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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 ...
Solving the moving mass problem on large finite element models with modal analysis – estimation of the discrete movement error
Bayer, Jan
2021 - anglický
Solving transient dynamic problems on large finite element (FE) models using a direct integration requires a high sampling rate and therefore also considerable computing times because of the large system matrices. Movement of a mass on a FE model has to follow the discrete pattern of the FEs, and is therefore of a discrete character. This introduces an unknown\nerror into the analytical results. Applying modal analysis (MA) reduces the number of equations used in the subsequent numerical integration by orders of magnitude. Resampling of the mode shapes to the required sampling rate makes it possible to solve the moving mass problem much more quickly and quasi-continuously. The performed comparative analytical study using ANSYS and MATLAB showed that using a discrete movement on the FE mesh when solving a moving mass problem can cause a considerable error.
Klíčová slova:
moving mass; FE analysis; modal analysis; discret-movement error; ANSYS & MATLAB
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Solving the moving mass problem on large finite element models with modal analysis – estimation of the discrete movement error
Solving transient dynamic problems on large finite element (FE) models using a direct integration requires a high sampling rate and therefore also considerable computing times because of the large ...
Description of the quasi-periodic response caused by combined harmonic and random excitation
Náprstek, Jiří; Fischer, Cyril
2021 - anglický
The generalized van der Pol equation exposed to combined harmonic and random excitation can exhibit a quasi-periodic response. The existence of this particular type of response depends on the detuning between the driving and resonance frequencies. The response is stationary for a ”small” or ”large” value of detuning. The contribution specifies in detail the detuning interval in which the quasi-periodic response occurs.
Klíčová slova:
van der Pol equation; resonance; vibrations
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Description of the quasi-periodic response caused by combined harmonic and random excitation
The generalized van der Pol equation exposed to combined harmonic and random excitation can exhibit a quasi-periodic response. The existence of this particular type of response depends on the detuning ...
Numerical study of the air flow around the U-profile
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2021 - anglický
Our contribution deals with the numerical simulations of the air flow around u-profiles at various angles of attack with the aim to investigate their proneness to galloping. The Unsteady Reynolds Averaged Navier- Stokes (RANS) simulations were performed in the COMSOL Multiphysics software, k-ω SST turbulence model was used. The values of the aerodynamic coefficients and Strouhal number were evaluated and the results were compared with the results obtained experimentally in the wind tunnel.
Klíčová slova:
bluff-body aerodynamics; URANS simulation; transversal galloping
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Numerical study of the air flow around the U-profile
Our contribution deals with the numerical simulations of the air flow around u-profiles at various angles of attack with the aim to investigate their proneness to galloping. The Unsteady Reynolds ...
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 ...
Numerical solution of a stochastic model of a ball-type vibration absorber
Fischer, Cyril; Náprstek, Jiří
2021 - anglický
The mathematical model of a ball-type vibration absorber represents a non-linear differential system which includes non-holonomic constraints. When a random ambient excitation is taken into account, the system has to be treated as a stochastic deferential equation. Depending on the level of simplifcation, an analytical solution is not practicable and numerical solution procedures have to be applied. The contribution presents a simple stochastic analysis of a particular resonance effect which can negatively influence efficiency of the absorber.
Klíčová slova:
stochastic model; Monte Carlo method; stochastic Euler method; dynamical systems; non-holonomic system
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Numerical solution of a stochastic model of a ball-type vibration absorber
The mathematical model of a ball-type vibration absorber represents a non-linear differential system which includes non-holonomic constraints. When a random ambient excitation is taken into account, ...
Aerodynamic wind tunnel testing of U-beams
Hračov, Stanislav; Macháček, Michael
2021 - anglický
The paper presents the outcomes from the experimental testing of the set of slender U-beams in the climatic wind tunnel. All analysed beams have identical basic geometry with the U-shaped cross section given by the side ratio equal to 2 (having the short side perpendicular to the flow), but they differ in the porosity of their flanges and in the depth of their profile. Two depths of the U-profile combined with six different levels of flange porosity are analysed. The U-beams were tested in the smooth flow in order to determine their aerodynamic coefficients for various angles of wind attack. The influences of the depth and porosity onto these coefficients are studied in detail. Moreover, the susceptibility of each individual case to transversal galloping is assessed based on the classical quasi-steady theory. The comparison with the results from the aerodynamic tests of the prisms with rectangular cross-sections having side rations equal to two, four and six is also given and discussed.
Klíčová slova:
wind tunnel testing; aerodynamic coefficients; galloping
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Aerodynamic wind tunnel testing of U-beams
The paper presents the outcomes from the experimental testing of the set of slender U-beams in the climatic wind tunnel. All analysed beams have identical basic geometry with the U-shaped cross ...
Stability of a bar influenced by small and large imperfections
Náprstek, Jiří; Fischer, Cyril
2020 - anglický
The geometrical and physical imperfections of systems can drastically reduce their critical loading. These imperfections are usually of stochastic character and, therefore, they act as random parametric perturbations of coefficients of corresponding differential equations. In this paper, the imperfections are introduced as multidimensional statistics on the set of a large number of realizations of the same system. As far as the amount of information is small or the imperfections themselves cannot be considered small, the convex analysis is preferable. The paper compares results obtained by both stochastic and convex analyses for hyperprism and demonstrates when each of them is more convenient to be used. Besides of the hyper-prism, the possibilities and properties of other modifications of convex method are considered, especially those based on the definition of imperfection zone marked as a centric hyper-ellipsoid or as an eccentric hyper-ellipsoid. The analytical background was brought up to the level when only a few configurations of imperfections are sufficient to be evaluated numerically. These configurations are obtained by means of the convex analysis as points of extreme critical loading using the Lagrange method of constrained extremes.
Klíčová slova:
convex domain method; system stability; hyper-prism and hyper-ellipsoid domains
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Stability of a bar influenced by small and large imperfections
The geometrical and physical imperfections of systems can drastically reduce their critical loading. These imperfections are usually of stochastic character and, therefore, they act as random ...
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