Prediction of Critical Submergence for a Rectangular Intake

The effects of the blockage of a rectangular intake duct and impervious flow boundaries on the critical submergence of a rectangular intake are presented. The potential solution, based on the Rankine stagnation point, is determined to be another approximate method for the prediction of the critical submergence of this kind of intake. It is found that a critical cylindrical sink surface capped with two critical hemispherical sink surfaces at both ends with a radius equal to the radial distance of the stagnation point (which is 2/π times the critical submergence of the rectangular intake) can also be used to predict critical submergence. Theoretical results and available experimental data are compared. The theory presented in this study acceptably (by about 1–20%) estimates the critical submergence for the cases where the distance (clearances) of the impervious solid boundaries are larger than 1/2 of the small inner dimension of the intake. On the other hand, the theory overestimates the critical submergence by about 80% for the cases where the distances of the solid boundaries (especially those cutting the free surface such as the dead-end wall) become zero.     

Critical Submergence for a Rectangular Intake

In this study, the critical submergence for a rectangular intake in a uniform canal flow is investigated. The potential solution for the combination of a line sink and a uniform flow is available and known as Rankine half-body. This study is based on the Rankine half-body. Theoretical and experimental results have indicated that, in general, the critical submergence for a rectangular intake can be predicted by means of a critical sink surface which consists of a critical cylindrical sink surface capped with two critical hemispherical sink surfaces at both ends. The effects of intake-duct pipe blockage and location of impervious boundaries on critical submergence of a rectangular intake are presented. Experiments were conducted on a rectangular intake sited in a dead-end uniform canal flow. The agreement between the theoretical and experimental results is found to be acceptable.     

Flow-Boundary Effects on Critical Submergence of Intake Pipe

In this study, the effects of intake-pipe blockage and location of impervious boundaries on critical submergence of an intake pipe are presented. Experiments were conducted on a horizontal intake pipe sited in a dead-end canal flow. Theoretical results and available experimental data are compared. It is shown that, as the distance between the intake-pipe entrance and the dead end gets smaller than the critical submergence depth, the deviation between theoretical and experimental results increases. A potential flow solution still gives acceptable results when this distance is smaller than the critical submergence, but it overpredicts by about 80% when the distance between the intake-pipe entrance becomes much smaller than the critical submergence depth.     

Observations of Air–Water Interaction in a Rapidly Filling Horizontal Pipe

This paper presents the results of an observational study related to the behavior of drainage sewers under conditions of hydraulic overloading. Specifically, the investigation focuses on the interaction of water and trapped air in surcharging drainage and pressurized pipeline systems, by studying the air–water flow behavior in a rapidly filling horizontal pipe. Air–water interface patterns, air entrainment, and air release through an orifice at the pipe end are documented photographically. Synchronously recorded pressure traces are also presented to illustrate the relation between the air–water phase evolution and the pressure oscillation patterns. Depending on the air release rate of the orifice, there are three types of pressure oscillation behavior, each corresponding to a particular behavior of the air–water interface in the rapidly filling horizontal pipe.     

Experimental Study of Flow in a Vortex Drop Shaft

Model experiments were conducted to investigate the performance of a vortex drop structure with a relatively small height to diameter ratio. Detailed measurements of wall pressure and water thickness of annular jet flow were obtained along the vertical drop shaft, and the rate of air entrainment was measured. The results confirmed the high efficiency of energy dissipation in the vortex drop structure even for a relatively small drop height. The air entrainment rate was found to be significant, and good correlation was observed between the rate of air entrainment and the water jet velocity. The one-dimensional frictional free-vortex flow model was extended to include the effects of pressure forces. While the energy loss in the drop shaft can be simulated by correcting the friction factor, both the frictional model and the extended model significantly underpredict the wall pressure.     

Case Study: Movable Bed Model Scaling for Bed Load Sediment Exclusion at Intake Structure on Rio Grande

Results of a laboratory modeling study are presented for excluding bed load sediment from a diversion/intake structure on the Rio Grande in Albuquerque, New Mexico. To achieve model similitude, crushed coal was used to model the prototype sediment in a 1:24 scaled model with an exaggerated slope such that shear force is adequately modeled. The Shields parameters and critical Shields parameters were matched between the prototype and the model, resulting in similar grain Reynolds numbers. Twenty-four tests, where guiding walls, submerged vanes, and/or the angle of the intake bay were altered, were conducted for a single river and diversion flow rate to develop the best performing sediment exclusion system at the intake structure. Independent vanes with 45° rotated intake bays were recommended for the most effective sediment exclusion at the intake structure.     

Critical Pool Level and Stability of Slopes in Granular Soils

The influence of pore-water pressure and the pool water pressure on stability of submerged slopes was investigated using the kinematic approach of limit analysis. For soils with some cohesive component of strength, the critical pool level is slightly below half of the slope height, whereas for slopes built of purely granular soils the critical pool level is not well defined. The most critical mechanism of failure for submerged granular slopes was found to have the failure surface intersecting the face of the slope, with one intersection point above, and the other one below the pool level. The solution to the stability problem was found to be independent of the length scale (slope height), and equally critical mechanisms of failure can be triggered “locally” with any water level in the pool. The safety factor associated with these mechanisms is lower than the well-known factor defined by a planar failure surface approaching the slope face.     

Computational Fluid Dynamics Study of a Noncontact Handling Device Using Air-Swirling Flow

The vortex gripper is a recently developed pneumatic noncontact handling device that takes advantage of air-swirling flow to cause upward lifting force and that thereby can pick up and hold a work piece placed underneath without any contact. It is applicable where, e.g., in the semiconductor wafer manufacturing process, contact should be avoided during handling and moving in order to minimize damage to a work piece. For the purpose of a full understanding of the mechanism of the vortex gripper, a computational fluid dynamics (CFD) study was conducted in this paper, and at the same time, experimental work was carried out to measure the pressure distribution on the upper surface of the work piece. First, three turbulence models were used for simulation and verified by comparison with the experimental pressure distribution. It is known that the Reynolds stress transport model (RSTM) can reproduce the real distribution better. Then, on the basis of the experimental and numerical result of RSTM, an insight into the vortex gripper and its flow phenomena, including flow structure, spatial velocity, and pressure distributions, and an investigation into the influence of clearance variation was given.     

Prediction of Intake Vortex Risk by Nearest Neighbors Modeling

Vortex formation at intakes can cause damage, clogging, reduced flow efficiency, and even loss of life. For practical prediction of vortex risk, engineers often compare expected design parameters with published data by using parameter proximity to evaluate the relative risk of vortex formation. Unfortunately, this procedure is ill-defined, and the resulting risk estimates are highly subjective. In response, a formal equivalent of the data proximity procedure was developed by implementing the nearest neighbors algorithm on available experimental and field data. This database was partitioned and the machine learning parameters adjusted to obtain a stochastic model with maximum predictive accuracy. Unlike the flow parameters and submergence, the approach geometry was not found to be a significant factor in the model, although this may be attributable to data noise and range of tested values. The final model, which excluded the channel approach geometry, fit all vertical intake vortex formation data to within 0.1% error and perfectly fit the horizontal intake data. Probability charts generated from the model show regions of vortex formation and problems more numerous and larger on average than regions of low vortex probability, thus validating consideration of potential vortex formation risk for conservative intake design.     

Hydraulics of Stacked Drop Manholes

This paper presents the results of an experimental investigation on flows inside stacked drop manholes (SDM). An SDM consists of two identical rectangular or square manhole chambers stacked together at an elevation difference. SDMs for different conditions were assessed on their ability to dissipate the energy of the approaching flow and their suitability to perform adequately under different flow conditions. Flow regimes were classified based on the inflow conditions and geometry of the structure in the first chamber and downstream outflows in the second chamber. An analysis based on the integral momentum equation was developed to estimate pool depths and energy losses under critical flow conditions. A fully surcharged stage with inflow and outflow pipes running full was also tested and velocity profiles were measured at a horizontal center plane to the opening connecting both shafts. Additionally, air flow rates were measured to assess the air demand into a large-height SDM.     

Energy Dissipation and Air Entrainment in Stepped Storm Waterway: Experimental Study

For the last three decades, research focused on steep stepped chutes. Few studies considered flat-slope stepped geometries such as stepped storm waterways or culverts. In this study, experiments were conducted in a large, flat stepped chute (θ=3.4°) based upon a Froude similitude. Three basic flow regimes were observed: nappe flow without hydraulic jump, transition flow, and skimming flow. Detailed air–water flow measurements were conducted. The results allow a complete characterization of the air concentration and bubble count rate distributions, as well as an accurate estimate of the rate of energy dissipation. The flow resistance, expressed in terms of a modified friction slope, was found to be about 2.5 times greater than in smooth-chute flow. A comparison between smooth- and stepped-invert flows shows that greater aeration and larger residence times take place in the latter geometry. The result confirms the air–water mass transfer potential of stepped cascades, even for flat slopes (θ<5°).     

Developing Flow Region and Pressure Fluctuations on Steeply Sloping Stepped Spillways

The hydrodynamic pressure field is important for the design and safety of steeply sloping stepped spillways, which are typically designed for considerably lower maximum specific discharges than smooth spillways. The hydraulic performance of stepped spillways at high velocities may compromise its use due to major concern with safety against cavitation damage. Hydraulic model investigations were conducted in different large-size stepped chutes to characterize the nonaerated flow region which is potentially prone to cavitation damage and the pressure field acting on the step faces. The clear water depths and energy dissipation in the developing flow region are described in terms of integral measures of the turbulent boundary layer. Expressions for the location of and the flow depth at the inception point of air entrainment are derived. Pressure distributions on the horizontal and vertical faces of the step along the spillway are presented. Measurements indicated a different behavior of the pressure field in the aerated and nonaerated flow region. The mean and fluctuating pressure coefficients along the spillway are approximated by a regression function. The vertical face near the outer step edge close to the inception point of air entrainment is identified as a critical region for predicting cavitation inception in flow over stepped spillways. From the analysis of the pressure fluctuations in that region a maximum velocity of 15 m/s is proposed as a criterion to avoid extreme negative pressures in typical prototype steeply sloping stepped spillways, eventually leading to the occurrence of cavitation in the nonaerated flow.     

Critical Path Method with Multiple Calendars

This paper presents the critical path method forward and backward passes with multiple calendars. Multiple calendars are required in many construction projects to effectively represent various project conditions such as work properties, resource availabilities, weather conditions, etc. For this reason, major project management software packages such as P3 and MS-Project provide functions to handle multiple calendars. However, the background theory of handling multiple calendars has not been disclosed, so users of those software packages simply assume without clear knowledge that the time data generated by them are correct. This paper provides how multiple calendars should be handled in scheduling. Applying the theory presented herein, it has been noticed that the P3 operations with two calendars may generate a wrong answer for a start-to-finish with zero lag and inconsistent results in all negative lags when nonworking days are involved. The theory covers all four relationships in the precedence diagramming method with lags of zero, positive, and negative values. This study should be of considerable benefit to the construction industry and academics because it details and advances the theory for scheduling with multiple calendars, which is real scheduling in practice.     

Evaluation of Preaeration with V-Notch Weir and Cascade Structures in Clarifiers

Hydraulic structures, such as stepped cascades and weirs, involve air entrainment (aeration) and oxygen transfer. Therefore, they can increase dissolved oxygen levels. Weir aeration occurs in rivers, fish hatcheries, and wastewater treatment plants. A stepped cascade aerator is another type of aeration structure. A stepped cascade consists of a series of steps or drops, built into the face of the chute. Often, the hydraulic head is naturally available and incurs no operating cost. For the preaeration process, weir and stepped cascade structures can be previously designed for clarifiers where weirs can be used as an aid to aeration process of treatment plants. Therefore, this paper aims to review the design considerations of circular clarifiers with combined weir and stepped cascade structures as a new approach and alternative preaeration system without energy requirement before aeration tank units. The detailed example for preaeration in circular clarifiers with combined weir and stepped cascade structures is presented. Thus, the circular clarifiers with weir and stepped cascade structures as effluent and preaeration strucures can be effectively redesigned with given new design considerations.     

Investigation on the Dimensions and Shape of a Submerged Vane for Sediment Management in Alluvial Channels

A submerged vane is a flow-training facility mounted vertically on the channel bed to control the sediment movement in the channel cross section, and has been utilized in various applications, such as prevention of bank erosion, sediment exclusion at water intakes, and deepening channels for navigation. The performance of a submerged vane is related to its dimensions and shape. This study aims to investigate a vane’s sediment control effectiveness as a function of its size and shape, with the expectation of an optimal combination of dimensions and shape. A model for the calculation of the transverse bed profile in a cross section of a straight alluvial channel induced by a single submerged vane is developed. The model is utilized to investigate the performances for three types of vanes: (1) rectangular plates with various height and length; (2) tapered plates with linear decreasing in length from the base to the top; and (3) plates of parallelogram with the top of the plates swept forward or backward. Design guidelines and suggestions on the dimensions and shape of the vane are provided based on the results.     

Computational and Experimental Study of Surcharged Flow at a 90° Combining Sewer Junction

Combining sewer junctions with a lateral inflow at 90° angle are commonly used in our sewer systems. A computational fluid dynamics (CFD) model based on Ansys CFX 10.0 was established to simulate fully surcharged flow at a 90° combining sewer junction. The model was carefully assessed by comparing its results with the measurements of detailed physical experiments. Good agreement was obtained between results of the computational model and of the laboratory experiments. The computational model was proved to be capable of simulating surcharged combining junction flow in the aspects of water depth, energy losses, velocity distributions, and turbulence. The verified CFD model was also used to investigate air entrainment and effects of the size of the junction chamber on the flow. Such CFD models can be used to optimize the design of sewer junctions and will also be useful in studying sediment transport at sewer junctions.     

Inception Point and Air Entrainment on Flows under Macroroughness Condition

Rock chutes or block ramps are fishway passages with low environmental impact. They also contribute to reaeration of rivers with low dissolved oxygen content, owing to the turbulence enhanced by their three-dimensional macroroughness conditions. This paper analyzes the air entrainment inception in flows over beds in macroroughness condition and the self-aerated flow features of the developing flow downstream of the inception point. Air concentration, inception point locations, and water depth elevations have been measured on two different scaled chutes for slopes ranging between 1V:5.88H and 1V:2.17H. Moreover, two different ogee crest lengths have been tested to assess the role of the inlet conditions on the location of the inception point. New equations have been developed to estimate the location of the point of inception and the respective water depth. Longitudinal variations of the mean air concentration downstream from the inception point have been studied and compared with data from the literature. An expression is presented to estimate the optimum length of the block ramp in natural rivers for maximizing air-water mixing.     

Inception Point Relationship for Flat-Sloped Stepped Spillways

A two-dimensional, physical model was constructed to evaluate the air entrainment inception point location in a 4(H):1(V) stepped spillway. Step heights of 38, 76, and 152 mm were evaluated. The physical model was constructed with a broad-crested weir, and model unit discharges ranging from 0.11?m3/(s?m) to 0.82?m3/(s?m) were tested. Hubert Chanson developed a relationship for predicting the inception point location for primarily steep (θ ≥ 22°) stepped spillways. In this study, Chanson’s relationship effectively predicts the location of the inception point for slopes as flat as 14° for Froude surface roughness values (F?)>10 which, in this study, corresponds to model step heights of 38 and 76 mm. A new relationship for predicting the location of the inception point was developed, applicable for flatter sloped (θ ≤ 22°) stepped spillways with 1相似文献   

Hydraulics of Circular Drop Manholes

Circular drop manholes are widely employed in steep urban drainage systems. Drop manholes may lead to poor hydraulic conditions if their energy dissipation is inadequate. The dominant hydraulic features of drop manholes depend on the flow regimes, characterized in terms of the dimensionless impact parameter. Depending on the latter parameter, the energy dissipation can vary within large limits, affecting thereby the downstream flow features. Also, the water pool depth inside the manhole and the air entrainment have been studied in terms of both the hydraulic and geometric parameters. Moreover, the conditions for which a drop manhole generates flow choking at its inlet or outlet have been investigated. Empirical equations for practical manhole design are provided. The importance of suitable manhole aeration is highlighted.