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Vliv drsnosti povrchu a vnější turbulence na turbulentní mezní vrstvu
Jonáš, Pavel ; Mazur, Oton ; Uruba, Václav
The individual and joint effects of surface roughness and external flow turbulence on turbulent boundary layer were experimentally investigated in the closed circuit wind tunnel IT AS CR. Fundamental mean flow characteristics were measured in turbulent boundary layers either on a smooth plate or on the plate covered with the sandpaper (80- grits) under turbulent flow with the intensity of almost isotropic fluctuations from the natural value, of about 0.003 up to 0.05 and with the relevant length parameter from 2.2 mm up to 30.5 mm .
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Loading processes with various spectral properties for fatigue tests
Balda, Miroslav
The paper describes mothods used for generating of Gaussian proceses with prescribed spectral densities and their implementation on electro-hydraulic testing machines for combined loading. Tube speciments were loaded by random forces and in torgue by diferent proceses. Since the machine does not interpret input proceses precisely, the actual proceses were measured, iterated and procesed into a complex damaging stres and its spectral properties.
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Influence of spectral properties of combined random loading on fatigue life
Svoboda, Jaroslav ; Balda, Miroslav
The contribution deals with an influence of power spectral densities of random loading processes on fatigue lives of structures. Experimental results of uniaxial loading are presented. A philosophy of multiaxial tests, which will be carried out in the new grant project, is also discussed. It is expected that a new numerical method for prediction of fatigue lives of structures loaded by random processes with known spectral densities will be developed.
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Určení objemového průtoku vazkoplastických kapalin mezikružím za pomoci aditivní metody
Filip, Petr ; David, Jiří
An additive method enabling a direct determination of axial flow rate for viscous (power-law model) and viscoplastic (Vočadlo model) fluids in concentric annuli is presented. Flow rate through the actual concentric annulus is possible to express as a sum of axial flow rates through individual partial concentric annuli forming the whole annulus. The resulting relation for axial flow rate is possible to express in analytical forms without necessity of otherwise complicated derivations. The only numerical calculation consists in a determination of location of a zero shear stress for the original whole concentric annulus.
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Poznámka k reptační teorii
Kharlamov, Alexander ; Filip, Petr ; Švrčinová, Petra
Avoiding the Independent Alignment (IA) approximation in the classical Doi-Edwards model causes the computation extremely time and hardware consuming. Nevertheless some flow situations cannot be modelled with the IA approximation. This contribution presents a probabilistic approach not taking into account the IA approximation.
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Měření elongační viskozity PE materiálů
Švrčinová, Petra ; Kharlamov, Alexander ; Filip, Petr
This contribution aims at the measurements of elongation viscosity for polyethylene materials. The approach is analysed from the viewpoint of possible degradation of materials tested and the emphasis is paid to admissible acceleration of the whole measuring process. There is presented a hint how to simplify (and accelerate) the measurements for a suitable class of materials.
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Numerické modelování ochranných sportovních přileb
Kunecký, Jiří ; Jíra, J.
The paper describes development of advanced methods used in research of protective devices. Explicit FE analysis is used for modeling of drop tests. Drop tests are one of common testing procedures used in the standards and are intended for testing of device's protective properties. If we were able to assess the acceleration history from numerical analysis with given geometry and material properties, we can also perform optimization procedure and design optimal protective helmet.
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