Number of found documents: 1258
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Innovative device for the simulation of environmental conditions and testing of building materials
Cacciotti, Riccardo; Wolf, Benjamin; Macháček, Michael; Frankl, Jiří
2022 - English
Excessive humidity influences the performance of building envelopes and the safety of their occupants. Moisture related problems can indeed impose significant health risks for buildings’ users and even lead, under extreme scenarios, to structural failures. This paper investigates an innovative experimental setup for evaluating the influence of changing environmental conditions on the performance of building materials. It stems out from a broader ongoing research aimed at studying the trends of mould growth on wooden building components. The presented results include the design, construction and numerical validation of a small-scale climatic wind tunnel (2m x 1.8m ca.) to be used for the simulation of natural ventilation and daily humidity and temperature fluctuations. Key findings include the final design of a low cost, modular construction which allows gathering reliable data on the response of building materials exposed to changing boundary conditions, intended for improving current mould growth models. Future work is also suggested. Keywords: building envelope; moisture; building material; wind tunnel; performance Available in digital repository of the ASCR
Innovative device for the simulation of environmental conditions and testing of building materials

Excessive humidity influences the performance of building envelopes and the safety of their occupants. Moisture related problems can indeed impose significant health risks for buildings’ users and ...

Cacciotti, Riccardo; Wolf, Benjamin; Macháček, Michael; Frankl, Jiří
Ústav teoretické a aplikované mechaniky, 2022

Application of first integrals in the construction of the Lyapunov function for the random response stability testing
Náprstek, Jiří; Fischer, Cyril
2022 - English
The paper deals with a possibility of using the properties of first integrals for the construction of Lyapunov function for the analysis of a dynamic system stability in the stochastic domain. It points out certain characteristics of first integrals resulting in the necessity to introduce additional constraints to assure the principal properties of the Lyapunov function. A number of these constraints has their physical interpretation with reference to system stability. The advantage of this method constructing the Lyapunov function consists in the fact that the Lyapunov function itself contains information on the examined system and, consequently, it is not merely a positive definite function without any relation to the actual case concerned. The presented theory finds application in many dynamical systems. The procedure is illustrated by a nonlinear SDOF example. Keywords: stochastic stability; Lyapunov function; first integrals; cyclic coordinates Available in digital repository of the ASCR
Application of first integrals in the construction of the Lyapunov function for the random response stability testing

The paper deals with a possibility of using the properties of first integrals for the construction of Lyapunov function for the analysis of a dynamic system stability in the stochastic domain. It ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2022

Výzkumná zpráva. Výzkum složení inkoustů v historické knize rentgenovou fluorescenční spektroskopií (XRF)
Vopálenský, Michal
2022 - Czech
V tomografu TORATOM v Centru Telč Ústavu teoretické a aplikované mechaniky, AVČR, byla provedena výpočetní tomografie (CT) vzácné knihy z Národní knihovny ČR – Slovanské knihovny. Jedná se o Euchologion, pocházející z Kyjeva ze 17. století. Během měření byla diskutována možnost měření složení inkoustů, kterými je kniha tištěna. Obecně se v knize vyskytují části tištěné černě a části tištěné červeně. Proto došlo k realizaci měření popisovaného v této zprávě, kde bylo změřeno několik stran díla v oblasti černého inkoustu, červeného inkoustu a v oblasti bez inkoustu. Computed tomography (CT) of a unique book from the National Library of the Czech Republic - Slavonic Library was performed in the TORATOM tomograph in Center Telč, Institute of Theoretical and Applied Mechanics, Czech Academy of Sciences. The book is a 17th century euchologion originating in Kiev. During the tomographic scanning, the possibility of measuring the composition of the inks used in the book was discussed. In general, there are parts printed in black and parts printed in red in the book. Therefore, the measurement described in this report was carried out, where several pages of the work were measured in the area of ​​black ink, red ink and in the area without ink. Keywords: TORATOM; computed tomography (CT); Euchologion Available at various institutes of the ASCR
Výzkumná zpráva. Výzkum složení inkoustů v historické knize rentgenovou fluorescenční spektroskopií (XRF)

V tomografu TORATOM v Centru Telč Ústavu teoretické a aplikované mechaniky, AVČR, byla provedena výpočetní tomografie (CT) vzácné knihy z Národní knihovny ČR – Slovanské knihovny. Jedná se o ...

Vopálenský, Michal
Ústav teoretické a aplikované mechaniky, 2022

Determination of aerodynamic coefficients for air flow around U-profiles with different flange porosities
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2022 - English
Our contribution presents the comparison of the experimental investigations and of the numerical 2D simulations of the air flow around U –profiles having different flange porosities. The U-shaped beams were exposed to the air flow having a given velocity at different angles of the wind attack for obtaining the curves of the aerodynamic coefficients depending on the impact angle. The numerical simulations of the wind tunnel testing were performed using the Unsteady Reynolds Averaged Navier-Stokes (RANS) method, k-ω SST turbulence model was assumed. Keywords: U-shaped beams; porosity; wind tunnel; RANS simulation; k-ω SST model Available in digital repository of the ASCR
Determination of aerodynamic coefficients for air flow around U-profiles with different flange porosities

Our contribution presents the comparison of the experimental investigations and of the numerical 2D simulations of the air flow around U –profiles having different flange porosities. The U-shaped ...

Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
Ústav teoretické a aplikované mechaniky, 2022

Theoretical analysis of selected trajectories inscribed by a ball freely rolling in a spherical cavity
Náprstek, Jiří; Fischer, Cyril
2022 - English
Indirect monitoring of structures is significantly complicated when an artificial vibration absorber has to be taken into account. Knowledge of the absorber’s behaviour is necessary in order to correctly distinguish the response types obtained during an drive-by measurement. In this work, the mathematical model of the ball-type vibration absorber is used, which is based on the Lagrangian formalism. Three first integrals are identified when no external excitation nor damping is assumed. The paper illustrates the power of this approach, which enables a detailed analysis of free movement of the ball in the spherical cavity. Properties of several particular trajectories depending on initial conditions are presented. Keywords: slender structure; vibration absorber; first integral; rolling sphere; structural health monitoring Available in digital repository of the ASCR
Theoretical analysis of selected trajectories inscribed by a ball freely rolling in a spherical cavity

Indirect monitoring of structures is significantly complicated when an artificial vibration absorber has to be taken into account. Knowledge of the absorber’s behaviour is necessary in order to ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2022

Ochrana památkových objektů proti vibracím
Urushadze, Shota; Pirner, Miroš; Bayer, Jan
2022 - Czech
Předkládaný památkový postup byl vytvořen v letech 2018–2021 při řešení úkolu NAKI č. DG18P02OVV040, nazvaného 'Památky v pohybu', financovaného MK ČR. Podkladem pro vypracování tohoto památkového postupu byla 30‐letá činnost Prof. Pirnera, Ing. Urushadzeho a Ing. Bayera v oblasti technické seizmicity a stavební dynamiky obecně. Navržený památkový postup je vlastně metodickým návodem, jak postupovat, pokud se objeví u památek nějaké poruchy nebo negativní projevy, které by mohly souviset s vibracemi, včetně způsobů jejich řešení. K jednotlivým bodům postupu jsou uváděny příklady z dlouholeté praxe. Obecně tato vyšetřování zahrnují teoretickou a experimentální analýzu včetně terénního průzkumu, nedestruktivní a laboratorní testy na modelech, modelování metodou konečných prvků.\n The presented heritage procedure was developed in 2018-2021 as part of the NAKI project no. DG18P02OVV040, entitled 'Monuments in Motion', funded by the Ministry of Culture of the Czech Republic. The basis for the design of this heritage procedure is the 30-year activity of Prof. Pirner, Ing. Urushadze and Ing. Bayer in the field of technical seismicity and building dynamics in general. The proposed heritage procedure is actually a methodological guide on how to proceed if there are any failures or negative effects that could be related to vibrations, as well as how to deal with them. For each of the various points of the procedure examples are given from our many years of practice. In general, these investigations involve theoretical and experimental analysis including in situ investigations, non-destructive and laboratory tests on models, using finite element modelling.\n Keywords: technical seismicity; modal analysis; measuring control panel; long-term monitoring; measuring shocks and movements; recorded data; frequency spectrum Available at various institutes of the ASCR
Ochrana památkových objektů proti vibracím

Předkládaný památkový postup byl vytvořen v letech 2018–2021 při řešení úkolu NAKI č. DG18P02OVV040, nazvaného 'Památky v pohybu', financovaného MK ČR. Podkladem pro vypracování ...

Urushadze, Shota; Pirner, Miroš; Bayer, Jan
Ústav teoretické a aplikované mechaniky, 2022

Long term optical monitoring technique of displacement fields based on ArUco markers
Kunecký, Jiří
2022 - English
In structural engineering it is often needed to measure tiny displacements of parts of the structure extremely precisely. For such a purpose it is often needed to use some type of sensor attached to the surface of the structure. This paper presents a new technique which simply uses computer vision libraries to measure displacement of markers originally developed for robotics. Such analysis can be under specific circumstances (2D planar movement) valid if we compare two images taken at different times with the same camera. Main advantage of this method is simplicity of use and low cost of markers, which can be printed in a standard office laser printer. The resolution (error) can be for standard cameras around 0.1 pixel. The method is especially developed for research of timber frames/joints behavior in real structures, because displacements of joints in creep or under load can reach an amplitude which is perfectly detectable by this method. Keywords: displacement measurement; long-term monitoring; ArUco markers Available at various institutes of the ASCR
Long term optical monitoring technique of displacement fields based on ArUco markers

In structural engineering it is often needed to measure tiny displacements of parts of the structure extremely precisely. For such a purpose it is often needed to use some type of sensor attached to ...

Kunecký, Jiří
Ústav teoretické a aplikované mechaniky, 2022

Zpráva o výsledcích chemické a mineralogické analýzy vzorku omítky z objektu: Zámek Opočno
Frankeová, Dita; Bauerová, Pavla; Slížková, Zuzana
2022 - Czech
V rámci stavebně-technického průzkumu byl proveden rozbor vzorků historických omítek s využitím termické analýzy a SEM‐EDS analýzy. Byla provedena charakterizace plniva a složek pojiva malt a jejich povrchových úprav. Výsledky průzkumných prací byly použity jako podklad pro návrh rekonstrukce objektu. An analysis of historical plaster was carried out using thermal analysis and SEM-EDS analysis. The binders and aggregates of mortars and their surface treatments were characterized. The survey results were used for the design of the repair mortars. Keywords: TGA; SEM/EDS; binder characterization Available at various institutes of the ASCR
Zpráva o výsledcích chemické a mineralogické analýzy vzorku omítky z objektu: Zámek Opočno

V rámci stavebně-technického průzkumu byl proveden rozbor vzorků historických omítek s využitím termické analýzy a SEM‐EDS analýzy. Byla provedena charakterizace plniva a složek pojiva malt a jejich ...

Frankeová, Dita; Bauerová, Pavla; Slížková, Zuzana
Ústav teoretické a aplikované mechaniky, 2022

Analysis of van der Pol equation on slow time scale for combined random and harmonic excitation
Náprstek, Jiří; Fischer, Cyril
2022 - English
Vortex shedding represents one of the most important processes that constantly attract the attention of experimental and theoretical research. A number of non-linear effects arise from the fluid-structure interaction. The non-stationary response in the vicinity of the lock-in region has a quasi-periodic character, beating frequency of which varies considerably with the distance from the lock-in frequency. This property is significantly affected by the assumption of combined random and harmonic excitation. This paper describes several details that contribute to the probabilistic characteristics of the system on a time-slow scale using partial response amplitudes. Keywords: SDOF oscillator; slow-time system; Fokker-Planck equation Available at various institutes of the ASCR
Analysis of van der Pol equation on slow time scale for combined random and harmonic excitation

Vortex shedding represents one of the most important processes that constantly attract the attention of experimental and theoretical research. A number of non-linear effects arise from the ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2022

Construction of the Lyapunov function reflecting the physical properties of the model
Náprstek, Jiří; Fischer, Cyril
2022 - English
Practical experience shows that the random excitation component can affect the system response and its dynamic stability not only negatively but also positively. Such mechanisms are usually developed heuristically and are often not sufficiently justified theoretically. The paper presents a possibility of using the properties of first integrals for the construction of a Lyapunov function for the analysis of a dynamic system stability in the stochastic domain. In such case, the Lyapunov function itself contains information on the examined system and, consequently, it is able to provide a more detailed insight into the system stability properties. The procedure is illustrated by a nonlinear SDOF example. Keywords: Lyapunov function; stability; spherical pendulum Available at various institutes of the ASCR
Construction of the Lyapunov function reflecting the physical properties of the model

Practical experience shows that the random excitation component can affect the system response and its dynamic stability not only negatively but also positively. Such mechanisms are usually developed ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2022

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