2023-11-12
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2023-11-12
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Consistency of mathematical and experimental model of the autoparametric system
Fischer, Cyril ; Náprstek, Jiří
This paper presents a long-overdue comparison of data obtained from experimental investigation of a spherical vibration absorber with the results of two mathematical models of the motion of a heavy sphere in a spherical surface. It shows that the danger posed by the potentially unstable self-parametric nature of the mathematical system is not too great in the case of realistic configurations, and that the values of the parameters describing the realistic structures remain within intervals corresponding to the stable behaviour of the absorber.
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2023-11-12
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Analysis suggestion for vehicle scanning method
Bayer, Jan
An analytical approach is suggested that can be conveniently applied in the framework of the Vehicle scanning method (VSM). It assumes that the modal parameters of a bridge will be imported from a finite element (FE) program into MATLAB, where the structural response caused by a moving mass and a moving spring mass is solved using coupling equations and numerical integration. A mathematical formulation of the solution is presented together with a short numerical case study that compares the results to a traditional closed form solution. It is shown that when comparing both forms of analysis the suggested approach is more accurate in the case of slow velocities of the passing sprung mass. Other advantages are that the method allows for the mass of the vehicle or (tractor) towing vehicle and a damping \nto be included in the calculation. The user-friendly preprocessing in commercial FE programs can also be considered an advantage.
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2023-11-12
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Mechanické zkoušky skelného laminátu: Vlákno - 3B the fibreglass company, N-4760 BIRKELAND, Norway, SE 2020 1200TEX, CoA 7841810_000010 od 15.6.23, Pryskyřice - Spolek pro chemickou a hutní výrobu a.s., CHS-EPODUR 532- 0542,CoA CA12210056,57 od 11.4.23
Šperl, Martin ; Vála, Ondřej ; Bejdl, Jan ; Frankeová, Dita
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2023-11-12
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Analyzing stochastic stability of a gyroscope through the stochastic Lyapunov function
Náprstek, Jiří ; Fischer, Cyril
The text delves into the application of first integrals in the construction of Lyapunov functions for analyzing the stability of dynamic systems in stochastic domains. It emphasizes the distinct characteristics of first integrals that warrant the introduction of additional constraints to ensure the essential properties required for a Lyapunov function. These constraints possess physical interpretations associated with system stability. The general approach to testing stochastic stability is illustrated using the example of a 3-degrees-of-freedom system representing a gyroscope.
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2023-11-12
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Adaptation of methods for cyclo-stationary processes for noisy structural health data
Fischer, Cyril ; Bayer, Jan ; Náprstek, Jiří ; Urushadze, Shota
In structural health analysis, various techniques, including indirect measurement via monitoring vehicles, often yield data with significant randomness and insufficient frequency separation. Conversely, the desired attributes under scrutiny are periodic in nature. Thus, methodologies designed to identify cyclo-stationary properties within noisy data can be adapted for such scenarios, assuming an adequate length of the recorded data.
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2023-11-12
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2023-11-12
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2023-11-12
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2023-10-29
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Studie zasolení stavebních konstrukcí pod III. nádvořím na Pražském hradě
Slížková, Zuzana ; Náhunková, Pavla
V roce 2022 bylo doplněno mapování chemického složení a množství výkvětů solí na archeologických stavebních konstrukcích pod Pražským hradem o dvě nové lokality (v místě základů kaple zv. sv. Bartoloměje a v okolí obvodové severní zdi zóny III). Ve výsledcích nebyly detekovány uhličitanové minerály jako v minulých letech (kromě kalcitu v malém množství). Ve výkvětech byl opět majoritní složkou síran sodný. Pomocí termické analýzy byla potvrzena přítomnost síranu sodného s navázanou krystalovou vodou v jeho struktuře (mirabilit) ve vzorcích odebraných v únoru. Z výluhů stavebního materiálů je patrná vysoká kontaminace opuky dusičnany a chloridy v dnešní koruně zdiva kaple tz. sv. Bartoloměje a zvýšená kontaminace sírany v soklové partii. Naopak v maltě a ani černých cihlách obvodové zdi nebyly zjištěny rizikové hodnoty vodorozpustných iontů.
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