Ano (41)
Použitá omezení
(3)
Počet nalezených dokumentů:
41
Publikováno od
do
Innovative device for the simulation of environmental conditions and testing of building materials
Cacciotti, Riccardo; Wolf, Benjamin; Macháček, Michael; Frankl, Jiří
2022 - anglický
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.
Klíčová slova:
building envelope; moisture; building material; wind tunnel; performance
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
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 ...
Application of first integrals in the construction of the Lyapunov function for the random response stability testing
Náprstek, Jiří; Fischer, Cyril
2022 - anglický
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.
Klíčová slova:
stochastic stability; Lyapunov function; first integrals; cyclic coordinates
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
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 ...
Determination of aerodynamic coefficients for air flow around U-profiles with different flange porosities
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2022 - anglický
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.
Klíčová slova:
U-shaped beams; porosity; wind tunnel; RANS simulation; k-ω SST model
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
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 ...
Theoretical analysis of selected trajectories inscribed by a ball freely rolling in a spherical cavity
Náprstek, Jiří; Fischer, Cyril
2022 - anglický
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.
Klíčová slova:
slender structure; vibration absorber; first integral; rolling sphere; structural health monitoring
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
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 ...
Aerodynamic interference forces acting on two square prisms in a model atmospheric boundary layer
Macháček, Michael; Lo, Y. L.; Máca, J.
2022 - anglický
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%.
Klíčová slova:
interference effect; two square prisms; wind tunnel experiments; turbulent boundary layer
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
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 ...
Tomographic investigation of the sandstone fracture toughness
Vavřík, Daniel; Beneš, Pavel; Fíla, Tomáš; Koudelka_ml., Petr; Kumpová, Ivana; Vavro, Martin
2022 - anglický
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.
Klíčová slova:
fracture process zone; crack path; quasi-brittle material; X-Ray computed tomography; four-point bending test
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
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 ...
Analýza měřených posunutí u tlakové zkoušky válcových těles
Frantík, P.; Lisztwan, D.; Kumpová, Ivana; Daněk, P.; Rovnaníková, P.; Keršner, Z.
2022 - český
Příspěvek se zabývá vybranými aspekty analýzy posunutí a deformační tuhosti tlačeného válce. Představen je korekční model, k jehož odladění byly vybrány dva druhy materiálu: beton stávající konstrukce a alkalicky aktivovaný alumosilikát. Korekční model byl kalibrován na ocelovém válci. The paper deals with selected aspects of the analysis of the displacement and deformation stiffness of cylindrical specimens during compressive tests. A developed correction model is presented, and two types of material were selected for the adjustment of the correction model: concrete from an existing structure, and alkali-activated aluminosilicate composite. The correction model was calibrated using the test response of a steel cylinder.
Klíčová slova:
compressive test; cylindrical specimen; concrete
Dokument je dostupný na externích webových stránkách.
Analýza měřených posunutí u tlakové zkoušky válcových těles
Příspěvek se zabývá vybranými aspekty analýzy posunutí a deformační tuhosti tlačeného válce. Představen je korekční model, k jehož odladění byly vybrány dva druhy materiálu: beton stávající konstrukce ...
Modeling the moving cogwheel load - analysis using ANSYS & Matlab
Bayer, Jan
2022 - anglický
A moving impulse load generated by a heavy cogwheel (CW) can be used as a testing excitation for bridges. This previously proposed type of dynamic testing offers theoretically short testing times. Laboratory experiments confirmed already its capability of damage indication by repeated testing. This contribution suggests an approach how to solve the cogwheel movement using a Finite Element (FE) solver and Matlab. As the solution is theoretically nonlinear, the necessary limiting conditions for its application are formulated. Then the analysis is applied to simulate the passage of the CW over a simple laboratory model in order to compare it to laboratory experiments.
Klíčová slova:
moving impulse load; modal analysis; finite element models
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Modeling the moving cogwheel load - analysis using ANSYS & Matlab
A moving impulse load generated by a heavy cogwheel (CW) can be used as a testing excitation for bridges. This previously proposed type of dynamic testing offers theoretically short testing times. ...
Aeroelastic instability of differently porous U-profiles in crosswind direction
Hračov, Stanislav; Macháček, Michael
2022 - anglický
Flow-induced vibrations of the flexibly mounted slender U-shaped beams allowed to oscillate in the crosswind direction only are studied experimentally in the wind tunnel. All beams are characterized by a cross section having a side ratio of along-wind to across-wind dimension equal to two. The effects of two depths of U profiles and two porosities of their flanges ( 0 % and 75 %) onto a loss of aeroelastic stability are investigated under the smooth flow conditions and for low Scruton numbers. The results indicate almost similar proneness of the non-porous beams to galloping-type oscillations to a rectangular prism with the same side ratio regardless their depth. The onset of across-wind galloping occurred in these cases at wind velocity very close to von-Kármán-vortex-resonance flow speed, even though the critical velocity predicted by the quasisteady theory is much lower. For porous and shallower U profile this asynchronous quenching also takes\nplace. However, the higher flange porosity reduces significantly not only the vortex-shedding effect, but also causes an increase in the onset galloping velocity above the critical speed determined for non-porous profiles. In the case of deeper U-shaped beam, the effect of higher porosity even suppresses the proneness to galloping
Klíčová slova:
aeroelastic instability; galloping; vortex shedding; asynchronous quenching; U profile
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Aeroelastic instability of differently porous U-profiles in crosswind direction
Flow-induced vibrations of the flexibly mounted slender U-shaped beams allowed to oscillate in the crosswind direction only are studied experimentally in the wind tunnel. All beams are characterized ...
Zacílená rentgenová tomografie s vysokým rozlišením
Kumpová, Ivana; Vopálenský, Michal
2021 - český
Metoda rentgenové mikro-tomografie je stále více využívána mimo jiné při výzkumu materiálových charakteristik a lomového chování stavebních materiálů. Poskytuje slibné výsledky v oblasti trojrozměrného pozorování a kvantifikace prvků mikrostruktury, včetně objektů lomu. Se standardním přístupem k získávání tomografických dat je však dosažitelné rozlišení výrazně omezeno velikostí zkoumaného objektu, což má za následek omezení nebo dokonce úplnou ztrátu užitečných informací týkajících se například tvaru a velikosti lomové procesní zóny. Z tohoto důvodu byly v této práci testovány možnosti tomografického cílení na zájmovou oblast s vyšším dosažitelným rozlišením, než je obvyklý limit tomografických systémů. The method of X-ray micro-tomography is increasingly used in the research of material characteristics and fracture behavior of building materials. It brings promising results in the field of three-dimensional observation and quantification of microstructure elements, including fracture objects. However, with the standard approach to the tomographic data acquisition, the achievable resolution is severely limited by the size of the examined object resulting in a reduction or even complete loss of useful information regarding, for example, the shape and size of the fracture process zone. For this reason, the possibilities of tomographic targetting of the region of interest with a higher achievable resolution than the usual limit of the tomographic systems have been tested in this work.
Klíčová slova:
X-Ray micro-tomography; spatial resolution; contrast to noise ratio; denoising filtering; 3D volume fitting
Dokument je dostupný na externích webových stránkách.
Zacílená rentgenová tomografie s vysokým rozlišením
Metoda rentgenové mikro-tomografie je stále více využívána mimo jiné při výzkumu materiálových charakteristik a lomového chování stavebních materiálů. Poskytuje slibné výsledky v oblasti ...
NUŠL poskytuje centrální přístup k informacím o šedé literatuře vznikající v ČR v oblastech vědy, výzkumu a vzdělávání. Více informací o šedé literatuře a NUŠL najdete na webu služby.
Vaše náměty a připomínky posílejte na email nusl@techlib.cz
Provozovatel
Zahraniční báze