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Experimental Determination of Human Arm Force/Elbow Joint Angle Relation
Krejsa, Jiří ; Zezula, M. ; Věchet, Stanislav
The achievable force at the end of human forearm depends on the forearm position. The actual value of this force is one of the most important variables affecting the design of the motorized splint, but reliable data are hard to find. Sophisticated measuring device was constructed to determine this force. The force is measured during the movement of the forearm, as such method yields better results than static measurement. The trajectory of movement is enforced by the measuring device, so the influence of the subject on the trajectory is eliminated.
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Processing flow visualisation records by correlation coefficient evaluation in sub-images
Tesař, Václav ; Něnička, Václav
Authors introduced a new method of processing flow visualisation images,aiming at identification of instability structures. In principle, the method utilises the structures' coherence. In two digital images, recorded at slightly differentinstants of time, the pixel pairs from the same position in the images are interrogated one by one. In each, vectors of the recorded quantity values are formed from n x n pixels in immediate neighbourhood, which form the sub-image. The correlation coefficient is then computed for the vector pair. High positive values of the coefficient indicate absence of change whereas values near zero indicate chaotic changes. Of interest are negative values, which indicate a coherent motion.
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To the time heteronymous damping in a non-linear parametric planetary systems
Hortel, Milan ; Škuderová, Alena
The present world development of mobile machines leads to a high-powered high-speed constructions with minimum dimensions and masses. By such light high-speed systems as are for example the speed reducers of turbines onto propellers occur in a discs of the cog wheels the lightening holes, which cause the speed heteronomy in the damping properties of wheel discs and thereby the total damping incidence in gear meshes. This study elaborates the methodology of analysis of the influence of time variable damping in gear mesh of kinematic pairs on the internal dynamics of non-linear parametric systems.
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Effect of dense slurry composition on its flow behaviour in horizontal pipe
Vlasák, Pavel ; Chára, Zdeněk
The paper deals with experimental investigation of the dense fine-grained slurries focused on the slurry pressure drops versus average velocity relationship. The content of fine, especially colloidal solid particles evokes a complex non-Newtonian behaviour of the slurry. Flow behaviour of dense slurry depends on particle size distribution, shape, density and chemical composition of the solid phase as well as on concentration of solids and carrier liquid properties. The re-circulation pipe loop with horizontal hydraulically smooth stainless steel pipes was used for measuring the slurry flow parameters. Different slurries containing kaolin, stony dust or sand conveyed in water were measured to document effect of the size distribution and chemical composition on the slurry flow behaviour.
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On behaviour of PVB solutions in electrospinning
Švrčinová, Petra ; Lubasová, D. ; Filip, Petr ; Martinová, L.
Electrospinning produces nanofibre sheets from polymer solutions under high electric field. Rheological properties of these solutions play a substantial role in a nanofibre formation simultaneously with properties of polymers and solvents applied. This contribution aims at a determination of dependence of shear viscosity of polyvinylbuthyral (PVB) on the intensity of electric field to which PVB solutions are exposed. PVB was dissolved consecutively in a series of solvents as 10% wt. solution. It was found that the viscosity ratio (viscosity of a solution in presence of electric field/viscosity of a solution in absence of electric field) depends on the polarity of solvent. This pre-determines the possibility of application of the individual solvents for the process of electrospinning.
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A note to the simplification in description of some molecular-based polymer models
Kharlamov, Alexander ; Filip, Petr
One type of integral is frequently met in various description of behaviour of polymer materials through molecular-based models starting with the classical Doi-Edwards one. The integrand in this integral for which an integrated region represents a solid angle is formed by a product of a unit vector (pointed at an element of this region) with a deformation gradient tensor. This product is raised to an exponent that is not usually an integer. The aim of this contribution is to derive substantially simplified expression for this integral respecting high accuracy of an approximation.
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Approximation of velocity distribution in open channel flow
Ivanova, Irina ; Vlasák, Pavel ; Chára, Zdeněk ; Kysela, Bohuš
The paper deals with approximation of spatial distribution of mean downstream velocity of sub-critical turbulent flow in an open rectangular channel with rough bed. New formulae of the local downstream velocity component Vx(y, z) dependence on the vertical coordinate y and lateral coordinate z were introduced. The vertical velocity profile was approximated by log-law and the power law was used to describe the effect of channel walls on the horizontal velocity profile. The suggested formulae of spatial downstream velocity component distribution were calibrated and verified using the experimental data obtained by PIV method. The proposed approximation is in good agreement with experimental data, the difference between experimental and calculated data is in range of 5 - 10% except the area near the channel’s corners and water level, where the maximal difference reaches 60% and 30% of experimental values, respectively.
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Choice of polymer samples geometry for measurement of elongational viscosity using ser universal testing platform
Filip, Petr ; Švrčinová, Petra
Generation of purely uniaxial elongational flow of polymer melts is very uneasy problem. It seems that each hitherto developed device for measurement of uniaxial elongational viscosity also produces - to some extent - a planar flow. During the last period there has been questioned - based on this reasoning - the applicability of a SER Universal Testing Platform and was recommended the range of rectangular dimensions of polymer samples for which measurements of uniaxial elongational viscosity is possible to take into account. The aim of this contribution consists in verification of invariantness of uniaxial elongational measurements using the SER Universal Testing Platform with respect to the dimensions of polymer samples applied. There is shown that for sufficiently broad region of admissible widths and thicknesses the results are identical. For these measurements there was used LDPE Escorene (Exxon, U.S.A.).
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