Number of found documents: 563
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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; turbulentní proudění; potrubní doprava 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

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; hydrologická bilance; hydrologický cyklus 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

Vliv extrémních srážek na vymývání draselného a sodného iontu z povodí Liz v období 2002–2009
Vondrka, A.; Tesař, Miroslav; Šír, M.
2014 - Czech
V posledních padesáti letech došlo na území ČR ke globálnímu nárůstu teplot ovzduší, a to asi o 0,16 až 0,33 °C za dekádu. Současně je pozorována extremalizace hydrologického cyklu, která se projevuje v teplém období roku výskytem krátkodobých srážek o vysokém úhrnu a výskytem dlouhých teplých a bezdeštných období, ve kterých významně klesá vodnost zejména malých toků. Všechny tyto jevy silně ovlivňují intenzitu vymývání sodíku a draslíku z půdy a podloží. Vzniká proto otázka, zda lze nalézt nějakou souvislost mezi oteplováním klimatu a ochuzováním povodí o kationy sodíku a draslíku (Vondrka et al., 2013). Extreme rains strongly influence the intensity of leaching of sodium and potassium from the soil cover. The question therefore arises whether it is possible to find some connection between extreme rains and sodium and potassium leaching. During the period of 2002-2009, measurement of rainfall, runoff, and chemical data on catchment Liz (Czech Republic, Bohemian Forest, 828–1074 m a. s. l., mature spruce forest, Podzolic Eutric Cambisol) gave the following conclusions about the washout of potassium and sodium ion from the basin: (1) In monthly periods, extreme loss of both potassium and sodium ions correlated with high precipitation amounts. (2) In annual periods, only extreme loss of sodium ions correlated with high precipitation amounts. Keywords: extreme rainfall; river basin; concentration of ions; soil chemistry; potassium leaching; sodium leaching; extreme rain; Bohemian Forest; povodí; ionty Available on request at various institutes of the ASCR
Vliv extrémních srážek na vymývání draselného a sodného iontu z povodí Liz v období 2002–2009

V posledních padesáti letech došlo na území ČR ke globálnímu nárůstu teplot ovzduší, a to asi o 0,16 až 0,33 °C za dekádu. Současně je pozorována extremalizace hydrologického cyklu, která se projevuje ...

Vondrka, A.; Tesař, Miroslav; Šír, M.
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

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

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

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

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

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