Number of found documents: 550
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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

Vyhodnocení monitoringu vodního režimu půdy v lokalitě Roklan
Čejková, E.; Sněhota, M.; Tesař, Miroslav; Dohnal, M.
2014 - Czech
Příspěvek se zabývá sledováním režimu půdní vlhkosti v horské lokalitě Roklan, která se nachází v první zóně Národního parku Šumava. Smrková monokultura v této lokalitě byla v minulých letech napadena kůrovcem a poté ponechána přirozené regeneraci. Od listopadu 2011 až dosud zde probíhá měření hydropedologických a meteorologických veličin. V příspěvku jsou uvedeny základní hydropedologické charakteristiky půdy v lokalitě Roklan, porovnáno stanovení objemové vlhkosti půdy měřené TDR čidly a získané přepočtem z tlakových výšek měřenými tenzometry s využitím v laboratoři měřených retenčních křivek. Dále je provedeno grafické zpracování a diskuze dat objemové vlhkosti a tlakové výšky během dvou vybraných srážkových epizod. Contribution focuses on soil water regime in the mountainous site Roklan, which is located in the first zone of the National Park Sumava. Spruce monoculture forest in the location was devastated by bark beetle and then left to natural regeneration. The soil hydrological and meteorological monitoring is performed since 2011. Presented paper reports on soil hydraulic properties of the soil from the site. Then, the TDR water contents data collected in the site are compared with the water content data obtained by calculation from the pressure head data using the known water retention curves. The data for two selected rain episodes are presented in detail and results are discussed. Keywords: retention curve; sandy soil; time domain reflectometry Available on request at various institutes of the ASCR
Vyhodnocení monitoringu vodního režimu půdy v lokalitě Roklan

Příspěvek se zabývá sledováním režimu půdní vlhkosti v horské lokalitě Roklan, která se nachází v první zóně Národního parku Šumava. Smrková monokultura v této lokalitě byla v minulých letech ...

Čejková, E.; Sněhota, M.; Tesař, Miroslav; Dohnal, M.
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

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

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; hustota; odhady 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

Testování parametrizací složek dlouhovlnného záření v podmínkách malého šumavského povodí
Muller, J.; Dohnal, M.; Tesař, Miroslav
2014 - Czech
Dlouhovlnné záření je významnou, zřídkakdy měřenou, částí radiační bilance zemského povrchu. Dopadající a vyzářené dlouhovlnné záření jsou často odhadovány z empirických vztahů s řadou kalibračních koeficientů. Při testování dostupných parametrizací složek dlouhovlnného záření v podmínkách malého horského povodí se podařilo prokázat spolehlivost a robustnost výpočtu vyzářeného dlouhovlnného záření. Naproti tomu odhad čistého dlouhovlnného záření je zatížen značnou nejistotou, kterou se nepodařilo zmenšit ani kalibrací příslušných koeficientů. The incoming and outgoing longwave radiations are often estimated from empirical relationships with a number of calibration coefficients. When testing the parameterization of available components of longwave radiation in the frame of a small mountaineous catchment we were able to demonstrate the reliability and robustness of calculating the outgoing longwave radiation. The estimate of net longwave radiation is burdened by considerable uncertainty, which could not be reduced by calibration of the coefficients. Keywords: emissivity of air; water vapor pressure; nonlinear optimization; pyrgeometr; radiated longwave radiation; longwave radiation; tepelné záření; geomorfologie Available on request at various institutes of the ASCR
Testování parametrizací složek dlouhovlnného záření v podmínkách malého šumavského povodí

Dlouhovlnné záření je významnou, zřídkakdy měřenou, částí radiační bilance zemského povrchu. Dopadající a vyzářené dlouhovlnné záření jsou často odhadovány z empirických vztahů s řadou kalibračních ...

Muller, J.; Dohnal, M.; Tesař, Miroslav
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; sněhová pokrývka; sníh 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

Plant transpiration, entropy production and gross primarily productivity
Šír, M.; Tesař, Miroslav; Lichner, Ľ.
2014 - English
The Earth is a self-organized system. The source of information for self-organization is the degradation of solar radiation. The solar energy is highly organized and carried by photons. Earth absorbs this energy and then releases it back to the Universe. However, energy released to the environment is in the form of electromagnetic radiation, which is on average at longer wavelengths than the absorbed photons. The flow of the entropy associated with the energy conversion, which is at disposal for the self-organization, is approximately equal to 1.16·10.sup.38./sup. bit·.sub.s./sub..sup.-1./sup. (Roland-Mieskowski, 1994). The nature of self-organization is a theme of contemporary scientific discussion. The core of this discussion is the role of biotic processes. Lovelock and Margulis (1974) formulated a theory that the self-organization in a global scale is an emergent characteristic of the Earth’s biota (Gaia theory). Keywords: plant transpiration; plant temperature; plant entropy production; Gaia theory; ecological optimality theory; rostlinná výroba; energetické zdroje sluneční Available on request at various institutes of the ASCR
Plant transpiration, entropy production and gross primarily productivity

The Earth is a self-organized system. The source of information for self-organization is the degradation of solar radiation. The solar energy is highly organized and carried by photons. Earth absorbs ...

Šír, M.; Tesař, Miroslav; Lichner, Ľ.
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

Saturation overshoot as a basis for emergent flow phenomena in unsaturated homogeneous porous media
Fürst, T.; Vodák, R.; Šír, Miloslav; Tesař, Miroslav
2014 - English
Understanding and description of fluid motion in unsaturated porous media rates among the most challenging and still not fully resolved problems. Traditionally, porous media flows were described by the continuum mechanics apparatus [1]. The continuum mechanics based models lead to partial differential equations which are mathematical formulations of the balance of mass, momentum, and energy. The most celebrated model is the so called Richards’ Equation (RE) [2]. Other continuum models (see [3], [4] and the reference and discussion therein) are various extensions built on similar principles as the RE. Keywords: unsaturated homogeneous porous media; emergent flow; saturation overshoot; oscillatory discharge; mechanika kontinua; média Available on request at various institutes of the ASCR
Saturation overshoot as a basis for emergent flow phenomena in unsaturated homogeneous porous media

Understanding and description of fluid motion in unsaturated porous media rates among the most challenging and still not fully resolved problems. Traditionally, porous media flows were described by ...

Fürst, T.; Vodák, R.; Šír, Miloslav; Tesař, Miroslav
Ústav pro hydrodynamiku, 2014

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