Number of found documents: 1089
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Analytical approach of slender structure vibration due to random component of the wind velocity
Náprstek, Jiří; Hračov, Stanislav
2017 - English
Along wind random vibration of slender structures represents one of the most important aeroelastic effects resulting from wind - structure interaction. The theoretical model being based on one-dimensional elements with continuously distributed mass and stiffness has been introduced in this paper. The system has been considered to be linear self-adjoint with strongly non-proportional linear damping due to both material of the structure and presence of vibration dampers. The additive random excitation continuously distributed in time and space is Gaussian, therefore the response is Gaussian as well. Consequently, mathematical mean value and correlation function are satisfactory for the full description of the generalized solution of the respective PDE in the stochastic meaning. The general results have been obtained mostly in the form of analytical formulae for important cases of input spectral densities. A numerical example dealing with real structure is presented. Keywords: random vibrations; slender structures; wind load; non-proportional damping; distributed-parameter systems Fulltext is available at external website.
Analytical approach of slender structure vibration due to random component of the wind velocity

Along wind random vibration of slender structures represents one of the most important aeroelastic effects resulting from wind - structure interaction. The theoretical model being based on ...

Náprstek, Jiří; Hračov, Stanislav
Ústav teoretické a aplikované mechaniky, 2017

Creep behavior of oak pegs under tension in dry and wet conditions
Kunecký, Jiří; Kloiber, Michal; Hasníková, Hana; Hrivnák, Jaroslav; Sebera, V.; Tippner, J.; Milch, J.
2017 - English
Carpentry joints equipped with oak pegs are well suited for applications where increased moisture is not a significant factor. However, for the use in outside conditions, e.g. in the repairs of historical timber bridges, the pegs connecting the two halves of the joint may deform and change their original shape. This happens especially during long-term loading and can be augmented significantly by environmental changes. Creep behavior can play a crucial role for some types of carpentry joints, especially when precise contacts of faces in the joint are required. The paper deals with experimental testing of creep behavior of 16 mm oak pegs under dry and wet conditions loaded by the combination of shear and bending between two planks made of spruce in the direction parallel to grain. The results show that the decrease of theoretical stiffness values over time plays a significant role in the force redistribution in the joint especially due to moisture effects (drop 50-70% of the original stiffness). Keywords: creep; oak; pegs; dowels; tension Available at various institutes of the ASCR
Creep behavior of oak pegs under tension in dry and wet conditions

Carpentry joints equipped with oak pegs are well suited for applications where increased moisture is not a significant factor. However, for the use in outside conditions, e.g. in the repairs of ...

Kunecký, Jiří; Kloiber, Michal; Hasníková, Hana; Hrivnák, Jaroslav; Sebera, V.; Tippner, J.; Milch, J.
Ústav teoretické a aplikované mechaniky, 2017

Mikroskopický laboratorní rozbor vzorku sgrafita z domu ve Venhudově ulici v Brně
Slížková, Zuzana; Kozlovcev, Petr; Koudelková, Veronika; Novák, Vladimír
2017 - Czech
Zpráva obsahuje výsledky mikroskopického rozboru vzorku sgrafita z 50.let 20. stol. na fasádě domu ve Venhudově ulici v Brně. Byla analyzována bílá povrchová vrstva a podkladní červenohnědá vrstva malty pomocí optické mikroskopie a elektronové mikroskopie ve spojení s prvkovou analýzou SEM-EDS. Report presents results of microscopic characterization of sgraffito from the the fifties of the twentieth century sampled from house façade in Brno, Venhudova street, CR. Light (optical) microscopy and electron microscopy SEM-EDS were used for characterization of the aggregate and the binder of two layers of sgraffito. Keywords: sgraffito, analysis; plaster; render; SEM-EDS; microscopy Available at various institutes of the ASCR
Mikroskopický laboratorní rozbor vzorku sgrafita z domu ve Venhudově ulici v Brně

Zpráva obsahuje výsledky mikroskopického rozboru vzorku sgrafita z 50.let 20. stol. na fasádě domu ve Venhudově ulici v Brně. Byla analyzována bílá povrchová vrstva a podkladní červenohnědá vrstva ...

Slížková, Zuzana; Kozlovcev, Petr; Koudelková, Veronika; Novák, Vladimír
Ústav teoretické a aplikované mechaniky, 2017

Výzkumná zpráva. Dýka v pochvě – Praha západ
Kumpová, Ivana
2017 - Czech
Byla provedena tomografie bronzové dýky z čerstvého archeologického nálezu a vytvořeny vizualizace. Výzkum byl proveden na zařízení TORATOM v Centru excelence Telč. Tomography of a bronze dagger from a recent archaeological finding was performed and visualizations were created. The research was done using the TORATOM device in the Centre of Excellence Telč. Keywords: bronze dagger; TORATOM; archaeology Available at various institutes of the ASCR
Výzkumná zpráva. Dýka v pochvě – Praha západ

Byla provedena tomografie bronzové dýky z čerstvého archeologického nálezu a vytvořeny vizualizace. Výzkum byl proveden na zařízení TORATOM v Centru excelence Telč....

Kumpová, Ivana
Ústav teoretické a aplikované mechaniky, 2017

Research report 2013-11-08 Calcite_S12
Kumpová, Ivana; Vopálenský, Michal; Vavřík, Daniel
2017 - English
Porosity was measured on a irregular sample of calcite, designated Calcite_S12, using the TORATOM device in the Centre of Excellence Telč. Keywords: calcite; TORATOM; measuring Available at various institutes of the ASCR
Research report 2013-11-08 Calcite_S12

Porosity was measured on a irregular sample of calcite, designated Calcite_S12, using the TORATOM device in the Centre of Excellence Telč.

Kumpová, Ivana; Vopálenský, Michal; Vavřík, Daniel
Ústav teoretické a aplikované mechaniky, 2017

Beton s ocelovou výztuží
Kumpová, Ivana; Jandejsek, Ivan; Vavřík, Daniel
2017 - Czech
Práce byla zaměřena na RTG tomografii a vytvoření 3D počítačových modelů deseti vzorků betonu s různým obsahem ocelové výztuže a různou technologií výroby. Z těchto modelů byly dále vypočteny objemové poměry jednotlivých složek (beton:výztuž:póry) a směrové rozložení jednotlivých vláken. The work was focused on X-Ray tomography and creating of 3D computer models of ten concrete samples with various steel reinforcement contents and different production technology. From these models, the volume ratios of individual components (concrete: reinforcement: pores) and directional layout of individual fibers were calculated. Keywords: X-Ray tomography; 3D computer model; reinforced concrete Available at various institutes of the ASCR
Beton s ocelovou výztuží

Práce byla zaměřena na RTG tomografii a vytvoření 3D počítačových modelů deseti vzorků betonu s různým obsahem ocelové výztuže a různou technologií výroby. Z těchto modelů byly dále vypočteny objemové ...

Kumpová, Ivana; Jandejsek, Ivan; Vavřík, Daniel
Ústav teoretické a aplikované mechaniky, 2017

Stochastic stability of the generalized van der Pol system under random additive excitation
Náprstek, Jiří; Fischer, Cyril
2017 - English
The paper is motivated by a series of wind tunnel experiments investigating aeroelastic SDOF and TDOF section models of various shape and aeroelastic properties. It reveals that most of them can be theoretically modeled by the van der Pol – Duffing type equations or their combination adjusting degree of individual nonlinear terms or their coefficients. It should be emphasized that this character of the system response is very stable and is obvious in linear as well as in weakly nonlinear domain when the post-critical effect emerges. Moreover, many special effects identified by an experimental way evoke properties recognized in the pure theory of differential equations. Keywords: wind tunnel experiment; random excitation; stochastic stability Available at various institutes of the ASCR
Stochastic stability of the generalized van der Pol system under random additive excitation

The paper is motivated by a series of wind tunnel experiments investigating aeroelastic SDOF and TDOF section models of various shape and aeroelastic properties. It reveals that most of them can be ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2017

Formace polymorfů uhličitanu vápenatého během mísení koncentrovaných roztoků solí
Ševčík, Radek; Mácová, Petra; Viani, Alberto
2017 - Czech
Příspěvek se zaobírá předběžnými výsledky studia gelové fáze vznikající během mísení koncentrovaných roztoků solí během syntézy polymorfů uhličitanu vápenatého. Během reakce bylo odebráno několik vzorků, které byly následně zkoumány instrumentálními technikami jako např. skenovací elektronový mikroskop. This contribution is demonstrated the preliminary results of the study of the gel phase forming during the synthesis of calcium carbonate's polymorphs. Several samples were collected during the reaction and they were subsequently investigated with instrumental techniques e.g. scanning electron microscopy. Keywords: CaCO3; polymorphs; synthesis; vaterite; ACC Available at various institutes of the ASCR
Formace polymorfů uhličitanu vápenatého během mísení koncentrovaných roztoků solí

Příspěvek se zaobírá předběžnými výsledky studia gelové fáze vznikající během mísení koncentrovaných roztoků solí během syntézy polymorfů uhličitanu vápenatého. Během reakce bylo odebráno několik ...

Ševčík, Radek; Mácová, Petra; Viani, Alberto
Ústav teoretické a aplikované mechaniky, 2017

Optimization of acquisition parameters in radiography and tomography
Vopálenský, Michal; Vavřík, Daniel; Kumpová, Ivana
2017 - English
Contrast in radiographic images is one of the most important parameters both in radiography and tomography. This paper investigates the possibility of adjusting the radiographic parameters, in particular the accelerating voltage of the X-ray tube, in order to maximize the difference in the detected intensity in response to the change in the thickness of the investigated object. Simplified model is used that allows finding the optimal operating point for the given material and thickness without an apriory knowledge about the X-ray spectra, detector response and the material composition. It is shown that in case of small changes of thickness, the optimum is met when the detected intensity behind the object of certain thickness is at approx. 37 % of the full range (i.e., of the value that would be measured under the same conditions in the absence of the object). In spite of simplifications made, the theoretical model shows a very good correspondence with the experimental data. A brief consideration is made on the case of a general difference in thicknesses. Keywords: X-ray computed tomography; X-ray radiography; X-ray optimization; image processing; contrast Fulltext is available at external website.
Optimization of acquisition parameters in radiography and tomography

Contrast in radiographic images is one of the most important parameters both in radiography and tomography. This paper investigates the possibility of adjusting the radiographic parameters, in ...

Vopálenský, Michal; Vavřík, Daniel; Kumpová, Ivana
Ústav teoretické a aplikované mechaniky, 2017

Early stage microstructure development of cement paste modified by crystalline admixture
Hrbek, V.; Petráňová, Veronika; Němeček, J.
2017 - English
This paper deals with the effect of crystalline admixture (CA) on the microstructure of the cementitious composite in first four weeks after the production. Previous investigation was performed on reference specimens consisting of pure cement. Samples of pure CA and cement modified by 1% of CA with the same w/c ratio were examined and compared in this paper. By investigation of these materials on the micro-scale, it is possible to identify the development of the microstructure of each and determine the impact of the modification. For this purpose, backscattered electrons microscopy (BSE) with energy-dispersive X-ray spectroscopy (EDX) was used for phase analysis as well as instrumental nano-indentation to obtain micro-mechanical properties. Presented results show the evolution of mechanical properties and microstructure in time and the impact of the crystalline admixture on modified cement. Keywords: cement; crystalline admixture; microstructure; nanoindentation; phase; SEM Available at various institutes of the ASCR
Early stage microstructure development of cement paste modified by crystalline admixture

This paper deals with the effect of crystalline admixture (CA) on the microstructure of the cementitious composite in first four weeks after the production. Previous investigation was performed on ...

Hrbek, V.; Petráňová, Veronika; Němeček, J.
Ústav teoretické a aplikované mechaniky, 2017

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