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Simulation of particle motion in a closed conduit validated against experimental data
Dolanský, Jindřich
2014 - anglický
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.
Klíčová slova:
particle motion; lattice Boltzmann method (LBM); simulations
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
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 ...
Kernel density estimates used in stochastic precipitation generator
Hnilica, Jan; Puš, V.
2014 - anglický
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.
Klíčová slova:
kernel density estimate; daily precipitation sum; stochastic generator
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
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 ...
Seasonal snow accumulation in the mid-latitude forested catchment
Šípek, Václav; Tesař, Miroslav
2014 - anglický
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.
Klíčová slova:
snow depth,; snow water equivalent; forested catchment
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
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 ...
Plant transpiration, entropy production and gross primarily productivity
Šír, M.; Tesař, Miroslav; Lichner, Ľ.
2014 - anglický
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).
Klíčová slova:
plant transpiration; plant temperature; plant entropy production; Gaia theory; ecological optimality theory
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
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 ...
Saturation overshoot as a basis for emergent flow phenomena in unsaturated homogeneous porous media
Fürst, T.; Vodák, R.; Šír, Miloslav; Tesař, Miroslav
2014 - anglický
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.
Klíčová slova:
unsaturated homogeneous porous media; emergent flow; saturation overshoot; oscillatory discharge
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
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 ...
Radioisotope method of compound flow analysis
Petryka, L.; Zych, M.; Hanus, R.; Sobota, J.; Vlasák, Pavel; Malczewska, B.
2014 - anglický
The paper presents gamma radiation application to analysis of a multicomponent or multiphase flow. Such information as a selected component content in the mixture transported through pipe is crucial in many industrial or laboratory installations. Properly selected sealed radioactive source and collimators, deliver the photon beam, penetrating cross section of the flow. Detectors mounted at opposite to the source side of the pipe, allow recording of digital signals representing composition of the stream. In the present development of electronics, detectors and computer software, a significant progress in know-how of this field may be observed. The paper describes application of this method to optimization and control of hydrotransport of solid particles and propose monitoring facilitating prevent of a pipe clogging or dangerous oscillations.
Klíčová slova:
compound flow analysis; Cross Correlation Analysis; hydrotransport of solid particles
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Radioisotope method of compound flow analysis
The paper presents gamma radiation application to analysis of a multicomponent or multiphase flow. Such information as a selected component content in the mixture transported through pipe is crucial ...
Evaluation and accuracy of the local velocity data measurements in an agitated vessel
Kysela, Bohuš; Konfršt, Jiří; Chára, Zdeněk; Kotek, M.
2014 - anglický
Velocity measurements of the flow field in an agitated vessel are necessary for the improvement and better understanding of the mixing processes. The obtained results are used for the calculations of the impeller pumping capacity, comparison of the power consumption etc. We performed various measurements of the local velocities in an agitated vessel final results of which should be processed for several purposes so it was necessary to make an analysis of the obtained data suitability and their quality. Analysed velocity data were obtained from the LDA (Laser Doppler Anemometry) and PIV (Particle Image Velocimetry) measurements performed on a standard equipment where the flat bottomed vessel with four baffles was agitated by the six-blade Rushton turbine. The results from both used methods were compared. The frequency analyses were examined as well as the dependency of the data rates, time series lengths etc. The demands for the data processed in the form of the ensemble-averaged results were also established.
Klíčová slova:
Laser Doppler Anemometry (LDA); Particle Image Velocimetry (PIV); velocity; measurements
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Evaluation and accuracy of the local velocity data measurements in an agitated vessel
Velocity measurements of the flow field in an agitated vessel are necessary for the improvement and better understanding of the mixing processes. The obtained results are used for the calculations of ...
Evaluation of Changes in Water Regime Caused by Long-term Development of Vegetation Cover
Chlumecký, M.; Tesař, Miroslav; Buchtele, Josef
2014 - anglický
Long monitoring of air temperature and precipitation for three catchments with up to 100 years series has been used as the input for the modelling of rainfall-runoff process and for the re-assessments of the evapotranspiration demand (ET.sub.demand./sub.). The resulting oscillations and the random changes of vegetation cover have been pursued as the indication of fluctuations also in the evapotranspiration. The intention is to appraise this complicated time series as the long-term process. The modified implementation of the conceptual model SAC-SMA enables the quicker simulation and facilitates also the conditions for automatic calibration of parameters in the used model; separately for individual, i.e. partial time intervals, namely with the diverse expected evapotranspiration. That process is to be identified simultaneously with the optimal parameters of the mode; the resulting actual evapotranspiration (ET.sub.act./sub.) is then represented as the modelling outputs, as such values could be hardly gained as measured or computed values, e. g. from other meteo-observations.
Klíčová slova:
vegetation cover; evapotranspiration; rainfall-runoff modelling; land-use
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Evaluation of Changes in Water Regime Caused by Long-term Development of Vegetation Cover
Long monitoring of air temperature and precipitation for three catchments with up to 100 years series has been used as the input for the modelling of rainfall-runoff process and for the re-assessments ...
Estimation of turbulence dissipation rate by Large eddy PIV method in an agitated vessel
Kysela, Bohuš; Jašíková, D.; Konfršt, Jiří; Šulc, R.; Ditl, P.
2014 - anglický
The distribution of turbulent kinetic energy dissipation rate is important for design of mixing apparatuses in chemical industry. Generally used experimental methods of velocity measurements for measurement in complex geometries of an agitated vessel disallow measurement in resolution of small scales close to turbulence dissipation ones. Therefore, Particle image velocity (PIV) measurement method improved by large eddy PIV approach was used. Large eddy PIV method is based on modeling of smallest eddies by a sub grid scale (SGS) model. This method is similar to numerical calculations using Large Eddy Simulation (LES) and the same SGS models are used. In this work the basic Smagorinsky model was employed and compared with power law approximation. Time resolved PIV data were processed by Large Eddy PIV approach and the obtained results of turbulent kinetic dissipation rate were compared in selected points for several operating conditions (impeller speed, operating liquid viscosity).
Klíčová slova:
PIV measurements; Particle image velocity; Large Eddy Simulation; SGS models
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Estimation of turbulence dissipation rate by Large eddy PIV method in an agitated vessel
The distribution of turbulent kinetic energy dissipation rate is important for design of mixing apparatuses in chemical industry. Generally used experimental methods of velocity measurements for ...
Simulation of motion of multiple particles in a closed conduit using the LBM based approach
Dolanský, Jindřich
2014 - anglický
The two-dimensional numerical model of motion of multiple circular particles in fluid flow based on the lattice Boltzmann method (LBM) is presented. The flow is driven by the power-law velocity profile at the inlet in a closed horizontal conduit. Motion of particles consists of free motion in the flow, particle-bed and particle-particle collisions. The simulation for both movements of particles and velocity field of the flow is developed. Stability issues of the simulation are considered and a resolution using the entropic LBM and extension of computational resources is proposed. Finally, an enhancement of the simulation for more complex processes is suggested
Klíčová slova:
motion of particles; hydrodynamic forces; lattice Boltzmann method; entropic LBM
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Simulation of motion of multiple particles in a closed conduit using the LBM based approach
The two-dimensional numerical model of motion of multiple circular particles in fluid flow based on the lattice Boltzmann method (LBM) is presented. The flow is driven by the power-law velocity ...
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