Number of found documents: 309
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Application of nuclear techniques in two-phase liquid-solid particles hydrotransport investigations
Zych, M.; Hanus, R.; Vlasák, Pavel; Petryka, L.; Jaszczur, M.
2015 - English
The paper presents gamma application to two-phase flow investigation in a vertical pipeline, where the flow of solid particles transported by water was examined by use of both: radiotracers and famma-absorption method. The simultaneous use of two methods allows analyzing of important parameters of solid particles hydrotransport. In the described experiments as solid phase the ceramic models representing natural polymetallic ocean nodules were used. Radiotracers allow to track the movements of selected models, representing specified grain size and the designation of its velocity. However gamma-absorption method enables measurement of average solid-phase velocity. For analysis of electrical signal obtained from scintillation detectors the cross-correlation method has been applied. Available on request at various institutes of the ASCR
Application of nuclear techniques in two-phase liquid-solid particles hydrotransport investigations

The paper presents gamma application to two-phase flow investigation in a vertical pipeline, where the flow of solid particles transported by water was examined by use of both: radiotracers and ...

Zych, M.; Hanus, R.; Vlasák, Pavel; Petryka, L.; Jaszczur, M.
Ústav pro hydrodynamiku, 2015

Simulation of saltation motion using LBE based methods
Dolanský, Jindřich
2014 - English
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. Keywords: saltation; particle motion; particle-bed collisions; particle-particle collisions; lattice Boltzmann method (LBM); implementation of LBM model; stability of LBM model; parallelization of LBM model Available on request at various institutes of the ASCR
Simulation of saltation motion using LBE based methods

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 ...

Dolanský, Jindřich
Ústav pro hydrodynamiku, 2014

Experimental investigation of coarse particle conveying in pipes
Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří; Krupička, Jan
2014 - English
The advanced knowledge of particle-water mixture flow behaviour is important for safe, reliable, and economical design and operation of the freight pipelines. The effect of the mixture velocity and concentration on the coarse particle – water mixtures flow behaviour was experimentally investigated on an experimental pipe loop of inner diameter D = 100 mm with horizontal, vertical, and inclined pipe sections. Narrow particle size distribution basalt pebbles were used as model of coarse-grained solid particles. The radiometric method was used to measure particle concentration distribution in pipe cross-section. Mixture flow behaviour and particles motion along the pipe invert were studied in a pipe viewing section. The study revealed that the coarse particlewater mixtures in the horizontal and inclined pipe sections were significantly stratified. The particles moved principally in a layer close to the pipe invert. However, for higher and moderate flow velocities the particles moved also in the central part of the pipe cross-section, and particle saltation was found to be dominant mode of particle conveying. Keywords: transport pipelines; Coulomb friction; coarse-grained mixtures; coarse particle Available on request at various institutes of the ASCR
Experimental investigation of coarse particle conveying in pipes

The advanced knowledge of particle-water mixture flow behaviour is important for safe, reliable, and economical design and operation of the freight pipelines. The effect of the mixture velocity and ...

Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří; Krupička, Jan
Ústav pro hydrodynamiku, 2014

Rainfall interception in a mature spruce forest – a case study
Černý, T.; Dohnal, M.; Tesař, Miroslav; Votrubová, J.
2014 - English
During rainfall events, an appreciable part of the precipitation is intercepted by the vegetation surfaces. This part of rainfall, usually called interception capacity of the surface, is subsequently evaporated back to the atmosphere. Currently available distributed hydrological models require detailed knowledge of all components of hydrological cycle, including the interception and key parameters affecting its amount and rate of evaporation. In the present study the interception of the spruce forest canopy at an experimental catchment in the Bohemian Forest is examined. Keywords: interception loss; saturated interception capacity; free throughfall; evaporation; hydrological balance of vegetation cover Available on request at various institutes of the ASCR
Rainfall interception in a mature spruce forest – a case study

During rainfall events, an appreciable part of the precipitation is intercepted by the vegetation surfaces. This part of rainfall, usually called interception capacity of the surface, is subsequently ...

Černý, T.; Dohnal, M.; Tesař, Miroslav; Votrubová, J.
Ústav pro hydrodynamiku, 2014

Concentration distribution of coarse-grained particle-water mixture in horizontal pipe
Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří; Krupička, Jan
2014 - English
The paper describes the results of coarse-grained particle-water mixture measurements in an experimental pipeline loop of inner diameter 100 mm. Graded basalt pebbles of mean diameter 11 mm, conveyed by water, were investigated. The concentration distribution measurements were carried out with application of gamma-ray based device. Presented results refer to the effect of mixture velocity and overall concentration on chord-averaged concentration and local concentration distribution in the horizontal pipe. The study revealed that the coarse-grained particle-water mixtures were significantly stratified, solid particles moved principally close to the pipe invert, for higher and moderate flow velocities saltation becomes dominant mode of the sediment transport. Keywords: particle-water mixture; horizontal conveying; coarse-grained slurry; gamma-ray radiometry; concentration distribution Available on request at various institutes of the ASCR
Concentration distribution of coarse-grained particle-water mixture in horizontal pipe

The paper describes the results of coarse-grained particle-water mixture measurements in an experimental pipeline loop of inner diameter 100 mm. Graded basalt pebbles of mean diameter 11 mm, conveyed ...

Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří; Krupička, Jan
Ústav pro hydrodynamiku, 2014

Some results of theoretical and experimental studies on slurry flows of coarse solid materials in vertical pipelines
Berman, V.; Kril, S.; Vlasák, Pavel
2014 - English
The paper presents the results of theoretical and experimental investigations of the pressure gradient for flow of a mixture of large solids particles and water in straight vertical pipelines. The mathematical model of vertical two-phase flow was developed. Based on the developed model and experimental data of the solid particles liquid and liquid relative velocity, the functional dependence of the pressure gradient on the corresponding parameters was derived. This method was generalized for hydraulic transport of a broad category of solid particles conveyed in water as a function of the average size and concentration. Comparisons of our computations with experimental data for the corresponding pressure gradients are also presented. Keywords: two-phase flow; vertical pipeline; hydraulic gradient; slip velocity Available on request at various institutes of the ASCR
Some results of theoretical and experimental studies on slurry flows of coarse solid materials in vertical pipelines

The paper presents the results of theoretical and experimental investigations of the pressure gradient for flow of a mixture of large solids particles and water in straight vertical pipelines. The ...

Berman, V.; Kril, S.; Vlasák, Pavel
Ústav pro hydrodynamiku, 2014

Flow of coarse-grained particles-water mixture in pipes
Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří; Krupička, Jan
2014 - English
The advanced knowledge of coarse-grained slurry flow behavior is important for safe, reliable, and economical design and operation of the pipeline transport. The effect of the mixture velocity, solid concentration, and pipe inclination on the coarse-grained particle – water mixtures flow behavior and pressure drop in the turbulent flow regime was experimentally studied in horizontal, vertical, and inclined pipe of inner diameter D = 100 mm. The respective experimental methods, including radiometric methods for particle concentration distribution in pipe cross-section, were used. Graded basalt gravel was used as a model of solid particles. Concentration distribution in the pipe cross-section and motion of particles along the horizontal pipe invert were also studied. The study revealed that the coarse-grained particle-water mixtures in the horizontal and inclined pipes were significantly stratified. The particles moved principally in a layer close to the pipe invert. However, for higher and moderate flow velocities particle saltation becomes dominant mode of particle conveying and particles moved also in the central and upper part of the pipe cross-section. Keywords: heterogeneous slurry; hydraulic conveying; concentration distribution; pressure drop; pipe inclination Available on request at various institutes of the ASCR
Flow of coarse-grained particles-water mixture in pipes

The advanced knowledge of coarse-grained slurry flow behavior is important for safe, reliable, and economical design and operation of the pipeline transport. The effect of the mixture velocity, solid ...

Vlasák, Pavel; Chára, Zdeněk; Konfršt, Jiří; Krupička, Jan
Ústav pro hydrodynamiku, 2014

Simulation of particle motion in a closed conduit validated against experimental data
Dolanský, Jindřich
2014 - English
Motion of a number of spherical particles in a closed conduit is examined by means of both simulation and experiment. The bed of the conduit is covered by stationary spherical particles of the size of the moving particles. The flow is driven by experimentally measured velocity profiles which are inputs of the simulation. Altering input velocity profiles generates various trajectory patterns. The lattice Boltzmann method (LBM) based simulation is developed to study mutual interactions of the flow and the particles. The simulation enables to model both the particle motion and the fluid flow. The entropic LBM is employed to deal with the flow characterized by the high Reynolds number. The entropic modification of the LBM along with the enhanced refinement of the lattice grid yield an increase in demands on computational resources. Due to the inherently parallel nature of the LBM it can be handled by employing the Parallel Computing Toolbox (MATLAB) and other transformations enabling usage of the CUDA GPU computing technology. The trajectories of the particles determined within the LBM simulation are validated against data gained from the experiments. The compatibility of the simulation results with the outputs of experimental measurements is evaluated. The accuracy of the applied approach is assessed and stability and efficiency of the simulation is also considered. Keywords: particle motion; lattice Boltzmann method (LBM); simulations Available on request at various institutes of the ASCR
Simulation of particle motion in a closed conduit validated against experimental data

Motion of a number of spherical particles in a closed conduit is examined by means of both simulation and experiment. The bed of the conduit is covered by stationary spherical particles of the size ...

Dolanský, Jindřich
Ústav pro hydrodynamiku, 2014

Kernel density estimates used in stochastic precipitation generator
Hnilica, Jan; Puš, V.
2014 - English
The kernel density estimates were tested to be suitable to describe the probability distribution of daily precipitation sums. For this purpose, a stochastic precipitation generator using the kernel density estimates was constructed and it was compared with the LARS-WG generator. The data from meteorological stations from the Cidlina river basin were used to evaluate the performances of the generators. It was found that the kernel density estimates capture the probability density better than histograms used in LARS-WG. Keywords: kernel density estimate; daily precipitation sum; stochastic generator Available on request at various institutes of the ASCR
Kernel density estimates used in stochastic precipitation generator

The kernel density estimates were tested to be suitable to describe the probability distribution of daily precipitation sums. For this purpose, a stochastic precipitation generator using the kernel ...

Hnilica, Jan; Puš, V.
Ústav pro hydrodynamiku, 2014

Seasonal snow accumulation in the mid-latitude forested catchment
Šípek, Václav; Tesař, Miroslav
2014 - English
The article deals with the snow cover characteristics (snow depth – SD and snow water equivalent - SWE) concerning the mid-latitude forested catchment. Namely, the influence of forest canopy (spruce and beech forest) and altitude (ranging from 835 m a.s.l. to 1118 m a.s.l.) was investigated. Forest cover was proved to have a significant influence on the snow cover accumulation, reducing the SWE by 48 % on average, compared to open sites. The elevation gradient concerning SWE ranged from 30 to 40 mm and from 5 to 20 mm per 100 m in open and forested sites, respectively. Its magnitude was found to be temporarily variable and positively related to total seasonal snowfall amount. The differences among interception losses, concerning various elevations and forest canopy, were not statistically significant. Keywords: snow depth,; snow water equivalent; forested catchment Available on request at various institutes of the ASCR
Seasonal snow accumulation in the mid-latitude forested catchment

The article deals with the snow cover characteristics (snow depth – SD and snow water equivalent - SWE) concerning the mid-latitude forested catchment. Namely, the influence of forest canopy (spruce ...

Šípek, Václav; Tesař, Miroslav
Ústav pro hydrodynamiku, 2014

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