Ústav teoretické a aplikované mechaniky

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2018-06-19
19:26
Poruchy skleněných výplní stropu nad studovnou Knihovny AV ČR
Drdácký, Miloš ; Hlobil, Michal
Ve výzkumné zprávě je popsán současný stav poškození skleněných výplní stropu nad studovnou Knihovny AV ČR. Prasklé skleněné tabule jsou zdokumentovány a je navrženo opatření, které by mělo jejich budoucí porušení minimalizovat.

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2018-06-19
19:26
Metodika měření poklesu rychlosti letících projektilů při průniku různými hmotami pomocí digitálního optomechanického zařízení
Šperl, Martin ; Gajdoš, Lubomír ; Wolf, Benjamin
Metodika popisuje postupy, použitá zařízení a software potřebná k měření průběhu poklesu rychlosti letících projektilů skrz různé sypké i pevné hmoty. Výhoda a unikátnost této metodiky spočívá v schopnosti měření útlumových charakteristik různých materiálů při impaktu projektilem o vysoké rychlosti. Metodika je založena na systému tenkých desek s optickým vláknem, které fungují při průletu střely jako světelné časové brány s definovanou vzájemnou roztečí.

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2018-05-28
15:54
Lávka pro pěší Radotín - zatížení větrem dle EN 1991-1-4 a měření ve větrném tunelu
Göringer, J. ; Hračov, Stanislav ; Macháček, Michael
S ohledem na atypickou konstrukci lávky v Radotíně bylo nutno v rámci statického ověření řešit nestandardní účinky zatížení větrem, kdy EN 1991-1-4 poskytuje pro takto atypické konstrukce jen málo podpory. Zatížení větrem u takovéto konstrukce nevystupuje pouze jako náhradní statický účinek, ale zejména je nutné posoudit případné ztráty aerodynamické stability. Příspěvek předkládá postup stanovení problematiky podle EN 1991-1-4 včetně porovnání s výsledky z větrného tunelu.

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2018-05-28
15:54
Engineering mechanics 2018. Book of full texts
Fischer, Cyril ; Náprstek, Jiří
The proceedings contains papers presented at the 24th International Conference on Engineering Mechanics, which has been held in Svratka resort in Czech Republic under auspices of the Czech Society of Mechanics and being a part of IFTOMM (The International Federation for the Promotion of Mechanism and Machine Science) activities. As it corresponds with character of the conference, this proceedings consists of several topic oriented parts: Biomechanics, Fluid mechanics, Dynamics, Fracture mechanics, Kinematics, Mechatronics, Reliability of structures, Mechanics of solids, Techological processes, Thermodynamics. The volume represents a well-balanced overview of theoretical, numerical and experimental work on fundamental and applied studies.

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2018-05-28
15:54

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2018-05-28
15:54
Proposal for loading tests of bridges - simulation and laboratory experiments
Bayer, Jan ; Urushadze, Shota ; Černý, Miloš
A new dynamic load testing of bridges is proposed and theoretically investigated. A transient analysis of passing vehicle over a bridge in ANSYS and an analytical program in MATLAB for the transient solution of piecewise linear mechanical structures were developed to assess the effects of the proposed dynamic load on a bridge model. According to the first laboratory experiments, it seems that the proposed travelling impulse load could surpass some of the shortcomings and limitations of the currently applied methods of bridge testing. The investigation is a part of a project aimed at drive-by identification of dynamic properties of bridges and further experimental and analytical research will follow.

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2018-05-28
15:54
Accuracy and numerical efficiency of approximate method for complex eigensolution of structure with specialized damping device
Hračov, Stanislav
The paper provides a detailed parametric analysis of the recently proposed approximate method for complex eigensolution of non-classically damped structures. This method is based on a combination of perturbation and incremental approaches and is applicable to the classically damped structures equipped with a specialized passive damping device. The numerical efficiency in terms of the required calculation times and the accuracy is demonstrated on a model of an existing structure for various combination of computational parameters. Wide numerical simulations revealed the selection of real eigenmodes of undamped system used in the approximate eigensolution as the most important parameter affecting the final accuracy.

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2018-05-28
15:54
Crystallization force of sodium chloride
Koudelková, Veronika ; Wolf, Benjamin
Soluble salts are one of the most deteriorating factor causing damage of historical building materials due to generation of crystallization pressure inside pore space. Direct measurement of crystallization force is quite challenging, hence we developed at our institute a novel device able to detect the force of growing crystal. The device is based on the monitoring of force developed with upper microscopic glass on the growing crystal to maintain constant position. The crystal could generate force because of the existence of thin liquid layer of solution between both surfaces come into contact. The driving force for the subsequent growth of crystal against obstacle is supersaturation, which is mainly induced by evaporation of the salt solution. In this experiment, the crystal of sodium chloride generated force 16.8 mN and the corresponding crystallization pressure was equal to the value 0.48 MPa.

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2018-05-28
15:54
Forced movement of a ball in spherical cavity under kinematic excitation
Náprstek, Jiří ; Fischer, Cyril
In the paper the response of a heavy ball rolling inside a semi-spherical cavity under horizontal kinematic excitation is investigated. The system with six degrees of freedom with three non-holonomic constraints is considered. The contact between the ball and the cavity surface is supposed to be perfect without any sliding. The mathematical model using the Appel-Gibbs function of acceleration energy is developed and discussed. The most important post-critical regimes are outlined and qualitatively evaluated on the frequency axis. Numerical experiments have been performed when excitation frequency is slowly swept up and down. Results obtained by means of semi-analytical investigation and numerical simulation are evaluated and physically interpreted. Some applications in civil engineering as a tuned mass damper used on slender structures is outlined. Strengths and weaknesses of solution method are evaluated.

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2018-03-26
17:54
Asymmetry of the response probability density of a system with parametric random noises
Náprstek, Jiří ; Fischer, Cyril
Recording of time variable processes is accompanied by various internal disturbing effects as a rule. They influence parameters of the measuring facility, transducer-device transmission, etc. These parasitic processes are usually of the random character and, consequently, they exercise as parametric noises. Moreover, the input signal mostly consists of a useful signal which can be taken as composed from deterministic and random additive part. Various combinations of these noises are the origin of random and also systematic measuring errors which can have under certain circumstances a cumulative character, deteriorate the output signal quality and can lead finally to the stochastic stability loss. These effects can be theoretically described using differential systems with stochastic coefficients and stochastic right hand side considering all input and output processes to be of the Markov type.

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