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Jedno-kamerové měření 3D pohybu částic
Chára, Zdeněk ; Kysela, Bohuš
V příspěvku je analyzována možnost měření 3D pohybu kulovitých částic pomocí jedné kamery a světelného nože. Zatímco pro určení 2D rychlostního pole částic byla použita standardní sledovací technika (Particle-Tracking-Velocimetry), pro měření třetí složky rychlosti kolmé na rovinu objektivu kamery byla použita jednoduchá metoda založená na měření intenzity světla dopadajícího na pohybující se částici.
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Simulation of saltation motion using LBE based methods
Dolanský, Jindřich
The numerical model of the motion of the circular particle close to the bed in an open channel with a rugged bed based on the lattice Boltzmann method (LBM) is presented. The LBM is used as a DNS approach in which hydrodynamic forces are expressed as sum of contributions from fluid elements interacting with the moving particle. The corresponding numerical simulation for the saltation motion which represents a dominant mode of the bed load transport is developed. Flow is driven by the logarithmic velocity profile at the inlet of a two dimensional channel with a bed formed by semi-circles of variable radii in a bed of particles. Translational and rotational movements of the particle are induced by gravitational force on one hand, and by hydrodynamic forces on the other hand. The LBE (lattice Boltzmann equation) based simulation provides the opportunity to study the behavior of saltation motion in the moderate and high Reynolds number regimes. Most of the input parameters, including boundary conditions or flow conditions, are adjustable within a range of values. Stability issues of the simulation are considered and a resolution using a combination of different LBE models and the extension of computational resources is proposed. Finally, an enhancement of the simulation for more complex processes is suggested.
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Oblique collisions of non-rotating spherical particles with a wall
Chára, Zdeněk ; Vlasák, Pavel ; Kysela, Bohuš
In the present paper non-rotating particle-wall collisions were experimentally investigated. By means of the PIV method a velocity field around falling spheres was analyzed. It was shown that the wake behind the particle which approached a bed in non-normal direction was asymmetrical and after the impact the wake passed the particle only along one side. This non-symmetrical velocity field resulted in additional forces which pushed the particle to an opposite direction than was the direction of the particle motion just after the impact.
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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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Numerical model of saltation in open channel with rough bed
Kharlamova, Irina ; Vlasák, Pavel
The present contribution deals with a numerical modelling of a saltation of solid spherical particle in turbulent flow along rough bed in the open channel. The goal of the research is to obtain the dependences of average characteristics of particle saltation motion (as length and height of one particle jump) on flow parameters (which can be characterized e.g. by shear velocity and water depth) and bed roughness. The suggested dependences and calculated results are compared with analogical relationships introduced by other authors in literature.
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Dependence of saltation parameters on bed roughness and bed porosity
Kharlamova, Irina ; Vlasák, Pavel
In numerical models of bed load transport a bed structure of channel could be described by two parameters, a size of bed particles and a standard deviation of normal distribution of bed particles in the vertical direction. The present paper deals with the effect of bed parameters on average length and height of one jump of saltating particle. A new formula was proposed for bed roughness based on size and standard deviation of the normal distribution of the bed particles. The dependences of length and height of the jump on the diameter of the saltating and bed particles were determined for different variation of vertical distribution of the bed particles.
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Motion of rotating spherical particles touching a wall
Chára, Zdeněk ; Vlasák, Pavel ; Keita, Ibrahima
The paper deals with an analysis of motion of rotating spherical particle in calm water, when the particle is in contact with a smooth, horizontal wall. The motion was visualized by a fast digital camera at 1000 frames/second. Based on software analysis the particle trajectories as well as rotational velocities were determined. Values of vertical, horizontal and rotational velocities were used as input parameters for numerical model and the results are compared with experimental data. Experiments were performed with glass particle of diameter 25 mm, initial values of rotational speeds varied from 500 to 3000 revolution per minute.
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Influence of the spheroid prolongation on the drag force
Lukerchenko, Nikolay ; Keita, Ibrahima ; Kvurt, Y. ; Miles, Jiří
The drag force acting on a spheroid moving perpendicularly to its axis of rotation in water was studied experimentally. Along the spheroid axis, which is normal to its axis of rotation, a round narrow hole was bored. The spheroid moved along a thin vertical thread stretched in water. A video system recorded the spheroid motion and the spheroid velocity was determined from the record. The drag force coefficient was calculated from the balance of forces acting on the spheroid. Two oblate, two prolate spheroids and one sphere with ratio of the axes 0.67; 0.81; 1.33; 2 and I (sphere), respectively, with approximately the same volumes, were used. The friction coefficient between the thread and spheroid was determined from the comparison of the experimental and calculated motions of the sphere, for which the drag force coefficient is known. The dependence of the drag force coefficient of the spheroid on the ratio of its semi-axes was obtained.
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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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