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 ...
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 ...
Analytical model of joint loaded perpendicular to wooden grain
Hataj, M.; Pošta, J.; Hasníková, Hana; Kunecký, Jiří
2022 - English
Computing models for structural behaviour and determination of traditional timber butt joints using analytical relations are presented in this paper. A component method is the base of the computing technique introduced herein. This method is usually used for steel joint design. The component method is based on dividing a joint into individual components. These are defined by partial joint component stiffness. An analytical solution includes a subsidence effect of wooden material close to compressive loading. Analytical computation results are compared with the experimental outputs. A design procedure according to Eurocode 5 for a load capacity determination of perpendicularly loaded structural elements is stated in the paper.
Keywords:
analytical models; load capacity; butt joint; carpentry; timber structures
Available at various institutes of the ASCR
Analytical model of joint loaded perpendicular to wooden grain
Computing models for structural behaviour and determination of traditional timber butt joints using analytical relations are presented in this paper. A component method is the base of the computing ...
Wooden construction of the movable roof of the garden pavilion in Český Krumlov castle
Bláha, Jiří; Kloiber, Michal
2022 - English
A remarkable technical monument is situated on one of the garden terraces belonging to the state castle and chateau in Český Krumlov. The umbrella-shaped roof of the lookout pavilion can be lifted about a meter above the masoned parapet allowing the visitor a beautiful view of the World Heritage town panorama when the weather is fine. In windy conditions or in case of heavy rain the roof could be lowered and the pavilion thus closed. The lifting is operated by means of a wooden lever mechanism with a counterweight box hidden in the basement level of the building. The unique construction was built in 1823 and needed to be partially altered in 1830-1835. However, since then it has been preserved in a surprisingly authentic state even allowing practical demonstrations of its original function. Prior to recent repairs in 2016, a comprehensive non-destructive survey was conducted. The extent of the damage discovered was determined by measuring the speed of elastic wave propagation using stress waves (Fakkop 2D) and measuring the mechanical resistance when drilling with a thin bit using resistance micro-drilling (Resistograph). Another method based on loading timber by means of a\nminiature loading jack inserted into a drilled hole was selected to determine the current mechanical properties.
Keywords:
lookout pavilion; gazebo; non-destructive testing; roof; timber; wood
Available at various institutes of the ASCR
Wooden construction of the movable roof of the garden pavilion in Český Krumlov castle
A remarkable technical monument is situated on one of the garden terraces belonging to the state castle and chateau in Český Krumlov. The umbrella-shaped roof of the lookout pavilion can be lifted ...
Stone surface topography of Prague historic monuments over the centuries
Kovářová, K.; Cihla, Michal; Malát, R.; Semerád, M.; Tryml, M.
2022 - English
Stonemasons tool traces on stone surface are undoubtably a significant part of monument historic value. As any other profession, stonemasons craft develops over time and has its own specifics in every period. Each work has its own unique pattern and bears traces of individual stonemason workshops, tradition, etc. The study of building stone cutting is based on evolving methods of mechanoscopy and analytical traceology. Stone traceology deals with traces in material and the subsequent reconstruction of tools and the processes of stoneworking. The interpretation of data in terms of determining the actual trace is called a mechanoscopy. When studying a stone surface, the latest 3D modelling technology is used with subsequent analyses by means of Global Mapper software. The use of these methods enables reconstruction of the craftsman’s tools. The presented article is an extract of a study that systematically maps the stone cutting work in the territory of Prague from the oldest buildings to the present day. For example, stonework in 9th century Prague was gradually evolving from simple stone block modelling to sophisticated cutting of blocks in the 12th century. This information can be very useful in the process of monument care.
Keywords:
stone topography; Prague; craftmanship; stonemason tool; tool traces
Available at various institutes of the ASCR
Stone surface topography of Prague historic monuments over the centuries
Stonemasons tool traces on stone surface are undoubtably a significant part of monument historic value. As any other profession, stonemasons craft develops over time and has its own specifics in every ...
Creep of oak dowel: various loading and environmental conditions
Hasníková, Hana; Kunecký, Jiří; Hataj, M.
2022 - English
For research of timber joints, the crucial role in force distribution inside the joint is played by distribution and variability of stiffness of the dowels. Not only the instant stiffness, but the one that we can encounter after some longer period. Also, this value and its statistical distribution is influenced by many other factors, however, humidity and temperature are in timber (oak) dowels of utmost importance. In the work results of a creep experiment made using a special testing rig is presented. It has been found, that biggest changes in creep behavior are in case if very humid conditions are present, and, also, that cycling the temperature in high humidity conditions can produce about 104% of the original instantaneous displacement. The result is not surprising, however, new insights are made thanks to relatively high number of samples and ability to produce some statistics. Another outcome is relation of dowel stiffness in time to the level of applied stress, which is quantified in the article.
Keywords:
oak dowel; creep; humidity
Available at various institutes of the ASCR
Creep of oak dowel: various loading and environmental conditions
For research of timber joints, the crucial role in force distribution inside the joint is played by distribution and variability of stiffness of the dowels. Not only the instant stiffness, but the one ...
Proceedings of the SHATIS 2022 – 6th International conference on structural health assessment of timber structures
Kunecký, Jiří; Hasníková, Hana
2022 - English
Structural health assessment of timber structures associates various procedures in order to evaluate the safety and serviceability of structures. Also, it helps to assure or extend the predicted service life of structures. Service life sustainability can be promoted by the incorporation of monitoring systems or by providing tools and methods that deliver accurate reports about the structural condition. Conservation and assessment of timber structures is based on a multidisciplinary approach. The conference topics cover the wide spectrum, from wood properties, through performance of joints and timber design, to modern monitoring and digital technologies. As the topics include both existing and historical timber structures, the need for reliable non destructive testing methods is part of the approach as well.
Keywords:
timber structures; monitoring and survey; design
Available at various institutes of the ASCR
Proceedings of the SHATIS 2022 – 6th International conference on structural health assessment of timber structures
Structural health assessment of timber structures associates various procedures in order to evaluate the safety and serviceability of structures. Also, it helps to assure or extend the predicted ...
Comparison of mechanical properties of wood determined by local gently destructive tests and fully destructive tests on building elements
Drdácký, Miloš; Kloiber, Michal; Valluzzi, M. R.; Casarin, F.
2022 - English
Demolition or repair of historic buildings is a valuable source of test materials for testing nondestructive and gently destructive methods for estimating the mechanical properties of built-in wood. The article uses the results of one such opportunity, when it was possible to study the mechanical properties of wood obtained by local measurements on a larger sample of historic and new wooden beams and compare them with the properties calculated from destructive tests of structural elements. Thirty-one wood elements (nineteen recovered from disassembled buildings and twelve new) were subjected to considerately destructive local tests using a loading mini-jack method. In this method, a small loading jack is inserted into a precisely drilled hole and a load test of the wood in compression along the fibers is performed on a part of the hole wall while measuring the achieved deformation under load. Red and white firs, and pine species constituted the recovered elements - red fir and larch the new ones. Destructive tests (in bending and compression) were also carried out on ten recovered and six new elements, and results were correlated with those of considerately destructive tests. Comparison of the assessed mechanical properties shows reasonably good correlation and promising conclusions for practical applications.
Keywords:
considerately destructive tests; mini-jack method; destructive tests; assessment of mechanical characteristics of wood; historic timber
Available at various institutes of the ASCR
Comparison of mechanical properties of wood determined by local gently destructive tests and fully destructive tests on building elements
Demolition or repair of historic buildings is a valuable source of test materials for testing nondestructive and gently destructive methods for estimating the mechanical properties of built-in wood. ...
Stucco decoration of the coffered dome in Boim Chapel, Lviv (Ukraine)
Svorová Pawełkowicz, Sylwia; Myślicka, M.; Witkowski, M.
2022 - English
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.
Keywords:
painted stucco; coffered dome; Mannerism; Boim Chapel (Lviv); Slava Ukraini!
Available at various institutes of the ASCR
Stucco decoration of the coffered dome in Boim Chapel, Lviv (Ukraine)
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 ...
GPR survey of the reinforcement above the long horizontal window case study: Ice ring stadium restaurant Fuchs on Štvanice Island
Válek, Jan; Kozlovcev, Petr; Eisler, Marek; Dušek, Ondřej
2021 - English
The aim of the survey was to assess the use of Ground Penetration Radar for the reinforcement position detection on the Ice ring restaurant – an early concrete building on Štvanice Island in Prague from 1932. For this case study a potentially critical section of a façade above the app. 16 m long horizontal window was selected. GPR from IDS company equipped with 2 GHz high frequency antenna was used.
Keywords:
Fuchs restaurant; GPR; reinforced concrete
Available at various institutes of the ASCR
GPR survey of the reinforcement above the long horizontal window case study: Ice ring stadium restaurant Fuchs on Štvanice Island
The aim of the survey was to assess the use of Ground Penetration Radar for the reinforcement position detection on the Ice ring restaurant – an early concrete building on Štvanice Island in Prague ...
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