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Turbulent
Terms modified by Turbulent Selected AbstractsTurbulent flow over a dune: Green River, ColoradoEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2005Jeremy G. Venditti Abstract Detailed echo-sounder and acoustic Doppler velocimeter measurements are used to assess the temporal and spatial structure of turbulent flow over a mobile dune in a wide, low-gradient, alluvial reach of the Green River. Based on the geometric position of the sensor over the bedforms, measurements were taken in the wake, in transitional flow at the bedform crest, and in the internal boundary layer. Spatial distributions of Reynolds shear stress, turbulent kinetic energy, turbulence intensity, and correlation coefficient are qualitatively consistent with those over fixed, two-dimensional bedforms in laboratory flows. Spectral and cospectral analysis demonstrates that energy levels in the lee of the crest (i.e. wake) are two to four times greater than over the crest itself, with minima over the stoss slope (within the developing internal boundary layer). The frequency structure in the wake is sharply defined with single, dominant peaks. Peak and total spectral and cross-spectral energies vary over the bedform in a manner consistent with wave-like perturbations that ,break' or ,roll up' into vortices that amalgamate, grow in size, and eventually diffuse as they are advected downstream. Fluid oscillations in the lee of the dune demonstrate Strouhal similarity between laboratory and field environments, and correspondence between the peak frequencies of these oscillations and the periodicity of surface boils was observed in the field. Copyright © 2005 John Wiley & Sons, Ltd. [source] The distribution and prevalence of sponges in relation to environmental gradients within a temperate sea lough: vertical cliff surfacesDIVERSITY AND DISTRIBUTIONS, Issue 6 2000James J. Bell Abstract. The prevalence and distribution of sponges was surveyed on vertical cliff surfaces at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland. The number of sponge species was recorded at 6-metre depth intervals at four sites within Lough Hyne, and at one site on the adjacent Atlantic coastline to examine differences in abundance and zonation patterns. Sites ranged from an exposed turbulent regime to sheltered, sedimented environments. Individual species showed different distributions and prevalence between sites and with increasing depth. Greatest differences were observed between the most- and least-disturbed sites. Distinct sponge zonation patterns were evident at all sites sampled. Twenty-five species were considered dominant at all five sites with the remaining 48 species considered rare. Only four of the 25 most-dominant species occurred at the site experiencing the most turbulent flow conditions, whereas 12 species were found at the site of unidirectional fast flow. At sites of moderate to slight water movement and high sedimentation, between 18 and 24 of the most dominant species were present. Encrusting forms constituted high proportions of sponge communities at all five sites sampled (although consisting of different species). At sites of turbulent and unidirectional fast flow massive forms also dominated whereas at the least turbulent sites, where sedimentation was high, arborescent sponges were abundant. Few species showed exclusive distribution to a single depth and site, but there was some degree of correlation between species distributions and abiotic factors such as sedimentation rate and flow regimes. Sponge distributions and densities are discussed with respect to the suitability of species' morphologies to particular environments, intra-specific and inter-specific competition and physiological adaptations that enable them to survive in different habitats. [source] The distribution and prevalence of sponges in relation to environmental gradients within a temperate sea lough: inclined cliff surfacesDIVERSITY AND DISTRIBUTIONS, Issue 6 2000James J. Bell Abstract. Sponge communities on inclined cliff surfaces (40°) at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland were sampled at five sites (four inside the lough and one on the adjacent Atlantic coast). Each site varied in sedimentation rate and flow regime. Sites ranged from turbulent (with negligible sedimentation) to very low flow (< 3 cm,1) and highly sedimented regimes. Sponge species showed variation between sites and depth. The greatest difference in sponge communities was observed between the most turbulent and most sedimented sites. The distinct zonation patterns, present at all sites, were most pronounced at the highly sedimented sites. Encrusting forms constituted a high proportion of the sponges at all sites. However encrusting species found at the turbulent site were different to those at the sedimented sites. Arborescent species were common, mainly at the sedimented sites within Lough Hyne. Distributions of sponge species are considered with respect to morphological adaptation, competition and physiological adaptation. The distributions of sponge species on inclined surfaces are also compared with those on vertical cliff faces. [source] Size distributions of suspended particles in open channel flow over bed materialsENVIRONMETRICS, Issue 2 2005B. S. Mazumder Controlled experiments have shown that the grain-size distribution of suspended sediments is related to bed material, flow velocity and height of suspension above the sand bed in an open channel flow. A theoretical model has been developed for computation of suspended grain-size distribution on the basis of continuity equations of sediment and water, using the computed bed-layer concentration as a reference. The proposed model includes the effect of suspension concentration into the mean velocity, turbulent and viscous shear stresses owing to the dynamic coupling between the flow and sediments in suspension. The effect of hindered settling due to the increased concentration in suspension is also taken into account. The model is considered to be a more general one than the existing models, and the results of the present model compare well with the experimental data. Copyright © 2004 John Wiley & Sons, Ltd. [source] Hydrographic features and seabird foraging in Aleutian PassesFISHERIES OCEANOGRAPHY, Issue 2005CAROL LADD Abstract Strong tidal currents crossing over the abrupt topography of the Aleutian Passes result in regions with high horizontal property gradients. These frontal regions vary with the tidal cycle and form the boundary between vertically mixed and stratified regions. Concentrations of seabirds were associated with convergence zones in the mixed water (MW) and with the front between North Pacific (NP) water and MW. Species that were foraging by picking at prey from the surface were associated with surface convergences that appeared to be associated with Langmuir circulation cells or tidal features (all fulmar aggregations) in the central passes (Samalga, Seguam). In contrast, subsurface foraging puffins and small alcids were mostly observed in areas of turbulent, well-mixed water near the shallow regions of the passes. Short-tailed shearwater flocks that were plunge-diving for prey were associated with the front between the NP water and MW in the passes. On our transects, we observed no significant aggregations of seabirds associated with Bering Sea water or NP water away from the frontal zones. The interaction of strong currents with bathymetric features results in zones of vertical advection, mixing, and surface convergences that make island passes attractive foraging regions for seabirds. Deep passes lacking these features, such as many of the passes in the western Aleutian Archipelago, are not as likely to facilitate trophic transfer to top predators as shallow passes, such as those found in the eastern Aleutian Islands. [source] Turbulent Flow Through Porous MediaGROUND WATER, Issue 5 2001Douglas W. Barr The pressure driving flow through porous media must be equal to the viscous resistance plus the inertial resistance. Formulas are developed for both the viscous resistance and the inertial resistance. The expression for the coefficient of permeability consists of parameters which describe the characteristics of the porous medium and the permeating fluid and which, for unconsolidated isotropic granular media, are all measurable. A procedure is proposed for testing for the occurrence of turbulence and calculating the effective permeability when it occurs. The formulas are applied to a set of data from 588 permeameter runs ranging from laminar to highly turbulent. The equations fit the data from the permeameter closely through the laminar flow conditions and quite closely through the turbulent conditions. In the turbulent range, the plotting of the data separates into three distinct lines for each of the three shapes of particles used in the tests. For the porous medium and fluid of these tests, turbulence begins at a head gradient of about 0.1. [source] Numerical model for the prediction of dilute, three-dimensional, turbulent fluid,particle flows, using a Lagrangian approach for particle tracking and a CVFEM for the carrier phaseINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2008L. A. Oliveira Abstract A numerical model for dilute, three-dimensional, turbulent, incompressible fluid,solid particle flows and its application to a demonstration problem are presented. An Eulerian description is used to model the flow of the fluid (carrier) phase, and the governing equations are solved using a control-volume finite element method (CVFEM). The motion of the solid (particulate) phase is simulated using a Lagrangian approach. An efficient algorithm is proposed for locating the particles in the finite element mesh. In the demonstration problem, which involves a particle-laden axisymmetric jet, a modified k,, turbulence model is used to characterize the velocity and length scales of the turbulent flow of the fluid phase. The effect of turbulence on the particle trajectories is accounted for through a stochastic model. The effect of the particles on the fluid time,mean velocity and turbulence (two-way coupling) is also addressed. Comparisons between predictions and available experimental data for the demonstration problem are presented. Satisfactory agreement is obtained. Copyright © 2008 John Wiley & Sons, Ltd. [source] Acoustic upwinding for sub- and super-sonic turbulent channel flow at low Reynolds numberINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2007H. C. de LangeArticle first published online: 13 FEB 200 Abstract A recently developed asymmetric implicit fifth-order scheme with acoustic upwinding for the spatial discretization for the characteristic waves is applied to the fully compressible, viscous and non-stationary Navier,Stokes equations for sub- and super-sonic, mildly turbulent, channel flow (Re,=360). For a Mach number of 0.1, results are presented for uniform (323, 643 and 1283) and non-uniform (expanding wall-normal, 323 and 643) grids and compared to the (incompressible) reference solution found in (J. Fluid. Mech. 1987; 177:133,166). The results for uniform grids on 1283 and 643 nodes show high resemblance with the reference solution. Expanding grids are applied on 643 - and 323 -node grids. The capability of the proposed technique to solve compressible flow is first demonstrated by increasing the Mach number to 0.3, 0.6 and 0.9 for isentropic flow on the uniform 643 -grid. Next, the flow speed is increased to Ma=2. The results for the isothermal-wall supersonic flows give very good agreement with known literature results. The velocity field, the temperature and their fluctuations are well resolved. This means that in all presented (sub- and super-sonic) cases, the combination of acoustic upwinding and the asymmetric high-order scheme provides sufficient high wave-number damping and low wave-number accuracy to give numerically stable and accurate results. Copyright © 2007 John Wiley & Sons, Ltd. [source] Numerical simulation of turbulent impinging jet on a rotating diskINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2007A. Abdel-Fattah, Article first published online: 25 OCT 200 Abstract The calculations of quasi-three-dimensional momentum equations were carried out to study the influence of wall rotation on the characteristics of an impinging jet. The pressure coefficient, the mean velocity distributions and the components of Reynolds stress are calculated. The flow is assumed to be steady, incompressible and turbulent. The finite volume scheme is used to solve the continuity equation, momentum equations and k,, model equations. The flow characteristics were studied by varying rotation speed , for 0,,,167.6 rad/s, the distance from nozzle to disk (H/d) was (3, 5, 8 and 10) and the Reynolds number Re base on VJ and d was 1.45 × 104. The results showed that, the radial velocity and turbulence intensity increase by increasing the rotation speed and decrease in the impingement zone as nozzle to disk spacing increases. When the centrifugal force increases, the radial normal stresses and shear stresses increase. The location of maximum radial velocity decreases as the local velocity ratio (,) increases. The pressure coefficient depends on the centrifugal force and it decreases as the distance from nozzle to plate increases. In impingement zone and radial wall jet, the spread of flow increases as the angular velocity decreases The numerical results give good agreement with the experiment data of Minagawa and Obi (Int. J. of Heat and Fluid Flow 2004; 25:759,766). Copyright © 2006 John Wiley & Sons, Ltd. [source] Prediction of unsteady, separated boundary layer over a blunt body for laminar, turbulent, and transitional flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2004D. Scott Holloway Abstract The focus of this paper is to study the ability of unsteady RANS-based CFD to predict separation over a blunt body for a wide range of Reynolds numbers particularly the ability to capture laminar-to-turbulent transition. A perfect test case to demonstrate this point is the cylinder-in-crossflow for which a comparison between experimental results from the open literature and a series of unsteady simulations is made. Reynolds number based on cylinder diameter is varied from 104 to 107 (subcritical through supercritical flow). Two methods are used to account for the turbulence in the simulations: currently available eddy,viscosity models, including standard and realizable forms of the k,, model; and a newly developed eddy,viscosity model capable of resolving boundary layer transition, which is absolutely necessary for the type and range of flow under consideration. The new model does not require user input or ,empirical' fixes to force transition. For the first time in the open literature, three distinct flow regimes and the drag crisis due to the downstream shift of the separation point are predicted using an eddy,viscosity based model with transition effects. Discrepancies between experimental and computational results are discussed, and difficulties for CFD prediction are highlighted. Copyright © 2004 John Wiley & Sons, Ltd. [source] A high-order finite difference method for incompressible fluid turbulence simulationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2003Eric Vedy Abstract A Hermitian,Fourier numerical method for solving the Navier,Stokes equations with one non-homogeneous direction had been presented by Schiestel and Viazzo (Internat. J. Comput. Fluids 1995; 24(6):739). In the present paper, an extension of the method is devised for solving problems with two non-homogeneous directions. This extension is indeed not trivial since new algorithms will be necessary, in particular for pressure calculation. The method uses Hermitian finite differences in the non-periodic directions whereas Fourier pseudo-spectral developments are used in the remaining periodic direction. Pressure,velocity coupling is solved by a simplified Poisson equation for the pressure correction using direct method of solution that preserves Hermitian accuracy for pressure. The turbulent flow after a backward facing step has been used as a test case to show the capabilities of the method. The applications in view are mainly concerning the numerical simulation of turbulent and transitional flows. Copyright © 2003 John Wiley & Sons, Ltd. [source] Taking the quantum leap: nonprofits are now in business. an Australian perspectiveINTERNATIONAL JOURNAL OF NONPROFIT & VOLUNTARY SECTOR MARKETING, Issue 4 2003Jacinta Goerke The fact that they need to deliver more essential social services is accepted by most professionals working in nonprofit organisations. Yet, needing to become more competitive, increasingly ,businesslike' and to start creating partnerships with profit-driven businesses may require a quantum leap to take place. This hard reality imposed by recent changes in government policy is challenging for many social service workers still coming to terms with a decade of turbulent and changing times. From origins of ,she'll be right mate' and a community-held belief that it is the government's responsibility to finance all essential social services, today's nonprofits are increasingly fighting over smaller funding budgets and feeling the pinch as they have to implement business practices that will ultimately make them more accountable, profitable and attractive to prospective business partnerships. The purpose of this paper is, therefore, to present an option to larger Australian nonprofit organisations keen to move away from a dependency model of service delivery and open to exploring the possibility of implementing a marketing communications charter which includes the appointment of a business development manager. Copyright © 2003 Henry Stewart Publications [source] Effect of flow regimes on the presence of Legionella within the biofilm of a model plumbing systemJOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2006Z. Liu Abstract Aims:, Stagnation is widely believed to predispose water systems to colonization by Legionella. A model plumbing system was constructed to determine the effect of flow regimes on the presence of Legionella within microbial biofilms. Methods and Results:, The plumbing model contained three parallel pipes where turbulent, laminar and stagnant flow regimes were established. Four sets of experiments were carried out with Reynolds number from 10 000 to 40 000 and from 355 to 2000 in turbulent and laminar pipes, respectively. Legionella counts recovered from biofilm and planktonic water samples of the three sampling pipes were compared with to determine the effect of flow regime on the presence of Legionella. Significantly higher colony counts of Legionella were recovered from the biofilm of the pipe with turbulent flow compared with the pipe with laminar flow. The lowest counts were in the pipe with stagnant flow. Conclusions:, We were unable to demonstrate that stagnant conditions promoted Legionella colonization. Significance and Impact of the Study:, Plumbing modifications to remove areas of stagnation including deadlegs are widely recommended, but these modifications are tedious and expensive to perform. Controlled studies in large buildings are needed to validate this unproved hypothesis. [source] Diagnostic criteria for locating acquired arteriovenous fistulas with color doppler sonographyJOURNAL OF CLINICAL ULTRASOUND, Issue 6 2002Jian-Chu Li MD Abstract Purpose. The purpose of this prospective study was to evaluate and determine criteria for locating acquired arteriovenous fistulas using color Doppler sonography. Methods. We performed color Doppler sonography on 12 consecutive patients with acquired arteriovenous fistulas. We evaluated the morphologic and hemodynamic changes in the involved vessels to help locate the fistulas (10 in the extremities, 1 in the neck, and 1 in the abdomen). Results. In all cases, turbulent high-velocity flow spectrum and flow signals were present at the fistula sites, and arterialized waveforms from the draining veins were detected. In the 10 cases of acquired arteriovenous fistulas in the extremities, the resistance indices in the arteries proximal to the fistulas were all less than 1.00 (mean, 0.65), whereas the resistance indices in the arteries distal to the fistulas were all 1.00 or greater (mean, 1.17). In 70% of the cases, the diameter of the artery proximal to the fistula was at least 1.2 mm larger than that distal to the fistula. The fistula site was inferred by the point of maximal venous dilatation in 70% of the cases and by the focal perivascular color artifact in 82% of the cases. The fistula site was identified on gray-scale sonography and color flow imaging in 33% and 75% of the cases, respectively. Conclusions. Fistula sites can be located effectively and quickly by a combination of major and minor diagnostic criteria. The major diagnostic criteria are (1) junction of low- and high-resistance flow in the supplying artery, (2) a high-velocity arterialized waveform in the draining vein, and (3) a turbulent, high-velocity flow spectrum at the junction of the artery and the vein. The minor diagnostic criteria are (1) direct communication between the involved artery and vein, (2) significant change in the diameter of the supplying artery, (3) a focal point of venous dilatation, and (4) a focal perivascular color artifact. © 2002 Wiley Periodicals, Inc. J Clin Ultrasound 30:336,342, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jcu.10084 [source] Mechanisms of particle dispersion in a turbulent, square duct flowAICHE JOURNAL, Issue 7 2009Michael Fairweather Abstract Particle dispersion in a square duct flow is studied using large eddy simulation combined with Lagrangian particle tracking under conditions of one-way coupling. The flow has a bulk Re = 250 k, with six particle sizes ranging from 5 to 1000 ,m. Results obtained for the fluid phase show good agreement with experimental data. For particles, predictions demonstrate that secondary flows within the duct dominate small particle dispersion and result in a uniform distribution, whereas gravity promotes the deposition of large particles on the duct floor. For the largest particles, the secondary flows contribute to particle concentration in corners on the duct floor, with these particles also clustering in low-velocity regions close to the floor. A detailed analysis of the influence of the flow on particle distribution is provided through consideration of the particle dispersion function, with the mechanisms of particle dispersion elucidated using a dynamical analysis. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] CFD modeling and validation of the turbulent fluidized bed of FCC particlesAICHE JOURNAL, Issue 7 2009Jinsen Gao Abstract An experimental and computational study is presented on the hydrodynamic characteristics of FCC particles in a turbulent fluidized bed. Based on the Eulerian/Eulerian model, a computational fluid dynamics (CFD) model incorporating a modified gas-solid drag model has been presented, and the model parameters are examined by using a commercial CFD software package (FLUENT 6.2.16). Relative to other drag models, the modified one gives a reasonable hydrodynamic prediction in comparison with experimental data. The hydrodynamics show more sensitive to the coefficient of restitution than to the flow models and kinetics theories. Experimental and numerical results indicate that there exist two different coexisting regions in the turbulent fluidized bed: a bottom dense, bubbling region and a dilute, dispersed flow region. At low-gas velocity, solid-volume fractions show high near the wall region, and low in the center of the bed. Increasing gas velocity aggravates the turbulent disorder in the turbulent fluidized bed, resulting in an irregularity of the radial particle concentration profile. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Demarcation of a new circulating turbulent fluidization regimeAICHE JOURNAL, Issue 3 2009Xiaobo Qi Abstract Transient flow behaviors in a novel circulating-turbulent fluidized bed (C-TFB) were investigated by a multifunctional optical fiber probe, that is capable of simultaneously measuring instantaneous local solids-volume concentration, velocity and flux in gas-solid two-phase suspensions. Microflow behavior distinctions between the gas-solid suspensions in a turbulent fluidized bed (TFB), conventional circulating fluidized bed (CFB), the bottom region of high-density circulating fluidized bed (HDCFB), and the newly designed C-TFB were also intensively studied. The experimental results show that particle-particle interactions (collisions) dominate the motion of particles in the C-TFB and TFB, totally different from the interaction mechanism between the gas and solid phases in the conventional CFB and the HDCFB, where the movements of particles are mainly controlled by the gas-particle interactions (drag forces). In addition, turbulence intensity and frequency in the C-TFB are significantly greater than those in the TFB at the same superficial gas velocity. As a result, the circulating-turbulent fluidization is identified as a new flow regime, independent of turbulent fluidization, fast fluidization and dense suspension upflow. The gas-solid flow in the C-TFB has its inherent hydrodynamic characteristics, different from those in TFB, CFB and HDCFB reactors. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Multiresolution analysis on identification and dynamics of clusters in a circulating fluidized bedAICHE JOURNAL, Issue 3 2009Tung-Yu Yang Abstract A new wavelet-threshold criterion was developed to distinguish the cluster and the void phases from the transient solids holdup/concentration fluctuation signals when measured in a 108 mm-i.d. × 5.75 m-high circulating fluidized bed with FCC particles (dp = 78 ,m, ,p = 1,880 kg/m3). An appropriate level of approximation subsignal was systematically specified as a threshold for cluster identification, based on multiresolution analysis (MRA) of wavelet transformation. By the established threshold, the dynamic properties of clusters including the appearance time fraction of clusters Fcl, average cluster duration time ,cl, cluster frequency fcl, and local average solids holdup in clusters ,sc, at different radial and axial positions were determined under the turbulent, transition and fast fluidization flow regimes. The results also describe the dynamic properties of clusters and flow patterns in the splash zone along with the dense bottom region of the circulating fluidized beds. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Collaborative partnerships for nursing faculties and health service providers: what can nursing learn from business literature?JOURNAL OF NURSING MANAGEMENT, Issue 3 2006DIANE BROWN PhD Collaborative partnerships between nursing faculties and health service providers are the cornerstone of successful clinical experience for nursing students. The challenge of providing an optimal learning environment can be enormous given the turbulent and rapidly changing environment in health. The present study uses the business literature to examine what nursing can learn from business about the development of successful collaborative partnerships. The characteristics of sound partnerships are described and a set of best practice guidelines is developed. The guidelines summarize the factors considered to be essential for the effective development of collaborative partnerships. In these times of nursing shortages and high turnover high quality, collaborative partnerships between nursing faculties and the health care sector are seen as a possible solution to optimize clinical learning and therefore graduate preparedness. [source] Experimental investigation of the hydrodynamics in a liquid,solid riserAICHE JOURNAL, Issue 3 2005Shantanu Roy Abstract Liquid,solid fluid dynamics has been investigated in a 6-in. (0.15 m) "cold-flow" circulating fluidized bed riser using non-invasive flow monitoring methods. Gamma-ray computed tomography (CT) was used to measure the time-averaged cross-sectional solids volume fraction distributions at several elevations. The time-averaged mean and "fluctuating" solids velocity fields were quantified using the computer-automated radioactive particle tracking (CARPT) technique. The experimental equipment, protocol of implementation, and data analysis have been discussed briefly, with particular emphasis on the specific features in the use of these techniques for studying high-density turbulent flows as in a liquid,solid riser. The experimental study examines nine operating conditions, that is, three liquid superficial velocities and three solids flow rates. The solids holdup profile is found to be relatively uniform across the cross section of the riser, with marginal segregation near the walls. The time-averaged solids velocity profiles are found to have a negative component at the walls, indicating significant solids backmixing. Detailed characterization of the solids velocity fields in terms of RMS velocities, kinetic energies, Hurst exponents, residence time distributions, trajectory length distributions, dispersion coefficients, and so forth are presented. Comparative and symbiotic analyses of the results were used to develop a coherent picture of the solids flow field. In addition, the work also serves to demonstrate the power and versatility of these flow-imaging techniques in studying highly turbulent and opaque multiphase systems. © 2005 American Institute of Chemical Engineers AIChE J, 51: 802,835, 2005 [source] Spanning the flow regimes: Generic fluidized-bed reactor modelAICHE JOURNAL, Issue 7 2003I. A. Abba Probabilistic averaging is used to model fluidized-bed reactors across the three fluidlization flow regimes most commonly encountered in industry (bubbling, turbulent, and fast fluidization), extending earlier work, which introduced this approach to bridge the bubbling and turbulent regimes of fluidization. In extending this concept to the fast fluidization regime, the probabilities of being in each of the three regimes are represented as probability density functions derived from regime boundary transition data. The three regime-specific models,a generalized version of a two-phase bubbling bed model at low gas velocities, a dispersed flow model for turbulent beds at intermediate velocities, and a generalized version of a core-annulus model at higher velocities,are employed, leading to improved predictions compared with any of the individual models, while avoiding discontinuities at the regime boundaries. Predictions from the new integrated model are in good agreement with available ozone decomposition data over the full range of applicability covered elsewhere. [source] SUPPLY MANAGEMENT, SUPPLY FLEXIBILITY AND PERFORMANCE OUTCOMES: AN EMPIRICAL INVESTIGATION OF MANUFACTURING FIRMSJOURNAL OF SUPPLY CHAIN MANAGEMENT, Issue 3 2010YING LIAO Increasingly, the global market environment is becoming more turbulent, complex and uncertain. Literature has explored the importance of supply management and its direct impact on performance. However, the nature of strategic supply management and its impact on supply flexibility needs further clarification in the context of the use of supplier resources and supplier network coordination. This research presents a model of supply management, supply flexibility and supply chain performance. In this study, we examine the relationships between supply management and supply flexibility, and extend the concept of supply flexibility in terms of supplier flexibility and supply network flexibility on relevant supply chain performance measures. Data for the study were collected from 201 manufacturing firms, and the measurement scales of supply flexibility were tested and validated using structural equation modeling. The results indicate strong, positive and direct relationships between supply management practices and supply flexibility, and between supply flexibility and supply chain performance. Concluding theoretical and managerial implications are discussed. [source] Rapid quantitation of cardiovascular flow using slice-selective fourier velocity encoding with spiral readoutsMAGNETIC RESONANCE IN MEDICINE, Issue 4 2007Joao L. A. Carvalho Abstract Accurate flow visualization and quantitation is important for the assessment of many cardiovascular conditions such as valvular stenosis and regurgitation. Phase contrast based methods experience partial volume artifacts when flow is highly localized, complex and/or turbulent. Fourier velocity encoding (FVE) avoids such problems by resolving the full velocity distribution within each voxel. This work proposes the use of slice selective FVE with spiral readouts to acquire fully localized velocity distributions in a short breath-hold. Scan-plane prescription is performed using classic protocols, and an automatic algorithm is used for in-plane localization of the flow. Time and spatially-resolved aortic valve velocity distributions with 26-msec temporal resolution and 25 cm/sec velocity resolution over a 600 cm/sec field-of-view were acquired in a 12-heartbeat breath-hold. In carotid studies, scan time was extended to achieve higher spatial resolution. The method was demonstrated in healthy volunteers and patients, and the results compared qualitatively well with Doppler ultrasound. Acquisition time could be reduced to 7 heartbeats (a 42% reduction) using partial Fourier reconstruction along the velocity dimension. Magn Reson Med 57:639,646, 2007. © 2007 Wiley-Liss, Inc. [source] Advanced models for erosion corrosion and its mitigation,MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2008G. Schmitt Erosion corrosion, i.e., flow-induced localized corrosion (FILC) is initiated when flow dynamic forces surpass the fracture energy of protective layers or scales on metals. With a new model the maximum interaction energies between flowing media and solid walls can be quantified in terms of "freak" energy densities created during singular events (freak events) of perpendicular impacts by near-wall microturbulence elements. The freak energy densities are in the megaPascal range and match well in the order of magnitude with fracture energies of protective layers and can be estimated from Wavelet diagnostics of electrochemical current noise measured at microelectrodes under mass transport controlled conditions. This solves the problem that wall shear stresses, generally used to quantify critical flow intensities for FILC initiation, range several orders of magnitude (Pa range) below the fracture energies of protective layers. The new advanced model allows for the first time to quantify the maximum fluid dynamic forces exerted on solid walls under different turbulent and disturbed flow conditions (one-phase liquid flow on jet impinged surfaces and on coupons in rotated cages, surfaces impacted by slug flow and gas-pulsed impinging jets). Drag reducing additives were shown to reduce freak energy densities to values significantly below fracture energies of protective layers and hence inhibit initiation of FILC. The onset of FILC can be monitored online with the newly developed CoulCount method, an easy-to-use, non-invasive diagnostic tool which evaluates electrochemical current noise between jet impinged electrode pairs made from the metals to be tested. [source] Comparison of plume structures of carbon dioxide emitted from different mosquito trapsMEDICAL AND VETERINARY ENTOMOLOGY, Issue 1 2006Miriam F. Cooperband Abstract., A large field wind tunnel was used to compare four types of CO2 -baited mosquito traps. This study compared the plume structure and concentration of CO2 emitted by each trap, flow of suction into the trapping systems, flow of CO2 being released, trap shape and configuration, differences in visual appearance, and differences in temperature and humidity of emissions at the source of CO2 compared to ambient air. The structure of the CO2 plumes emitted by each trap differed considerably. All four plumes were turbulent, causing the concentration of CO2 within several metres of the source to attenuate to between 375 and 875 p.p.m. The Encephalitis Virus Surveillance (EVS) trap emitted concentrations of CO2 exceeding 20 000 p.p.m., the detection limits of our equipment, whereas the Mosquito Magnet® Freedom (MMF), Mosquito Magnet® Liberty (MML) and Mosquito Magnet® X (MMX) traps released CO2 at peaks of about 3500, 7200 and 8700 p.p.m., respectively. The MMX trap produced the greatest air velocity at both the suction inlet and CO2 outlet, followed by the MMF, MML and the EVS traps, respectively. [source] Gas dynamics of the central few parsec region of NGC 1068 fuelled by the evolving nuclear star clusterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010M. Schartmann ABSTRACT Recently, high-resolution observations with the help of the near-infrared adaptive optics integral field spectrograph Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) at the Very Large Telescope proved the existence of massive and young nuclear star clusters in the centres of a sample of Seyfert galaxies. With the help of three-dimensional high-resolution hydrodynamical simulations with the Pluto code, we follow the evolution of such clusters, especially focusing on stellar mass loss feeding gas into the ambient interstellar medium and driving turbulence. This leads to a vertically wide distributed clumpy or filamentary inflow of gas on large scales (tens of parsec), whereas a turbulent and very dense disc builds up on the parsec scale. In order to capture the relevant physics in the inner region, we treat this disc separately by viscously evolving the radial surface density distribution. This enables us to link the tens of parsec-scale region (accessible via SINFONI observations) to the (sub-)parsec-scale region (observable with the mid-infrared interferometer instrument and via water maser emission). Thereby, this procedure provides us with an ideal testbed for data comparison. In this work, we concentrate on the effects of a parametrized turbulent viscosity to generate angular momentum and mass transfer in the disc and additionally take star formation into account. Most of the input parameters are constrained by available observations of the nearby Seyfert 2 galaxy NGC 1068, and we discuss parameter studies for the free parameters. At the current age of its nuclear starburst of 250 Myr, our simulations yield disc sizes of the order of 0.8,0.9 pc, gas masses of 106 M, and mass transfer rates of 0.025 M, yr,1 through the inner rim of the disc. This shows that our large-scale torus model is able to approximately account for the disc size as inferred from interferometric observations in the mid-infrared and compares well to the extent and mass of a rotating disc structure as inferred from water maser observations. Several other observational constraints are discussed as well. [source] The fundamental difference between shear alpha viscosity and turbulent magnetorotational stressesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008Martin E. Pessah ABSTRACT Numerical simulations of turbulent, magnetized, differentially rotating flows driven by the magnetorotational instability (MRI) are often used to calculate the effective values of alpha viscosity that is invoked in analytical models of accretion discs. In this paper, we use various dynamical models of turbulent magnetohydrodynamic stresses, as well as numerical simulations of shearing boxes, to show that angular momentum transport in MRI-driven accretion discs cannot be described by the standard model for shear viscosity. In particular, we demonstrate that turbulent magnetorotational stresses are not linearly proportional to the local shear and vanish identically for angular velocity profiles that increase outwards. [source] A smoothed particle hydrodynamics simulation of the collapse of the interstellar mediumMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2001Y. Golanski A smoothed particle hydrodynamic (SPH) code is used to model a collapsing region of the interstellar medium (ISM). A region of the ISM is seeded with coolant material ejected from a supernova. The resulting pressure imbalance between the cooling region and the surrounding ISM induces collapse. The collapse first forms dense low-temperature regions (protoclouds) each containing several tens of solar masses of material and in quasi-equilibrium with the surrounding ISM. Turbulence is generated within the collapsing regions as they form. Collisions between protoclouds leads to regions of further increased mass and density, the final outcome being a dense cold cloud with mean density 10,18 kg m,3, mean temperature about 20 K and total mass a few hundred solar masses. The final cloud is sufficiently turbulent for star formation to occur within it. A new form of boundary condition was used in the SPH simulation to solve the problem inherent in modelling a continuum. [source] Detection of compact radio emission from Circinus X-1 with the first Southern hemisphere e-VLBI experimentMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2007C. J. Phillips ABSTRACT Circinus X-1 has recently returned to a state of strong radio flaring. Here we report on the first VLBI observations, and detection, undertaken in the 25 years since the 1975,1985 period of strong recurrent flaring activity. We detected Circinus X-1 with the first observations conducted by a recently developed Southern hemisphere e-VLBI array, at both 1.6 and 8.4 GHz, over a three-day period. At 1.6 GHz, the compact source has a total flux density of 11 mJy and a size of 60 ± 15 mas (Gaussian model full width at half maximum). At 8.4 GHz, the compact source is less than 60 mas. The size variation with frequency is consistent with a broadened image due to scattering in the turbulent, ionized interstellar medium of our Galaxy. However, these size measurements appear inconsistent with the ,2.2 variation expected for strong interstellar scattering and previous VLBI observations made at 2.3 GHz in the early 1980s. To explain this apparent inconsistency, we suggest that Circinus X-1 supports a weak, non-varying component of 35 mas extent (175 au at 5 kpc distance), corresponding to compact structure in the extended radio nebula. No significant variation in the flux density at 1.6 GHz is evident between two observations 24 h apart. No jet-like structures are evident on scales of tens of mas, simply a scatter broadened source, presumably coincident with the suggested neutron star in the binary system. [source] A comparison of algebraic Reynolds stress models for the prediction of the turbulent flow inside a turbomachine rotorPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003Marco Antonello Dr. An algebraic Reynolds stress model has been developed and tested simulating the turbulent flow inside a centrifugal impeller. The prediction of the model are compared with those of other algebraic turbulent stress models, in order to analyse the capability of properly account for effects such as flow curvature, flow separation, and solid wall rotation. [source] | |||||||||||||||||||||||||||||||