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Saltation of sand in vicinity of cylindrical column
Kharlamova, Irina ; Kharlamov, Alexander ; Vlasák, Pavel
The paper presents a model of sand sediment transport in water stre am in vicinity of a high cylindrical col umn. It is assumed that an averaged turbulent flow is horizontally layered in vicinity of the cylinder. In ea ch layer the flow around the cylinder is modelled as a potential flow generated by a vertical dipole line. Flow in viscous sub-layer on the surface of the cylinder is neglected. The presented flow model is approximate; however it is simple for use. Trajectories of saltating particles near the cylinder were calculated. Further investigation of such flow will allow a determination of zones where solid particles will collide with the column. That might be useful for prevention of its damage or destruction
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Motion of multiple cylinders in potential flow of ideal fluid
Kharlamov, Alexander A. ; Filip, Petr
The flow field past multiple arbitrarily moving cylinders is calculated using a generalisation of the conventional images method. The flow is presented by a flow from an infinite set of dipoles. For calculation purposes the infinite series must be, however, truncated. The kinetic energy of fluid is presented as a sum over all modelling dipoles. A rather good convergence of the method is observed. However, if the distances between any cylinders tend to zero, the method fails in zones close to the contact point. Nevertheless, even for the case of touching cylinders the series for the kinetic energy remain convergent. In case of just two cylinders the method projects on the classical method of images. Method is validated by several comparisons with solutions known from the literature.
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Modelling of bed in process of particle saltation in channel
Kharlamova, Irina ; Kharlamov, Alexander A. ; Chára, Zdeněk ; Vlasák, Pavel
For numerical modelling particle saltation in channel with rough bed is important to define a bed configuration. The paper deals with the bed consisting of spherical particles of the different size then the saltating particle. In horizontal x-z plane the particles are arranged hexagonally. In vertical direction the particles are distributed according to Gaussian distribution. Before each collision of the saltating particle with bed the bed is shifted on a random distance and it is rotated by a random angle, so there is uniform probability to find a bed particle in any point of the x-z plane. The bed structure is chosen with aim to represent the natural bed as much as possible, thus the known information about distribution of the bed particles along y-direction is used and the location of bed particles in the x-z plane is controlled by principles of equal probability and minimal dense packing.
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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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A note to the measurement of extensional viscosity using SER Universal Testing Platform with different shapes of polymer samples
Švrčinová, Petra ; Filip, Petr ; Kharlamov, Alexander
For polymer melts, with respect to their numerical simulations, there were recommended to apply polymer samples (rectangles) with a width not exceeding 8 mm and a thickness less than 0.4 mm. The aim of this contribution is to document - for material used (LDPE Escorene, Exxon, USA) - the invariantness of the elongational viscosity measured with respect to sample dimensions including its width and thickness. The width of the samples used consecutively attained 12.7, 11.0, 9.3, and 7.4 mm; the thickness also ranged across a sufficiently broad interval (0.3-1.1mm). Temperature was set to 180, 190, and 200oC. For the measurements there were used the SER Universal Testing Platform from the Xpansion Instruments; the model SER-HV-P01 was applied with a Physica MCR501 rotational rheometer host system. The results obtained justify usage of a 'classical' width 12.7 mm (1/2") more suitable for better manipulation with a sample, especially its fixing to both drums perpendicularly to the clamps.
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Polyvinyl chloride filled with bismuth oxychloride powder
Polášková, M. ; Sedláček, T. ; Kharlamov, Alexander ; Pivokonský, Radek ; Saha, P.
Mixing of polymers with radiopaque agents enables the polymers visibility on X-ray images and represents the easiest way to accurately locate the polymeric surgical device during a critical procedure. Medical-grade polyvinyl chloride was compounded with various amounts of bismuth oxychloride, chosen for its unique properties such as high radiopacity, non-toxicity, excellent chemical and physical stability and good dispersibility in the polymeric matrix. Micro-compounder Haake MiniLab II, consisting of a conical co-rotating twin-screw compounder with an integrated backflow channel, was used for melt mixing and simultaneously for rheological measurement. Rheological data received from micro-compounder were supplemented and correlated with the data obtained from Anton Paar rotational rheometer. Structure of prepared composites was studied by scanning electron microscopy, and their thermo-mechanical properties were tested using dynamic mechanical analysis.
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A note to the tube theory
Kharlamov, Alexander ; Filip, Petr ; Švrčinová, Petra
The classical Doi-Edwards (DE) model represents a basic issue for tube theories. The model describes dynamics of polymer strands between entanglements and predicts stress in linear polymers. In this contribution there is considered the dynamics of the whole molecules within the same tube picture. When the molecule end-to-end vector is considered as a Hookean spring the damping function shows weaker thinning. The presented model describes one of the possible mechanisms leading to weaker damping exhibited by branched polymers.
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Experimentální výzkum Magnusovy síly působící na hladkou kouli při vysokých Reynoldsových číslech
Kharlamov, Alexander ; Chára, Zdeněk ; Vlasák, Pavel
Článek popisuje výsledky pokusů s rotující hladkou kulovou částicí při kvazi-stabilním pohybu v klidné vodě. Pohyb částice byl zaznamenán digitální videokamerou a kinematické parametry pohybu částice numericky analyzovány. Bezrozměrný součinitel Magnusovy síly, Reynoldsovo číslo a spin parametr Γ (poměr obvodové rychlosti rotující částice a její translační rychlosti) byly vyhodnoceny z časových řad souřadnic a úhlů rotace částice. Magnusova síla byla určena v závislosti na Reynoldsově čísle a spin parametru pro oblast 3000 < Re < 42000 a 0,1 < Γ <7. Výsledky byly porovnány s literárními údaji a data byly aproximovány jednoduchou funkcí platnou pro oblast 0,5 < Re < 140000 a 0,1 < Γ <10.
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