Ústav teoretické a aplikované mechaniky

Nejnovější přírůstky:
2017-08-02
12:52
Remarks on inverse of matrix polynomials
Fischer, Cyril ; Náprstek, Jiří
Analysis of a non-classically damped engineering structure, which is subjected to an external excitation, leads to the solution of a system of second order ordinary differential equations. Although there exists a large variety of powerful numerical methods to accomplish this task, in some cases it is convenient to formulate the explicit inversion of the respective quadratic\nfundamental system. The presented contribution uses and extends concepts in matrix polynomial theory and proposes an implementation of the inversion problem.

Úplný záznam
2017-06-12
14:36
Formace polymorfů uhličitanu vápenatého během mísení koncentrovaných roztoků solí
Ševčík, Radek ; Mácová, Petra ; Viani, Alberto
Příspěvek se zaobírá předběžnými výsledky studia gelové fáze vznikající během mísení koncentrovaných roztoků solí během syntézy polymorfů uhličitanu vápenatého.\nBěhem reakce bylo odebráno několik vzorků, které byly následně zkoumány instrumentálními technikami jako např. skenovací elektronový mikroskop.

Úplný záznam
2017-06-12
14:36
Materiálový průzkum břidlicové krytiny pro účel památkové obnovy objektu Nové proboštství, nám. sv. Jiří č.p. 34, Pražský Hrad
Drdácký, Miloš ; Slížková, Zuzana ; Frankeová, Dita ; Hasníková, Hana ; Hauková, Petra ; Koudelková, Veronika ; Kozlovcev, Petr ; Valach, Jaroslav ; Wolf, Benjamin
Zpráva obsahuje výsledky studie zaměřené na materiálové vlastnosti historické břidlicové střešní krytiny a posouzení jejího stavu vzhledem k plánované obnově budovy.

Úplný záznam
2017-06-12
14:36
Materiálové průzkumy pro účel památkové obnovy objektu Nové proboštství, nám. sv. Jiří č.p. 34, Pražský Hrad
Drdácký, Miloš ; Slížková, Zuzana ; Frankeová, Dita ; Hasníková, Hana ; Hauková, Petra ; Koudelková, Veronika ; Kozlovcev, Petr ; Ševčík, Radek ; Wolf, Benjamin
Zpráva obsahuje výsledky materiálových analýz vzorků omítek a kamene, odebraných z fasád a vnitřních omítek objektu Nové proboštství (Pražský hrad, nám. sv. Jiří č.p. 34). Předmětem studia bylo chemické složení a mikrostruktura omítek, petrografie pískovce, pórovitost materiálů rtuťovou porozimetrií, povrchová nasákavost omítek, obsah a distribuce vlhkosti ve zdivu, obsah a chemické složení vodorozpustných solí v omítkách. Výsledky analýz jsou podkladem pro budoucí návrh stavební obnovy objektu a postupy restaurování uměleckých prvků.

Úplný záznam
2017-05-25
15:15
Lyapunov exponents – practical computation
Fischer, Cyril ; Náprstek, Jiří
The Lyapunov exponents serve as numerical characteristics of dynamical systems, which measure possible divergence of nearby trajectories of the solution. In this way they express dependence of the dynamical system on initial conditions. However, the value of Lyapunov exponents consists in their ability to characterise deterministic chaos. The limiting process intrinsic in the definition of Lyapunov exponents, unfortunately, seriously complicates their computation. The short paper presents an overview of difficulties in numerical approaches to enumeration of Lyapunov exponents or at least the largest one and shows a promising method based on QR decomposition of the system Jacobian.

Úplný záznam
2017-05-25
15:15
A concept for testing and monitoring of building structures – theoretical case study
Bayer, Jan
A mere comparison of measured and analytical deformations, natural frequencies and mode\nshapes provides us with just a small part of the information contained in the data, especially when component- level damage prevention is needed. The presented analysis studies in detail a few criteria for evaluation of measured data, with the example of simulated plane trusses in respect to the ultimate limit state. It demonstrates the high potential of a systematic approach, while combining several criteria, particularly when using simultaneous strain and deformation measurements, as it documents the proposed Relative Mode Difference (RMD) criterion. On the other hand, the study points out the major limitation of practical applications that is caused by unknown inherent uncertainties of various kinds, providing us with the incentive for further experimental research.

Úplný záznam
2017-05-25
15:15
Non-holonomic planar and spatial model of a ball-type tuned mass damping device
Náprstek, Jiří ; Fischer, Cyril
The area of tuned mass dampers is a wide field of inspiration for theoretical studies in non-linear dynamics and dynamic stability. The studies attempt to estimate behaviour of diverse damping devices and their reliability. The current paper deals with the response of a heavy ball rolling inside a spherical cavity under horizontal kinematic excitation. The non-linear system consists of six degrees of freedom with three non-holonomic constraints. The contact between the ball and the cavity surface is supposed to be perfect without any sliding. The mathematical model using the Appell-Gibbs function of acceleration energy is developed and discussed. Comparison with previous planar (SDOF) model which is based on the Lagrangian procedure is given. The system has an auto-parametric character and therefore semi-trivial solutions and their dynamic stability can be analysed. The most important post-critical regimes are outlined and qualitatively evaluated in resonance domain. Numerical experiments were performed when excitation frequency is slowly swept up and down to identify different modes of response. Some applications in civil engineering as a tuned mass damper, which can be used on slender structures, are mentioned. The proposed device is compared with a conventional pendulum damper. Strengths and weaknesses of both absorbers types\nare discussed.

Úplný záznam
2017-03-27
15:27
Acta Polytechnica CTU Proceedings 7
Kytýř, Daniel ; Zlámal, Petr
The International Symposium on Experimental Methods and Numerical Simulation in Engineering Sciences continues the tradition of the Czech-German bilateral symposium founded by prof. Karl-Hans Laermann and prof. Stanislav Holý in 1985. In the following years, the symposium was extensively developed by prof. Josef Jíra. The symposium shall bring together mainly young scientists who are actively involved in experimental solid mechanics, theoretically and practically, in order to exchange experience, to report on the present state-of-art as well as on running research projects, to discuss due questions and problems and to promote the co-operation between individuals as well as between institutions. Therefore in the symposium discussions will play a highly significant role.

Úplný záznam
2017-03-27
15:27
Semi-automated assessment of micromechanical properties of the metal foams on the cell-wall level
Krčmářová, Nela ; Šleichrt, J. ; Doktor, T. ; Kytýř, Daniel ; Jiroušek, O.
Metal foams are innovative porous material used for wide range of application such as\ndeformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict mechanical properties of the metal foam is necessary to precisely describe elasto–plastic properties of the foam on cell–wall level. Indentation with low load is suitable tool for this purpose.\nIn this paper custom designed instrumented microindentation device was used for measurement of cell-wall characteristics of two different aluminium foams (ALPORAS and ALCORAS). To demonstrate the possibility of automated statistical estimation of measured characteristics the device had been enhanced by semi-automatic indent positioning and evaluation procedures based on user-defined grid. Vickers hardness was measured on two samples made from ALPORAS aluminium foam and one sample from ALCORAS aluminium foam. Average Vickers hardness of ALPORAS foam was 24.465 HV1.019 and average Vickers hardness of ALCORAS was 36.585 HV1.019.

Úplný záznam
2017-03-27
15:27
Deformation behaviour of gellan gum based artificial bone structures under simulated physiological conditions
Krčmářová, N. ; Šleichrt, J. ; Fíla, Tomáš ; Koudelka_ml., Petr ; Kytýř, Daniel
The paper deals with investigation of deformation behaviour of gellan gum (GG) based\nstructures prepared for regenerative medicine purposes. Investigated material was synthesized as porous spongy-like scaffold reinforced by bioactive glass (BAG) nano-particles in different concentrations. Deformation behavior was obtained employing custom designed experimental setup. This device equipped with bioreactor chamber allows to test the delivered samples under simulated physiological conditions with controlled flow and temperature. Cylindrical samples were subjected to uniaxial quasi-static loading in tension and compression. Material properties of plain scaffold buffered by 50 wt% and 70 wt% BAG were derived from a set of tensile and compression tests. The results are represented in form of stress-strain curves calculated from the acquired force and displacement data.

Úplný záznam