2024-08-25
00:01 |
Materiálová analýza vzorků malt z archeologického kontextu baziliky sv. Václava ve Staré Boleslavi
Válek, Jan ; Kozlovcev, Petr ; Svorová Pawełkowicz, Sylwia ; Kotková, Kristýna
Vzorky malt byly popsány pomoci optické mikroskopie a SEM-EDS. Cílem studie bylo jejich vzájemné porovnání. Všechny tři vzorky mají podobnou strukturu i materiálové složení. Surovinou pro výrobu vápna byl jemnozrnný sedimentární vápenec s vysokým obsahem CaCO3. Vápenná matrice má charakter vzdušného vápna. Kromě vápenného pojiva se vyskytuje též prachovojílové pojivo. To je odděleno od vápenného. Zrna písku jsou obalena vápenným pojivem a v meziprostoru je prachovojílová výplň, což ukazuje na přidání této složky jako příměsi do malty až během použití při stavbě. Použitý písek odpovídá místním poměrům, a to jak eolickým pískům (spraším a sprašovým sedimentům) s dominantním výskytem opracovaných křemenných klastů, tak částečně i sedimentům fluviálního původu (zde se jedná především o litoklasty transportované na větší vzdálenost).
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2024-08-25
00:01 |
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2024-08-17
00:01 |
Stucco decoration of the coffered dome in Boim Chapel, Lviv (Ukraine)
Svorová Pawełkowicz, Sylwia ; Myślicka, M. ; Witkowski, M.
The Boim Chapel in Lviv, erected at the beginning of the 17th c. (1609–1611) as a family mausoleum by Jerzy (Georg) Boim, a wealthy merchant originating from Hungary, since 1967 is part of the Lviv National Art Gallery. Although today it forms a visual dominant of the Cathedral Square, until the end of 18th c. it was surrounded by other funeral chapels as part of the city’s cemetery. It represents one of the most important examples of Mannerist, profusely decorated, architectural style on the historical territory of the Polish-Lithuanian Commonwealth (covering today’s territories of Poland, Lithuania, Byelorussia and western Ukraine). Its exterior and interior decoration has mostly been executed\nin local stone except the stuccoworks in the coffered dome. The hemisphere has been divided into three rows of coffers, where at the bottom portrait busts of the Boim family, in the middle of prophets and at the top of saints have been placed. The space between the coffers, painted most probably in 1925 in blue, has been decorated with gilded stucco stars. In 2019, an archival and material research was launched to plan future restoration works in the chapel. For the time being, only a few samples have been taken to study the technique of stuccoworks in the coffered dome. The results of this preliminary research gave us an insight into the original technique and subsequent renovation works. The architectural decoration, such as frames, have been moulded on site, while the portrait busts and stars have been mounted as precast elements. The archival research was helpful in interpreting the material research results.
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2024-08-10
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2024-06-02
00:00 |
Book of Abstracts. 19th Youth symposium on experimental solid mechanics
Kytýř, Daniel ; Zlámal, Petr ; Pagliaro, A. ; Doktor, T.
The YSESM symposium provides a forum for young researchers and engineers, PhD students and students dealing with subjects of experimental mechanics. The Symposium concentrates on current work in all areas of experimental research and its application in solid and fluid mechanics. The topic will particularly concern to: Conventional and advanced experimental methods in solid and fluid mechanics - Non-destructive testing and inspection - Measurements in material science - Computer assisted testing and simulation - Engineering design simulation - Hybrid methods, experimental techniques – Numerical simulation - Optical methods and image processing - Measurements in biomechanics - Sensor techniques for micro- and nano-applications - Measurement methods for forensic engineering
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2024-05-25
00:00 |
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2024-05-25
00:00 |
Stochastic version of the arc-length method
Náprstek, Jiří ; Fischer, Cyril
The solution of a nonlinear algebraic system using the incremental method, based on pre-defined loading steps, fails in the vicinity of local extrema as well as around bifurcation points. The solution involved the derivation of the so-called ’Arc-Length’ method. Its essence lies in not incrementing the system parameter or any of the independent variables but rather the length of the response curve. The stochastic variant of this method allows for working with a system where system parameters include random imperfections. This contribution presents a variant that tracks the first two stochastic moments. Even in this simple case, interesting phenomena can be observed, such as the disappearance of the energy barrier against equilibrium jump due to random imperfections in the system.
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2024-05-25
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Galloping of insulated bundled overhead line - nonlinear numerical analysis in time domain
Macháček, Michael ; Hračov, Stanislav
Our contribution focuses on a 3D numerical nonlinear analysis of galloping in a specific bundled overhead line with ice accretion. We studied the susceptibility to this self-excited oscillation, critical onset wind speeds, and global dynamic response of a very low-tensioned line with simulated icing observed on similar real conductors. Due to the highly nonlinear mechanical behavior of such a flexible cable, we employed the Newmark integration method combined with the iterative Newton-Raphson method. We analyzed two numerical models of the overhead line loaded by the wind: one assuming nonlinearity only in the wind load, while retaining the linearity of the mechanical system itself, and the other representing a fully nonlinear system including geometrical nonlinearity. Our analysis revealed that the determined critical wind speeds for the onset of galloping are in relatively close ranges for both models. However, numerical simulations with the fully nonlinear system indicated significantly lower amplitudes of limit cycle oscillations, especially at higher wind speeds, compared to the linear model of the line. This underscores the necessity of using fully nonlinear models during the design stage of such low-tensioned aerial conductors.
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2024-05-25
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LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Ledvinková, Blanka ; Hračov, Stanislav ; Macháček, Michael
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.
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2024-05-25
00:00 |
Galloping of insulated bundled overhead line simplified analysis
Hračov, Stanislav ; Macháček, Michael
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.
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