Number of found documents: 15187
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Moving dynamic test loads for road bridges - a case study
Bayer, Jan; Urushadze, Shota
2019 - English
Two types of dynamic testing load for bridges - driving sprung mass and driving impulse load - areexamined from the drive-by identification point of view. Numerical studies in ANSYS using contact elements and in MATLAB using a modal solution together with coupling force were performed. Equations for the estimation of the impulse load caused by a rolling cogwheel were suggested. The experiments confirmed that a driving impulse load is more efficient in exciting bridge vibrations. This, together with the fact that impulse loading is not sensitive to surface roughness, leads to the conclusion that, as a method for bridge health monitoring, impulse loading is more promising than using a driving sprung mass Keywords: drive-by identification; bridge testing; moving sprung mass; impulse loading; vibration measurements; laboratory experiments Available at various institutes of the ASCR
Moving dynamic test loads for road bridges - a case study

Two types of dynamic testing load for bridges - driving sprung mass and driving impulse load - areexamined from the drive-by identification point of view. Numerical studies in ANSYS using contact ...

Bayer, Jan; Urushadze, Shota
Ústav teoretické a aplikované mechaniky, 2019

Shaanxi 2018 - první velké objevy
Motyčka, Z.; Filippi, Michal
2019 - Czech
Keywords: Shaanxi 2018 expedition; speleology; caves Available at various institutes of the ASCR
Shaanxi 2018 - první velké objevy

Motyčka, Z.; Filippi, Michal
Geologický ústav, 2019

Deformation response of polydimethylsiloxane substrates subjected to uniaxial quasi-static loading
Martino, F.; Vinařský, V.; Šleichrt, Jan; Kytýř, Daniel
2019 - English
To investigate cellular response of cardiomyocytes to substrate mechanics, biocompatible material with stiffness in physiological range is needed. Polydimethylsiloxane (PDMS) based material Sylgard 184 is used for construction of microfluidic organ on chip devices for cell culture due to ease of device preparation, bonding, and possibility of surface functionalization. However it has stiffness orders of magnitude out of physiological range. Therefore we adapted recently published protocol [1] aiming to prepare substrates which offer stiffness in physiological range 5−100 kPa using various mixtures of Sylgard 527 and Sylagard 184. The inhouse developed loading device with the loading capacity of 3 kN with 1 μm position tracking accuracy and sub-micron position sensitivity was employed for this experimental campaign. The experiments were controlled by the proprietary LinuxCNC software running on the real-time kernel [2]. All batches of the samples were subjected to monotonic compression loading. During the displacement driven experiment with loading rate 10 μm · s−1 the samples with diameter 12.00 ± 0.05mm and height 14 − 16mm were compressed to minimally 50% deformation. Because of high differences in the samples stiffness various load cells with nominal capacity 50N, 10N, and 1N was used for the most reliable force logging. Material properties for all batches were derived from a set of tests under dry and simulated physiological conditions. The results are represented in the form of stress-strain curves calculated from the acquired force and displacement data and elastic moduli are estimated as secant up to 10% deformation. Keywords: compression loading; hyperelasticity; polydimethylsiloxane substrates Available at various institutes of the ASCR
Deformation response of polydimethylsiloxane substrates subjected to uniaxial quasi-static loading

To investigate cellular response of cardiomyocytes to substrate mechanics, biocompatible material with stiffness in physiological range is needed. Polydimethylsiloxane (PDMS) based material Sylgard ...

Martino, F.; Vinařský, V.; Šleichrt, Jan; Kytýř, Daniel
Ústav teoretické a aplikované mechaniky, 2019

Probability density determination by means of Gibbs entropy probability density
Náprstek, Jiří; Fischer, Cyril
2019 - English
A method of random response investigation of a nonlinear dynam-ical system is discussed. In particular, the solution of the probability density of a single/multi-degree of freedom (SDOF/MDOF) system response is investigated. Multiple stable equilibrium states with possible jumps of the snap-through type among them are considered. The system is Hamiltonian with weak damping excited by a set of non-stationary Gaussian white noises. The solution, which is based on the Gibbs principle of the maximum entropy of probability, can be employed in various branches of engineering. The search for the extreme of the Gibbs entropy functional is formulated as a constrained optimization problem. The secondary constraints follow from the Fokker-Planck equation (FPE) for the system considered or from the system of ordinary di_erential equations for the stochastic moments of the response derived from the relevant FPE Keywords: Fokker-Planck equation; Gibbs entropy functional; maximum entropy; probability density principle Available at various institutes of the ASCR
Probability density determination by means of Gibbs entropy probability density

A method of random response investigation of a nonlinear dynam-ical system is discussed. In particular, the solution of the probability density of a single/multi-degree of freedom (SDOF/MDOF) system ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2019

Laser-generated nanoparticles to change physical properties of solids, liquids and gases
Torrisi, Alfio; Cutroneo, Mariapompea; Ceccio, Giovanni; Cannavó, Antonino; Horák, Pavel; Torrisi, L.; Vacík, Jiří
2019 - English
Synthesis of nanoparticles was possible employing a Nd: YAG pulsed laser at fundamental harmonic. The production of nanoparticles in water depends mainly on the laser parameters (pulse duration, energy, wavelength), the irradiation conditions (focal spot, repetition rate, irradiation time) and the medium where the ablation occurs (solid target, water, solution concentration). The nanoparticles can be introduced in solids, liquids or gases to change many physical characteristics. The optical properties of polymers and solutions, the wetting ability of liquids, the electron density of laser-generated plasma, represent some examples that can be controlled by the concentration of metallic nanoparticles (Au, Ag, Ti, Cu). Some bio-medical applications will be presented and discussed. Keywords: bio-medical applications; laser; nanoparticles Available at various institutes of the ASCR
Laser-generated nanoparticles to change physical properties of solids, liquids and gases

Synthesis of nanoparticles was possible employing a Nd: YAG pulsed laser at fundamental harmonic. The production of nanoparticles in water depends mainly on the laser parameters (pulse duration, ...

Torrisi, Alfio; Cutroneo, Mariapompea; Ceccio, Giovanni; Cannavó, Antonino; Horák, Pavel; Torrisi, L.; Vacík, Jiří
Ústav jaderné fyziky, 2019

Experimentální vyšetřování vhodné poréznosti protiprašné stěny
Nosek, Štěpán
2019 - Czech
Článek seznamuje čtenáře se základními principy fyzikálního modelování atmosférické mezní vrstvy ve větrných tunelech a jejich aplikací na řešení prašnosti. Je uveden praktický příklad použití těchto metod v rámci řešení šíření prašnosti z pásových dopravníků do bezprostředního okolí protiprašnou stěnou. The paper introduces the reader to the basic principles of physical modelling of the atmospheric boundary layer in wind tunnels and their application to the solution of dustiness. A practical example elucidates the use of these methods in the solution of dustiness from conveying belts to immediate surroundings. Keywords: atmospheric boundary layer; physical modelling; porosity; dustiness; wind tunnel Available at various institutes of the ASCR
Experimentální vyšetřování vhodné poréznosti protiprašné stěny

Článek seznamuje čtenáře se základními principy fyzikálního modelování atmosférické mezní vrstvy ve větrných tunelech a jejich aplikací na řešení prašnosti. Je uveden praktický příklad použití těchto ...

Nosek, Štěpán
Ústav termomechaniky, 2019

Characterization of fine-grained montmorillonite fractions suitable for composite preparation
Valovičová, Věra; Vaculíková, Lenka; Plevová, Eva; Dolinská, S.; Znamenáčková, I.; Danková, Z.
2019 - English
The aim of this experimental study was to characterize a fine-grained fraction of montmorillonites (SAz-2, STx-1, SWy-2 and Kunipia-F). It was investigated in order to provide more precise information of used montmorillonites than could be obtained by analysis of the unfractioned montmorillonites. At first, the fine fraction of montmorillonites were prepared by sedimentation and activation by means of Na2CO3. The prepared clay materials were characterized by the X-ray diffraction analysis and FTIR spectroscopy. The thermal behaviour of the studied samples was determinated according to the characteristic temperatures obtained from TG/DTA curves. The temperatures of dehydratation and dehydroxylation were evaluated and kinetic parameters were also calculated. The porosity and surface properties of the studied samples were gained by the nitrogen adsorption measurements. The obtained results confirmed that the fine fraction of montmorillonites could be a suitable material for subsequent preparation of composites with enhanced sorption properties, especially montmorillonite/MnO2 composite. Keywords: montmorillonite; activation; characterization; composites Available in digital repository of the ASCR
Characterization of fine-grained montmorillonite fractions suitable for composite preparation

The aim of this experimental study was to characterize a fine-grained fraction of montmorillonites (SAz-2, STx-1, SWy-2 and Kunipia-F). It was investigated in order to provide more precise information ...

Valovičová, Věra; Vaculíková, Lenka; Plevová, Eva; Dolinská, S.; Znamenáčková, I.; Danková, Z.
Ústav geoniky, 2019

Note on the problem of compressible non-Newtonian fluids
Caggio, M.; Nečasová, Šárka
2019 - English
The aim of the paper is to consider the compressible non-Newtonian fluids of power law type when the viscosity coeffcients depend not only on invariants of velocity field but also on the density. We introduce approximation scheme using model of multipolar fluids. After then passing with higher viscosity to zero we get the measure valued solution of the problem. Keywords: non-Newtonian fluid; compressible fluid; multipolar fluid; measure-valued solution Available in digital repository of the ASCR
Note on the problem of compressible non-Newtonian fluids

The aim of the paper is to consider the compressible non-Newtonian fluids of power law type when the viscosity coeffcients depend not only on invariants of velocity field but also on the density. We ...

Caggio, M.; Nečasová, Šárka
Matematický ústav, 2019

Large Scale Motions in Turbulent Flows
Kellnerová, Radka; Jurčáková, Klára; Procházka, Pavel P.
2019 - English
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. Keywords: wind tunnel; large scale motion; quadrant analysis Fulltext is available at external website.
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 - English
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*. Keywords: wind tunnel; turbulence intensity; rough-wall; friction velocity Fulltext is available at external website.
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

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