« Previous |
1 - 10 of 11
|
Next »
Number of results to display per page
Search Results
2. Automated reverse Engineering of CAN protocols
- Creator:
- Weiß, Nils, Pozzobon, Enrico, Mottok, Jürgen, and Matoušek, Václav
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- controller area networks, statistical analysis, and neural networks
- Language:
- English
- Description:
- Car manufacturers define proprietary protocols to be used inside their vehicular networks, which are kept an industrial secret, therefore impeding independent researchers from extracting information from these networks. This article describes a statistical and a neural network approach that allows reverse engineering proprietary controller area network (CAN)-protocols assuming they were designed using the data base CAN (DBC) file format. The proposed algorithms are tested with CAN traces taken from a real car. We show that our approaches can correctly reverse engineer CAN messages in an automated manner.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3. Coherence of EEG Signals and Biometric Signals of Handwriting under Influence of Nicotine, Alcohol, and Light Drugs
- Creator:
- Maršálek, Tomáš, Matoušek, Václav, Mautner, Pavel, Merta, Michal, and Mouček, Roman
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- computerized EEG signal evaluation, biometric signals, and signal coherence
- Language:
- English
- Description:
- Subject matter of investigations being carried out at the University of West Bohemia in Pilsen and described in this chapter is the objective evaluation of possible coherence of EEG signals and signals of handwriting generated by special developed BiSP pen. The influence of nicotine, alcohol and light drugs on the vigility and activity of human operators was investigated and evaluated; the results of the experiments being realized during the last five months are summarized in the last paragraph.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
4. Distribution of medium-sand particles in flow above erodible bed at high shear stress
- Creator:
- Matoušek, Václav
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- sheet flow, particle dispersion, suspension, concentration profile, bed shear stress, smykové proudění, disperze částic, suspenze, koncentrační profil, and smykové napětí ve dně
- Language:
- Slovak
- Description:
- If the Shields number of a flow above an erodible bed is higher than one, then the current exerts so high shear stress at the top of a granular bed that the upper part of the bed is eroded and the top of the non-eroded rest of the bed is flat (no bed forms occur). This flow regime is typical for flows over a stationary bed in pipes but it can occur also in open-channel flows, particularly under flood conditions when both the depth and velocity of the flow are high. The current picks up particles from the eroded part of the bed and transports them within the flow. The total load of transported particles is composed of particles transported either as the contact load or as the suspended load, depending on the dispersive mechanism that keeps the particles inside the flow. Solids distribution (i.e. the shape of the concentration profile) of the transported particles across the flow helps to identify an acting dispersive mechanism and hence a mechanism through which the transported particles contribute to flow friction. The paper analyzes the concentration-profile measurements in a medium-sand-slurry current above an erodible stationary bed in a 150-mm pipe. The experiments revealed interesting effects of high shear stress on the shapes of concentration profiles across the flow above the bed. The analysis suggests that carrier turbulence is a prevailing dispersion mechanism within the upper part of the discharge area above the bed for flow conditions characterized by values of the ratio u*b/vt higher than say 4.5. It seems that the shearing action as an exclusive particle dispersion mechanism is confined to the region not far above the top of the bed. Apparently, the high shear stress at the top of the stationary bed is capable of producing turbulent suspension that transports a considerable amount of medium-sand particles (average delivered volumetric concentrations of transported particles up to 0.26) through the 150-mm pipe. and Při proudění vody nad pohyblivým dnem za podmínek vysokého smykového napětí na povrchu dna (Shieldsovo číslo větší než 1) je horní vrstva dna erodována proudem vody a na povrchu neerodované části dna nevznikají dnové útvary. Takové proudění se vyskytuje například v potrubí dopravujícím směs nad sedlinou na dně potrubí, ale může se vyskytnout i v otevřeném korytě, zvláště za povodňové situace, kdy jsou pro proudění typické velká rychlost a velká hloubka vody. Proud unáší částice z erodované vrstvy dna. Mechanismy, které mohou udržovat částice v proudu, jsou v principu dva: turbulentní suspenze a mezičásticový kontakt. Každý z těchto mechanismů způsobuje jiné rozdělení částic, tj. jiný koncentrační profil, po svislici proudu. Měřením koncentračních profilů by tedy mělo být možné odhadnout, jaký mechanismus převažuje v proudění za určitých sledovaných podmínek. Příspěvek analyzuje koncentrační profily měřené v potrubí průměru 150 mm při proudění vodní směsi střednězrnného písku nad pískovou sedlinou. Analýza výsledků měření ukázala, že turbulence v proudu vody je převažujícím mechanismem podpory částic přinejmenším v horní polovině výšky průtočné části potrubí při podmínkách charakterizovaných hodnotou poměru třecí rychlosti ve dně a usazovací rychlosti unášené částice (u*b/vt) větší než přibližně 4,5. Na rozdíl od dřívějších závěrů v literatuře se zdá, že mezičásticové kolize se jako výhradní mechanismus disperze částic uplatňují jen v poměrně omezené oblasti proudu nad povrchem dna. Vysoké smykové napětí ve dně tak přispívá nejen ke vzniku mezičásticových kolizí, ale i k turbulentní podpoře částic. Turbulentní podpora umožňuje dosažení vysokých hodnot (až do 0,26) dopravní koncentrace částic střednězrnného písku ve směsi proudící potrubím průměru 150 mm.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
5. Erosion of plane bed by sand slurry current in pipe
- Creator:
- Matoušek, Václav
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- pick-up, hindered erosion, suspension flow, bed friction, sběr částic erozí (pick-up), rušená eroze, proud suspenze, and dnové tření
- Language:
- Slovak
- Description:
- If a sand slurry current flows over a plane bed the thickness of the bed remains constant providing that equilibrium is established between the vertical fluxes that govern the exchange of particles between the slurry current and the sand bed. These solids fluxes are the settling flux and the erosion (pick-up) flux through the top of the bed. In the literature, relations to quantify the erosion flux from a sand bed consider the water current above an erodible bed. The effect of the presence of solid particles in the current is not taken into account. However, it has been observed that the presence of solid particles tends to suppress pick-up. This phenomenon is called hindered erosion. At present, the knowledge of the process of hindered pick-up is very limited although it is suspected that the hindered pick-up plays an important role in many practical situations. The paper discusses the results of the plane-bed test recently carried out in a 150-mm pipe of the Laboratory of Dredging Engineering of Delft University of Technology. Measurements of the thickness of the bed, the concentration profiles in the pipe cross section, the mean velocity, and the pressure drop allowed us to evaluate the conditions governing the vertical exchange of solids at the top of the stationary bed for currents of different solids concentrations. and Při proudění písčité hydrosměsi nad nepohyblivým ložem v tlakovém potrubí dochází k výměně pískových částic mezi proudem a ložem. Tloušťka lože zůstává neměnná, pokud při výměně existuje rovnováha mezi vertikálním proudem částic ze suspenze do sedliny (sedimentační proud) a opačně (erozní proud). V literatuře existující modely pro erozní proud jsou navrženy pro situace, kdy eroze je způsobena prouděním vody nad ložem, vliv přítomnosti unášených částic v proudu tedy není uvažován. V minulosti však již bylo pozorováno, že přítomnost suspendovaných částic může vést k zmenšení schopnosti proudu sbírat částice ze dna. Tento jev se nazývá rušená eroze. V současnosti jsou ještě poznatky o rušené erozi velmi omezené, přestože se dá předpokládat, že rušená eroze hraje významnou roli v mnoha situacích vyskytujících se v praxi. Tento příspěvek pojednává o výsledcích nedávných měření proudění písčité směsi nad nepohyblivým ložem v kruhovém potrubí průměru 150 mm v Laboratoři Dredging Engineering Technické univerzity v Delftu. Měřeny byly tloušťky lože, koncentrační profily nad ložem, střední rychlosti a tlakové ztráty v potrubí. Tato měření umožnila vyhodnocení vertikálního erozního proudu částic z povrchu lože pro různé koncentrace unášených částic ve směsi proudící nad ložem a vlivu koncentrací na erozi.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
6. Experimental investigation of internal structure of open-channel flow with intense transport of sediment
- Creator:
- Matoušek, Václav, Bareš, Vojtěch, Krupička, Jan, Picek, Tomáš, and Zrostlík, Štěpán
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- acoustic anemometry, plane bed, solid-liquid flow, and tilting flume experiment
- Language:
- Slovak
- Description:
- Gravity-driven open-channel flows carrying coarse sediment over an erodible granular deposit are studied. Results of laboratory experiments with artificial sediments in a rectangular tilting flume are described and analyzed. Besides integral quantities such as flow rate of mixture, transport concentration of sediment and hydraulic gradient, the experiments include measurements of the one-dimensional velocity distribution across the flow. A vertical profile of the longitudinal component of local velocity is measured across the vertical axis of symmetry of a flume cross section using three independent measuring methods. Due to strong flow stratification, the velocity profile covers regions of very different local concentrations of sediment from virtually zero concentration to the maximum concentration of bed packing. The layered character of the flow results in a velocity distribution which tends to be different in the transport layer above the bed and in the sediment-free region between the top of the transport layer and the water surface. Velocity profiles and integral flow quantities are analyzed with the aim of evaluating the layered structure of the flow and identifying interfaces in the flow with a developed transport layer above the upper plane bed.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
7. Gamma-ray-based measurement of concentration distribution in pipe flow of settling slurry: vertical profiles and tomographic maps
- Creator:
- Krupička, Jan and Matoušek, Václav
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- two-phase flow, gamma radiometry, computational tomography, and slurry flow experiment
- Language:
- Slovak
- Description:
- Principles of gamma-ray-based measurement are summarized and their application is demonstrated on an operation of the radiometric facility installed in the test loop for slurry flows at the Institute of Hydrodynamics. The facility is able to measure vertical profiles of chord-averaged concentrations and concentration maps in the pipe cross section. A methodology of measurement is proposed including detection and quantification of random and systematic errors. Experimental results are discussed in the light of the proposed methodology. Experimentally determined vertical profiles of concentration are presented for slurry flows of four different fractions of glass beads. The tomographic application of the radiometric device is demonstrated on a measured concentration map and a suitable image reconstruction method is tested. High reliability of measured concentration distributions is proved except for regions near the pipe wall. The radiometric method is shown to be a useful tool for measurement of concentration distribution in slurry flow through a pipe.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
8. Gradually varied transport of bed load in sheet flow: mathematical and physical modeling
- Creator:
- Zrostlík, Štěpán, Krupička, Jan, Picek, Tomáš, Bareš, Vojtěch, and Matoušek, Václav
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- intense sediment transport, unsteady flow, steady flow, bed roughness, flume experiment, and steep slope
- Language:
- English
- Description:
- Intense transport of sediment is studied in flows of steep slopes. Transport- and friction formulae suitable for flows at high shear stress above eroded bed are discussed. The formulae are further incorporated to a proposed simple model for open-channel flow with gradually varied transport of sediment. Two variants of the formulae are used alternatively in the model. Tilting-flume experiments are described that provided steady-flow data suitable for a validation of the formulae and unsteady-sediment-transport data for a validation of the designed model of gradually varied transport. A comparison of experimental results with formulae predictions and model simulations shows a very reasonable agreement for both variants of the transport and friction formulae. and Obsahuje seznam literatury a znaků
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
9. Laboratory testing of granular kinetic theory for intense bed load transport
- Creator:
- Matoušek, Václav and Zrostlík, Štěpán
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- granular flow, sheet flow, sediment transport, grain collision, and tilting flume experiment
- Language:
- Slovak
- Description:
- Collisional interactions in a sheared granular body are typical for intense bed load transport and they significantly affect behavior of flow carrying bed load grains. Collisional mechanisms are poorly understood and modelling approaches seldom accurately describe reality. One of the used approaches is the kinetic theory of granular flows. It offers constitutive relations for local shear-induced collision-based granular quantities – normal stress, shear stress and fluctuation energy – and relates them with local grain concentration and velocity. Depth distributions of the local granular quantities produced by these constitutive relations have not been sufficiently verified by experiment for the condition of intense bed load transport in open channels and pressurized pipes. In this paper, results from a tilting-flume facility including measured velocity distribution and deduced concentration distribution (approximated as linear profiles) are used to calculate distributions of the collision-based quantities by the constitutive relations and hence to test the ability of the kinetic-theory constitutive relations to predict conditions observed in these collision-dominated flows. This test indicates that the constitutive relations can be successfully applied to model the local collisional transport of solids at positions where the local concentration is not lower than approximately 0.18 and not higher than approximately 0.47.
- Rights:
- http://creativecommons.org/publicdomain/mark/1.0/ and policy:public
10. On equivalent roughness of mobile bed at high shear stress
- Creator:
- Matoušek, Václav and Krupička, Jan
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- bed shear, experiment, hydraulic transport, sediment transport, tření o dno, hydraulická doprava, and pohyb splavenin
- Language:
- Slovak
- Description:
- 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). and Příspěvek se zabývá mechanismem tření na povrchu erodovatelného dna za podmínek horního režimu pohybu splavenin nad plochým dnem, to jest při hodnotách Shieldsova parametru větších než přibližně 0,6. Zvláštní pozornost je věnována proudění při Shieldsově parametru větším než 2. Z literatury byla sebrána experimentální data pro proudění za vysokých smykových napětí, ke kterým byla přidána nová data z vlastních měření s pískem velikosti středního zrna 1,36 mm v potrubí průměru 100 mm trubního okruhu Ústavu pro hydrodynamiku AV ČR. Databáze obsahuje výsledky měření pro částice různých vlastností v širokém rozsahu hodnot Shieldsova parametru až do hodnoty okolo 23. Příspěvek analyzuje data za účelem stanovení závislosti hydraulické drsnosti povrchu sedliny na ostatních parametrech proudění. Je navržen semiempirický vztah, který předpokládá závislost hydraulické drsnosti na Shieldsově parametru, poměru rychlosti proudění k usazovací rychlosti částic a poměru hydraulického poloměru průtočného profilu k velikosti částic. Tento vztah se doporučuje především pro proudění nesoucí jak dnové splaveniny, tak suspendované částice.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public