Weir Length Research Articles

Prediction of Discharge Coefficient for Trapezoidal Labyrinth Side Weir Using a Neuro-Fuzzy Approach

Adaptive neuro-fuzzy inference system (ANFIS) is considered for flow over trapezoidal labyrinth side weirs located on a straight channel as a substantial part of distribution channels in irrigation systems and treatment units. To estimate the outflow over a trapezoidal labyrinth side weir, the discharge coefficient in the side weir equation needs to be determined in according with the effective dimensionless parameters which is Froude number, the sidewall angle, the ratios of weir length to channel width, weir length to total crest length and weir height to flow depth. 670 laboratory test results are used for determining discharge coefficient of trapezoidal labyrinth side weirs. The performance of the ANFIS model is compared with artificial neural networks (ANN), non-linear regression (NLR) and multi-linear regression (MLR) models. The comparing criteria used for the evaluation of the models’ performances are root mean square errors (RMSE), mean absolute errors (MAE) and determination coefficient (R2) statistics. Comparison results indicated that the ANFIS technique could be successfully employed in modeling discharge coefficient. It is found that the ANFIS model with RMSE of 0.090 in test period is superior in estimation of discharge coefficient than the nonlinear and linear regression models with RMSE of 0.124 and 0.279, respectively.

Discharge coefficient for compound sharp crested side weirs in subcritical flow conditions

Summary Side weirs are one of the most common diversion structures used for flow control, irrigation, drainage networks, and waste-water channels. Side weirs are generally rectangular sharp crested in form and hence, have some limitations in precise flow measurement. For accurate flow measurement and management in wide range of discharges, use of compound side weirs are suggested in this study. Experiments have been carried out in a rectangular compound side weir with variable heights and widths. It was determined that discharge coefficient of a compound side weir is a function of upstream Froude number (Fr1), ratio of weighted crest height of weir to upstream water depth w ¯ / y 1 and 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 prediction of the discharge coefficient and an equation has been proposed for estimation of flow discharge in compound rectangular sharp crested side weirs. Through comparison of results of these equations and experimental data, good agreement was achieved. The mean and maximum relative errors of the discharge equation were −2.3% and 10.7%, respectively.

Hydrodynamic characteristic of Conical Cap tray: Experimental studies on dry and total pressure drop, weeping and entrainment

This paper addresses an experimental investigation in the hydrodynamic behavior of a new type of cap trays called Conical Cap tray (ConCap tray). The hydrodynamics of the tray was investigated in a commercial scale air–water column with an internal diameter of 1.2m. The experimental liquid loads were 29.9, 44.4, 60 and 74.4(m3/h)/m of weir length and gas flow in terms of Fs in the range of 0.2–1.5m/s(kg/m3)0.5. The dry pressure drop, total pressure drop, weeping and entrainment for the ConCap tray and a valve tray were measured and compared. Correlations for pressure drop, weeping and entrainment of the ConCap tray were provided using regression analysis method. Standard deviations of correlations, R2, are quoted. The ConCap tray was compared with a bubble cap tray using correlations. The pressure drop of the ConCap tray was less than the bubble cap and close to the valve tray. The weeping rate of the ConCap tray was less than the valve tray. Its entrainment is more than the valve tray and less than the bubble cap tray. Good turndown ratio is important characteristic of the ConCap tray which is achieved without having too much pressure drop.

New Method for Modeling Thin-Walled Orifice Flow under Partially Submerged Conditions

AbstractOrifices are often used in stormwater detention facilities for reducing runoff peak flow and achieving extended detention times to improve water quality. Orifices often flow partially full; therefore, accurate and easily implemented methods of modeling basin outflow under such conditions are needed. In this paper we describe two models of partially submerged flow in thin-walled orifices and conduct full-scale testing of these models. The best model (termed the top-width weir approach) treats the orifice as an equivalently sized rectangular weir, where the equivalent weir length equals the top width of flow in the orifice until half-full and the diameter of the orifice when greater than half-full. A single fitting coefficient Cw is required, which is directly proportional to the discharge coefficient for submerged orifice flow. This method provides results that, except for low submergence conditions, are within 2 to 5% of experimental data for steady flow, a significant improvement over the existin...

Coefficient of Discharge for Labyrinthine Side Weir

The main objective of this investigation is to be obtain the coefficient of discharge for labyrinthine side weir. 24 labyrinthine side weirs were constructed and built in upstream of side channel of a 15 cm width and 30 cm depth and 2 m long with constant horizontal bed. The weir height were varied three times as 9cm, 12 cm, and 15 cm and each height tested for four different angels of the weir crest ( ). The weirs were used with direction and opposite direction of flow with different discharges. From the analysis of results it was found that the labyrinthine side weir with small height and small angle is more efficient when put in the direction of flow. Two general expressions were obtained to estimate the coefficient of discharge in terms of the hydraulic parameters in direction and opposite direction of flow, also it was found that the rate between length of weir to the depth of flow is the most effective parameter. Key words: side weir, discharge coefficient

Discharge coefficient of side weirs in curved channels

Side weirs are flow diversion devices commonly used in irrigation, land drainage and urban sewage systems. It is essential for hydraulic and environmental engineers involved in the design of side weirs to predict the discharge coefficient correctly. The aim of this study is to present an accurate equation for discharge coefficients along the bend of sharp-crested rectangular side weirs based on a total of 1504 experimental runs. The discharge coefficient of the rectangular side weir along the bend depends on the dimensionless parameters of Froude number in the main channel F1, the angle of bend curvature α, the ratio of weir length to main channel width L/b, the ratio of weir length to radius of main channel centreline L/rc and the ratio of weir height to upstream flow depth p/h1. In particular, the variables L/rc and p/h1 are not seen in any equation for a rectangular side weir located on a curved channel. However, it was found that these dimensionless parameters were significantly important for the overflow rate. Moreover, the equation in the literature needs interpolation in order to obtain the discharge coefficient for different L/b and α values. Therefore, a reliable equation containing all dimensionless parameters for calculating the discharge coefficient was introduced.

A discharge coefficient for a trapezoidal broad-crested side weir in subcritical flow

An experimental investigation of the flow over trapezoidal broad-crested side weir in rectangular channels under subcritical flow conditions is reported. It was found that the discharge coefficient of a trapezoidal broad-crested side weir is related to the Froude number at the upstream of the weir, ratios of weir height to depth of flow, weir length to width of main channel and length of broad-crested weir to width of main channel for different side slopes. Additionally, a reliable equation for calculating the discharge coefficient of trapezoidal broad-crested side weirs is presented.

Discharge coefficients for free and submerged flow over Piano Key weirs

A comprehensive experimental investigation was performed to better understand the effect of the weir geometry of a Piano Key weir (PKW) on the discharge coefficient for both free and submerged flow conditions. Experiments were conducted in a 12 m long, 0.4 m wide and 0.7 m deep rectangular glass-walled flume. The effects of the PKW geometry, including weir length and height, up- and downstream key widths as well as up- and downstream apex overhangs on the weir flow discharge coefficient were investigated, so that the governing weir head-discharge relationship resulted. In addition, on the basis of a comprehensive data set, practical discharge coefficient relations associated with the standard weir equation were proposed for both free and submerged flows over PKWs. The present correlations cover various types of PKWs. From the experimental data, optimum values of the primary dimensionless weir parameters result produce the maximum discharge efficiency.

Flow over trapezoidal side weir

In this paper, the hydraulic characteristics of a sharp crested trapezoidal side weir have been experimentally and theoretically investigated. It was found that the DeMarchi coefficient of discharge for a sharp crested trapezoidal side weir in subcritical flow is related to the main channel Froude number, the side slope of weir, ratio of weir height to upstream depth of flow and ratio of weir length to upstream depth of flow. Suitable equations for the discharge coefficient are also obtained.

Discharging capacity of rectangular side weirs in straight open channels

A side weir is a hydraulic control structure used in irrigation and drainage systems and combined sewer systems. A comprehensive laboratory study, including 843 tests for the discharge coefficient of a sharp-crested rectangular side weir in a straight channel, was conducted in a large physical model under subcritical flow conditions. The discharge coefficient is a function of the upstream Froude number, the ratios of weir length to channel width, weir length to flow depth, and weir height to flow depth. An equation was developed considering all dimensional parameters for discharge coefficient of the sharp-crested rectangular side weir. The average error of the proposed equation is 4.54%. The present study data were compared with ten different discharge coefficient equations developed by several researchers. The study also presents water surface profile and surface velocity streamlines.

Stage-Discharge Relationships for U-, A-, and W-Weirs in Un-submerged Flow Conditions1

Thornton, Christopher I., Anthony M. Meneghetti, Kent Collins, Steven R. Abt, and S. Michael Scurlock, 2011. Stage-Discharge Relationships for U-, A-, and W-Weirs in Un-submerged Flow Conditions. Journal of the American Water Resources Association (JAWRA) 47(1):169-178. DOI: 10.1111/j.1752-1688.2010.00501.x Abstract: Instream rock weirs are routinely placed into stream systems to provide grade control, reduce streambank erosion, provide energy dissipation, and allow fish passage. However, design and performance criteria for site specific applications are often anecdotal or qualitative in nature, and based upon the experience of the design team. A study was conducted to develop generic state-discharge relationships for U-, A-, and W-weirs. A laboratory testing program was performed in which scaled, near-prototype U-, A-, and W-rock weir structures were constructed in 11 configurations. Each configuration encompassed a unique weir shape, bed material, and/or bed slope. Thirty-one tests were conducted in which each structure was subjected to a sequence of predetermined discharges that minimally included the equivalent of 1/3 bankfull, 2/3 bankfull, and bankfull conditions. All tests were performed in subcritical, un-submerged flow conditions. Stage-discharge relationships were developed using multivariant, power regression techniques for each of the U-, A-, and W-rock weirs as a function of the effective weir length, flow depth, mean weir height, rock size, and discharge coefficient. Unique coefficient expressions were developed for each weir shape, and a single discharge coefficient was proposed applicable to the weirs for determining the channel stage-discharge rating.

INVESTIGATION OF WATER SURFACE PROFILE ALONG LABYRINTH SIDE WEIR LOCATED STRAIGHT CHANNELS

There are a lot of studies related to the rectangular and triangular side weirs located on straight channels. The most of these studies are generally related to discharge coefficient and water level surface of these side-weirs. In this study, the labyrinth weirs have used instead of sharp crested side weirs. A labyrinth weir is defined as a weir crest that is not straight in planform. The increased sill length provided by labyrinth weirs effectively reduces upstream head for a particular discharge. They can therefore be used to a particular advantage where the width of a channel is restricted and a weir is required to pass a range of discharges with a limited variation in upstream water levels. A series of laboratory experiments were conducted in order to determine water surface profiles of the labyrinth side weirs at the straight channel for different labyrinth weir included angles, weir lengths, and crest heights. As a result, it is shown that water surface profile of the labyrinth side weirs is similar to that of classical side weirs. However, it is observed that vortex occurs over the labyrinth side weir for large Froude numbers.

Discharge Coefficient for Trapezoidal Labyrinth Side Weir in Subcritical Flow

The discharge coefficient of a trapezoidal labyrinth side weir is a function of the Froude number F1, the dimensionless effective crest length L/l, the dimensionless weir length L/B, the dimensionless weir height p/h1, and the sidewall angle α. A labyrinth weir is an overflow weir, folded in plan view to provide a longer total effective length for a given overall weir width. These weirs have advantages compared to the straight overflow weir and the standard ogee crest. Previous studies on the subject have generally focused on rectangular side weirs located on a straight channel. The present study investigates the hydraulic behavior of a trapezoidal labyrinth side weir. The results show that the discharge coefficient of labyrinth side weirs gives a significantly higher coefficient value compare to that of conventional straight side weirs. Discharge coefficient of the trapezoidal labyrinth side weir is 1.5 to 5.0 times higher than the conventional straight side weir. Consequently, an equation for the coefficient of discharge is introduced. The results predicted by the equation were shown to be very satisfactory using root mean square error (RMSE), mean absolute error (MAE) and correlation coefficient (R) statistics.

Discharge coefficient of a semi-elliptical side weir in subcritical flow

A labyrinth weir is an overflow weir, folded in plan view to provide a longer total effective length for a given overall weir width. The total length of the labyrinth weir is typically three to five times the weir width. In this study, a semi-elliptical labyrinth weir was used as a side weir structure. Rectangular side weirs have attracted considerable research interest. The same, however, is not true for labyrinth side weirs. The present study investigated the hydraulic effects of semi-elliptical side weirs in order to increase their discharge capacity. To estimate the outflow over a semi-elliptical side weir, the discharge coefficient in the side weir equation needs to be determined. A comprehensive laboratory study including 677 tests was conducted to determine the discharge coefficient of the semi-elliptical side weir. The results were analyzed to find the influence of the dimensionless weir length L / B , the dimensionless effective length L / ℓ , the dimensionless weir height p / h 1 , the dimensionless ellipse radius b / a , and upstream Froude number F 1 on the discharge coefficient. It was found that the discharge coefficient of semi-elliptical side weirs is higher than that of classical side weirs. Additionally, a reliable equation for calculating the discharge coefficient of semi-elliptical side weirs is presented.

Hydraulic behaviour of flow over an oblique weir

A comprehensive set of experiments was performed on weirs placed obliquely in a rectangular open channel. The main objectives were to investigate the effect of the weir angle relative to the approach flow direction on the behaviour and the hydraulic flow characteristics and to examine methods such as using upstream guide vanes and inclined aprons to increase the effective oblique weir length. Results indicate that by increasing the oblique angle, the effective length of the oblique weir increases significantly. Relationships are provided for the threshold submergence and the effective length of the oblique weir. Design recommendations are also presented for the use of guide vanes and upstream inclined aprons.

An Expert Model for Estimation of Distillation Sieve Tray Efficiency Based on Artificial Neural Network Approach

Knowledge of the efficiency of sieve tray columns as most common distillation equipments is necessary for the interpretation of separation and purification processes performance. In this study a new method based on Artificial Neural Network (ANN) for estimation of sieve tray efficiency has been proposed. In this case to develop data base several experimental data were collected from literatures. The network inputs are liquid and vapor density, liquid and vapor viscosity, liquid and vapor diffusivity, surface tension, slope of the equilibrium curve, hole diameter, weir height, weir length, liquid and gas flux, ratio of hole area to active area of the tray while the output is point efficiency. In order to find the best efficiency estimator of sieve tray, different training schemes for the back-propagation learning algorithm, such as; Scaled Conjugate Gradient (SCG), Levenberg-Marquardt (LM), Gradient Descent with Momentum (GDM), variable learning rate BP (GDA) and Resilient BP (RP) methods were examined. Finally among those trained networks, the SCG algorithm with ten neurons in the hidden layer shows the best suitable algorithm with the minimum average absolute relative error 0.029817. Finally, the capability of ANN and two recently published empirical models were compared. This ANN model reduced the prediction error by 64.03 and 92.64% relative to Garcia and Fair and Chan and Fair models, respectively. This is further proof that the proposed procedure can build a useful and robust model.

Flow over Gabion Weirs

A conventional weir typically consists of an impermeable body constructed of concrete, since its primary functions are to heading up water and efficiently regulate flow. However, an impermeable body prevents the longitudinal movement of aquatic life and transportation of physical and chemical substances in water, eventually having a negative impact on the water environment. One of the advantages of gabions as a building material is that the motion of individual stones comprising the gabion is not of much concern. The wire mesh of the gabion basket serves to restrain any significant movement. Also, gabion weirs offer an alternative design that could be adopted for flash flood mitigation. In this study, a series of laboratory experiments was performed in order to investigate the flow over gabion weirs. For this purpose, two different gabion weir models were tested in two horizontal laboratory flumes of 10-m and 17-m length, 0.3-m width, and 0.3- and 0.5-m depth, respectively, for a wide range of discharge, upstream water depth, downstream water depth, weir height, weir length, and gabion filling gravel material size. The results of the gabion weir were compared with those of experiments carried out on solid weirs having the same dimension and it was found that there is a large deviation when the solid weirs equation is applied to gabion weirs (permeable weirs). So, using one of the existing solid weir flow formulas would lead to an erroneous calculated value. Multiple regression equations based on the dimensional analysis theory were developed for computing the discharge over gabion weirs for both free and submerged flow regimes. Also, equations were introduced for computing the discharge coefficient to be applied with the traditional solid weir equation.

THE CAPACITY OF THE LOW-HEIGHT PIANO KEY WEIR TYPE A IN DRAINAGE CANAL

The capacity of PK piano weir is 4-5 times higher than conventional weir. This paper describes some hydraulic tests on the low-height P.K. weirs Type A, in order to show that it is possible to build in a drainage canal such a weir, which also improves safety and takes less labor to operate the system. The results of the performed tests can be used in practice as a design hydraulic feature for this weir type (the length of weir, the length of jump). In some cases, an adaptation of these tests could be required.

Discharge Capacity of Labyrinth Side Weir Located on a Straight Channel

Side weirs, also known as lateral weirs, are flow diversion devices widely used in irrigation as a head regulator of distributaries and escapes, land drainage, and urban sewage systems. The studies on the subject have been generally focused on rectangular and triangular side weirs located on a straight channel. However, the same is not true for labyrinth side weirs. The current studies deal with sediment transport and scour problems around side weirs and lateral structures. The investigation of the hydraulic effects of labyrinth side weirs to increase discharge capacity of them has been studied in this particular work. In the study, 2,830 laboratory tests were conducted for determining discharge coefficient of labyrinth side weirs, and results were analyzed to find the influence of the dimensionless weir length L/b , the dimensionless effective length L/l , the dimensionless weir height p/ h1 , triangular labyrinth side weir included angle θ , and upstream Froude number F1 on the discharge coefficient, wa...

ِِDischarge Coefficient in Oblique Side Weirs

Side weirs are flow diversion devices that are widely used in irrigation, drainage and urban sewage systems. The present study focuses on the investigation of the effect of oblique side weirs on the discharge coefficient of a side weir under subcritical flow condition in rectangular channels. In this study 106 laboratory tests were conducted and the results were analyzed to find out the influence of non-dimensional parameters on the discharge coefficient of the weirs. The angles of side weirs varied from 0 to 17.5 degrees in six steps, three heights (5, 10 and 15 centimeters) and three lengths (100, 80 and 40 centimeters). Two descriptions of the discharge coefficient (traditional side weir coefficients, Cd, and De-Marchi, CM), along with different discharges and related parameters were used. According to the results, Cd is more sensitive to b1/b2 (ratio of channel bottom widths), whereby CM is sensitive to L/b1 (ratio of side weir length to bottom width). The correction formula for estimating the oblique side weir discharge coefficient with a traditional shape shows that a 17.5 degree angle with side wall causes 40 percent change in the discharge coefficient.