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Drag
Kinds of Drag Terms modified by Drag Selected AbstractsTernary complex formation between AmtB, GlnZ and the nitrogenase regulatory enzyme DraG reveals a novel facet of nitrogen regulation in bacteriaMOLECULAR MICROBIOLOGY, Issue 6 2007Luciano F. Huergo Summary Ammonium movement across biological membranes is facilitated by a class of ubiquitous channel proteins from the Amt/Rh family. Amt proteins have also been implicated in cellular responses to ammonium availability in many organisms. Ammonium sensing by Amt in bacteria is mediated by complex formation with cytosolic proteins of the PII family. In this study we have characterized in vitro complex formation between the AmtB and PII proteins (GlnB and GlnZ) from the diazotrophic plant-associative bacterium Azospirillum brasilense. AmtB,PII complex formation only occurred in the presence of adenine nucleotides and was sensitive to 2-oxoglutarate when Mg2+ and ATP were present, but not when ATP was substituted by ADP. We have also shown in vitro complex formation between GlnZ and the nitrogenase regulatory enzyme DraG, which was stimulated by ADP. The stoichiometry of this complex was 1:1 (DraG monomer : GlnZ trimer). We have previously reported that in vivo high levels of extracellular ammonium cause DraG to be sequestered to the cell membrane in an AmtB and GlnZ-dependent manner. We now report the reconstitution of a ternary complex involving AmtB, GlnZ and DraG in vitro. Sequestration of a regulatory protein by the membrane-bound AmtB,PII complex defines a new regulatory role for Amt proteins in Prokaryotes. [source] Ideology, Power Orientation and Policy Drag: Explaining the Elite Politics of Britain's Bill of Rights DebateGOVERNMENT AND OPPOSITION, Issue 1 2009David Erdos This article argues that three factors have framed elite political debate and outcomes on a Bill of Rights in Britain , the degree of commitment to an ideology of social liberalism, the executive/non-executive power orientation of key actors and the phenomenon of policy drag. These factors explain not only the overall historical contours of political debate but also (1) Labour's ,aversive' conversion to the Bill of Rights agenda and passage of the Human Rights Act (1998); and (2) the Conservatives' more positive recent attitude to the Bill of Rights agenda. [source] A two-step Taylor-characteristic-based Galerkin method for incompressible flows and its application to flow over triangular cylinder with different incidence anglesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2010Yan Bao Abstract An alternative characteristic-based scheme, the two-step Taylor-characteristic-based Galerkin method is developed based on the introduction of multi-step temporal Taylor series expansion up to second order along the characteristic of the momentum equation. Contrary to the classical characteristic-based split (CBS) method, the current characteristic-based method does not require splitting the momentum equation, and segregate the calculation of the pressure from that of the velocity by using the momentum,pressure Poisson equation method. Some benchmark problems are used to examine the effectiveness of the proposed algorithm and to compare with the original CBS method, and the results show that the proposed method has preferable accuracy with less numerical dissipation. We further applied the method to the numerical simulation of flow around equilateral triangular cylinder with different incidence angles in free stream. In this numerical investigation, the flow simulations are carried out in the low Reynolds number range. Instantaneous streamlines around the cylinder are used as a means to visualize the wake region behind, and they clearly show the flow pattern around the cylinder in time. The influence of incidence angle on flow characteristic parameters such as Strouhal number, Drag and Lift coefficients are discussed quantitatively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of electron-electron interaction on the diffusion current of spin-polarized electronsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008Yutaka Takahashi Abstract Electron-electron interaction modifies carrier transport in the spin-polarized system. The effects are investigated in the two-dimensional electron gas in semiconductor heterostructures. We find that the diffusion currents of spin-up and spin-down electrons are reduced, compared to the non-interacting values, by the momentum exchange between spin-up and spin-down electrons through their collisions (Spin Drag), and also by the electron energy renormalization arising from the manyparticle correlations. We numerically calculate the diffusion coefficients of spin-up and spin-down electrons separately in high-quality heterostructures of GaAs at low temperatures, including the effect of finite spin life time. Our calculations show that the diffusion coefficients are reduced down to less than half of their non-interacting values. We also find the negative diffusivity at low temperatures. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Drag on a fibre in a counterflow air streamPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003Brendan Redmond Dr. This paper evaluates the drag on the surface of a fibre moving axially in a counterflow air stream. It is assumed that the fibre velocity is very much greater than the velocity of the air stream. [source] Novel software architecture for rapid development of magnetic resonance applicationsCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2002Josef Debbins Abstract As the pace of clinical magnetic resonance (MR) procedures grows, the need for an MR scanner software platform on which developers can rapidly prototype, validate, and produce product applications becomes paramount. A software architecture has been developed for a commercial MR scanner that employs state of the art software technologies including Java, C++, DICOM, XML, and so forth. This system permits graphical (drag and drop) assembly of applications built on simple processing building blocks, including pulse sequences, a user interface, reconstruction and postprocessing, and database control. The application developer (researcher or commercial) can assemble these building blocks to create custom applications. The developer can also write source code directly to create new building blocks and add these to the collection of components, which can be distributed worldwide over the internet. The application software and its components are developed in Java, which assures platform portability across any host computer that supports a Java Virtual Machine. The downloaded executable portion of the application is executed in compiled C++ code, which assures mission-critical real-time execution during fast MR acquisition and data processing on dedicated embedded hardware that supports C or C++. This combination permits flexible and rapid MR application development across virtually any combination of computer configurations and operating systems, and yet it allows for very high performance execution on actual scanner hardware. Applications, including prescan, are inherently real-time enabled and can be aggregated and customized to form "superapplications," wherein one or more applications work with another to accomplish the clinical objective with a very high transition speed between applications. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 216,237, 2002 [source] Organic litter: dominance over stones as a source of interrill flow roughness on low-gradient desert slopes at Fowlers Gap, arid western NSW, AustraliaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2003David Dunkerley Abstract Thirty-six runoff plot experiments provide data on flow depths, speeds, and Darcy,Weisbach friction coefficients (f) on bare soil surfaces, and surfaces to which were added sufficient extra plant litter or surface stones to provide projected cover of 5, 10 and 20 per cent. Precision flow depth data were derived with a computer-controlled gantry and needle gauge for two different discharges for each plot treatment. Taking a fixed flow intensity (Reynolds number, Re = 150) for purposes of comparison shows means of f = 17·7 for bare soil surfaces, f = 11·4 for added stone treatments, and f = 23·8 for added litter treatments. Many individual values of f for stone treatments are lower than for the bare soil surface, but all litter treatments show increases in fcompared to bare soil. The lowering of f in stone treatments relates to the submerged volume that the stones occupied, and the associated concentration of flow onto a smaller part of the plot surface. This leads to locally higher flow intensities and lower frictional drag along threads of flow that the obstacles create. Litter causes higher frictional drag because the particles are smaller, and, for the same cover fraction, are 100 times more numerous and provide 20 times the edge or perimeter length. Along these edges, which in total exceed 2·5 m g,1 (equivalent to 500 m m,2 for a loading of 2 t ha,1), surface tension draws up water from between the litter particles. This reduces flow depth there, and as a consequence of the lower flow intensity, frictional drag rises. Furthermore, no clear passage remains for the establishment of flow threads. These findings apply to shallow interrill flows in which litter is largely immobile. The key new result from these experiments is that under these conditions, a 20 per cent cover of organic litter can generate interrill frictional retardation that exceeds by nearly 41 per cent that of a bare soil surface, and twice that contributed by the same cover fraction of surface stones. Even greater dominance by litter can be anticipated at the many dryland sites where litter covers exceed those tested here. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effects of radio-transmitter antenna length on swimming performance of juvenile rainbow troutECOLOGY OF FRESHWATER FISH, Issue 4 2004K. J. Murchie Abstract,,, Technological advances have lead to the production of micro radio-transmitters capable of being implanted in fish as small as c. 5 g. Although the actual tags are small, transmitters are equipped with long antennas that can increase drag and tangle in debris. We examined the effects of radio-transmitter antenna length on the swimming performance of juvenile rainbow trout, Oncorhynchus mykiss, (N = 156, mean mass = 34 g, mean fork length = 148 mm). Although we tested a variety of different antenna lengths up to a maximum of 300 mm, only the longest antenna significantly impaired swimming performance relative to control fish (P < 0.001). There was no difference in swimming performance between the sham (surgery, but no transmitter) and the control fish (handled, but no surgery), suggesting that the surgical procedure itself did not negatively affect the fish. Regression analysis, however, indicated that there was a significant decrease in swimming performance associated with increased antenna length (R2 = 0.11, P < 0.001). In addition, when held in laboratory tanks, fish with the three longest antennas (150, 225 and 300 mm) frequently became entangled with the standpipe. We suggest that researchers, under the guidance of the tag manufacturer, trim antennas to the shortest possible length required to detect fish in their specific study area. Antenna length is clearly an important issue for small fish, especially for species that inhabit complex habitats where antennas may become entangled, and where fish must attain speeds near limits of their swimming capacity. Resumen 1. Los avances tecnológicos han llevado a producir micro radio-trasmisores capaces de ser implantados en peces de muy pequeño tamaño (,5 g). Aunque las marcas actuales son pequeñas, los trasmisores están equipados con antenas largas que pueden llegar a enredarse en los restos de vegetación. Examinamos los efectos de la longitud de la antena sobre la rutina natatoria de juveniles de Oncorhynchus mykiss (n = 156, peso medio = 34 g, longitud furcal media = 148 mm). 2. Aunque analizamos varias longitudes de antena, hasta 300 mm, solamente las de mayor longitud alteraron la rutina natatoria en relación a los peces control (P < 0.001). No hubo diferencia en la rutina natatoria entre individuos bajo cirugía pero sin trasmisores respecto de los individuos control (manipulados pero sin cirugía) lo que sugiere que los procedimientos de cirugía no afectaron negativamente a los peces. Sin embargo, análisis de regresión indicaron un declive significativo en la rutina natatoria asociado a la longitud de la antena (R2 = 0.11, P < 0.001). Además, al ser mantenidos en tanques, los individuos con las tres antenas mas largas (150, 225, y 300 mm) frecuentemente se enredaron con las tuberías. 3. Sugerimos a los investigadores que, bajo la dirección de los productores de marcas y antenas, consideren el uso de las antenas más pequeñas que permitan detectar a los peces en sus respectivas áreas de estudio. La longitud de la antena es una cuestión importante para los pequeños peces, especialmente para especies en hábitats complejos donde las antenas pueden llegar a enredarse y donde los peces pueden alcanzar velocidades casi al limite de su capacidad natatoria. [source] Electrohydrodynamic-mediated dielectrophoretic separation and transport based on asymmetric electrode pairsELECTROPHORESIS, Issue 24 2008E. Du Abstract This paper presents a system for continuous separation and transport of micron and submicron particles in fluidic environment based on dielectrophoretic fractionation in concert with AC electrothermal (AC ET)-induced fluidic pumping action. In this system, high frequency AC signals are used to energize asymmetric electrode pairs. AC ET-driven fluidic pumping is utilized as an alternative to the commonly used external pressure-driven fluid flow. Distinct collection sites for negative-dielectrophoretic and positive-dielectrophoretic particle populations are identified. The coupling effects of dielectrophoretic force and viscous drag from AC ET fluid flow on particle motions are investigated theoretically and numerically. We demonstrate that these two forces can be efficiently coupled to achieve continuous separation and transport of particle mixture in a fluidic medium when the dielectric properties of the particles and the fluidic environment are different. The combination of dielectrophoretic separation and AC ET pumping function provides a promising approach to further miniaturize and integrate these mechanisms into lab-on-chip devices. [source] Length-dependent DNA separations using multiple end-attached peptide nucleic acid amphiphiles in micellar electrokinetic chromatographyELECTROPHORESIS, Issue 13 2008Jeffrey M. Savard Abstract End-labeled free-solution electrophoresis (ELFSE) is an alternative approach to gel-based methods for size-based electrophoretic separation of DNA. In ELFSE, an electrically neutral "drag-tag" is appended to DNA to add significant hydrodynamic drag, thereby breaking its constant charge-to-friction ratio. Current drag-tag architecture relies on covalent attachment of polymers to each DNA molecule. We have recently proposed the use of micellar drag-tags in conjunction with sequence-specific hybridization of peptide nucleic acid amphiphiles (PNAAs). This work investigates the effect of multiple PNAA attachment on DNA resolution using MEKC. Simultaneous PNAA hybridization allows for the separation of long DNA targets, up to 1012,bases, using micellar drag-tags. Each PNAA handle independently interacts with the micellar phase, reducing the overall mobility of this complex relative to individual PNAA binding. The sequence- and size-based dependence of this separation technique is maintained with multiple PNAA binding over a range of DNA sizes. Results are accurately described by ELFSE theory, yielding , = 54 for single-micelle tagging and , = 142 for dual-micelle tagging. This method is the first example of a non-covalent drag-tag used to separate DNA of 1000,bases based on both size and sequence. [source] Evaluation of factors influencing membrane performanceENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 4 2005Weihua Peng Abstract Three commercial water treatment membranes, TFC-S (Koch membranes, San Diego, CA), ESPA1, and NTR7450 (Hydranautics, San Diego, CA), were tested under various physical and chemical conditions to investigate their fouling behaviors. It was found that TFC-S always displayed the greatest rate of flux decline, ESPA1 displayed a mild trend in flux decline, and NTR7450 presented a nearly stable flux. Multivariable regression models showed that the flux decline rates for TFC-S and ESPA1 were controlled by the initial permeate flux, whereas their initial (that is, instantaneous) foulings were controlled by the interaction between permeate drag and electrostatic repulsions. Feed bacteria concentration also contributed to the initial fouling of ESPA1 as a result of cell deposition on the membrane surface. NTR7450 showed an initial decline in flux followed by a steady flux, and its initial fouling was significantly affected by feed water total organic carbon (TOC) arising from the initial accumulation of colloidal organic particles on the surface. © 2005 American Institute of Chemical Engineers Environ Prog, 2005 [source] Recrystallization Modeling of AA8XXX Alloys with Cellular Automata Considering Recovering Kinetics,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Carmen Schäfer A through-process modeling scheme for the prediction of recrystallization textures and microstructures after final annealing, subsequent to cold rolling is proposed and applied to a commercial AlFeSi alloy. The heart of the setup is a cellular automaton for modeling of recrystallization which considers changes in dislocation density by recovery and changes in Zener and solute drag due to microchemistry evolution. However, recrystallization is the crucial point in the whole setup, since it leads to significant changes in microstructure and texture. The simulated results are compared to experiments. [source] Crayfish as geomorphic agents and ecosystem engineers: effect of a biomass gradient on baseflow and flood-induced transport of gravel and sand in experimental streamsFRESHWATER BIOLOGY, Issue 1 2003B. Statzner SUMMARY 1.,Using experimental streams, we studied the impact of the crayfish Orconectes limosus on (i) the transport of gravel and sand at baseflow; (ii) the sediment surface (bedform, particle consolidation, proportion of sand, algal and gravel cover); and (iii) the critical shear stress (,C) causing incipient gravel and sand motion during simulated floods. We examined (i) and (ii) in experimental outdoor flumes that replicated riffle-pool sequences and (iii) in a larger laboratory flume, in which we exposed sediments retrieved from the outdoor flumes to a progressively increasing discharge. 2.,Habitat changes induced by crayfish, such as bedform alterations in riffles (downstream displacement of riffle heads) and the increase of gravel on sand dunes in pools, had major impacts on the spatial and temporal patterns of the baseflow transport of gravel and sand. 3.,In addition to their impact on bedform in riffles and on gravel cover in pools, crayfish prevented the physical consolidation of particles in riffles and reduced the algal cover and the proportion of sand in the surface layer in both riffles and pools. These crayfish impacts on sediment surface variables had complex, interacting effects on the mobilisation of gravel and sand during subsequent flood simulations. For sand, crayfish progressively decreased the ,C (i.e. the sum of bedform drag and skin friction) by about 50% along the entire biomass gradient in pools, whereas the presence of crayfish abruptly decreased the ,C by about 75% in riffles. For gravel, the discharge causing motion in riffles produced a shear stress (in terms of skin friction) on an even bedform that was about 75% lower in all flumes with crayfish compared with the flumes without crayfish. Crayfish had no impact on ,C for gravel in pools. 4.,Scaling-up these experimental results to real streams suggests that crayfish could affect the patch dynamics of major sediment transport events and habitat suitability for other organisms that, at larger spatial scales, could increase the overall spatio-temporal habitat diversity and thus the overall structural and functional biodiversity of lotic communities. [source] Influence of temperature on hydrodynamic costs of morphological defences in zooplankton: experiments on models of Eubosmina (Cladocera)FUNCTIONAL ECOLOGY, Issue 3 2000R. Lagergren Abstract 1.,If swimming speed is correlated to fitness (e.g. by affecting food intake or the chance to evade predators) or considerable energy is expended in swimming, zooplankton wearing protruding structures (as predator defence) that significantly increase drag resistance must pay a cost for the better protection against predators that these traits imply. 2.,In an experiment with plastic models, the drag and energy consumption of swimming in two species of Eubosmina were examined. Eubosmina longispina has a typical Bosmina morphology with a low carapace and short antennule, whereas E. coregoni gibbera has a very high carapax and long antennule. 3.,At 5 °C, E. c. gibbera had 32,45% higher drag than E. longispina. At 20 °C, the difference is 20,45%. 4.,A mathematical model of swimming predicts that these differences in drag should result in 18,20 (at 5 °C) or 14,16 (at 20 °C) percentage lower speed for E. c. gibbera than for E. longispina if they use the same amount of energy in swimming. 5.,The relative difference in drag or swimming speed between the two species was highest at low Reynolds number (i.e. low speed or low temperature). These results show that hydrodynamic costs of extreme morphology may increase with decreasing temperature. 6.,The increased cost of morphological antipredator defence at low temperatures may be enlightening with regard to the role of temperature in the induction of cyclomorphic traits in zooplankton. This may be one explanation for why extreme forms of E. c. gibbera and some Daphnia are only found in the summer when water temperature is high. [source] Ideology, Power Orientation and Policy Drag: Explaining the Elite Politics of Britain's Bill of Rights DebateGOVERNMENT AND OPPOSITION, Issue 1 2009David Erdos This article argues that three factors have framed elite political debate and outcomes on a Bill of Rights in Britain , the degree of commitment to an ideology of social liberalism, the executive/non-executive power orientation of key actors and the phenomenon of policy drag. These factors explain not only the overall historical contours of political debate but also (1) Labour's ,aversive' conversion to the Bill of Rights agenda and passage of the Human Rights Act (1998); and (2) the Conservatives' more positive recent attitude to the Bill of Rights agenda. [source] Viscosity measurements of ethylene glycol solution with flow drag reduction additivesHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 8 2006Naoto Haruki Abstract The viscous characteristics of ethylene glycol (EG) solution with flow drag reduction additive have been investigated experimentally. In this study, oleyldihydoroxyetyl amineoxide (ODEAO) was used as the flow drag reduction additive, and an aqueous solution of EG was used as a secondary refrigerant. The viscosity of the EG solution with ODEAO was measured with a rotational rheometer. The experimental parameters of viscosity measurement were the temperature of the EG solution with ODEAO, the ODEAO concentration, and the EG concentration. From the experimental results, the apparent viscosity of the EG solution with ODEAO showed SIS (shear induced state). The non-linear dependence of shear stress on shear rate has been well approximated by the power-law model under high shear conditions. The power-law contents, pseudoplastic viscosity, and index number have been estimated for each experimental parameter. Using the measured viscosity and non-dimensional analysis, the flow drag and heat transfer reduction effect of the EG solution with ODEAO has been investigated. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(8): 553,567, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20134 [source] Minimum shear wind strength required for dynamic soaring of albatrossesIBIS, Issue 1 2005GOTTFRIED SACHS The transfer of energy from the moving air in the shear wind above the sea surface to a bird is considered as an energy source for dynamic soaring, with the goal to determine the minimum shear wind strength required for the dynamic soaring of albatrosses. Focus is on energy-neutral trajectories, implying that the energy gain from the moving air is just sufficient to compensate for the energy loss due to drag for a dynamic soaring cycle. A mathematical optimization method is used for computing minimum shear wind energy-neutral trajectories, using a realistic flight mechanics model for the soaring of albatrosses. Thus, the minimum shear wind strength required for dynamic soaring is determined. The minimum shear wind strength is of a magnitude that often exists or is exceeded in areas in which albatrosses are found. This result holds for two control cases dealt with, one of which shows a freely selectable and the other a constant lift coefficient characteristic. The mechanism of energy transfer from the shear flow to the bird is considered, and it is shown that there is a significant energy gain in the upper curve and a loss in the lower curve. As a result, the upper curve can be qualified as the characteristic flight phase of dynamic soaring to achieve an energy gain. [source] Flight characteristics of birds:IBIS, Issue 2 2001I. radar measurements of speeds This is the first part of a study on flight characteristics of birds and presents an annotated list of flight speeds of 139 western Palearctic species. All measurements were taken with the same tracking radar and corrected for wind influence according to radar-tracked wind-measuring balloons. Graphical presentation of the birds' air speeds emphasizes the wide variation of speeds within species and allows easy comparison between taxonomic groups, species, and types of flight. Unlike theoretical predictions, speeds increase only slightly with size. The larger species seem to be increasingly limited to speeds close to their speed of minimum power consumption Vmp',. Released birds, apparently reluctant to depart with migratory speed, fly at considerably lower speeds than migrating conspecifics. While large birds seem to be limited to speeds around Vmp', smaller birds seem to be capable of selecting between various speeds, approaching predicted Vmp, when tending to remain airborne at low cost, but flying at much higher speeds when tending to make best progress at low cost (around predicted speed of maximum range Vmr,). Predictions of air speeds by aerodynamic models proved to be too low for small birds because the models do not account for the gain in speed attained by the reduction in profile drag during bounding flight of small passerines. The models predict excessive speeds for large birds because the power output available for flight seems to decline much more with size than previously assumed. [source] Use of neural networks for the prediction of frictional drag and transmission of axial load in horizontal wellboresINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2003Tanvir Sadiq Abstract The use of mud motors and other tools to accomplish forward motion of the bit in extended reach and horizontal wells allows avoiding large amounts of torque caused by rotation of the whole drill string. The forward motion of the drill string, however, is resisted by excessive amount of friction. In the presence of large compressive axial loads, the drill pipe or coiled tubing tends to buckle into a helix in horizontal boreholes. This causes additional frictional drag resisting the transmission of axial load (resulting from surface slack-off force) to the bit. As the magnitude of the frictional drag increases, a buckled pipe may become ,locked-up' making it almost impossible to drill further. In case of packers, the frictional drag may inhibit the transmission of set-up load to the packer. A prior knowledge of the magnitude of frictional drag for a given axial load and radial clearance can help avoid lock-up conditions and costly failure of the tubular. In this study a neural network model, for the prediction of frictional drag and axial load transmission in horizontal wellbores, is presented. Several neural network architectures were designed and tested to obtain the most accurate prediction. After cross-validation of the Back Propagation Neural Network (BPNN) algorithm, a two-hidden layer model was chosen for simultaneous prediction of frictional drag and axial load transmission. A comparison of results obtained from BPNN and General Regression Neural Network (GRNN) algorithms is also presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Multiple-relaxation-time lattice Boltzmann computation of channel flow past a square cylinder with an upstream control bi-partitionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2010M. A. Moussaoui Abstract The present paper deals with the application of the multiple-relaxation-time lattice Boltzmann equation (MRT-LBE) for the simulation of a channel flow with a bi-partition located upstream of a square cylinder in order to control the flow. Numerical investigations have been carried out for different heights and positions of the bi-partition at Reynolds number of 250. Key computational issues involved are the computation of fluid forces acting on the square cylinder, the vortex shedding frequency and the impact of such bluff body on the flow pattern. A particular attention is paid to drag and lift coefficients on the square cylinder. The predicted results from MRT-LBE simulations show that in most cases, the interaction was beneficial insofar as the drag of the square block was lower with the bi-partition than without it. Fluctuating side forces due to vortex shedding from the main body were also reduced for most bi-partition positions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Optimal airfoil shapes for low Reynolds number flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2009D. N. Srinath Abstract Flow over NACA 0012 airfoil is studied at , = 4, and 12, for Re,500. It is seen that the flow is very sensitive to Re. A continuous adjoint based method is formulated and implemented for the design of airfoils at low Reynolds numbers. The airfoil shape is parametrized with a non-uniform rational B-splines (NURBS). Optimization studies are carried out using different objective functions namely: (1) minimize drag, (2) maximize lift, (3) maximize lift to drag ratio, (4) minimize drag and maximize lift and (5) minimize drag at constant lift. The effect of Reynolds number and definition of the objective function on the optimization process is investigated. Very interesting shapes are discovered at low Re. It is found that, for the range of Re studied, none of the objective functions considered show a clear preference with respect to the maximum lift that can be achieved. The five objective functions result in fairly diverse geometries. With the addition of an inverse constraint on the volume of the airfoil the range of optimal shapes, produced by different objective functions, is smaller. The non-monotonic behavior of the objective functions with respect to the design variables is demonstrated. The effect of the number of design parameters on the optimal shapes is studied. As expected, richer design space leads to geometries with better aerodynamic properties. This study demonstrates the need to consider several objective functions to achieve an optimal design when an algorithm that seeks local optima is used. Copyright © 2008 John Wiley & Sons, Ltd. [source] Drag reduction by flow separation control on a car after bodyINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2009Mathieu Rouméas Abstract New development constraints prompted by new pollutant emissions and fuel consumption standards (Corporate Average Economy Fuel) require that automobile manufacturers develop new flow control devices capable of reducing the aerodynamic drag of motor vehicles. The solutions envisaged must have a negligible impact on the vehicle geometry. In this context, flow control by continuous suction is seen as a promising alternative. The control configurations identified during a previous 2D numerical analysis are adapted for this purpose and are tested on a 3D geometry. A local suction system located on the upper part of the rear window is capable of eliminating the rear window separation on simplified fastback car geometry. Aerodynamic drag reductions close to 17% have been obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source] Numerical simulations of viscous flows using a meshless methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2008Changfu You Abstract This paper uses the element-free Galerkin (EFG) method to simulate 2D, viscous, incompressible flows. The control equations are discretized with the standard Galerkin method in space and a fractional step finite element scheme in time. Regular background cells are used for the quadrature. Several classical fluid mechanics problems were analyzed including flow in a pipe, flow past a step and flow in a driven cavity. The flow field computed with the EFG method compared well with those calculated using the finite element method (FEM) and finite difference method. The simulations show that although EFG is more expensive computationally than FEM, it is capable of dealing with cases where the nodes are poorly distributed or even overlap with each other; hence, it may be used to resolve remeshing problems in direct numerical simulations. Flows around a cylinder for different Reynolds numbers are also simulated to study the flow patterns for various conditions and the drag and lift forces exerted by the fluid on the cylinder. These forces are calculated by integrating the pressure and shear forces over the cylinder surface. The results show how the drag and lift forces oscillate for high Reynolds numbers. The calculated Strouhal number agrees well with previous results. Copyright © 2008 John Wiley & Sons, Ltd. [source] Drag prediction, decomposition and visualization in unstructured mesh CFD solver of TAS-codeINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2008Wataru Yamazaki Abstract The accuracy of drag prediction in unstructured mesh CFD solver of TAS (Tohoku University Aerodynamic Simulation) code is discussed using a drag decomposition method. The drag decomposition method decomposes total drag into wave, profile, induced and spurious drag components, the latter resulting from numerical diffusion and errors. The mesh resolution analysis is conducted by the drag decomposition method. The effect of an advanced unstructured mesh scheme of U-MUSCL reconstruction is also investigated by the drag decomposition method. The computational results show that the drag decomposition method reliably predicts drag and is capable of meaningful drag decomposition. The accuracy of drag prediction is increased by eliminating the spurious drag component from the total drag. It is also confirmed that the physical drag components are almost independent of the mesh resolution and scheme modification. Copyright © 2007 John Wiley & Sons, Ltd. [source] On the orbital motion of a rotating inner cylinder in annular flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2007Shunxin Feng Abstract In this paper, numerical calculations have been performed to analyse the influence of the orbital motion of an inner cylinder on annular flow and the forces exerted by the fluid on the inner cylinder when it is rotating eccentrically. The flow considered is fully developed laminar flow driven by axial pressure gradient. It is shown that the drag of the annular flow decreases initially and then increases with the enhancement of orbital motion, when it has the same direction as the inner cylinder rotation. If the eccentricity and rotation speed of the inner cylinder keep unchanged (with respect to the absolute frame of reference), and the orbital motion is strong enough that the azimuthal component (with respect to the orbit of the orbital motion) of the flow-induced force on the inner cylinder goes to zero, the flow drag nearly reaches its minimum value. When only an external torque is imposed to drive the eccentric rotation of the inner cylinder, orbital motion may occur and, in general, has the same direction as the inner cylinder rotation. Under this condition, whether the inner cylinder can have a steady motion state with force equilibrium, and even what type of motion state it can have, is related to the linear density of the inner cylinder. Copyright © 2006 John Wiley & Sons, Ltd. [source] Numerical modelling of free-surface flows in ship hydrodynamicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2003U. P. Bulgarelli Abstract Current trends in the investigation of ship hydrodynamics are reviewed with emphasis on the problem of wave-body interaction. This includes the classical seakeeping problem and as a special case, the problem of prediction for the drag encountered by a ship advancing in calm water. Specific issues related to the numerical treatment of the air,water interface are examined, with emphasis on the modelling of wave breaking. The discussion on the large-scale modelling of the flow around ships is focused on the prediction of wave loads, ship motions and resistance in calm water. Copyright © 2003 John Wiley & Sons, Ltd. [source] Design and operation of unbaffled aerated agitated vessels with unsteadily forward,reverse rotating impellers handling viscous Newtonian liquidsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2003Masanori Yoshida Abstract Design and operation of unbaffled aerated agitated vessels with multiple unsteadily forward,reverse rotating impellers (AJITERs) for viscous Newtonian liquids were studied. The effects of operating conditions such as gas sparging rate, agitation rate and the number of impeller stages, geometrical conditions such as the diameters of vessel and impeller, and the physical properties of liquids on the drag and added moment of inertia coefficients, necessary to predict the average and maximum power consumptions of the impellers in AJITERs, were evaluated and the empirical relationships which estimate values of each of these coefficients are presented. The effects of operating conditions, geometrical conditions and liquid physical properties on the gas hold-up, ,gD, and volumetric oxygen transfer coefficient, kLaD, were evaluated in relation to the total power input which is the sum of the average power consumption of impellers, ie average agitation power input, and aeration power input. Empirical relationships, useful for design and operation of AJITERs, were obtained for each viscosity range, where the dependences of ,gD and kLaD on the specific total power input and superficial gas velocity differed, to predict ,gD and kLaD respectively as a function of the specific total power input, superficial gas velocity and liquid physical properties. © 2003 Society of Chemical Industry [source] Evaluation of electroosmotic drag coefficient of water in hydrated sodium perfluorosulfonate electrolyte polymerJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2009Liuming Yan Abstract The electroosmotic drag coefficient of water molecules in hydrated sodium perfluorosulfonate electrolyte polymer is evaluated on the basis of the velocity distribution functions of the sodium cations and water molecules with an electric field applied using molecular dynamics simulations. The simulation results indicate that both velocity distribution functions of water molecules and of sodium cations agree well with the classic Maxwellian velocity distribution functions when there is no electric field applied. If an electric field is applied, the distribution functions of velocity component in directions perpendicular to the applied electric field still agree with the Maxwellian velocity distribution functions but with different temperature parameters. In the direction of the applied electric field, the electric drag causes the velocity distribution function to deviate from the Maxwellian velocity distribution function; however, to obey the peak shifted Maxwellian distribution function. The peak shifting velocities coincide with the average transport velocities induced by the electric field, and could be applied to the evaluation of the electroosmotic drag coefficient of water. By evaluation of the transport velocities of water molecules in the first coordination shells of sodium cations, sulfonate anion groups, and in the bulk, it is clearly shown that the water molecules in the first coordination shell of sodium cations are the major contribution to the electroosmotic drag and momentum transfer from water molecules within the first coordination shell to the other water molecules also contributes to the electroosmotic drag. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Flipper bands do not affect foraging-trip duration of Magellanic PenguinsJOURNAL OF FIELD ORNITHOLOGY, Issue 4 2009P. Dee Boersma ABSTRACT Flipper bands are used to mark penguins because leg bands can injure their legs. However, concerns remain over the possible effects of flipper bands on penguins. We examined the effects of stainless-steel flipper bands on the duration of foraging trips by Magellanic Penguins (Spheniscus magellanicus) at Punta Tombo, Argentina, using an automated detection system. We predicted that, if bands were costly and increased drag, flipper-banded penguins would make longer foraging trips than those with small or no external markings. We tagged 121 penguins with radio-frequency identification (RFID) tags and an additional external mark. We placed either a stainless-steel band on the left flipper (N= 62) or a 2×10-mm small-animal ear tag in the outside web of the left foot (N= 59). We measured foraging-trip durations (N= 376 trips) for 68 adult penguins with chicks from 15 December 2007 to 28 February 2008. Contrary to predictions, trip duration was similar for banded and web-tagged penguins (P= 0.22) and for males and females (P= 0.52), with no interaction between tag type and sex (P= 0.52). No penguins marked in the 2007 breeding season and recaptured between 30 September and 30 November 2008 (N= 113) lost flipper bands or web tags, but three RFID tags failed between March and September 2008. Properly designed and applied flipper bands were a reliable marking method for Magellanic Penguins, had a lower failure rate than RFIDs, and did not affect foraging-trip duration. RESUMEN Los anillos de ala son usados para marcar pingüinos porque los anillos de tarso pueden causar heridas en sus piernas. Sin embargo, existen dudas sobre los posibles efectos de los anillos de ala sobre los pingüinos. Usando un sistema de detección automatizado, examinamos los efectos de anillos de ala hechos de acero inoxidable sobre la duración de los viajes para forrajeo por el pingüino Spheniscus magellanicus en Punta Tombo, Argentina. Predecimos que si los anillos afectarían a los pingüinos e incrementaran la fricción con el agua, los pingüinos con anillos de ala harían viajes para forrajeo de mayor duración en comparación a los que no portaban marcadores externos o que llevaban marcadores externos de menor tamaño. Marcamos a 121 pingüinos con marcadores de identificación por radio frecuencia, además de otro marcador al exterior del ave. Colocamos un anillo de acero inoxidable al ala izquierdo (N= 62), o un marcador de oreja (2×10 mm) para animales pequeños de en la membrana interdigital exterior del pie izquierdo (N= 59). Desde el 15 de diciembre del 2007 hasta el 28 de Febrero del 2008 medimos la duración de los viajes para forrajeo (N= 376 viajes) para 68 pingüinos adultos con pichones. Contrariamente a nuestras predicciones, la duración de los viajes fue similar para pingüinos con anillos y para pingüinos con marcadores en el pie (P = 0.22), así como entre machos y hembras (P= 0.52), con ninguna interacción entre el tipo de marca y el sexo (P= 0.52). Ningún pingüino marcado en la temporada reproductiva del 2007 y recapturado entre el 30 de Septiembre y el 30 de Noviembre del 2008 (N= 113) perdió el anillo de ala o el marcador en el pie, pero tres marcadores de identificación por radio frecuencia fallaron entre Marzo y Septiembre del 2008. Los anillos de ala apropiadamente diseñadas y aplicadas fueron un método de marcaje confiable para S. magellanicus, tuvieron una tasa de fallo menor a los marcadores de identificación por radio frecuencia y no afectaron a la duración de los viajes para forrajeo. [source] Reduced swimming abilities in fast-growing transgenic common carp Cyprinus carpio associated with their morphological variationsJOURNAL OF FISH BIOLOGY, Issue 1 2009D. Li Critical swimming speeds (Ucrit) and morphological characters were compared between the F4 generation of GH-transgenic common carp Cyprinus carpio and the non-transgenic controls. Transgenic fish displayed a mean absolute Ucrit value 22·3% lower than the controls. Principal component analysis identified variations in body shape, with transgenic fish having significantly deeper head, longer caudal length of the dorsal region, longer standard length (LS) and shallower body and caudal region, and shorter caudal length of the ventral region. Swimming speeds were related to the combination of deeper body and caudal region, longer caudal length of the ventral region, shallower head depth, shorter caudal length of dorsal region and LS. These findings suggest that morphological variations which are poorly suited to produce maximum thrust and minimum drag in GH-transgenic C. carpio may be responsible for their lower swimming abilities in comparison with non-transgenic controls. [source] | |||||||||||||||||||||||||||||||