Yes (122)
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Simulation of water and heat transport considering preferential flow. Experimental site Na Lizu
Votrubová, J.; Dohnal, M.; Vogel, T.; Tesař, Miroslav
2011 - English
Coupled water and heat transport in soil profile at the experimental site Na Lizu (Volynka headwater catchment, Sumava Mountains, southern Bohemia) is studied. The site is located on a mild slope cov-ered with grass. The soil is Cambisol developed upon biotite paragneiss bedrock. One-dimensional dual-continuum model with semi-separate flow domains representing the soil matrix and the network of preferential pathways (S1D) is employed. Hydraulic parameters of the model are set based on labo-ratory retention curve measurements and in-situ measurements of hydraulic conductivity. Thermal pa-rameters are estimated using methodology of Cote and Konrad (2005). Simulation is conducted for the summer season of 2009. The in-situ monitored precipitation and soil surface temperatures are used as the model upper boundary condition. Model performance was evaluated through comparison with soil water pressure and soil temperatures monitored in situ.
Keywords:
soil heat transport; advective heat flux; preferential flow; dual-continuum approach
Available in digital repository of the ASCR
Simulation of water and heat transport considering preferential flow. Experimental site Na Lizu
Coupled water and heat transport in soil profile at the experimental site Na Lizu (Volynka headwater catchment, Sumava Mountains, southern Bohemia) is studied. The site is located on a mild slope ...
Experimental investigation of drag force, Magnus force and drag torque acting on rough sphere moving in calm water
Lukerchenko, Nikolay; Keita, Ibrahima; Chára, Zdeněk; Vlasák, Pavel
2010 - English
The paper describes the results of experiments with a rotating golf ball moving quasi-steadily in calm water. The motion of the ball was recorded on a digital video camera. The dimensionless drag force, Magnus force, and drag torque coefficients were determined from the comparison of the calculated translational and angular velocities and trajectory with experimental ones for the rough particle. The proper value of the correction coefficients were established from condition of the best fitting of the experimental trajectory by the calculated one.
Keywords:
drag force; Magnus force; particle trajectory
Available in digital repository of the ASCR
Experimental investigation of drag force, Magnus force and drag torque acting on rough sphere moving in calm water
The paper describes the results of experiments with a rotating golf ball moving quasi-steadily in calm water. The motion of the ball was recorded on a digital video camera. The dimensionless drag ...
Choice of polymer samples geometry for measurement of elongational viscosity using ser universal testing platform
Filip, Petr; Švrčinová, Petra
2010 - English
Generation of purely uniaxial elongational flow of polymer melts is very uneasy problem. It seems that each hitherto developed device for measurement of uniaxial elongational viscosity also produces - to some extent - a planar flow. During the last period there has been questioned - based on this reasoning - the applicability of a SER Universal Testing Platform and was recommended the range of rectangular dimensions of polymer samples for which measurements of uniaxial elongational viscosity is possible to take into account. The aim of this contribution consists in verification of invariantness of uniaxial elongational measurements using the SER Universal Testing Platform with respect to the dimensions of polymer samples applied. There is shown that for sufficiently broad region of admissible widths and thicknesses the results are identical. For these measurements there was used LDPE Escorene (Exxon, U.S.A.).
Keywords:
uniaxial elongational flow; planar flow; polymer melts; uniaxial elongational viscosity; SER Universal Testing Platform; LDPE
Available in digital repository of the ASCR
Choice of polymer samples geometry for measurement of elongational viscosity using ser universal testing platform
Generation of purely uniaxial elongational flow of polymer melts is very uneasy problem. It seems that each hitherto developed device for measurement of uniaxial elongational viscosity also produces - ...
Approximation of velocity distribution in open channel flow
Ivanova, Irina; Vlasák, Pavel; Chára, Zdeněk; Kysela, Bohuš
2010 - English
The paper deals with approximation of spatial distribution of mean downstream velocity of sub-critical turbulent flow in an open rectangular channel with rough bed. New formulae of the local downstream velocity component Vx(y, z) dependence on the vertical coordinate y and lateral coordinate z were introduced. The vertical velocity profile was approximated by log-law and the power law was used to describe the effect of channel walls on the horizontal velocity profile. The suggested formulae of spatial downstream velocity component distribution were calibrated and verified using the experimental data obtained by PIV method. The proposed approximation is in good agreement with experimental data, the difference between experimental and calculated data is in range of 5 - 10% except the area near the channel’s corners and water level, where the maximal difference reaches 60% and 30% of experimental values, respectively.
Keywords:
spatial velocity profile; channel flow; vertical profile; lateral profile; power law; logarithmic law
Available in digital repository of the ASCR
Approximation of velocity distribution in open channel flow
The paper deals with approximation of spatial distribution of mean downstream velocity of sub-critical turbulent flow in an open rectangular channel with rough bed. New formulae of the local ...
A note to the simplification in description of some molecular-based polymer models
Kharlamov, Alexander; Filip, Petr
2010 - English
One type of integral is frequently met in various description of behaviour of polymer materials through molecular-based models starting with the classical Doi-Edwards one. The integrand in this integral for which an integrated region represents a solid angle is formed by a product of a unit vector (pointed at an element of this region) with a deformation gradient tensor. This product is raised to an exponent that is not usually an integer. The aim of this contribution is to derive substantially simplified expression for this integral respecting high accuracy of an approximation.
Keywords:
polymer materials; Doi-Edwards model; integral
Available in digital repository of the ASCR
A note to the simplification in description of some molecular-based polymer models
One type of integral is frequently met in various description of behaviour of polymer materials through molecular-based models starting with the classical Doi-Edwards one. The integrand in this ...
Počáteční rychlosti volně sedimentující kulovité částice
Chára, Zdeněk; Kysela, Bohuš
2010 - Czech
Příspěvek se zabývá experimentálním výzkumem počáteční fáze volně sedimentující kulovité částice, jejíž hustota je blízká hustotě vody. Experimenty byly prováděny s hladkou částicí i s částicí s drsným povrchem. Z dosažených výsledků vyplývá, že v počáteční fázi sedimentace dochází ke vzniku vírových struktur, jenž se projevují nárůstem hodnot odporového koeficientu. The paper deals with experimental research of the initial phase of free-settling spherical particle which density is close to the density of water. The experiments were carried out with a smooth particle as well as with a particle with a rough surface. The obtained results show that in the initial phase of sedimentation, there is a formation of vortex structures, which are reflected in the increase of resistance in coefficient values.
Keywords:
sedimentation; spherical particle; visualization
Available in digital repository of the ASCR
Počáteční rychlosti volně sedimentující kulovité částice
Příspěvek se zabývá experimentálním výzkumem počáteční fáze volně sedimentující kulovité částice, jejíž hustota je blízká hustotě vody. Experimenty byly prováděny s hladkou částicí i s částicí s ...
Effect of dense slurry composition on its flow behaviour in horizontal pipe
Vlasák, Pavel; Chára, Zdeněk
2010 - English
The paper deals with experimental investigation of the dense fine-grained slurries focused on the slurry pressure drops versus average velocity relationship. The content of fine, especially colloidal solid particles evokes a complex non-Newtonian behaviour of the slurry. Flow behaviour of dense slurry depends on particle size distribution, shape, density and chemical composition of the solid phase as well as on concentration of solids and carrier liquid properties. The re-circulation pipe loop with horizontal hydraulically smooth stainless steel pipes was used for measuring the slurry flow parameters. Different slurries containing kaolin, stony dust or sand conveyed in water were measured to document effect of the size distribution and chemical composition on the slurry flow behaviour.
Keywords:
dense slurry; flow behaviour; pressure drop; particle size distribution effect; concentration effect
Available in digital repository of the ASCR
Effect of dense slurry composition on its flow behaviour in horizontal pipe
The paper deals with experimental investigation of the dense fine-grained slurries focused on the slurry pressure drops versus average velocity relationship. The content of fine, especially ...
On behaviour of PVB solutions in electrospinning
Švrčinová, Petra; Lubasová, D.; Filip, Petr; Martinová, L.
2010 - English
Electrospinning produces nanofibre sheets from polymer solutions under high electric field. Rheological properties of these solutions play a substantial role in a nanofibre formation simultaneously with properties of polymers and solvents applied. This contribution aims at a determination of dependence of shear viscosity of polyvinylbuthyral (PVB) on the intensity of electric field to which PVB solutions are exposed. PVB was dissolved consecutively in a series of solvents as 10% wt. solution. It was found that the viscosity ratio (viscosity of a solution in presence of electric field/viscosity of a solution in absence of electric field) depends on the polarity of solvent. This pre-determines the possibility of application of the individual solvents for the process of electrospinning.
Keywords:
nanofibre; electrospinning; polymer solution; viscosity ratio; electric field
Available in digital repository of the ASCR
On behaviour of PVB solutions in electrospinning
Electrospinning produces nanofibre sheets from polymer solutions under high electric field. Rheological properties of these solutions play a substantial role in a nanofibre formation simultaneously ...
Transition from the saltation mode of bed load transport to the rolling mode
Lukerchenko, Nikolay; Ivanova, Irina; Chára, Zdeněk; Vlasák, Pavel
2009 - English
The paper deals with the sediment transport of sand particles conveyed by water in an open channel. A 3D numerical model developed by the authors was used for simulation of the sand particles movement in the channel with rough bed. Similarly to Shields theory of sediment transport incipient motion of the bed load particles the shear stress for the transition process from saltation mode to rolling mode can be defined. The shear stress value can be determined as a function of two dimensionless parameters, particle parameter and equivalent bed roughness. The particle parameter is a function of the particle size and density, and the carrier liquid density and viscosity. The presented numerical solution reveals that the shear stress for the transition process from saltation mode to rolling mode is less than the shear stress for the incipient sediment motion and depends on channel bed roughness. Příspěvek se zabývá sedimentačním pohybem písčitých částic unášených vodou podél dna otevřeného koryta. Pro simulaci pohybu částice v kanále s drsným dnem byl použit 3D model vyvinutý autory. Podmínky změny saltačního pohybu částice na rotační (valivý) podél dna koryta byly určeny obdobně jako podle Shieldsova teorému. Hodnota smykového napětí byla určena jako funkce dvou bezrozměrných parametrů, bezrozměrného průměru částice, který je funkcí velikosti a hustoty částice a hustoty a viskozity vody, a ekvivalentní drsnosti dna. Provedené numerické řešení potvrdilo, že smykové napětí pro přechod ze saltačního do rotačního pohybu je menší než smykové napětí pro počátek pohybu sedimentující částice a je závislé na drsnosti dna koryta.
Keywords:
bed-load transport; particle saltation; particle rolling; numerical modelling
Available in digital repository of the ASCR
Transition from the saltation mode of bed load transport to the rolling mode
The paper deals with the sediment transport of sand particles conveyed by water in an open channel. A 3D numerical model developed by the authors was used for simulation of the sand particles movement ...
Measurement of elongational viscosity of PE materials
Švrčinová, Petra; Kharlamov, Alexander; Filip, Petr
2009 - English
This contribution aims at the measurements of elongation viscosity for polyethylene materials. The approach is analysed from the viewpoint of possible degradation of materials tested and the emphasis is paid to admissible acceleration of the whole measuring process. There is presented a hint how to simplify (and accelerate) the measurements for a suitable class of materials. Je provedeno měření elongační viskozity vybraných polyetylénových materiálů a ukázána možnost zefektivnění klasického postupu.
Keywords:
elongational viscosity; SER Universal Testing Platform
Available in digital repository of the ASCR
Measurement of elongational viscosity of PE materials
This contribution aims at the measurements of elongation viscosity for polyethylene materials. The approach is analysed from the viewpoint of possible degradation of materials tested and the emphasis ...
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