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A high speed/high flow test facility was designed and implemented to study experimentally the supercavitating flow behind a projectile nose in a controlled laboratory setting. The simulated projectile nose was held in position in the flow and the cavity interior was made visible by having the walls of the visualization facility 'cut through' the supercavity. Direct visualization of the cavity interior and measurements of the properties of the cavity contents were made. Transducers were positioned in the test section within the supercavitation volume to enable measurement of the sound speed and attenuation as a function of the flow and geometry parameters. These characterized indirectly the content of the cavity Photography, high speed videos, and acoustic measurements were used to investigate the contents of the cavity A side sampling cell was also used to sample in real time the contents of the cavity and measure the properties. Calibration tests conducted in parallel in a vapor cell enabled confirmation that, in absence of air injection, the properties of the supercavity medium match those of a mixture of water vapor and water droplets. Such a mixture has a very high sound speed with strong sound attenuation. Injection of air was also found to significantly decrease sound speed and to increase transmission. [DOI: I 0.1115/1.2409356]

The technology developed for photolithographically patterning the electric surface charge to be negative, positive, or neutral enables the realization of complex liquid flows even in straight and uniform microchannels with extremely small Reynolds number. A theoretical model to analyze a steady incompressible electrokinetically driven two-dimensional liquid flow in a microchannel with an inhomogeneous surface charge under externally applied electric field is derived. The flow field is obtained analytically by solving the biharmonic equation with the Hehnholtz-Smoluchowski slip boundary condition using the Fourier series expansion method. The model has been applied to study three basic out-of-plane vortical flow fields: single vortex and a train of corotating and a series of counterrotating vortex pairs. For model verification, the solution for the single vortex has been tested against numerical computations based on the full Navier-Stokes equations revealing the dominant control parameters. Two interesting phenomena have been observed in out-of-plane multivortex dynamics: merging of corotating vortices and splitting of counterrotating vortices. The criteria for the onset of both phenomena are discussed. Index Terms--Electrokinetic effect, microchannel, microfluidics, surface charge pattern, vortex.

Analytical and numerical models of capillary barrier performance commonly use hydraulic characteristics measured using pure water. However, the potential exists for an infiltrating solution to have a surface tension lower than that of pure water due to the presence of surface-active contaminants (surfactants). A lower surface tension solution may impact capillary barrier performance due to the dependence of capillarity on surface tension. An existing analytical solution for capillary diversion length (L) was modified to include the effect of surface tension reduction on steady-state capillary barrier performance during uniform and constant infiltration. The L for a surfactant-contaminated system was found to be less than for a pure water system and equal to L for a pure water system multiplied by the relative surface tension. Numerical modeling using HYDRUS-2D also showed that diversion was less in the surfactant-contaminated system and that the difference in the performance of the two systems was due to the fact that the fine layer in the capillary barrier retains less liquid when wetted with surfactant solution. DOI: 10.1061/(ASCE) 1090-0241(2007)133:2(231) CE Database subject headings: Unsaturated flow; Contaminants; Surface-active agents; Numerical models: Barriers: Water quality.

It is demonstrated that reactions for impulsive loads in saturated sand soil are speed dependent and can be far higher than the reactions for the corresponding slow loads. The reason is that soils rupture and pore water flow interacts, both for contractive sand and for dilatant sand and create additional pore water pressures and additional effective stresses. The traditional geotechnical methods, the extreme method, and the equilibrium methods have been extended to also include the interaction between ruptures and pore water flow. It is shown that zone ruptures generally will be dilatant except possibly for the loosest layering. This means that the pore water will be sucked into the rupture zone when it develops. This may not be the case with line ruptures, where the soil may be mainly contractive and squeeze out pore water during the development. Analytical methods have been developed and compared with laboratory results for falling cones penetrating into saturated sand. Both tests and analysis compared well and showed an increase from 2 to 70 times in average resistance compared with dry sand depending on the relative density of the sand and the ratio between speed of penetration and permeability. DOI: 10.1061/(ASCE)0733-950X(2007)133:1(39) CE Database subject headings: Water flow; Pore water; Saturated soils; Impulsive loads.

The present study was undertaken to examine the effect of surface roughness on the higher-order velocity moments in a turbulent open-channel flow. The wall roughness is large and the ratio of the roughness size to the depth of flow ranges from 0.1 to 0.15. Flow over two types of roughness conditions (ribs and dunes) are examined and compared with that over a smooth open channel. In the case of the rib roughness, three different spacings are used: p/k=4.5, 9, and 18; here, p=distance between the leading edges of two consecutive ribs and k=height of a rib with square cross section. The shape of the smooth wall dunes was geometrically similar to that commonly used in previous studies. In an effort to understand the influence of local wall roughness, rough-wall dunes are also used in the present study. The variables of interest include higher-order moments, conditional statistics based on a quadrant analysis, relationship of higher-order moments to the Reynolds stress and energy production. Although there are some similarities between open-channel flows and turbulent boundary layers, there are important differences as indicated by the third-order moments. The triple products and the second quadrant events are sensitive to the wall condition. Ejection events are found to be prevalent throughout the depth. It is also clear from the study that one needs to explicitly account for the surface condition in any model development to be able to predict transport characteristics. DOI: 10.1061/(ASCE)0733-9429(2007)133:1(77) CE Database subject headings: Velocity; Open channel flow; Hydraulic roughness.

The interaction between soil particles and pore water makes the behavior of saturated and unsaturated soil complex. In this note, upward seepage flow through a granular material was idealized using a one-column particle model. The motion of the individual particles was numerically simulated using the discrete-element method taking the interaction with the fluid into account. The fluid behavior was simulated by the Navier-Stokes equation using the semi-implicit method for pressure-linked equation. This approach has already been applied in powder engineering applications. However, there are very few studies that have used this approach in geotechnical engineering. This note first describes the qualitative and quantitative validation of this method for hydraulic gradients below the critical one by comparing the results with an analytical solution. Then, the ability of the method to simulate the macroscale behavior due to the interaction between particles and pore water at hydraulic gradients exceeding the critical hydraulic gradient is discussed. DOI: 10.1061/(ASCE)1090-0241(2007)133:1(104) CE Database subject headings: Discrete elements; One dimensional flow; Seepage; Two phase flow; Simulation.

A new model to compute nucleate boiling heat and mass transfer in which fully transient heat and fluid flow is computed with a free surface of the rising bubble and a periodic calculation of repeated cycles of bubble growth, detachment, and rise, is presented. The model makes it possible to evaluate, the influence of transient heat conduction, heat storage, and conversion in liquid as well as heat transfer in the wall on overall heat transfer performance.

The Agilent all-optical bubble switch uses bubbles in an organic fluid index matched to a silica planar lightwave circuit. The bubble is created and sustained by heaters that are deposited on an attached silicon substrate. Testing of the bubble shows how heater power and ambient pressure affect bubble shape, size, and optical reflection characteristics. Heat and fluid flow in the bubble were modeled in 2D and 3D using the homogeneous bubble model ill the Flow3D modeling software. Fluid condensing on the trench wall causes a dimple on the bubble and hence nonoptinmm optical reflection. To aid understanding, the bubble, silica walls, and heaters were also modeled as a thermal resistance network. Because the pressure drop across the bubble wall is fixed, the bubble size is determined by [P.sub.res]/[DELTA][T.sub.t], where [P.sub.res] is the heater power and [DELTA][T.sub.t] is the temperature difference between the bubble and the substrate. Heating the trench walls beyond the bubble temperature with heaters located underneath the trench wall will dry out the trench wall and give a stable optical reflection. As [DELTA][T.sub.t] approaches zero, a bubble is sustained without any heater power and with zero fluid flow. This 'static' bubble provides for a very stable optical reflection. Index Terms--Bubbles, fluidics, optical switches, microactuaturs, microelectromechanical devices, resistance heating.

Earlier electron microscopy studies demonstrated morphological signs of fluid flow in the juxtaglomerular apparatus (JGA), including fenestrations of the afferent arteriole (AA) endothelium facing renin granular cells. We aimed to directly visualize fluid flow in the JGA, the putative function of the fenestrated endothelium, using intravital multiphoton microscopy of Munich-Wistar rats and C57BL6 mice. Renin content of the AA correlated strongly with the length of the fenestrated, filtering AA segment. Fluorescence of the extracellular fluid marker lucifer yellow (LY) injected into the cannulated femoral vein in bolus was followed in the renal cortex by real-time imaging. LY was detected in the interstitium around the JG AA before the plasma LY filtered into Bowman's capsule and early proximal tubule. The fluorescence intensity of LY in the JGA interstitium was 17.9 [+ or -] 3.5% of that in the AA plasma (n = 6). The JGA fluid flow was oscillatory, consisting of two components: a fast (one every 5-10 s) and a slow (one every 45-50 s) oscillation, most likely due to the rapid transmission of both the myogenic and tubuloglomerular feedback (TGF)-mediated hemodynamic changes. LY was also detected in the distal tubular lumen about 2-5 s later than in the AA, indicating the flow of JGA interstitial fluid through the macula densa. In the isolated microperfused JGA, blocking the early proximal tubule with a micropipette caused significant increases in MD cell volume by 62 [+ or -] 4% (n = 4) and induced dilation of the intercellular lateral spaces. In summary, significant and dynamic fluid flow exists in the JGA which may help filter the released renin into the renal interstitium (endocrine function). It may also modulate TGF and renin signals in the JGA (hemodynamic function). intravital microscopy; fenestration; short-loop feedback; quinacrine; lucifer yellow

In this study, filtration flows through the walls of the rat aorta, pulmonary artery (PA), and inferior vena cava (IVC), vessels with very different susceptibilities to atherosclerosis, were measured as a function of transmural pressure ([DELTA]P), with intact and denuded endothelium on the same vessel. Aortic hydraulic conductivity ([L.sub.p]) is high at 60 mmHg, drops ~40% by 100 mmHg, and is pressure independent to 140 mmHg. The trends are similar in the PA and IVC, dropping 42% from 10 to 40 mmHg and flat to 100 mmHg (PA) and dropping 33% from 10 to 20 mmHg and essentially flat to 60 mmHg (IVC). Removal of the endothelium renders Lp([DELTA]P) flat: it increases [L.sub.p] of the aorta by ~75%, doubles [L.sub.p] of the PA, and quadruples [L.sub.p] of the IVC. Specific resistance (1/[L.sub.p]) of the aortic endothelium is ~47% of total resistance; i.e., the endothelium accounts for ~47% of the [DELTA]P drop at 100 mmHg. The PA value is 55% at >40 mmHg, and the IVC value is 23% at 10 mmHg. [L.sub.p] of the intact aorta, PA, and IVC are order [10.sup.-8], [10.sup.-7], and 5 x [10.sup.-7] cm*[s.sup.-1] * [mmHg.sup.-1], and wall thicknesses are 145.8 [micro]m (SD 9.3), 78.9 [micro]m (SD 3.3), and 66. [micro]m (SD 4.1), respectively. These data are consistent with the different wall structures of the three vessels. The rat aortic [L.sub.p] data are quantitatively consistent with rabbit [L.sub.p]([DELTA]P) (Tedgui A and Lever MJ. Am J Physiol Heart Circ Physiol 247: H784-H791, 1984; Baldwin AL and Wilson LM. Am J Physiol Heart Circ Physiol 264: H26-H32, 1993), suggesting that intimal compression under pressure loading may also play a role in [L.sub.p]([DELTA]P) in these other vessels. Despite very different driving [DELTA]p, nominal transmural water fluxes of these three vessels are very similar and, therefore, cannot alone account for their differences in disease susceptibility. The different fates of macromolecular tracers convected by these water fluxes into the walls of these vessels may account for this difference. transmural water flow; filtration; intima compression

The bed forms generated by the flow of water over alluvial beds are predominantly treated in terms of stability concepts. These generally postulate a constant wavelength, and describe the variation of amplitude. Yet, the wavelength is one of the most variable parameters of these features. The features are also described as ripples, dunes, and antidunes. But there is no explanation on how ripples transform into dunes. On the basis of available data, this paper offers a description of the generation of ripples and their transformation into dunes. DOI: 10.1061/(ASCE)0733-9429(2006) 132:12(1316) CE Database subject headings: Dunes; Water flow; Parameters; Wavelength.

Modeling contaminant and water flow through soil requires accurate estimates of soil hydraulic properties in field scale. Although artificial neural networks (ANNs) based pedotransfer functions (PTFs) have been successfully adopted in modeling soil hydraulic properties at larger scales (national, continental, and intercontinental), the utility of ANNs in modeling saturated hydraulic conductivity ([K.sub.s]) at a smaller (field) scale has rarely been reported. Hence, the objectives of this study are (i) to investigate the applicability of neural networks in estimating Ks at field scales, (ii) to compare the performance of the field-scale PTFs with the published neural networks program Rosetta, and (iii) to compare the performance of two different ensemble methods, namely Bagging and Boosting in estimating [K.sub.s]. Datasets from two distinct sites are considered in the study. The performances of the models were evaluated when only sand, silt, and clay content (SSC) were used as inputs, and when SSC and bulk density [[rho].sub.b] (SSC+ [[rho].sub.b]) were used as inputs. For both datasets, the field scale models performed better than Rosetta. The comparison of field-scale ANN models employing bagging and boosting algorithms indicates that the neural network model employing the boosting algorithm results in better generalization by reducing both the bias and variance of the neural network models.

Conventional stability analysis methods for determining rock armor size to protect steep (tan [theta] > 0.1) embankments from erosion due to downslope flow do not predict the correct dependency of armor size on the slope. Consequently, such methods become very conservative (discharge factor of safety ~8) at high slopes. We review published large-scale measurements recorded in the literature and show that adequate representation of flow aeration is important as proposed by Hartung and Scheuerlein in 1970. However, the assembled measurements show that the Hartung and Scheuerlein design method is not conservative. The aerated flow equations of Hartung and Scheuerlein, when combined with a correctly formulated stability equation, yield good collapse of the available large-scale data and a conservative design method. CE Database subject headings: Rocks; Erosion; Water flow; Slopes; Embankments.

The electrical conductivity profiles recorded in a well using the flowing fluid electric conductivity (FEC) logging method can be analyzed to estimate interval-specific hydraulic conductivity and estimates of the salinity concentration with depth. A study demonstrates that a modified, miniaturized FEC logging system can be successfully used in irrigation wells with limited access and large diameters.

The ability of local gradient estimators consisting of three wells at unique locations to accurately and precisely estimate the magnitude and orientation of the hydraulic gradient with respect to the relative head measurement error (RHME), the orientation of the ground water flow direction, and triangle shape (base to height ratio). Simulation results show that those estimators with base to height ratios between 0.5 and 5.0 produce the most precise estimates of the magnitude and orientation of the hydraulic gradient for four different levels of RHME.

A new approach to detect, characterize, and quantify hydraulic short-circuits in boreholes with faulty seals, which is applicable to an aquifer-aquitard-aquifer system is presented. The method is a relatively simple and quantitative approach for reducing the risk of aquifer cross contamination and to avoid potentially expensive treatment costs at water supply wells.

A model is developed to account for the vertical distribution of velocity and nonhydrostatic pressure in one-dimensional open-channel flows. The model is based on both classical multilayer models and depth-averaged and moment equations. The establishment of its governing equations and the flow simulation are performed over a number of flow layers as in classical multilayer models. However, the model also allows for vertical distributions within a flow layer by including both Boussinesq terms and effective stress terms due to depth-averaging operations. These terms are evaluated on the basis of vertically linearly approximated profiles of velocity and pressure. The resulting additional coefficients can be solved by the moment equations for the relevant layers. Three verifications demonstrate satisfactory simulations for water surface profile, as well as vertical distributions for horizontal velocity, vertical velocity, and nonhydrostatic pressure. Sensitivity analysis shows that the model can be applied with fewer flow layers, more flexibility of layer division, and less computational cost than classical multilayer models, without a remarkable compromise in accuracy. CE Database subject headings: Velocity profile; Open channel flow; Sensitivity analysis; Simulation.

This work is part of a long term project which aims at developing a hydraulic model for real-time simulation of unsteady flows in sewers ranging from gravity flows, to partly gravity-partly surcharged flows to fully surcharged flows. The success of this project hinges on the ability of the hydraulic model to handle a wide range of complex boundaries and to provide accurate solutions with the least central processing unit time. This first paper focuses on the development and assessment of two second-order explicit finite-volume Godunov-type schemes (GTS) for unsteady gravity flows in sewers, but with no surcharging. Traditionally, hydraulic transients have been modeled using the method of characteristics (MOC), which is noted for its ability to handle complex boundary conditions (BCs). The two GTS described herein incorporate BCs in a similar manner to the MOC. The accuracy and efficiency of these GTS schemes are investigated using problems whose solution contains features that are relevant to transient flows in sewers such as shock, expansion, and roll waves. The results show that these GTS schemes are significantly faster to execute than the fixed-grid MOC scheme with space-line interpolation, and in some cases, the accuracy produced by the two GTS schemes cannot be matched by the accuracy of the MOC scheme, even when a Courant number close to one and a large number of grids is used. Furthermore, unlike the MOC solutions, which exhibit increasing numerical dissipation with decreasing Courant numbers, the resolution of the shock fronts was maintained by the GTS schemes even for very low Courant numbers (0.001). CE Database subject headings: Sewers; Transient flow; Hydraulic models.

A horizontal two-dimensional mobile bed model for simulating the formation of river-dominated deltas in the river mouth or reservoir is presented, which is composed of shallow water equations, sediment transport formula, and a sediment continuity equation. Geometry similarity of river deltas during the processes of formation is discussed. Stability analysis and sensitivity analysis of parameters in the model are analyzed, which indicates that bed configuration is sensitive to the incipient-motion criteria of bed-load particles. The effect of gravity component on the initiation of sediment movement, therefore, is recommended to be considered in the modeling. The bed configuration including the reverse slope in the longitudinal profile and concave in the transverse profiles are correctly simulated with help from the correction of incipient-motion criteria. Simulation results are verified with a series of experiments and are consistent with series geometric functions and dimensionless profiles inducted from experimental data. This reflects the great reliability of the model. Historical topographical records of two typical in-land deltas depicting their earlier developmental stages are discussed to show the usefulness of this study. CE Database subject headings: Bed load; Gaussian process; Configuration; Channel flow; Simulation.

This paper presents the results of an experimental study on the mean and turbulence structures of flow in a vertical slot fishway with slopes of 5.06 and 10.52%. Two flow patterns existed in the fishway and for each one, two flow regions were formed in the pools: a jet flow region and a recirculating flow region. The mean kinetic energy decays rapidly in the jet region and the dissipation rate in most of the areas in the pool is less than 200 W/[m.sup.3]. For the jet flow, the nondimensional mean velocity profile across the jet agrees very well with that of a plane turbulent jet in the central part of the jet with some scatter near its boundaries. Its maximum velocity decays faster compared to a plane turbulent jet in a large stagnant ambient. The jet presents different turbulence structure for the two flow patterns and for each pattern, the turbulence characteristics appear different between the left and right halves of the jet. However, the turbulence characteristics show some similarity for each case. The normalized energy dissipation rate shows some similarity and has a maximum value on the center of the jet. The results are believed to provide useful insight on the turbulence characteristics of flow in vertical slot fishways and can be used to verify numerical models and also for guidance in the design of fishways in the future. CE Database subject headings: Fish habitats; Turbulence; Energy dissipation; Hydraulic structures; Water flow.

Three forms of the solution (a closed-form solution, an integral to be calculated numerically with a worksheet, and a simplified solution) giving the travel time to a well pumping an ideal, horizontal unconfined aquifer, under steady-state conditions are presented. The three forms of the solution give travel times nearly identical to those obtained using a finite-element code for saturated and unsaturated flow and particle tracking.

Operational problems and system damage have been linked to the flow regime transition between free surface and pressurized flow in rapidly filling stormwater and combined sewer systems. In response, emphasis has been placed on the development of numerical models to describe hydraulic bores and other flow phenomena that may occur in these systems. Current numerical models are based on rigid column analyses, shock-fitting techniques, or shock-capturing procedures employing the Preissmann slot concept. The latter approach is appealing due to the comparative simplicity, but suffers from the inability to realistically describe subatmospheric full-pipe flows. A new modeling framework is proposed for describing the flow regime transition utilizing a shock-capturing technique that decouples the hydrostatic pressure from surcharged pressures occurring only in pressurized conditions, effectively overcoming the cited Preissmann slot limitation. This new approach exploits the identity between the unsteady incompressible flow equations for elastic pipe walls and the unsteady open-channel flow equations, and the resulting numerical implementation is straightforward with only minor modifications to standard free surface flow models required. A comparison is made between the model predictions and experimental data; good agreement is achieved. DOI: 10.1061/(ASCE)0733-9429(2006) 132:6(553) CE Database subject headings: Transient flow; Pipes; Simulation; Sewers; Open channel flow.

Steep and short rough channels, such as rock chutes, are used in river restoration as grade stabilization structures. The stability of these channels can be increased using boulders placed over the base material. The boulders can be placed with different configurations such as randomly or in rows. In each case, their presence affects the geometry of the channel and modifies the hydraulic resistance. This paper shows the results of tests conducted on rough channels with or without the insertion of protruding boulders. The parameters that influence the flow resistance, such as slope, relative submergence, and blocks disposition, were systematically investigated to describe the hydraulic behavior of the structure. The aim is to define a relationship, useful for practical design, which relates the flow resistance in terms of both Darcy-Weisbach friction factor and Manning coefficient. The results were combined with available data for loose rock riprap, to determine new experimental relationships. DOI: 10.1061/(ASCE)0733-9429(2006) 132:6(545) CE Database subject headings: Slopes; Ramps; Flow resistance; Boulders.

This paper presents a versatile two-parameter model describing the hydraulic performance of highway culverts operating under inlet control for both unsubmerged and submerged conditions. Applications show that the model can accurately represent the Federal Highway Administration (FHwA) performance curves (which use four parameters) for a range of culvert types and materials. Laboratory data from an investigation of the hydraulic performance of single- and multiple-barrel low-headwater box culverts are also used, and the resulting model predicts a smaller culvert size as compared with the FHwA equations for a given design discharge. Design recommendations are presented for low-headwater box culverts. DOI: 10.1061/(ASCE)0733-9429(2006)132:5(474) CE Database subject headings: Culverts; Performance characteristics; Coefficients; Critical flow; Highways.

Abstract: The steady flow of an incompressible Oldroyd 8-constant fluid in the annular region between two spheres, or so-called spherical Couette flow, is investigated. The inner sphere rotates with an [...]

Fast-flowing ice streams are responsible for the bulk of mass transfer through large ice sheets. We use extensive three-dimensional seismic data from the western Norwegian margin to explain how a several-hundred-kilometer-long ice stream has undergone major switching in flow direction from one glaciation to the next. The direction of ice flow is inferred from the pattern of buildup of thousands of cubic kilometers of glacier-derived debris and observations of large-scale streamlined landforms on former subglacial beds. We demonstrate that ice streams can undergo major changes in flow direction through modification of their large-scale topographic setting. Whereas ice-stream switching in modern ice sheets has been regarded mainly as a reflection of internal changes in ice-sheet dynamics, switching over successive 100 k.y. glacial cycles may in this case be a response to the effects of continuing sediment deposition and the large-scale development of ice-influenced continental margins. Keywords: ice streams, Norwegian margin, three-dimensional seismic data, glacial lineations, glacial bedforms.

The aim of the paper is to present the results of investigations conducted on the free surface flow in a Pelton turbine model bucket. Unsteady numerical simulations, based on the two-phase homogeneous model, are performed together with wall pressure measurements and flow visualizations. The results obtained allow defining five distinct zones in the bucket from the flow patterns and the pressure signal shapes. The results provided by the numerical simulation are compared for each zone. The flow patterns in the buckets are analyzed from the results. An investigation of the momentum transfer between the water particles and the bucket is performed, showing the regions of the bucket surface that contribute the most to the torque. The study is also conducted for the backside of the bucket, evidencing a probable Coanda interaction between the bucket cutout area and the water jet. [DOI: 10.1115/1.2170120]

Flow fields near the exit and the global performance parameters of the various types of axial flow fans are studied with Particle Image Velocimetry and a standard AMCA 210 flow bench. The fans used in this study included the shrouded, shroudless, and wingletblade types. The velocity vectors, streamlines, vorticity contours, velocity distributions, and performances are presented and discussed. The flow patterns on the radial and axial planes show that a vortex always exists near the exit of the fans at various impeller angles. The experimental results demonstrate that the shrouded fan with winglets has the most stable flow field and the best fan performance. [DOI: 10.1115/1.2169809] Keywords: axial flow fan, PIV, fan performance, winglet-blade

Microscopic particle image velocimetry (microPIV) was used to measure velocities in rectangular microchannels with aspect ratios ranging from 0.97 to 5.69 for 200 / [u.sub.max] and / [u.sub.max] fluctuations at the channel centerline were 6% and 3%-3.5% and generally agreed well with macroscale results. As aspect ratio increased, the /[u.sub.max] and /[u.sub.max] profiles became flatter, with nearly uniform values extending for some distance from the centerline of the channel. This region of uniform /[u.sub.max] and /[u.sub.max] became larger with increasing aspect ratio. The Reynolds shear stress for fully turbulent flow also displayed a strong dependence on aspect ratio. For the W/H=0.97 microchannel, /[u.sup.2.sub.max] steadily increased in value moving from the centerline to the wall, but for the higher aspect ratio microchannels, /[u.sup.2.sub.max] remained close to zero in the center region of the microchannel before increasing in value at locations close to the wall, and this region of near zero /[u.sup.2.sub.max] became larger with increasing aspect ratio. This behavior in the Reynolds shear stress is due to the region of uniform velocity and, hence, small mean shear, near the channel centerline of the high aspect ratio microchannels.

An algorithm based on the combination of time-derivative preconditioning strategies with low-diffusion upwinding methods is developed and applied to multiphase, compressible flows characteristic of underwater projectile motion. Multiphase compressible flows are assumed to be in kinematic and thermodynamic equilibrium and are modeled using a homogeneous mixture formulation. Compressibility effects in liquid-phase water are modeled using a temperature-adjusted Tait equation, and gaseous phases (water vapor and air) are treated as an ideal gas. The algorithm is applied to subsonic and supersonic projectiles in water, general multiphase shock tubes, and a high-speed water entry problem. Low-speed solutions are presented and compared to experimental results for validation. Solutions for high-subsonic and transonic projectile flows are compared to experimental imaging results and theoretical results. Results are also presented for several multiphase shock tube calculations. Finally, calculations are presented for a high-speed axisymmetric supercavitating projectile during the important water entry phase of flight. [DOI: 10.1115/1.2169816] Keywords: compressible multiphase flows, supercavitation, high-speed water entry

In this paper, general motion of a two-dimensional body is modeled using a new moving mesh concept. Solution domain is divided into the three zones. The first zone, with a circular boundary, includes the moving body and facilitates the rotational motion of it. The second zone, with a square boundary, includes the first zone and facilitates the translational motion of the body. The third zone is a background grid in which the second zone moves. With this configuration of grids any two-dimensional motion of a body can be modeled with almost no grid insertion or deletion. However, in some stages of motion we merge or split a few number of elements. The discretization method is control-volume based finite-element, and the unsteady form of the Euler equations are solved using AUSM algorithm. To demonstrate the excellent performance of the present method two moving cases including rotational and translational motions are solved. The results show excellent agreement with experimental data or other numerical results. [DOI: 10.1115/1.2170124] Keywords: general motion, moving mesh, 2D equations, inviscid flow

In general, the water content (θ) form of Richards' equation is not used when modeling water flow through layered soil since θ is discontinuous across soil layers. Within the literature, there have been some examples of models developed for layered soils using the θ-form of Richards' equation. However, these models usually rely on an approximation of the discontinuity at the soil layer interface. For the first time, we will develop an iterative scheme based on Newton's method, to explicitly solve for θ at the interface between 2 soils within a numerical scheme. The numerical scheme used here is the Method of Lines (MoL); however, the principles of the iterative solution could be used in other numerical techniques. It will be shown that the iterative scheme is highly effective, converging within 1 to 2 iterations. To ensure the convergence behaviour holds, the numerical scheme will be tested on a fine-over-coarse and a coarse-over-fine soil with highly contrasting soil properties. For each case, the contrast between the soil types will be controlled artificially to extend and decrease the extent of the θ discontinuity. In addition, the numerical solution will be compared against a steady-state analytical solution and a numerical solution from the literature. Additional keywords: heterogeneous soils, unsaturated zone, water flow, numerical solution., Introduction The study of water flow through layered soils has been an important environmental problem, which has relevance in various fields such as contaminant transport, agricultural science, and waste disposal [...]

This paper describes an improved microfluidic device that enables hydrodynamic particle concentration and size-dependent separation to be carded out in a continuous manner. In our previous study, a method for hydrodynamic filtration and sorting of particles was proposed using a microchannel having multiple branch points and side channels, and it was applied for continuous concentration and separation of polymer particles and cells. In the current study, the efficiency of particle sorting was dramatically improved by geometrically splitting fluid flow from a main stream and recombining. With these operations, particles with diameters larger than a specific value move toward one sidewall in the mainstream. This control of particle positions is followed by the perfect particle alignment onto the sidewall, which increases the selectivity and recovery rates without using a liquid that does not contain particles. In this study, a microchannel having one inlet and five outlets was designed and fabricated. By simply introducing particle suspension into the device, concentrations of 2.1-3.0-[micro]m particles were increased 60-80-fold, and they were collected independently from each outlet. In addition, it was demonstrated that the measured flow rates distributed into each side channel corresponded well to the theoretical values when regarding the microchannel network as a resistive circuit.

The motion of a SECM tip above a substrate generates a flow of the surrounding fluid. Finite element calculations show that this flow is a simple linear-shear flow (Couette flow) for small tip--substrate separations and deviates from Couette's law at larger ones. The effect of fluid flow on the tip current response was determined numerically. Different mass-transfer regimes are observed depending on the insulating or conducting nature of the substrate, the tip speed (or fluid velocity), and the tip--substrate separation. Those observations are tested experimentally, and good agreement is obtained between numerical and experimental results.

Abstract: In two preceding works, the idea of partial conservation theorems was introduced and conservation equations for partial energy and partial angular momentum were established. A similar conservation theorem for [...]

A coupled hydromechanical model was used to analyze the mesoscale pore fluid flow and microscale solid phase deformation of saturated granular soils. The fluid motion was idealized using averaged Navier--Stokes equations, and the discrete element method was employed to model the assemblage of solid particles. The fluid--particle interactions were quantified using established semiempirical relationships. Simulations were conducted to investigate the three-dimensional response of sandy deposits when subjected to critical and overcritical upward pore fluid flow. These simulations revealed complex response patterns alter the onset of quicksand conditions and provided valuable insight into the associated mechanisms. The employed model provides an effective tool to assess the microscale mechanisms and characteristics of the partially drained response of saturated granular media. DOI: 10.1061/(ASCE)0733-9399(2005)131:4(413) CE Database subject headings: Discrete elements: Porous media: Saturated soils: Water flow: Granular media: Hydromechanics.

The hydraulic conductivity (K) variation has important ramifications for ground water flow and the transport of contaminants in ground water. The delineation of the nature of that variation can be critical to complete characterization of a site and the planning of effective and efficient remedial measures. Site-specific features (such as high-conductivity zones) need to be quantified. Our alluvial field site in the Kansas River valley exhibits spatial variability, very high conductivities, and nonlinear behavior for slug tests in the sand and gravel aquifer. High-resolution, multilevel slug tests have been performed in a number of wells that are fully screened. A general nonlinear model based on the Navier-Stokes equation, nonlinear frictional loss, non-Darcian flow, acceleration effects, radius changes in the wellbore, and a Hvorslev model for the aquifer has been used to analyze the data, employing an automated processing system that runs within the Excel spreadsheet program. It is concluded that slug tests can provide the necessary data to identify the nature of both horizontal and vertical K variation in an aquifer and that improved delineation or higher resolution of K structure is possible with shorter test intervals. The gradation into zones of higher conductivity is sharper than seen previously, and the maximum conductivity observed is greater than previously measured. However, data from this project indicate that well development, the presence of fines, and the antecedent history of the well are important interrelated factors in regard to slug-test response and can prevent obtaining consistent results in some cases., Introduction The major control on water flow and the transport and fate of a pollutant as it moves through an aquifer is the spatial distribution of hydraulic conductivity (K). The [...]

Potential flow solutions of a point/line sink are extended to study the velocity field upstream of a finite-size orifice and sluice gate. It is found that, in the 'near field' zones, the iso-velocity surfaces appear to be semiellipsoidal; while in the 'far field' zones they become hemispheres. The shape and size of the orifice/sluice gate were found to be of no effect on the flow behavior beyond a certain distance. The development of velocity profile away from the orifice and sluice gate is examined, and the effects of water depth are studied. The results of this study compare very well with other numerical and experimental studies, and provide a general understanding of the flow field upstream of orifices and sluice gates. CE Database subject headings: Gates; Potential flow; Velocity.

This research intends to clarify the limitations of a local scour equation recently proposed, based on extended laboratory data collected at VAW, Zurich, Switzerland. The present project is concerned with four items: (1) clarification of the minimum laboratory dimensions required to apply Froude similitude; (2) effect of sloping abutments on scour advance; (3) extension of scour formula to spur dikes; and (4) effect of unsteady flow on scour development. These items were investigated mainly from an experimental point of view based on some 150 laboratory experiments and accounted for by a hydraulic approach. It was found that the basic scour equation mentioned may be applied provided additional limitations are specified. These are discussed in the light of the densimetric particle Froude number, the threshold Froude number, and other important parameters that influence the progress of local scour. The results of this study may be applied to practice, provided the limitations of the computational approach are respected. CE Database subject headings: Bridge abutments; Hydraulics; Piers; Scour.

More than 50 years' river training practices in the Lower Yellow River provide valuable experience in river management for flood control in rivers having rapid flow changes, silting beds, and active channel migrations and are of importance in understanding the fluvial processes in regulated rivers with high sediment loads. Planned channel alignments for river training in the Lower Yellow River usually consist of a series of consecutive moderate bends representing the natural tendency of flows. Flow guide works, namely spur dikes, were constructed on the concave banks of the planned bends to protect the channel against scouring and migration by deflecting the current away from bends and further guiding the main flow from one bend to the next one. As a result, well-planned flow guide works can play a crucial role in limiting channel shifting and migration and in establishing a relatively stable channel. Enough flow guide works, on both sides together reaching about 80% of the channel length, may change the transitional and braided channel patterns to a confined meandering pattern. CE Database subject headings: Channel stabilization; Channel improvements; Bank stabilization; Geometry; Fluvial hydraulics; China.

Local clear-water scour tests were performed with three different diameter circular piles (0.114, 0.305. and 0.914 m), three different uniform cohesionless sediment diameters (0.22, 0.80, and 2.90 mm) and a range of water depths and flow velocities. The tests were performed in the 6.1 m wide, 6.4 m deep, and 38.4 m long flume at the United States Geological Survey Conte Research Center in Turners Falls, Mass. These tests extend local scour data obtained in controlled experiments to prototype size piles and ratios of pile diameter to sediment diameter to 4,155. Supply water for this flow through flume was supplied by a hydroelectric power plant reservoir and the concentration of suspended fine sediment (wash load) could not be controlled. Equilibrium scour depths were found to depend on the wash load concentration. DOI: 10.1061/(ASCE)0733-9429(2004)130:10(957) CE Database subject headings: Scour; Cohesionless sediment; Suspended sediments; Piers; Piles: Velocity.

An upwind conservative scheme with a weighted average water-surface-gradient approach is proposed to compute one-dimensional open channel flows. The numerical scheme is based on the control volume method. The intercell flux is computed by the one-sided upwind method. The water surface gradient is evaluated by the weighted average of both upwind and downwind gradients. The scheme is tested with various examples, including dam-break problems in channels with rectangular and triangular cross-sections, hydraulic jump, partial dam-break problem, overtopping flow, a steady flow over bump with hydraulic jump, and a dam-break flood case in a natural river valley. Comparisons between numerical and exact solutions or experimental data demonstrated that the proposed scheme is capable of accurately reproducing various open channel flows, including subcritical, supercritical, and transcritical flows. The scheme is inherently robust, stable, and monotone. The scheme does not require any special treatment, such as artificial viscosity or front tracking technique, to capture steep gradients or discontinuities in the solution. DOI: 10.1061/(ASCE)0733-9429(2004)130:10(977) CE Database subject headings: Open channels; Unsteady flow; Dam failure; Numerical models.

Mechanism of sediment transport is composed of complicated interactions between turbulent flow, particle motion, and bed configurations. Of particular significance is the interaction between turbulence and particle motion, although turbulence measurements of particle-laden two phase flow have been a problem for a long time, especially in the near-wall region. In this study, simultaneous measurements of both the particles and fluid (water) were conducted in particle-laden two phase open channel flows by means of a discriminator particle-tracking velocimetry. The mean velocity and turbulence characteristics for fluid and particles each were examined in comparison with those in clear-water (particle-free) flow, together with previous existing data measured by laser Doppler anemometer and phase Doppler anemometer. The relative velocity and the turbulence modulation, which are the most important topics in two phase-flow approach, were revealed by varying the particle diameter and specific density. The fluid-sweeps are more contributory to the motion of particles than the fluid ejections in the near-wall region. In turn, the particle-sweeps transport the high momentum to the cartier fluid and enhance the turbulence intensities of fluid. DOI: 10.1061/(ASCE)0733-9429(2004)130:10(988) CE Database subject headings: Turbulence; Open channel flow; Particle interactions; Two phase flow.

The nonuniformity of bed material affects the bed-material load calculations. A size gradation correction factor [K.sub.d] is developed to account for the lognormal distribution of bed material. The use of [K.sub.d] in conjunction with bed-material load equations originally developed for single particle sizes improves the accuracy of transport calculations for sediment mixtures. This method is applicable to laboratory flumes and natural rivers with median diameter [d.sub.50] of bed material in the sand size ranges. The improvement on transport rate by [K.sub.d] factor is significant for data with standard deviation [[sigma].sub.g] of bed material greater than 2, while the correction is negligible for data with [[sigma].sub.g] less than 1.5. Sediment in transport also follows a lognormal distribution with a median diameter [d.sub.50t] generally finer than the corresponding [d.sub.50]. As the size gradation increases, [d.sub.50t] becomes much finer than the corresponding value of [d.sub.50]. The relationship between [d.sub.50t] and [d.sub.50] is defined as a function of [[sigma].sub.g] and agrees well with field data. The previously recommended use of [d.sub.35] as representative size of the bed material is found not to be generally applicable. DOI: 10.1061/(ASCE)0733-9429(2004)130:10(1002) CE Database subject headings: Sediment; Sediment transport; Transport rate: Bed material: Particle size distribution; Alluvial streams.

A depth-averaged two-dimensional (2D) numerical model for unsteady flow and nonuniform sediment transport in open channels is established using the finite volume method on a nonstaggered, curvilinear grid. The 2D shallow water equations are solved by the SIMPLE(C) algorithms with the Rhie and Chow's momentum interpolation technique. The proposed sediment transport model adopts a nonequilibrium approach for nonuniform total-load sediment transport. The bed load and suspended load are calculated separately or jointly according to sediment transport mode. The sediment transport capacity is determined by four formulas which are capable of accounting for the hiding and exposure effects among different size classes. An empirical formula is proposed to consider the effects of the gravity on the sediment transport capacity and the bed-load movement direction in channels with steep slopes. Flow and sediment transport are simulated in a decoupled manner, but the sediment module adopts a coupling procedure for the computations of sediment transport, bed change, and bed material sorting. The model has been tested against several experimental and field cases, showing good agreement between the simulated results and measured data. DOI: 10.1061/(ASCE)0733-9429(2004)130:10(1013) CE Database subject headings: Unsteady flow; Sediment transport; Open channels: Numerical models: Two dimensional.