Number of found documents: 1301
Published from to

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 in a digital repository NRGL
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

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 ...

Hataj, M.; Pošta, J.; Hasníková, Hana; Kunecký, Jiří
Ústav teoretické a aplikované mechaniky, 2022

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 ...

Bláha, Jiří; Kloiber, Michal
Ústav teoretické a aplikované mechaniky, 2022

Chemická a mikrostrukturní analýza vzorku omítky ze zámku Sychrov – oprava Bretaňské věže
Slížková, Zuzana; Frankeová, Dita; Bauerová, Pavla; Náhunková, Pavla
2022 - Czech
Analyzovaná malta obsahuje 76,5 % hm. křemičitého písku a 23,5 % hm. tvoří vápenné pojivo - jedná se o silně hydraulické vápno. Kamenivo malty je tvořeno v naprosté většině křemenem. Hydraulicitu obsaženého vápenného pojiva dokazuje jednak přítomnost belitických slínků, silně nehomogenní mikrostruktura (typické střídání hutných, Ca nabohacených částí a poréznějších dekalcifikovaných oblastí) a dále přítomnost silikátových složek v různé míře zreagování. Nabízí se domněnka, že použité hydraulické pojivo mohlo být připraveno uměle smícháním vápna s hydraulickou silikátovou přísadou. The analysed mortar contains 76.5% by weight quartz sand and 23.5% wt. the lime binder - it is highly hydraulic lime. The aggregate of the mortar is made up mostly of quartz. The hydraulicity of the contained lime binder is evidenced by the presence of belitic clinkers, a strongly inhomogeneous microstructure (typical alternation of dense, Ca-enriched parts and more porous decalcified areas) and the presence of silicate components in varying degrees of reaction. It is suggested that the hydraulic binder used could have been artificially prepared by mixing lime with a hydraulic silicate additive. Keywords: historic mortar; lime mortar; chemical analysis; SEM-EDS; termal analysis Available at various institutes of the ASCR
Chemická a mikrostrukturní analýza vzorku omítky ze zámku Sychrov – oprava Bretaňské věže

Analyzovaná malta obsahuje 76,5 % hm. křemičitého písku a 23,5 % hm. tvoří vápenné pojivo - jedná se o silně hydraulické vápno. Kamenivo malty je tvořeno v naprosté většině křemenem. Hydraulicitu ...

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

Průzkum terénu a konstrukcí pod podlahou kostela Matky Boží na Starém Městě v Telči
Válek, Jan; Kotková, Kristýna; Kozlovcev, Petr
2022 - Czech
Byl realizován nedestruktivní průzkum stavebních konstrukcí skrytých pod současnou úrovní kostela Matky Boží na Starém Městě v Telči pomocí zemního radaru. Průzkum odhalil výskyt skrytých konstrukcí, které mají vztah k současnému pojetí kostela a jeho stavebního řešení. A non-destructive survey of the building structures hidden under the current level of the Church of the Mother of God in the Old Town of Telč was carried out using ground-penetrating radar. The survey revealed the occurrence of hidden constructions that are related to the current concept of the church and its construction solution. Keywords: ground penetrating radar (GPR); cultural heritage; non-destructive testing Available at various institutes of the ASCR
Průzkum terénu a konstrukcí pod podlahou kostela Matky Boží na Starém Městě v Telči

Byl realizován nedestruktivní průzkum stavebních konstrukcí skrytých pod současnou úrovní kostela Matky Boží na Starém Městě v Telči pomocí zemního radaru. Průzkum odhalil výskyt skrytých konstrukcí, ...

Válek, Jan; Kotková, Kristýna; Kozlovcev, Petr
Ústav teoretické a aplikované mechaniky, 2022

Aerodynamic interference forces acting on two square prisms in a model atmospheric boundary layer
Macháček, Michael; Lo, Y. L.; Máca, J.
2022 - English
The presented experimental analysis focuses on the definition of interference factors for aerodynamic forces acting on two square prisms depending on their relative position. Both prisms used had the same dimensions and a height to width ratio of 6 - this ratio is relatively common in high-rise buildings. The experiment was performed in a wind tunnel with a model atmospheric boundary layer, which represented a dense urban area. The forces acting at the base of one of the buildings were measured, and by moving the other building it was possible to measure 204 mutual configurations, i.e., 204 interference positions. In all positions, the windward facades of the small-area model were placed perpendicular to the direction of the incoming flow. This created a detailed map of the interference effect on a wind-loaded pair of buildings. The results show a significant effect of the relative position of buildings on wind loads. A significant increase in\nload occurred due to the proximity of buildings. Due to the interference effect, wind load fluctuations can increase by up to 28% and average values by up to 36%. Keywords: interference effect; two square prisms; wind tunnel experiments; turbulent boundary layer Available in digital repository of the ASCR
Aerodynamic interference forces acting on two square prisms in a model atmospheric boundary layer

The presented experimental analysis focuses on the definition of interference factors for aerodynamic forces acting on two square prisms depending on their relative position. Both prisms used had the ...

Macháček, Michael; Lo, Y. L.; Máca, J.
Ústav teoretické a aplikované mechaniky, 2022

Tomographic investigation of the sandstone fracture toughness
Vavřík, Daniel; Beneš, Pavel; Fíla, Tomáš; Koudelka_ml., Petr; Kumpová, Ivana; Vavro, Martin
2022 - English
It is well known that the measured values of the fracture toughness of quasi brittle materials are influenced by material heterogeneity, dimensions, boundary conditions, and unequal tension and compression properties. Standard testing methods supposing isotropic material, in contrary the quasi-brittle materials differ from this theoretical expectation, therefore this approach may fail. The authors present Local Fracture Toughness Testing (LFTT) method to overcome this obstacle. LFFT based on a complex methodology using a series of tomographic reconstructions recorded during specimen loading is calculated independently of the outside boundary conditions. Keywords: fracture process zone; crack path; quasi-brittle material; X-Ray computed tomography; four-point bending test Available in digital repository of the ASCR
Tomographic investigation of the sandstone fracture toughness

It is well known that the measured values of the fracture toughness of quasi brittle materials are influenced by material heterogeneity, dimensions, boundary conditions, and unequal tension and ...

Vavřík, Daniel; Beneš, Pavel; Fíla, Tomáš; Koudelka_ml., Petr; Kumpová, Ivana; Vavro, Martin
Ústav teoretické a aplikované mechaniky, 2022

Výběr vzorků malt pro radiouhlíkové datování
Válek, Jan; Kozlovcev, Petr; Fialová, Anna; Kotková, Kristýna; Frankeová, Dita; Skružná, Olga; Maříková-Kubková, Jana; Tomanová, Pavla; Herichová, Iva; Světlík, Ivo; Pachnerová Brabcová, Kateřina; Šimek, Pavel
2022 - Czech
Radiokarbonové datování organických zbytků nemusí vždy správně vypovídat o stáří analyzované historické malty. Proto se zdá výhodné využití možnosti datace uhlíku obsaženého ve struktuře vápenné malty, který při správném zpracování poskytne reprezentativní údaje o době vzniku studované konstrukce. Metodika představuje základní návod pro výběr vzorků, jejich zpracování a vyhodnocení. Cílem metodiky je identifikace případů, kdy je radiouhlíková datace pojiva vhodná a vymezení důvodů proč se u některých pojivových systémů nedaří získat relevantní výsledky. Radiocarbon dating of organic residues may not always correctly determine the age of analysed historic mortars. Therefore, it seems advantageous to use of carbon dating of the carbon contained in the structure of the lime mortar, which will provide representative data of the age of the investigated structure. The methodology presents basic instructions and rules for sample selection, processing, and evaluation. The aim of this methodology is the identification of cases where the radiocarbon dating of a binder is appropriate and to define the reasons why some binder systems fail to provide relevant results. Keywords: historic binders; mortars; radiocarbon Available in a digital repository NRGL
Výběr vzorků malt pro radiouhlíkové datování

Radiokarbonové datování organických zbytků nemusí vždy správně vypovídat o stáří analyzované historické malty. Proto se zdá výhodné využití možnosti datace uhlíku obsaženého ve struktuře vápenné ...

Válek, Jan; Kozlovcev, Petr; Fialová, Anna; Kotková, Kristýna; Frankeová, Dita; Skružná, Olga; Maříková-Kubková, Jana; Tomanová, Pavla; Herichová, Iva; Světlík, Ivo; Pachnerová Brabcová, Kateřina; Šimek, Pavel
Ústav teoretické a aplikované mechaniky, 2022

About project

NRGL provides central access to information on grey literature produced in the Czech Republic in the fields of science, research and education. You can find more information about grey literature and NRGL at service web

Send your suggestions and comments to nusl@techlib.cz

Provider

http://www.techlib.cz

Facebook

Other bases