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Objective time derivative defined as covariant deriative
Fiala, Zdeněk
A geometrically based approach, definining the time derivative as a covariant derivative in an appropriate nonlinear space - the infinite dimensional Riemannian manifold of deformation tensors, will be employed, and, via coordinate approach, the covariant derivative and its corresponding time derivative of an arbotrary tensor field will be explicitly expressed.
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Contact pressure between head and helmet loaded by external forces
Micka, Michal ; Jírová, Jitka
The simple test of the bike helmet loaded by statical forces on the top of the head is simulated using program ANSYS. The standardized model for laboratory tests of helmets is used as the model of the head. The goal of the project is to obtain details about contact forces or stresses between the cranium and the helmets, which will be used for future development of safety helmets or by modelling of a hurt of the head at accident.
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Evaluation of accuracy of steel plate girder initial imperfections measurement carried out by means of fringe projection method
Valach, Jaroslav
The method of fringe projection and its application to investigation of steel plate girders subjected to repeated loading is described in this contribution. The well known fact of decisive role of production-based girders imperfections on the girders period of service emphasizes the need of a reliable measurement method of the imperfections. The optical method described in this paper is based on determination of out-of-plane deviations by means of analysis of geometrical relations in the image of projected fringe pattern on the girder surface. The advantage of the method is its simplicity, scalable sensitivity and absence of any constrains regarding the size of the studied object. The results obtained using the method are compared to that attained by the existing method and their accuracy and time consumption is considered. Finally, applicability of the proposed method in other fields is discussed.
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Experimentální výzkum spolehlivosti těsnění kabelových prostupů v Pražském metru po povodních v létě 2002
Jíra, J. ; Jírová, Jitka ; Bouška, P. ; Vokáč, M.
Confluence of the rivers Berounka and Sázava and outflows from the Vltava dam cascade caused the flow in the lower part of the river Vltava in Prague. The Vltava culminated in Prague on 14 August with a flow of 5160 m3.s-1; this corresponds to a period of recurrence of 500 years. The extension of floods in the Vltava valley in Prague caused penetration of water into underground spaces of the Metro and water flooded 19 of 53 underground stations. Looseness of cable bushings through pressure interfaces and non-closure of some pressure interfaces were the most important cause of spreading of water in underground spaces. After the floods of August 2002 the accredited laboratory CTU in Prague, Klokner Institute designed a methodology of experiments and testing system and performed tests on reliability of cable bushings and on material properties of the U 5000. Results of experiments lead to the recommendation to replace all the existing cable bushing in Prague Metro
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Use of X-ray computed tomography for construction of FE models of bones
Jiroušek, Ondřej ; Jírová, Jitka ; Máca, J.
The article reports on procedures used for development of FE models of bones on basis of data obtained from series of computed tomography (CT) scans. These models include mechanical properties reflecting the bone inhomogeneity through apparent density which can be easily retrieved from the CT scans. Experimental procedures used for evaluation of mechanical properties of cancellous bone using small samples of cylindrical shape were designed in such a way, which allows for determination of the viscoelastic properties of cancellous bone. Both compressive and tensile specimens are tested while for the strain measurement an optical method utilizing CCD camera of high resolution is used. Relationship between the apparent density and mechanical properties of cancellous bone in a power-law form is proposed.
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