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Application of first integrals in the construction of the Lyapunov function for the random response stability testing
Náprstek, Jiří; Fischer, Cyril
2022 - English
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.
Keywords:
stochastic stability; Lyapunov function; first integrals; cyclic coordinates
Available in digital repository of the ASCR
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 - 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 ...
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 ...
Protection of historic buildings against vibrations
Urushadze, Shota; Pirner, Miroš; Bayer, Jan
2022 - Czech
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 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
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
Protection of historic buildings against vibrations
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 ...
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 ...
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 ...
Selection of mortars samples for radiocarbon dating
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
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. 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.
Keywords:
historic binders; mortars; radiocarbon
Available in a digital repository NRGL
Selection of mortars samples for radiocarbon dating
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 ...
Preparation of mortars samples for radiocarbon dating by mechanical separation
Válek, Jan; Kotková, Kristýna; Fialová, Anna; Kozlovcev, Petr; Králová, Karolína; Světlík, Ivo; Pachnerová Brabcová, Kateřina
2022 - Czech
The methodology establishes the procedure for mechanical separation of the binder from the mortars to determine their age using the radiocarbon method. Along with the procedure, there is also a method of verifying the quality of purification using optical microscopy supplemented with cathode luminescence. The methodology is developed on the basis of the current state of knowledge and presents the basic sample preparation procedure in the form of a detailed description of the proven method of mechanical separation of the binder from lime mortar samples together with possible problems and an evaluation of the separation quality. Metodika stanovuje postup mechanické separace pojiva z malt pro stanovení jejich stáři radiouhlíkovou metodou. Spolu s postupem souvisí i způsob ověřování kvality přečištění pomocí optické mikroskopie doplněné o katodovou luminiscenci. Metodika je vypracovaná na základě současného stavu poznání a předkládá základní postup přípravy vzorků v podobě podrobného popisu ověřeného způsobu mechanické separace pojiva ze vzorků vápenných malt spolu s možnými problémy i hodnocením kvality separace.
Keywords:
mortars; lime binder; radiocarbon; AMS dating
Available in a digital repository NRGL
Preparation of mortars samples for radiocarbon dating by mechanical separation
The methodology establishes the procedure for mechanical separation of the binder from the mortars to determine their age using the radiocarbon method. Along with the procedure, there is also a method ...
Analysis of displacement measured during the compressive testing of cylindrical specimens
Frantík, P.; Lisztwan, D.; Kumpová, Ivana; Daněk, P.; Rovnaníková, P.; Keršner, Z.
2022 - Czech
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. 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.
Keywords:
compressive test; cylindrical specimen; concrete
Fulltext is available at external website.
Analysis of displacement measured during the compressive testing of cylindrical specimens
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 ...
Modeling the moving cogwheel load - analysis using ANSYS & Matlab
Bayer, Jan
2022 - English
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.
Keywords:
moving impulse load; modal analysis; finite element models
Available in digital repository of the ASCR
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. ...
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