Weir Length Research Articles

Discharge coefficient of semi-circular labyrinth side weir in subcritical flow

Side weirs are flow diversion or intake devices that are widely used in irrigation and drainage networks and urban sewage systems. Labyrinth weirs have a proven hydraulic advantage due to their increased discharge rate at the same head for a given design condition. A labyrinth weir is defined as a weir crest that is not straight in plan-form. The increased sill length provided by labyrinth weirs effectively reduces upstream head to the particular discharge. In this study, a comprehensive laboratory study was conducted in a physical model of a semi-circular labyrinth side weir and the model is evaluated for three heights and three radii. In this particular study, the hydraulic effects of this shape of side weir in increasing discharge capacity was investigated. The discharge coefficient of semi-circular labyrinth side weirs was determined and the results were analysed to find the influence of the dimensionless parameters of weir height ( w/b ), weir length ( r/b ), nape height (( y 1 −w)/r ), and upstream Froude number ( Fr 1 ) on discharge coefficient ( Cd ), based on the experimental conditions and previous studies. It was found that the discharge coefficient of the semi-circular labyrinth side weir gives a relatively high discharge coefficient value compared to other types of classic side weir positioned on a straight channel. Additionally, reliable equations for calculating the discharge coefficient ( Cd ) of semi-circular labyrinth side weirs are proposed. According to the proposed equation, Cd depends on dimensionless parameters, which are the ratios of r/b, r/w , ( y 1 −w ) /r , ( y 2 −w )/ r and Fr 1 . Keywords: side-weir, discharge coefficient, semi-circular labyrinth side weir, subcritical flow

SIDE WEIR FLOW INVESTIGATION IN A CIRCULAR CHANNEL USING COMPUTATIONAL FLUID DYNAMICS (CFD) FOR SUBCRITICAL FLOW CONDITION

The 3D flow over side weirs is investigated using Computational Fluid Dynamic (CFD). The study aims to assess the capability of ANSYS CFX code for modeling flow characteristics in a circular channel with side weir for subcritical flow condition. Twelve models were studied for some ranges of variables such as discharge, length and height of side weir. The numerical simulation was based on the solution of continuity and momentum equations for three dimensional, incompressible, steady and turbulent flow. The volume of fluid (VOF) method was used to predict the free surface changes and the RNG k-e model was employed for simulating the flow field. The experimental data of Uyumaz and Muslu (1985) were used for verification. For all models, the specific energy is obtained and the average energy difference at the upstream and downstream side of the weir was very small and the assumption of constant energy in the circular channel was acceptable. The numerical results predicted the changes in the water surface profile at the main channel central axis and indicated that the water level rises from upstream to downstream end of the weir. The discharge coefficient (Cd) variation with the upstream Froude number (Fr1) for different weir height and length were studied and it was found that the value of (Cd) decreased with the increase of (Fr1) value. For each side weir length, the variation of (Cd) with the ratio of the weir height to channel diameter (P/D) were studied and it was observed that with the increase of (P/D) ratio the value of the (Cd) increased. The relation between the (Cd) and the ratio of the side weir length to channel diameter (L/D) for different weir height were also investigated. It was noticed that the (Cd) value increased gradually as the (L/D) ratio increased. The combined effects of (Fr1), (P/D) and (L/D) on the (Cd) were studied for all models and an empirical expressions for describing this relation was obtained and it was found that (Cd) was a function of all the above parameter.

Rock-weir fishway I: flow regimes and hydraulic characteristics

ABSTRACTIn recent years, ecologically oriented river engineering practices such as nature-like fishways have become a common solution to mitigate or compensate for negative environmental impacts. This study investigated the flow regimes and hydraulics of rock-weir-type nature-like fishways for different structure geometries (weir configurations, pool spacing and boulder diameter) and channel characteristics (bed slope and flow rate). A criterion was proposed to predict three distinct flow regimes (weir, transitional and streaming) based on quantitative thresholds associated with three dimensionless parameters for discharge, pool spacing and pool water depth. For the depth–discharge relationship, a new equation to predict the weir flow based on water depth, weir length and bed slope of the fishway was introduced. Finally, a maximum velocity reduction factor as a function of discharge was proposed to predict maximum weir velocity in rock-weir fishways. These results must be compared with the swimming ability of the fish that the fishway is being designed for to assess passability.

Optimum Support Vector Regression for Discharge Coefficient of Modified Side Weirs Prediction

Designing procedure of economical and safe side weirs that are used in various hydraulic structures such as intakes and deviation systems, essentially needs the ability to predict the side weirs’ discharge capacity accurately. In this paper, the discharge coefficient of a modified labyrinth side weir was modeled by employing the support vector regression (SVR) method. To find the optimum SVR scenario, eight different kernel functions and six different input combinations were investigated. The accuracy of the SVR models were compared with two nonlinear regression equations from other published studies. The results showed that the SVR model with Polynomial Kernel Function and $$w/L,Fr_{1} /\sin \theta^{\prime},w/Y_{1}$$ and $$w\sin \theta^{\prime}/Y_{1}$$ as input parameters performs better than other models in predicting the discharge coefficient. Where w, L, θ′, and Y 1 are the height of crest, weir length, oblique side-weir included angle, and upstream flow depth, respectively. Also, the results showed that the SVR model with mean square error (RMSE) of 0.050 performs much better than the two other nonlinear regression published equations with RMSE of 0.121 and 0.4270, respectively.

Sensitivity analysis of the factors affecting the discharge capacity of side weirs in trapezoidal channels using extreme learning machines

Side weirs are installed on the side walls of main channels to control and regulate flow. In this study, sensitivity analysis is planned using Extreme Learning Machines (ELM) to recognize the factors affecting the discharge coefficient in trapezoidal channels. A total of 31 models with 1 to 5 parameters are developed. The input parameters are ratio of side weir length to trapezoidal channel bottom width (L/b), Froude number (Fr), ratio of side weir length to flow depth upstream of the side weir (L/y1), ratio of flow depth upstream of the side weir to the main channel bottom width (y1/b) and trapezoid channel side wall slope (m). Among the models with one input parameter, the model including Froude number modeled the discharge coefficient more accurately (MAPE=4.118, R2=0.835). Between models with two input parameters, the model using Fr and L/b produced MAPE and R2 values of 2.607 and 0.913 respectively. Moreover, among the models with four input parameters, the model containing Fr, L/b, L/y1 and y1/b was the most accurate (MAPE=2.916, R2=0.925).

A cell sorting and trapping microfluidic device with an interdigital channel

The growing interest in cell sorting and trapping is driving the demand for high performance technologies. Using labeling techniques or external forces, cells can be identified by a series of methods. However, all of these methods require complicated systems with expensive devices. Based on inherent differences in cellular morphology, cells can be sorted by specific structures in microfluidic devices. The weir filter is a basic and efficient cell sorting and trapping structure. However, in some existing weir devices, because of cell deformability and high flow velocity in gaps, trapped cells may become stuck or even pass through the gaps. Here, we designed and fabricated a microfluidic device with interdigital channels for cell sorting and trapping. The chip consisted of a sheet of silicone elastomer polydimethylsiloxane and a sheet of glass. A square-wave-like weir was designed in the middle of the channel, comprising the interdigital channels. The square-wave pattern extended the weir length by three times with the channel width remaining constant. Compared with a straight weir, this structure exhibited a notably higher trapping capacity. Interdigital channels provided more space to slow down the rate of the pressure decrease, which prevented the cells from becoming stuck in the gaps. Sorting a mixture K562 and blood cells to trap cells demonstrated the efficiency of the chip with the interdigital channel to sort and trap large and less deformable cells. With stable and efficient cell sorting and trapping abilities, the chip with an interdigital channel may be widely applied in scientific research fields.

Discharge Coefficient of Rectangular Side Weirs on Circular Channels

AbstractIn this study, the flow turbulence and variations of the supercritical free surface flow in a circular channel along a side weir are simulated as three dimensional using the RNGk-εturbulence model and volume of fluid (VOF) scheme. Comparison between the numerical model and experimental measurements shows that the numerical model simulates the free surface flow with good accuracy. According to the numerical model results, the specific energy variations along the side weir for the supercritical flow regime are almost constant and the energy drop is not significant but by increasing the side weir length the energy difference between the side weir upstream and downstream increases. Next, using the nonlinear regression (NLR) and analysis of the simulation results, some relationships for calculating the discharge coefficient of side weir on circular channels in supercritical flow regime are provided.

3D Hydrodynamics of Trapezoidal Piano Key Spillways

This paper compares the hydraulics and 3D flow features of the ordinary rectangular and trapezoidal plan view piano key weirs (PKWs) using two phase RANS numerical simulations. The main aim is to investigate effects of the inlet key area and angle of the side walls on discharge capacity of the PKW, while keeping the developing length of the crest intact. The numerical model has been used to carry out a sensitivity analysis for geometrical parameters and hydrodynamics of the rectangular and trapezoidal weirs (TPKWs) have been compared for wide range of the water head on the weir. Results show that the trapezoidal weir has higher efficiency than the ordinary rectangular PKW. This is partly related to the inlet key flow conditions. The trapezoidal geometry increases the inlet flow area resulting in reduction of the velocity along the key axis. Consequently, flow is distributed more uniformly over the side crests. The gradual transition of the inlet key limits the development of the recirculation zones along the side walls, and it also limits the formation of the critical section along the inlet key. These phenomena result in increase of the effective weir length and thus discharge capacity increases in trapezoidal weir compared with rectangular one. Discretization of the discharge along the crest of the tested weirs clearly confirms these findings.

Comparison of Subcritical and Supercritical Flow Patterns Within Triangular Channels Along the Side Weir

Abstract Side weirs with triangular channel are used as flow controlling devices in draining and irrigation networks. By installing a side weir on the main conduits side walls, the runoff overflows from the weir and are conducted toward the diversion channel. In this study, changing of the flow free surface and the turbulence of the flow field in triangular channels with side weir are numerically simulated using volume of fluid (VOF) scheme and RNG k–ε turbulence model. In the present paper, the pattern of the spatially varied flow with decreasing discharge in both subcritical and supercritical flow regimes for triangular channels with side weirs was simulated. The present numerical model has precisely predicted the changes of the water surface and the specific energy. In subcritical regime, the flow depth is from the beginning of the weir toward its end is followed by an increase and in supercritical conditions is followed by a reduction in depth. For both subcritical and supercritical regimes, a drop in the surface in the first third of the weir’s opening and a surface jump in the final third of its length has occurred. Along the mentioned surface jump the amount of the kinetic energy increases and the potential energy reduces. According to results of the simulation, the maximum longitudinal velocity for subcritical flow regime occurs in the first third of the length of the side weir and for supercritical flow regime, almost in the middle of the weir opening happens. In both subcritical and supercritical regimes, the maximum transverse velocity has occurred in the final third of the length of the side weir.

A flow field characterization in a circular channel along a side weir

Side weirs have been used for centuries in urban drainage and flood control for their ability to divert high incoming flow rates. The flow along a side weir may be studied by means of different approaches. However, although the question of side weir has been debating for many decades, there are few studies on the local hydraulic characteristics of the flow along these structures in circular channels.An experimental study of the flow field in a circular channel along a side weir using a commercial TSI Particle Image Velocimetry (PIV) system is shown in this paper. Weakly supercritical flows running into different geometric configurations of the weir were investigated, with Froude numbers varying from 1.1 to 1.6. Free surface profiles have been obtained by an image processing technique. An empirical equation has been proposed for their representation. Longitudinal velocity profiles along the side weir can be well predicted by an entropic approach. Local outflow along the side weir may be represented by an asymmetric curve. The peak outflow generally occurs between the 30% and the 50% of the weir length. The elementary discharge coefficient significantly increases from upstream to downstream. An energy head reduction was observed under the investigated configurations. Most of the head variation occurs in the central part of the weir. Finally, the flow power decreases along the weir according to a non-linear function.A thorough knowledge of the flow field features should allow to improve side weir analysis and design, whatever approach is used for the study.

Prediction of side weir discharge coefficient by support vector machine technique

Side weirs have many possible applications in the field of hydraulic engineering. They are also considered an important structure in hydro systems. In this study, the support vector machine (SVM) technique was employed to predict the side weir discharge coefficient. The performance of SVM was compared with other types of soft computing techniques such as artificial neural networks (ANN) and adaptive neuro fuzzy inference systems (ANFIS). While ANN and ANFIS models provided a good prediction performance, the SVM model with a radial basis function kernel function outperforms them. The best SVM model was developed with a gamma coefficient and epsilon of 15 and 0.3, respectively. The SVM yielded a coefficient of determination (R2) equal to 0.96 and 0.93 for the training and testing data. Sensitivity analyses of the ANN, ANFIS and SVM models showed that the Froude number and ratio of weir length to the flow depth upstream of the weir are the most effective parameters for the prediction of the discharge coefficient.

Computer Aided Design of a Multi-Component Distillation Column for Processing of Nigerian Bonny Light Crude Oil

The design of the multi-component distillation column for processing of Bonny light crude is presented using advanced process simulation software (Aspen Hysys). The steady state design models were developed from Mesh equations and were used to obtain the design parameters based on the principle of conservation of mass and energy. The design parameters were column diameter, column cross sectional area, height of the column, downcomer area, hole area, weir length, wet area and tray spacing. The equations developed are capable of predicting compositions, partial pressures and temperature of the components of interest from the mixtures of crude oil. The accuracy of the design parameters were ascertained by comparing predicted results with literature data of a distillation unit. The simulation of the design models were performed using Aspen Hysys to obtain optimum values of the most significant variables/parameters (column diameters 1.558m, column height 17.048m, cross section area 1.907m2, downcomer area 0.229m2, tray spacing 0.5m, weir length 1.200m, hole area 0.191m2 and wet area 1.678m2). The result obtained from the steady state simulation shows that the feed flow rate, temperature and pressure influence the efficiency of the distillation column.

Gene expression programming to predict the discharge coefficient in rectangular side weirs

In this study, gene expression programming (GEP) is employed as a new method for estimating the side weir discharge coefficient. The accuracy of existing equations in evaluating the side weir discharge coefficient is first examined. Afterward, taking into consideration the dimensionless parameters that affect the estimation of this parameter and sensitivity analysis, five different models are presented. Coefficient determination (R2), root mean square error (RMSE), mean absolute relative error (MARE), scatter index (SI) and BIAS are used for measuring the models’ performance. Two sets of experimental data are applied to evaluate the models. According to the results obtained indicate that the model with Froude number (F1), dimensionless weir length (b/B), ratio of weir length to depth of upstream flow (b/y1), and ratio of weir height to its length (p/y1) parameters of R2=0.947, MARE=0.05, RMSE=0.037, BIAS=0.01 and SI=0.067, performed the best. Accordingly, this new equation proposed through GEP can be utilized for estimating the discharge coefficient in rectangular sharp-crested side weirs.

Discharge coefficient of compound triangular–rectangular sharp-crested side weirs in subcritical flow conditions

Side weirs are among the important hydraulic structures for flow diversion in flood schemes or sewer networks. Side weirs are generally rectangular or triangular in shape and have a limitation for precise measurement of low and high flow. Therefore compound side weirs are suggested for accurate flow measurement in a wide range of discharges. In this study, the discharge coefficient of compound sharp-crested side weir consisting of rectangular and triangular part was studied experimentally. The results are in agree with previous study which show the discharge coefficient of a compound side weir is a function of the upstream Froude number ((Fr1), the ratio of weighted crest height of the weir to upstream water depth (w¯/y1) and the ratio of weir length to upstream water depth (L/y1). Based on the experimental data and regression modeling, a dimensionless equation has been developed for estimation of the discharge coefficient and two equations have been proposed for estimation of flow discharge in compound triangular–rectangular sharp-crested side weirs. The results also show that there is a good agreement between estimated and measured data.

GMDH-type neural network approach for modeling the discharge coefficient of rectangular sharp-crested side weirs

Estimating the discharge coefficient using hydraulic and geometrical specifications is one of the influential factors in predicting the discharge passing over a side weir. Taking into account the fact that existing equations are incapable of estimating the discharge coefficient well, artificial intelligence methods are used to predict it. In this study, Group Method of Data Handling (GMDH) was used for the purpose of predicting the discharge coefficient in a side weir. The Froude number (F1), weir dimensionless length (b/B), ratios of weir length to depth of upstream flow (b/y1) and weir height to its length (p/y1) were taken as input parameters to express a new model for predicting the discharge coefficient. Two different sets of laboratory data were used to train the artificial network and test the new model. Different statistical indexes were used to evaluate the performance of the GMDH model presented for two states, training and testing. The results indicate that the proposed model predicts the discharge coefficient precisely (MAPE = 5.263 & RMSE = 0.038) and this model is more accurate in predicting than the feed-forward neural network model and existing nonlinear regression equations.

The flow pattern in triangular channels along the side weir for subcritical flow regime

Side weirs in triangular channels are used for control and measurement of flow in irrigation networks and drainage systems. The main purpose of this study is investigation of the effects of side weirs on the subcritical flow conditions parameters in the triangular channels that is not 3D simulated numerically, so far. The turbulent RNG k−ε model and the volume of fluid (VOF) scheme were used to simulate turbulent flow field and flow free surface in a triangular channel along the side weir, respectively. Comparison of numerical and experimental results shows that the numerical model simulates the free surface and flow field characteristics with acceptable accuracy. First, the flow pattern within triangular channel along the side weir in subcritical flow regime is investigated numerically. Due to the side weir inlet effects, a sudden drop occurred at the first quarter of the side weir length. Then, the effects of subcritical regime Froude numbers in range of 0.406–0.793 are investigated. At all the Froude numbers, a surface jump occurred along the end quarter of the weir length. The length of this surface jump increased with increasing the Froude number. The angle of spilling jet pattern (φ) was similar for all the Froude numbers. However, the minimum φ decreased upon increasing Froude number. For all the Froude numbers, a secondary flow cell was produced after the side weir, which developed as it moved downstream in the main channel.

The Flow Field and Free Surface Pattern of the Submerged Side Weir with Different Lengths

A side weir is set in the side of a channel and is used for water level control, diverting excess water, as in sewage systems. In this study, firstly, a numerical simulation for prediction-free surface turbulent flow over the sharp crest side weir was performed by commercial software using the volume of fluid scheme and Reynolds-stress model (RSM) turbulence model. Comparison between numerical results and laboratory measurements showed that the model predicts experimental trends with reasonable accuracy. Then, the side weir length effects on the flow pattern and free surface were numerically investigated in the low, medium and high overflow rates. With decreasing the side weir length, the separation zone moves toward the downstream, and also the width of this zone and the distance of dividing stream surface from the left wall of the main channel were reduced at the free surface near the side weir crest level. In all cases, the side weir length and overflow rate variations had no any substantial effect on the secondary flow strength in main channel and the variations of the minimum water depth in the branch channel.

Determining side-weir discharge coefficient using Anfis

The effects of parameters such as weir length, height of weir, water depth at weir entrance and bed slope on the discharge coefficient of a rectangular sharp-crested side weir were analysed using standard linear regression and the adaptive neuro-fuzzy inference system (Anfis). The results showed that the Anfis model performed better than the regression model in all different scenarios defined in this study. Anfis can simulate the discharge coefficient better than the regression model and always works better. Without considering the channel slope, both models represent satisfactory results, but the Anfis model shows more sensitivity to channel slope than does the regression model. Based on the results of this study, the Anfis model is suggested for estimation of side weir discharge coefficient.

ANALYSIS OF THE PERFORMANCE RESPONSE OF OFFLINE DETENTION BASINS TO INLET STRUCTURE DESIGN

ABSTRACTA detention basin is a structural measure used to manage floods by temporarily storing a portion of the incoming water volume in selected areas. The design of the inlet and outlet structures is crucial for the optimal efficiency of the detention system. This paper investigates the sensitivity of flood peak reduction through an offline detention basin to the design characteristics of the inlet structures. The response of the efficiency is studied by varying the design characteristics of the different inlet components: elevation and length of the lateral weir and elevation, location and type of in‐line structure. The response of the detention basin to the different inlet layouts is evaluated by means of three performance criteria, two at the detention basin section and one at a downstream control section. Laboratory data available for the detention basin under implementation on the Navile channel (Italy) were used to calibrate a 1D numerical model in steady‐state conditions. The calibrated model was then used in simulating different inlet alternatives in unsteady state to determine the most influential layout characteristics on flood peak reduction. The results of this study can provide general guidelines for the design of the inlet structure of detention basins having similar structural components. Copyright © 2013 John Wiley & Sons, Ltd.

Discharge coefficient of a broad crested side weir in an earthen channel

Side weirs are widely used to divert flows from rivers and channels. However, the hydraulic behavior of this type of weir is complex and difficult to predict accurately. Previous studies on side weirs have generally focused on side weirs in rectangular channels with a smooth bed. However, one of the applications of side weirs is in irrigation systems which have trapezoidal cross sections and significant bed roughness. The present study investigates the hydraulic behavior of a broad crested side weir in an earthen channel with a rough bed under subcritical flow. These investigations showed that the side weir discharge coefficient is influenced by four main parameters which are upstream Froude number, ratio of the main channel width to the upstream flow depth, ratio of the length of the side weir to the main channel width and ratio of side weir height to the upstream flow depth. The results showed that the discharge coefficient of the side weir gives a lower coefficient value compared to other researchers’ equations. Nearly 90 experimental tests were carried out and finally new equations are proposed for prediction of discharge coefficient of a broad crested side weir in an earthen channel under subcritical conditions which can be mainly used in common irrigation systems.