Number of found documents: 11138
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Proposal for loading tests of bridges - simulation and laboratory experiments
Bayer, Jan; Urushadze, Shota; Černý, Miloš
2018 - English
A new dynamic load testing of bridges is proposed and theoretically investigated. A transient analysis of passing vehicle over a bridge in ANSYS and an analytical program in MATLAB for the transient solution of piecewise linear mechanical structures were developed to assess the effects of the proposed dynamic load on a bridge model. According to the first laboratory experiments, it seems that the proposed travelling impulse load could surpass some of the shortcomings and limitations of the currently applied methods of bridge testing. The investigation is a part of a project aimed at drive-by identification of dynamic properties of bridges and further experimental and analytical research will follow. Keywords: dynamic loading tests; transient analysis; vibrations; vehicle-bridge interaction Available at various institutes of the ASCR
Proposal for loading tests of bridges - simulation and laboratory experiments

A new dynamic load testing of bridges is proposed and theoretically investigated. A transient analysis of passing vehicle over a bridge in ANSYS and an analytical program in MATLAB for the transient ...

Bayer, Jan; Urushadze, Shota; Černý, Miloš
Ústav teoretické a aplikované mechaniky, 2018

Lávka pro pěší Radotín - zatížení větrem dle EN 1991-1-4 a měření ve větrném tunelu
Göringer, J.; Hračov, Stanislav; Macháček, Michael
2018 - Czech
S ohledem na atypickou konstrukci lávky v Radotíně bylo nutno v rámci statického ověření řešit nestandardní účinky zatížení větrem, kdy EN 1991-1-4 poskytuje pro takto atypické konstrukce jen málo podpory. Zatížení větrem u takovéto konstrukce nevystupuje pouze jako náhradní statický účinek, ale zejména je nutné posoudit případné ztráty aerodynamické stability. Příspěvek předkládá postup stanovení problematiky podle EN 1991-1-4 včetně porovnání s výsledky z větrného tunelu. Due to the atypical design of the footbridge in Radotín the procedures for evaluation of the force coefficients presented in EN 1991-1-4 were experimentally verified in the wind tunnel. For the lack of the information about the structure behaviour on the edge of the aerodynamic instability the critical velocity for flutter was experimentally verified as well. The paper presents comparison of the approaches from EN 1991-1-4 with the results of the experiment. Keywords: wind load; footbridge; wind tunnel experiments Available at various institutes of the ASCR
Lávka pro pěší Radotín - zatížení větrem dle EN 1991-1-4 a měření ve větrném tunelu

S ohledem na atypickou konstrukci lávky v Radotíně bylo nutno v rámci statického ověření řešit nestandardní účinky zatížení větrem, kdy EN 1991-1-4 poskytuje pro takto atypické konstrukce jen málo ...

Göringer, J.; Hračov, Stanislav; Macháček, Michael
Ústav teoretické a aplikované mechaniky, 2018

Tourist interest in illicit zone of ice caves
Nováková, Eva; Kuda, František; Kubalíková, Lucie
2018 - English
Ledové sluje (Ice Caves) in the Podyjí National Park represents one of the most spectacular sites within the area. It consists of the large boulder field and several pseudokarst caverns on the north-western slope of the ridge that are very important from the ecological and geomorphological point of view. The access to the site is restricted for the visitors of National Park as there exists a risk of damage and disturbance of these unique phenomena; tourist can use the marked paths leading around the site, they can reach the top part of the ridge.\nCurrently, there are only several persons who have legal access to the site (employees of the National Park Administration and other researches with the permission issued by NP Administration). However, the installed sensor that counts the passages proved that the site is visited more frequently than it should be. The number of people who visit this site (situated within the first zone of National Park where there is no marked path and so the access is forbidden by decree) is quite alarming. Based on these findings, some proposals for the solution of this unfavourable situation are proposed and other possibilities how to avoid this undesirable phenomenon are discussed.\n Keywords: Podyji National Park; restricted area; passages monitoring Available in a digital repository NRGL
Tourist interest in illicit zone of ice caves

Ledové sluje (Ice Caves) in the Podyjí National Park represents one of the most spectacular sites within the area. It consists of the large boulder field and several pseudokarst caverns on the ...

Nováková, Eva; Kuda, František; Kubalíková, Lucie
Ústav geoniky, 2018

Asymmetry of the response probability density of a system with parametric random noises
Náprstek, Jiří; Fischer, Cyril
2018 - English
Recording of time variable processes is accompanied by various internal disturbing effects as a rule. They influence parameters of the measuring facility, transducer-device transmission, etc. These parasitic processes are usually of the random character and, consequently, they exercise as parametric noises. Moreover, the input signal mostly consists of a useful signal which can be taken as composed from deterministic and random additive part. Various combinations of these noises are the origin of random and also systematic measuring errors which can have under certain circumstances a cumulative character, deteriorate the output signal quality and can lead finally to the stochastic stability loss. These effects can be theoretically described using differential systems with stochastic coefficients and stochastic right hand side considering all input and output processes to be of the Markov type. Keywords: random vibration; signal reconstruction; parametric noise; response asymmetry Available at various institutes of the ASCR
Asymmetry of the response probability density of a system with parametric random noises

Recording of time variable processes is accompanied by various internal disturbing effects as a rule. They influence parameters of the measuring facility, transducer-device transmission, etc. These ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2018

Dynamic Bayesian Networks for the Classification of Sleep Stages
Vomlel, Jiří; Kratochvíl, Václav
2018 - English
Human sleep is traditionally classified into five (or six) stages. The manual classification is time consuming since it requires knowledge of an extensive set of rules from manuals and experienced experts. Therefore automatic classification methods appear useful for this task. In this paper we extend the approach based on Hidden Markov Models by relating certain features not only to the current time slice but also to the previous one. Dynamic Bayesian Networks that results from this generalization are thus capable of modeling features related to state transitions. Experiments on real data revealed that in this way we are able to increase the prediction accuracy. Keywords: Dynamic Bayesian Network; Sleep Analysis Fulltext is available at external website.
Dynamic Bayesian Networks for the Classification of Sleep Stages

Human sleep is traditionally classified into five (or six) stages. The manual classification is time consuming since it requires knowledge of an extensive set of rules from manuals and experienced ...

Vomlel, Jiří; Kratochvíl, Václav
Ústav teorie informace a automatizace, 2018

Vliv organických látek na charakter agregátů tvořených koagulací/flokulací při úpravě vody
Filipenská, Monika; Pivokonská, Lenka; Vašatová, Petra; Pivokonský, Martin
2018 - Czech
Cílem práce bylo popsat vliv různých znečišťujících příměsí (kaolinitové částice, COM peptidy/proteiny a jejich směs) na velikost, velikostní distribuci, tvar a strukturu agregátů tvořených v proměnných hydrodynamických podmínkách (různá gradient rychlosti) v konečné fázi vývoje agregace, tzv. steady state. Jako míchací zařízení byl zvolen Taylor-Couettův reaktor, který umožňuje neinvazivní pozorování agregátů. Vlastnosti agregátů byly vyhodnocovány metodou obrazové analýzy. Bylo zjištěno, že velikost a tvar agregátů je závislá na typu koagulačního činidla, typu koagulované přímesi a aplikovaném gradientu rychlosti. Železité koagulační činidlo produkuje větší a méně pravidelné agregáty než činidlo hlinité. Podle příměsi roste velikost (zároveň klesá kompaktnost a roste neuspořádanost) agregátů v pořadí kaolinit < COM < kaolinit + COM. Bylo zjištěno, že velikost agregátů se na aplikovaném gradientu rychlosti nemění plynule, jak bylo doposud předpokládání, ale při překročení hodnoty tzv. kritických gradientů rychlosti, dochází k její prudké změně. Změny ve velikosti agregátů se liší v závislosti na charakteru koagulovaných příměsí a byly vysvětleny pomocí rozdílných interakcí mezi znečišťující příměsí a koagulačním činidlem. Available at various institutes of the ASCR
Vliv organických látek na charakter agregátů tvořených koagulací/flokulací při úpravě vody

Cílem práce bylo popsat vliv různých znečišťujících příměsí (kaolinitové částice, COM peptidy/proteiny a jejich směs) na velikost, velikostní distribuci, tvar a strukturu agregátů tvořených v ...

Filipenská, Monika; Pivokonská, Lenka; Vašatová, Petra; Pivokonský, Martin
Ústav pro hydrodynamiku, 2018

The role of solvents in the preparation of hydrophobic nanofibrous membrane containing fumed silica
Peer, Petra; Polášková, M.; Musilová, I.; Filip, Petr
2018 - English
It is well-known that a type of used fumed silica nanoparticles plays a dominant role in wettability of the corresponding nanofibrous mats. As a result, the desired contact angle can be approximately achieved by a choice of adequate fumed silica nanoparticles. However, less attention has been hitherto paid to an active role of solvents in connection with the tailoring this contact angle. For analysis we used poly(vinyl butyral) representing electrospun-friendly material, various types of fumed silica nanoparticles and two solvents - methanol and ethanol. It is demonstrated that a choice of polymer solvents plays a significant role in contact angle changes. Hence, in combination of the type of fumed silica nanoparticles and the type of solvent it is possible to achieve a finer partition of the required contact angles. Keywords: PVB solution; solvents; fumed silica; electrospinning; rheology Available at various institutes of the ASCR
The role of solvents in the preparation of hydrophobic nanofibrous membrane containing fumed silica

It is well-known that a type of used fumed silica nanoparticles plays a dominant role in wettability of the corresponding nanofibrous mats. As a result, the desired contact angle can be approximately ...

Peer, Petra; Polášková, M.; Musilová, I.; Filip, Petr
Ústav pro hydrodynamiku, 2018

Thermal induced morphological changes of poly(ethylene oxide) nanofibrous webs
Polášková, M.; Peer, Petra; Ponížil, P.; Čermák, R.
2018 - English
The crystallinity of fibres prepared by electrospinning shows lower level in comparison with samples processed by common technologies such as moulding or film casting. Thus, the attempts to improve the structure of electrospun fibres in order to increase physical and mechanical properties of nonwoven webs are obvious. Post-process thermal treatment is one of the possibilities of the crystallinity enhancement that can be easily included to the finishing operation of final products. For the experiment we used poly(ethylene oxide) representing electrospun-friendly material and two solvents - methanol and water, both ensuring good electrospinnability. It is demonstrated that a choice of polymer solvents plays a significant role in fibre diameter and their capabilities to resist applied heat. However, in all cases the enhancement of crystallinity is detected at the short time of thermal exposure. Keywords: PEO nanofibres; degree of crystallinity; electrospinning Available at various institutes of the ASCR
Thermal induced morphological changes of poly(ethylene oxide) nanofibrous webs

The crystallinity of fibres prepared by electrospinning shows lower level in comparison with samples processed by common technologies such as moulding or film casting. Thus, the attempts to improve ...

Polášková, M.; Peer, Petra; Ponížil, P.; Čermák, R.
Ústav pro hydrodynamiku, 2018

Modelling of non-monotonous course of shear viscosity
Filip, Petr
2018 - English
A number of parameters appearing in the 'classical' empirical constitutive equations usually oscillate between two and five. With the onset of new rheologically more complex materials exhibiting non-monotonous behaviour of flow curves this range (2-5) is no longer tenable and more additional parameters are required for a proper description of the flow curves. An 8-parameter model is presented and testified. Keywords: viscosity; flow curve; constitutive equation; empirical modelling Available at various institutes of the ASCR
Modelling of non-monotonous course of shear viscosity

A number of parameters appearing in the 'classical' empirical constitutive equations usually oscillate between two and five. With the onset of new rheologically more complex materials exhibiting ...

Filip, Petr
Ústav pro hydrodynamiku, 2018

The role of microstructure on wettability of plasma sprayed yttria stabilized zirconia coatings
Komarov, P.; Čelko, L.; Remešová, M.; Skorokhod, K.; Jech, D.; Klakurková, L.; Slámečka, K.; Mušálek, Radek
2018 - English
Atmospheric plasma spraying utilizing initial powder materials in micrometric size has been successfully used for various applications in different fields of the industry over the past several decades. Nowadays, the new trend in plasma spraying is to use sub-micron or nano-sized powder feedstocks in the form of colloidal suspension. This relatively new technology enables to obtain specific types of dense vertically cracked, fully dense or columnar microstructure. The aim of this work is to investigate the influence of coatings microstructure and topography on its water wetting properties. Two different microstructures, i.e. lamellar and columnar, were sprayed from chemically the same yttria-stabillized zirconia (YSZ) ceramics powders by the means of conventional atmospheric plasma spray and suspension hybrid water stabilized plasma spray techniques, respectively. Microstructural and phase composition of the initial powders and as-sprayed coatings were investigated using optical microscopy, scanning electron microscopy and X-ray diffraction techniques. Topography of coatings surface was measured by means of non-contact optical profilometry. The YSZ coatings wettability was evaluated based on water droplet contact angle using Sessile droplet method. The coatings microstructure reveals the important role in the change of droplet contact angle, where lamellar microstructure was found close to hydrophilic-hydrophobic transition and columnar microstructure was found superhydrophobic Keywords: Contact angle; Plasma spraying; Sessile drop method; Water; Yttria stabilized zirconia Available at various institutes of the ASCR
The role of microstructure on wettability of plasma sprayed yttria stabilized zirconia coatings

Atmospheric plasma spraying utilizing initial powder materials in micrometric size has been successfully used for various applications in different fields of the industry over the past several ...

Komarov, P.; Čelko, L.; Remešová, M.; Skorokhod, K.; Jech, D.; Klakurková, L.; Slámečka, K.; Mušálek, Radek
Ústav fyziky plazmatu, 2018

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