Design and Hydraulics of a Combined Storm Overflow Structure

Storm overflow structures in combined sewers are used to separate sewage from storm water. For subcritical approach flow, sideweirs are currently used; however, they often behave hydraulically poor. This study was conducted to explore a combined storm overflow structure able to improve the hydraulic performance of sewer sideweirs. Such a structure consists of a low-crested sideweir and a bottom opening just downstream from the sideweir end. First, the hydraulic design procedure is described, and then, based on laboratory experiments and by using the governing flow equations, the main hydraulic features are highlighted. The results indicate that the proposed device has advantageous characteristics in terms of hydraulic efficiency, reliability, and maintenance.     

Bernoulli Theorem, Minimum Specific Energy, and Water Wave Celerity in Open-Channel Flow

One basic principle of fluid mechanics used to resolve practical problems in hydraulic engineering is the Bernoulli theorem along a streamline, deduced from the work-energy form of the Euler equation along a streamline. Some confusion exists about the applicability of the Bernoulli theorem and its generalization to open-channel hydraulics. In the present work, a detailed analysis of the Bernoulli theorem and its extension to flow in open channels are developed. The generalized depth-averaged Bernoulli theorem is proposed and it has been proved that the depth-averaged specific energy reaches a minimum in converging accelerating free surface flow over weirs and flumes. Further, in general, a channel control with minimum specific energy in curvilinear flow is not isolated from water waves, as customary state in open-channel hydraulics.     

Broad-Crested Weirs with Rectangular Compound Cross Sections

A series of laboratory experiments was performed in order to investigate the effects of width of the lower weir crest and step height of broad-crested weirs of rectangular compound cross section on the values of the discharge coefficient, the approach velocity coefficient, and the modular limit. For this purpose, nine different broad-crested weir models with rectangular compound cross sections and a model with a rectangular cross section were tested in a horizontal laboratory flume of 11.0 m length, 0.29 m width, and 0.70 m depth for a wide range of discharges. The compound cross sections were formed by a combination of three sets of step heights and three sets of lower weir crest widths. The sill-referenced heads at the approach channel and at the tailwater channel were measured in each experiment. The dependence of the discharge coefficient, approach velocity coefficient, and modular limit values on model parameters was investigated, and these quantities were compared with those of the broad-crested weir models with a rectangular cross section.     

Lateral Weir Flow Model using a Curve Fitting Analysis

A numerical approach is considered for flow over side weirs as a substantial part of distribution channels in irrigation systems and treatment units. The model is based on the energy principle and a curve-fitting technique. For this purpose, the side weir was divided into elementary strips to develop generalized equations for discharge and surface profile. The change in water surface elevation towards the weir crest and the inclination of the deflected flow over the weir were also taken into account. Dimensionless parameters were used and the normalized equations solved to obtain the hydraulic parameters of side weirs. The results were plotted to determine general relationships based on the curve-fitting technique. A practical application of the derived equations to obtain hydraulic parameters of side weirs is performed using literature data.     

Hydraulic Design of a Tilting Weir Allowing for Periodic Fish Migration

The hydraulic design of a tilting weir is presented, which allows for periodic exchange of potadromous fish between freshwater ecosystems. The application domain includes inland waters that need to be isolated hydraulically, preserving the existing ecological connection with the surrounding areas as much as possible. In the absence of a hydraulic gradient, the weir is opened in its neutral position and fish can bypass through passages sideways of the weir. When a hydraulic gradient develops in either of two directions, the weir rotates until a new balance of moments of force is reached, while fish can still bypass. Above a threshold value of the hydraulic gradient, the weir falls shut. When the hydraulic gradient returns to zero, the weir reopens, restoring the ecological connection. Four variants of the weir were investigated in the Hydraulics Laboratory at Wageningen University. The versatility of the design is demonstrated by showing that the hydraulic gradients required for closure and reopening can be manipulated largely independently. Patterns of flow velocity and turbulence kinetic energy were analyzed, which suggest that relevant fish species can bypass the weir unimpeded. The effectiveness of the weir will mainly depend on hydrostatic aspects, which determine when the weir is opened and closed, and on the absence of large hydraulic gradients in the migration season.     

Hydraulic Characteristics of Gabion-Stepped Weirs

Experimental studies on the hydraulics of flow through and over gabion-stepped weirs are presented. Two flow components were observed, i.e., base flow through the void between filled stones and overflow on the gabions. The energy loss ratios in the gabion-stepped weirs are greater than those in the corresponding horizontal stepped weirs by approximately 7, 10, and 14% for weir slopes of 30, 45, and 60°, respectively. As a result, the velocity at the outlet is lower. Stone size and shape have little influence on the energy loss and flow velocity as compared to the increasing effect of the weir slope. The pressure acting on the step face for the gabion-stepped weirs is less than that of the horizontal steps owing to the cushioning effect generated by filled stones. To reduce pressure on a step face at a fixed discharge for different weir slopes, the void ratio of the filled stones should be low to allow a small amount of base flow. The pressure distribution pattern on the horizontal face of a step is provided.     

Method of Solution of Nonuniform Flow with the Presence of Rectangular Side Weir

An iterative step method for solving the nonlinear ordinary differential equation, governing spatially varied flows with decreasing discharge, like the flow over side weirs, is developed. In the procedure, starting at a known flow depth and discharge in the control section, the analytical integration of the dynamic equation with bed and friction slope is carried out. The specific energy, the weir coefficient and the velocity distribution coefficient are considered as local variables, then for the explicit integration, the respective average values along the short side weir elements are assumed. The water surface profiles and the discharges for flow over side weirs, obtained with the proposed relation and valid for rectangular channels, are compared with experimental data for subcritical and supercritical flow conditions. The validation of the method is accomplished by the comparison with the solution obtained by De Marchi’s classical hypothesis, about the specific energy, which is constant along a side weir. In addition, the influence of the coefficient velocity distribution is considered.     

加强环冷机的技术改造 全面提升链窑的潜能

马钢第三炼铁总厂链窑生产线自2007年9月份投产以来,环冷机运行效果均不佳,出现了很多问题,严重地影响了链窑的生产。在对环冷机各部结构及存在的问题进行了认真分析后,采取了不同的改进方案并予以实施。实践结果表明,这些改进方案均取得了成功,环冷机的运行效果大大提升,在节能降耗的工作上取得了很好的效果。     

Calibration of weirs using unsteady flow

This paper presents a method for unsteady calibration of rectangular and triangular weirs using height measurement instead of another flow measurement device as a standard. The theoretical equation of the dependence of the flow with the head for that weir, as long as the covered area, must be known. The method is theoretically developed and applied to a rectangular and to a triangular type of weir obtaining very good results when compared to other studies. In both cases the coefficients of discharge values were 0.617 and 0.587, respectively, which is very well within the values obtained by other researchers. In those analysis, the coefficient of determination of was as high as 0.998.     

Minimizing the hydraulic side effects of weirs construction by using labyrinth weirs

It is no doubt that weirs are one of the most important hydraulic structures that play a vital role in irrigation project. So, it is necessary to minimize the hydraulic side effects of weirs. Throughout this paper, experiments were conducted to investigate the suitable dimensions and shape of weir's crest to increase head loss, decrease upstream bank level upstream weir and get the most economic structure. Various crest angles of labyrinth weir were tested under different flow conditions. Also back water curve upstream weir was studied according to different weir crest angles. A case of linear weir crest was also included in the test program. The experimental results indicated that labyrinth weirs have lower operating heads and longer crest length compared with a linear weir having the same lateral space and the same discharge. Results showed that the crest weir angle of 60° is the best angle of weir crest. It reduces water level above crested level and the relative jump depth by 18% and 20%, respectively. In addition, it increase the average values of the dissipated energy and the discharge coefficient by 15% and 14%, respectively. It also gave maximum reduction in backwater curve profile by about 17%. Furthermore, the model was verified using CFD numerical model. The numerical results agreed with the experimental results.