Number of found documents: 2298
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Applying a two degree of freedom model for drive-by identification
Bayer, Jan
2024 - English
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving spring-mass the second DOF. The response of the moving spring-mass is simulated on a bridge model using different road profiles and compared to parameters of the corresponding two DOF system. The focus is the spectral shift that can be observed on the moving spring-mass during its passage along the bridge and could possibly be applied for drive-by identification. The accuracy mainly depends on the relation of the moving spring-mass to the bridge mass and the relation between the natural frequency of the spring-mass and those of the bridge. The simulations showed that road profile can significantly reduce the accuracy of identified results, which imposes limits on practical applications. Keywords: drive-by identification; structural health monitoring; finite element analysis; road roughness; two DOF system Available in digital repository of the ASCR
Applying a two degree of freedom model for drive-by identification

A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving ...

Bayer, Jan
Ústav teoretické a aplikované mechaniky, 2024

Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Fischer, Cyril; Náprstek, Jiří
2024 - English
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type nonlinear model. Determining the response probability density function involves solving the Fokker-Planck equation, which is generally a challenging task. Hence, semi-analytical and numerical methods come into play. This contribution reviews several possible techniques and spotlights the exponential-polynomial-closure method. The shown results are limited, as the paper reflects an early stage of the relevant research direction. Keywords: Fokker-Planck equation; stochastic averaging; numerical solution; Galerkin approximation; van der Pol-type oscillator; partial amplitudes; exponential-polynomial-closure method Available in digital repository of the ASCR
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation

Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type ...

Fischer, Cyril; Náprstek, Jiří
Ústav teoretické a aplikované mechaniky, 2024

Galloping of insulated bundled overhead line simplified analysis
Hračov, Stanislav; Macháček, Michael
2024 - English
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by polyethylene, and used for low-voltage power lines. The susceptibility to loss of stability is analyzed for cable without and with simulated icing observed on similar real conductors. In the first case, the proneness to galloping was excluded based on the results of CFD simulation and the Den Hartog criterion. In latter case, the possible occurrence of galloping was confirmed. The critical wind velocity for the ice-covered cable was calculated utilizing quasi-steady theory. Finally, the amplitudes of limit cycle oscillation for supercritical wind speeds were estimated based on simplified numerical analysis. Keywords: aerial bundled cable; wind effects; galloping; limit cycle oscillation Available in digital repository of the ASCR
Galloping of insulated bundled overhead line simplified analysis

Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by ...

Hračov, Stanislav; Macháček, Michael
Ústav teoretické a aplikované mechaniky, 2024

LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2024 - English
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The rectangle object was exposed to the airflow having a given velocity at different angles of the wind attack in the wind tunnel with the aim to obtain the curves of the aerodynamic coefficients and Strouhal number depending on the impact angle. The comparative numerical 3D simulations of the wind tunnel testing were performed using COMSOL Multiphysics and OpenFoam both incorporating the Large Eddy Simulation (LES) method. Keywords: rectangle 2:1; wind tunnel; LES simulation; aerodynamic characteristics Available in digital repository of the ASCR
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments

Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The ...

Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
Ústav teoretické a aplikované mechaniky, 2024

Gas sensors based on diamond heterostructures for air quality monitoring
Kočí, Michal; Szabó, Ondrej; Izsák, T.; Sojková, M.; Godzierz, M.; Wróbel, P.; Husák, M.; Kromka, Alexander
2024 - English
Currently, great emphasis is placed on air quality and the presence of pollutants. Attention is therefore focused on new gas-sensing materials enabling detection even at low (up to room) temperatures with sufficient response and short reaction time. Here, we investigate the suitability of H-NCD films and their heterostructures with MoS2, GO, rGO, SH-GO, or Au NPs for gas sensing applications. Electrical properties are measured for oxidizing gas NO2, reducing gas NH3, and chemical vapor of ethanol, and at temperatures varied from room temperature to 125 °C. In contrast to the individual forms of employed materials with limited response to the exposed gases, the HNCD heterostructures revealed better sensing properties. In particular, the Au NPs/H-NCD heterostructures revealed a higher response at 125 °C in contrast to H-NCD, MoS2/H-NCD had quite good response even at room temperature and GO/H-NCD revealed high sensitivity to chemical vapor, which further improved for the SH-GO/HNCD. Keywords: gas sensors; nanocrystalline diamond; heterostructures; air quality monitoring Fulltext is available at external website.
Gas sensors based on diamond heterostructures for air quality monitoring

Currently, great emphasis is placed on air quality and the presence of pollutants. Attention is therefore focused on new gas-sensing materials enabling detection even at low (up to room) temperatures ...

Kočí, Michal; Szabó, Ondrej; Izsák, T.; Sojková, M.; Godzierz, M.; Wróbel, P.; Husák, M.; Kromka, Alexander
Fyzikální ústav, 2024

The Influence of Geometric Parameters of 3D Printed Structured Beds on Hydrodynamic Characteristics of Trickle-Bed Reactor
Nyklíčková, Kateřina
2024 - English
The study examines a parametric set of POCS structures, where cubic cell is the basic element. The parameters such as strut diameter sd and cell size cs were varied1. These modifications are implemented with an emphasis on maintaining similar porosity and specific surface area for these structures. Keywords: trickle-bed reactor; pressure dop; POCS structures Available in digital repository of the ASCR
The Influence of Geometric Parameters of 3D Printed Structured Beds on Hydrodynamic Characteristics of Trickle-Bed Reactor

The study examines a parametric set of POCS structures, where cubic cell is the basic element. The parameters such as strut diameter sd and cell size cs were varied1. These modifications are ...

Nyklíčková, Kateřina
Ústav chemických procesů, 2024

Surface changes induced by plasma treatment and high temperature annealing of silicon dioxide microparticles
Babčenko, Oleg; Remeš, Zdeněk; Beranová, Klára; Kolářová, Kateřina; Lörinc, J.; Prošek, Z.; Tesárek, P.
2024 - English
Due to the high surface to volume ratio, the particles’ surface properties modification defines its properties in general, which is crucial for their use. From this point of view, plasma processing or high temperature annealing can be considered as the universal techniques for efficient modification of materials in the form of powder. In this study, the silicon dioxide microparticles have been treated in a hydrogen, oxygen or vacuum by low temperature plasma or annealing. The change of SiO2 microparticles properties was investigated by photoluminescence spectroscopy at room and low temperature. High temperature annealing in hydrogen induced under UV excitation photoluminescence in the near UV and visible light indicating the change of defect states on the surface of the microparticles. We believe that observed findings clearly demonstrate useful method for analysis of SiO2 microparticles surface modification attractive also for fundamental research. Keywords: silicon dioxide; plasma treatment; annealing; photoluminescence; measuring setup Fulltext is available at external website.
Surface changes induced by plasma treatment and high temperature annealing of silicon dioxide microparticles

Due to the high surface to volume ratio, the particles’ surface properties modification defines its properties in general, which is crucial for their use. From this point of view, plasma processing or ...

Babčenko, Oleg; Remeš, Zdeněk; Beranová, Klára; Kolářová, Kateřina; Lörinc, J.; Prošek, Z.; Tesárek, P.
Fyzikální ústav, 2024

Development of Polymeric Enantioselective Membranes
Čížek, Jan
2024 - English
Enantiomers are molecules that share the same chemical formula but in space form mirror images of each other. Their reactions with other chiral molecules can be remarkably different, which is crucial mainly for pharmaceuticals and agrochemicals. However, industrialscale synthetic production of enantiomerically pure compounds is not always available. Therefore, the need for pure enantiomeric compounds drives the development and research on various separation methods. However, most methods used on the industrial scale are limited to specific compounds (diastereomeric recrystallization) or generally difficult and/or expensive to scale up (chromatography-related methods). Separation of enantiomers using membranes is promising\nthanks to the easy scalability and continuous operation of membrane processes. Various ideas about how the enantioselective membranes should look like have been published in the last thirty years. The mechanism of enantiomeric separation on a membrane is, however, highly specific, and still requires extensive research. In this work, four types of enantioselective polymeric membranes are presented. Available in a digital repository NRGL
Development of Polymeric Enantioselective Membranes

Enantiomers are molecules that share the same chemical formula but in space form mirror images of each other. Their reactions with other chiral molecules can be remarkably different, which is crucial ...

Čížek, Jan
Ústav chemických procesů, 2024

Synthesis of Fluorinated Methyl β-Lactosides
Krčil, Aleš
2024 - English
In my contribution, I will describe the synthesis of a complete series of mono-deoxyfluorinated methyl β-lactosides (1–7). Their affinity towards hgals will be determined by analytical method ELISA. The synthesis relies on monosaccharide building blocks, which serves as key intermediates that are transformed into the target products through glycosylation followed by final deprotection steps. Keywords: flurinated carbohydrates; galectin; deoxyfluorination Available in a digital repository NRGL
Synthesis of Fluorinated Methyl β-Lactosides

In my contribution, I will describe the synthesis of a complete series of mono-deoxyfluorinated methyl β-lactosides (1–7). Their affinity towards hgals will be determined by analytical method ELISA. ...

Krčil, Aleš
Ústav chemických procesů, 2024

Investigation of Mechanical Processing of Solar Photovoltaic Panels
Šperlich, Antonín
2024 - English
This work aims to describe the possibilities of mechanical treatment of solar photovoltaic panels. In the first part, the shredding and milling process for the transformation of the product (whole panel) into material that can be further processed, was investigated. Milled material was sieved and analyzed. It was observed that this shredding also works as a selective grinding because three main products were produced. The second part of this work was aimed at the physical concentration of silver in real samples of milled solar photovoltaic panels by Knelson separator. This device (type of centrifugal separator) showed the ability to significantly increase the amount of silver in the outcome stream. Keywords: solar photovoltaic panels; selective milling; Knelson Available in a digital repository NRGL
Investigation of Mechanical Processing of Solar Photovoltaic Panels

This work aims to describe the possibilities of mechanical treatment of solar photovoltaic panels. In the first part, the shredding and milling process for the transformation of the product (whole ...

Šperlich, Antonín
Ústav chemických procesů, 2024

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