Search Results

You are looking at 1 - 10 of 14 items for :

Clear All
Open access

Nikolay Lukerchenko, Siarhei Piatsevich, Zdenek Chara, Pavel Vlasak, Zdeněk Chára and Pavel Vlasák

3D Numerical Model of the Spherical Particle Saltation in a Channel with a Rough Fixed Bed

The paper describes a 3D numerical model of the spherical particle saltation. Two stages of particle saltation were distinguished — the particle free motion in water and the particle-bed collision. The particle motion consists of the translational and rotational particle motion. A stochastic method of calculation of the particle-bed collision was developed. The collision height and the contact point were defined as random variables. Impulse equations were used and the translational and angular velocity components of the moving particle immediately after the collision were expressed as functions of the velocity components just before the collision. The dimensionless coefficients of the drag force and drag torque were determined as functions of both translational and rotational Reynolds numbers. The model is in good agreement with known experimental data. Examples of calculation of the particles' lateral dispersion and the mean absolute values of the deviation angle of the particle trajectory are presented.

Open access

Nikolay Lukerchenko, Siarhei Piatsevich, Zdenek Chara and Pavel Vlasak

Numerical model of spherical particle saltation in a channel with a transversely tilted rough bed

This paper deals with the numerical simulation of spherical particle saltation in a channel with a rough transversely tilted bed. The numerical model presented is based on the 3D model of spherical particle saltation developed by the authors, which takes into account the translational and rotational particle motion. The stochastic method and the concept of a contact zone were used for the calculation of a particle trajectory and its dependence on the bed lateral slope, particle diameter, and shear velocity. The effect of the bed lateral slope results in a deviation of the particle trajectory from the downstream direction. Some examples of the calculation are presented. The trajectories of the saltating particles starting their movements from one point were calculated and it was shown that they are of random character and together create a bundle or fascicle of trajectories. It was found that the centrelines of the bundles can be approximated by the straight lines for low and moderate values of the bed transverse slope, i.e. slopes less than 20°. The angle of deviation of the centreline from the downstream direction increases when the bed lateral slope and/or the particle diameters increase. However, with increasing shear velocity, the deviation angle decreases. Due to the lateral bed slope the particles are sorted according to their size, and the criteria for sorting particles were defined. An example of the particle sorting was calculated and the separable and non-separable regions were determined.

Open access

Nikolay Lukerchenko, Jindrich Dolansky and Pavel Vlasak

In numerical models of fluid flow with particles moving close to solid boundaries, the Basset force is usually calculated for the particle motion between particle-boundary collisions. The present study shows that the history force must also be taken into account regarding particle collisions with boundaries or with other particles. For saltation - the main mode of bed load transport - it is shown using calculations that two parts of the history force due to both particle motion in the fluid and to particle-bed collisions are comparable and substantially compensate one another. The calculations and comparison of the Basset force with other forces acting on a sand particle saltating in water flow are carried out for the different values of the transport stage. The conditions under which the Basset force can be neglected in numerical models of saltation are studied.

Open access

Michal Vojtíšek and Martin Pechout

Shrnutí

Částice obsažené ve výfukových plynech spalovacích motorů jsou jejich pro lidské zdraví nejvíce škodlivou složkou. Se snižující se celkovou hmotností emitovaných částic se zvyšují nároky na její měření, které vyžaduje plnoprůtočný ředicí tunnel nebo proporcionální vzorkovač s ředěním části toku s rychlou odezvou. Pro umožnění takových měření během jízdy vozidla a v méně vybavených laboratořích bylo vytvořeno nízkonákladové zařízení pro proporcionální vzorkování výfukových plynů. Zařízení využívá dvojici regulátorů hmotnostního průtoku, z nichž jeden dodává proměnlivé množství ředicího vzduchu do miniaturního ředicího tunelu, a druhý udržuje konstantní průtok směsi ředicího vzduchu a výfukových plynů přes filtr, na který jsou částice vzorkovány. Výsledky naměřené tímto systémem během dynamických jízdních cyklů jsou, po korekci systematického rozdílu, v rozmezí faktoru dvou od výsledků gravimetrické analýzy vzorků odebraných z klasického plnoprůtočného ředicího tunelu.

Open access

Marcela Gergeľová, Žofia Kuzevičová and Štefan Kuzevič

Abstract

In general, air quality is determined from the concentrations of pollutants in ambient air. Air quality criteria (limit and target values, margin of tolerances, upper and lower assessment thresholds) are based on the current legislative framework. In Slovakia, the air quality criteria are imposed by Decree No 360/2010 Coll, on air quality, of the Ministry of Environment [1]. In relation to the implemented measurements, it is necessary to choose effective tools needed for the pre-processing and post-processing of overall air quality assessment. The article aims at applying suitable GIS tools in the assessment process of air quality in the Košice agglomeration for the selected period 2008-2010. In the overall assessment of the area in question, the processing of information on emissions declared as particulate matter (PM) was considered in terms of a conservative approach to the assessment of air quality for PM10. For the assessment, the yearbooks and reports on air quality in Slovakia in 2008-2010 of the Slovak Hydrometeorological Institute (SHMI) and professional publications were used

Open access

Viliam Novák and Peter Šurda

The water retention of a granite rock fragments in High Tatras stony soils

The water retention capacity of coarse rock fragments is usually considered negligible. But the presence of rock fragments in a soil can play an important role in both water holding capacity and in hydraulic conductivity as well. This paper presents results of maximum water holding capacity measured in coarse rock fragments in the soil classified as cobbly sandy loam sampled at High Tatra mountains. It is shown, that those coarse rock (granite) fragments have the maximum retention capacity up to 0.16 volumetric water content. Retention curves of the four particular granite fragments have shown water capacity available for plants expressed in units of volumetric water content of 0.005 to 0.072 in the soil water potential range (0, -0.3 MPa). Available water capacity of stone fragments can contribute to the available water capacity of soil fine earth considerably and help to plants to survive during dry spells.

Open access

Anna Řehořková

References [1] Ameka, F. (2006). Interjections. In Brown, K., editor, Encyclopaedia of Language and Linguistics , pages 743–746, Elsevier, Amsterdam. [2] Atwell, E. S. (2008). Development of tag sets for part-of-speech tagging. In Ludeling, A. and Kyto, M., editors, Corpus Linguistics: An International Handbook , Volume 1, pages 501–526, Walter de Gruyter. [3] Bedřichová, Z. (2008). Částice implikující presupozici jako podstatná složka větného významu. Čeština doma a ve světě 3–4:119–126. [4] Collins COBUILD Dictionary. Accessible at

Open access

Václav Matoušek and Jan Krupička

On equivalent roughness of mobile bed at high shear stress

The friction conditions at the top of a mobile bed are discussed for flows in the upper-plane-bed regime, i.e. for the flows with values of the bed Shields parameter larger than approximately 0.6. A special attention is devoted to flows of the bed Shields parameter bigger than 2. Experimental data for flows at high bed shear are collected from literature and new data are added from own measurements of flows of a 1.36-mm sand slurry in the 100-mm pipe loop of the Institute of Hydrodynamics. The database represents flows of very different solids and covers friction conditions within a broad range of Shields parameters up to the maximum value of about 23. The paper analyses the data in order to evaluate a relationship among the equivalent roughness of the top of the bed and other relevant parameters. A semi-empirical formula is proposed that relates the equivalent roughness to the bed Shields parameter, the ratio of flow velocity and particle settling velocity, and the ratio of flow hydraulic radius and particle diameter. The formula is applicable primarily to flows of combined load (contact- and suspended loads together).

Open access

J. Rapouch

Během expozice vřetena z vysokochromové oceli X22Cr-MoV12-1 s HVOF povlakem na bázi Cr3C2-NiCr v prostředí přehřáté páry došlo po několika hodinách provozu k degradaci tohoto povlaku. V této studii je hodnocena úroveň poškození povlaku za pomoci analýzy chemického a fázového složení na povrchu i v řezu vrstvy. V degradované i nedegradované vrstvě byly detekovány fáze Ni-Cr, Cr3C2 a Cr2O3. Během expozice došlo k úbytku tloušťky vrstvy o jeden řád. Pravděpodobnou příčinou degradace vrstvy je oxidace v prostředí páry, negativní roli mohly hrát i objemné částice na rozhraní ocel/povlak.

Open access

Viktor Varga, Lenka Lackoóvá, Jozef Streďanský and Tomáš Urban

Abstract

Despite the fact that wind erosion seriously affects the sustainable use of land in large part of the world and even though in Slovakia there is not that big percentage of agricultural land influence by wind erosion it still has an effect on the soil. Valid wind erosion model that predicts wind-blown mass transport on regional scale is lacking. The objective of this research was to compare two empiric methods to determine wind erosion. One of them is deflametric method, in which we capture soil units in one hour during wind erosion events. Second method we used was volumetric method where we calculate amount of eroded soil behind the wind barrier. With deflametric method we determined that actual wind speed needed to lift and carry soil unites is 9 - 10 m.s-1. With volumetric calculation we found out that our measurement is 1.7 times higher than in WEQ model. We can say that models can portray certain areas and soil types, but only field measurement can provide precise amount of eroded soil on particular land.