particle size distribution, respectively.
Final report on the MIT project no. CZ.01.1.02/0.0/0.0ú20_321/0023673
Zolotarev, Igor ; Pešek, Luděk ; Gabriel, Dušan ; Procházka, Pavel P.
The MIT project entitled Development of a switchgear for severe conditions and reduction of risks of critical infrastructure threat was focused on research, development of optimized design and provision of configuration technology for repeated production of different variants of modular system switchgear for use in severe conditions and reduction of risks of seismic threat, to ensure the reliability of critical infrastructure. The output is to be a prototype seismically robust device with a dynamically lightweight design, high reliability of switchgear and electrical equipment assembly function, and a software application for interactive design and documentation.
A new blade cascade for flutter studies
Šnábl, Pavel ; Pešek, Luděk ; Procházka, Pavel P. ; Skála, V.
In this paper, a new blade cascade, developed in the Institute of Thermomechanics, is presented. The geometry of the cascade was modified so now the stall flutter can occur. It has some major construction improvements over the original cascade which now allow more precise and reliable measurements. The stability of the new blade cascade with five NACA 0010 profiles with rotational degree of freedom is assessed by Travelling Wave Mode approach and Aerodynamic Influence Coefficient approach.
Spectral Indices as a Tool for Hop Growth Evaluation
Seidlová, Jana ; Procházka, Pavel ; Kumhálová, Jitka
The use of unmanned aerial vehicles (UAV) to monitor crop growth is nowadays a common non-invasive way how to obtain information on the current state of crops. Spectral indices derived from multispectral images obtained in the right growth stage can then serve as a good data source for agro-technical interventions and yield estimation. Hop belongs among the crops where it is possible to scan the individual growth parameters very exactly. In the year 2021, significant precipitation amounts were recorded during the growing season, when it turned out that UAVs are a very powerful tool for determining the quality of production or quantification of vegetation damage compared to the previous year (2020). It was found that the common spectral indices were possible to use for calculation leaf area, structure, vigor and chlorophyll content of hop gardens.
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Growth of organic heterostructures on metal surfaces
Kugler, David ; Novák,, Jiří (referee) ; Procházka, Pavel (advisor)
Během depozice organických molekul na kovové substráty často dochází k spontánnímu uspořádání molekul vlivem mezimolekulárních a molekulárně-substrátových interakcí. Tento jev se nazývá samouspořádání a může být využit k vytváření atomárně přesných funkčních struktur. Vzrůstající zájem vzbuzují zejména tenké vrstvy organických polovodičů pro jejich potenciální využití v polovodičovém průmyslu. Efektivita takovýchto zařízení je však nevyhnutelně spojena s přechodovým odporem na rozhraní polovodiče a kovové elektrody. Studium typu růstu organických polovodičů na kovových substrátech je tak zcela zásadní pro jejich budoucí využití. Tato diplomová práce se nejprve zabývá vytvořením krycí monovrstvy substrátu Ag(111) z dobře uspořádaných molekul kyseliny 1,3,5-benzen-trikarboxylové (BTB). Hlavním cílem práce je pak použití této vrstvy jako substrátu pro růst dalších vrstvev tvořených molekulami pentacenu, což je jeden z intenzivně zkoumaných organických polovodičů. Bylo dosaženo pokrytí povrchu uspořádanou vrstvou pentacenu o rozloze vhodné pro praktické využití. Pro studium růstu molekulárních vrstev a jejich vlastností byla použita nízkoenergiová elektronová mikroskopie, skenovací tunelovací mikroskopie, rentgenová fotoelektronová spektroskopie a ultrafialová fotoelektronová spektroskopie.
Organic semiconductors on topological insulators
Hrubá, Daniela ; Průša, Stanislav (referee) ; Procházka, Pavel (advisor)
This bachelor thesis is focused on the utilization of the topological insulator Bi2Se3 as a substrate for the deposition of different types of organic molecules. The substrate was prepared by exfoliation method under ultrahigh vacuum (UHV) conditions. The pentacene, 4,4'-biphenylcarboxylic acid (BDA), and tetracyanoquinodimethane (TCNQ) molecules were subsequently deposited using effusion cells. The quality and arrangement of the fabricated layers were characterized by low-energy electron microscopy (LEEM). The measured results and the behavior of the molecules on the crystal surface after their deposition are discussed. Diffraction patterns were used for design of real-space molecular arrangement model.
Microscopic and spectroscopic analysis of elementary 2D materials
Jeřábek, František ; Procházka, Pavel (referee) ; Kolíbal, Miroslav (advisor)
Tato práce se zabývá analýzou struktur tvořených při depozici fosforu na monokrystal mědi Cu(111) za podmínek ultravysokého vakua. Součástí práce je komplexní shrnutí aktuálního pokroku v oblasti syntézy černého a modrého fosforenu. Kromě samotných metod přípravy je diskutována také předpovězená stabilita těchto struktur. V práci jsou prezentovány výsledky analýzy tří struktur pomocí skenovací tunelové mikroskopie a spektroskopie, prokazující možnost přípravy jednovrstvého modrého fosforenu na měděném substrátu. In-situ analýza stability připravených struktur pomocí skenovací tunelovací mikroskopie prokazuje velmi rychlou degradaci modrého fosforenu i za podmínek ultravysokého vakua.
Applications of blade vibration measurements in the laboratory of rotational laser vibrometry
Maturkanič, Dušan ; Procházka, Pavel ; Hodboď, Robert ; Mekhalfia, Mohammed Lamine ; Voronova, Evgeniya
The Laboratory of Rotational Laser Vibrometry was established at the Institute of Thermomechanics AS CR, v.v.i. in 2015 and the first experiments were started the following year. The measurements are intended for the research of vibration of rotating blades. The paper includes a summary of measurement results using a special turbine model and their consequences in theoretical research, as well as measurements with a real compressor of aircraft engine and comparison with computational analysis. The paper also describes the complex system for measurement and analysis.
Aeroacoustic Noise Source Investigation in the Case of the Blade Cascade
Procházka, Pavel P. ; Antoš, Pavel ; Šnábl, Pavel
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.

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