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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 ...
Flow behaviour of highly concentrated slurries
Vlasák, Pavel; Chára, Zdeněk
2009 - English
The paper describes results of experimental investigation of the highly concentrated fine-grained slurry. The flow behaviour of the slurry was experimentally investigated for the laminar and turbulent regimes with respect to the effect of solid concentration and flow velocity. The re-circulation pipe loop with smooth stainless steel pipe of the inner diameter D = 17.5 mm was used. Stony dust from Mistrovice quarry (d50 = 8 μm, ρs = 2 701 kg/m3) was used as a solid phase, water was used as a carrier liquid. Volumetric concentration and slurry velocity reached up to 44% and 6 m/s, respectively. Příspěvek se zabývá experimentálním výzkumem vysoce koncentrovaných jemnozrnných suspenzí složených z kamenného prachu z lomu Mistrovice (d50 = 8 μm, ρs = 2 701 kg/m3) a vody. Objemová koncentrace pevné fáze dosahovala hodnot až 44%, rychlost proudění až 6 m/s. Tokové chování těchto suspenzí bylo zkoumáno na recirkulační experimentální trase s hladkým nerezovým potrubím o vnitřním průměru D = 17,5 mm pro laminární i turbulentní režim s ohledem na vliv koncentrace pevné fáze a rychlosti proudění.
Keywords:
dense fine-grained slurry; experimental investigation; effect of concentration; effect of flow velocity; pressure drop
Available in digital repository of the ASCR
Flow behaviour of highly concentrated slurries
The paper describes results of experimental investigation of the highly concentrated fine-grained slurry. The flow behaviour of the slurry was experimentally investigated for the laminar and turbulent ...
Vliv nastavení jednotlivých parametrů na UVP měření v kanále s volnou hladinou
Chára, Zdeněk; Kysela, Bohuš
2009 - Czech
V příspěvku je řešen vliv nastavení jednotlivých parametrů na ultrazvukové měření rychlostních profilů pomocí UVP monitoru. Měření se uskutečnila při proudění s volnou hladinou v kanále s drsným dnem. The contribution deals with an investigation on parameter setting of ultrasound measurements on velocity profiles. UVP monitor was used as measuring technique and the measurements were performed in a channel with rough bottom.
Keywords:
Ultrasound; UVP monitor
Available in digital repository of the ASCR
Vliv nastavení jednotlivých parametrů na UVP měření v kanále s volnou hladinou
V příspěvku je řešen vliv nastavení jednotlivých parametrů na ultrazvukové měření rychlostních profilů pomocí UVP monitoru. Měření se uskutečnila při proudění s volnou hladinou v kanále s drsným ...
A remark to the reptation theory
Kharlamov, Alexander; Filip, Petr; Švrčinová, Petra
2009 - English
Avoiding the Independent Alignment (IA) approximation in the classical Doi-Edwards model causes the computation extremely time and hardware consuming. Nevertheless some flow situations cannot be modelled with the IA approximation. This contribution presents a probabilistic approach not taking into account the IA approximation. Neuvažování IA aproximace v klasickém Doi-Edwardsově modelu způsobuje značné výpočetní potíže, nicméně některé tokové situace nemohou být modelovány pomocí této aproximace, kterou také nově presentovaný přístup nebere v potaz.
Keywords:
tube model; reptation theory; probabilistic approach
Available in digital repository of the ASCR
A remark to the reptation theory
Avoiding the Independent Alignment (IA) approximation in the classical Doi-Edwards model causes the computation extremely time and hardware consuming. Nevertheless some flow situations cannot be ...
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