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Determining turbulent flow friction coefficient using adaptive neuro-fuzzy computing technique

In the analysis of water distribution networks, the main required design parameters are the lengths, diameters, and friction coefficients of rough-pipes, as well as nodal demands and water levels in the reservoirs. Although some of these parameters such as the pipe lengths are precisely known and would remain the same at different points of the networks whereas some parameters such as the pipe diameters and friction coefficients would changed during the life of network and therefore they can be treated as imprecise information. The primary focus of this study is to investigate the accuracy of a fuzzy rule system approach to determine the relationship between pipe roughness, Reynolds number and friction factor because of the imprecise, insufficient, ambiguous and uncertain data available. A neuro-fuzzy approach was developed to relate the input (pipe roughness and Reynolds number) and output (friction coefficient) variables. The application of the proposed approach was performed for the data derived from the Moodys diagram. The performance of the proposed model was compared with respect to the conventional procedures using some statistic parameters for error estimation. The comparison test results reveal that through fuzzy rules and membership functions, the friction factor can be identified, precisely.

Computer-based analysis of explicit approximations to the implicit Colebrook-White equation in turbulent flow friction factor calculation

The implicit Colebrook-White equation has been widely used to estimate the friction factor for turbulent fluid-flow in rough-pipes. In this paper, the state-of-the-art review for the most currently available explicit alternatives to the Colebrook-White equation, is presented. An extensive comparison test was established on the 20x500 grid, for a wide range of relative roughness (@e/D) and Reynolds number (R) values (1x10^-^6=<@e/D=<5x10^-^2; 4x10^3=

Predicting discharge coefficient of compound broad-crested weir by using genetic programming (GP) and artificial neural network (ANN) techniques

Compound broad-crested weir is a typical hydraulic structure that provides flow control and measurements at different flow depths. Compound broad-crested weir mainly consists of two sections; first, relatively small inner rectangular section for measuring low flows, and a wide rectangular section at higher flow depths. In this paper, series of laboratory experiments was performed to investigate the potential effects of length of crest in flow direction, and step height of broad-crested weir of rectangular compound cross-section on the discharge coefficient. For this purpose, 15 different physical models of broad-crested weirs with rectangular compound cross-sections were tested for a wide range of discharge values. The results of examination for computing discharge coefficient were yielded by using multiple regression equations based on the dimensional analysis. Then, the results obtained were also compared with genetic programming (GP) and artificial neural network (ANN) techniques to investigate the applicability, ability, and accuracy of these procedures. Comparison of results from the GP and ANN procedures clearly indicates that the ANN technique is less efficient in comparison with the GP algorithm, for the determination of discharge coefficient. To examine the accuracy of the results yielded from the GP and ANN procedures, two performance indicators (determination coefficient (R2) and root mean square error (RMSE)) were used. The comparison test of results clearly shows that the implementation of GP technique sound satisfactory regarding the performance indicators (R2 = 0.952 and RMSE = 0.065) with less deviation from the numerical values.

A MathCAD procedure for commercial pipeline hydraulic design considering local energy losses

Using a power type equation for friction factor, this paper presents a design procedure which provides accurate solutions for three types of pipe design problems (Types A-C) taking into consideration the effect of local losses. The parameters introduced in the power type equation are related to the type and size of commercial pipes. Thus, several dimensionless physical numbers, obtained by suitably combining the variables relevant for the solution of Type B and Type C problems, are also introduced. For solution of the general case of a Type B problem (sloping pipe with pumping power), a user-friendly MathCAD procedure, which produces a consistent framework for analyzing and solving common piping-system applications problem, is also developed. In order to evaluate the accuracy of the proposed procedure, several design examples are analyzed for three types of commercial pipes and a wide range of uniform pipe slope, and the results are shown as design curves. These curves have practical importance, because they permit to quickly determine the values of required variables for a given pipe slope. The results of the proposed method are compared with those obtained from the methods existing in the professional practice.

Computer-Based Analysis of Hydraulic Design Variables for Uniformly Sloping Microirrigation System Laterals

AbstractAdequate analysis of lateral hydraulics is a very important concern for the design and evaluation of microirrigation systems. One of the main tasks of the lateral hydraulic calculation is to determine the pipe geometric characteristics (pipe size and length) with the required operating inlet pressure head, and the total friction head losses along the lateral line, assuming that the total flow rate at the inlet, characteristics of the emitter, and the acceptable level of uniformity are known in advance. This paper aims to present an efficient computer program in Visual Basic 6.0, named “Multi-flowCAD,” which is based on a stepwise computation algorithm for determining the hydraulic design variables (pipe size, pipe length, and operating inlet pressure head) and the hydraulic flow characteristics (emitter outflow-pressure head distribution, lateral discharge, and total friction losses) along the energy-grade line. The stepwise algorithm takes into account the velocity head change and variation of th...

Discussion of “Survey of Irrigation Methods in California in 2010” by Gwen N. Tindula, Morteza N. Orang, and Richard L. Snyder

The authors are appreciated for presenting an extensive examination to evaluate agricultural water-demand trends in cropping and irrigation methods in California. Essentially, the present work extends the previous research, which was completed in 1991 (Snyder et al. 1996) and 2001 (Orang et al. 2008), on the same concern. In these works (Snyder et al. 1996; Orang et al. 2008), the survey data are analyzed and compared with earlier surveys to study how irrigation methods have changed and to make projections of future changes. In the present research, a sample of the irrigation survey in the form of a useful questionnaire is presented to collect information on irrigated land by crop and irrigation method in 2010, as shown in Fig. 1 of the discussed paper. For the sake of comparison, similar survey sheets were used previously in Snyder et al. (1996) and Orang et al. (2008). Fig. 1 of the discussed paper lists 20 crop categories to gather irrigated acreages by crop and by irrigation method. As a matter of fact, a series of works (Snyder et al. 1996; Orang et al. 2008) conducted by California Department of Water Resources (CDWR) are very useful to present a survey approximately every 10 years, thereby updating California’s record on crops and irrigation methods during recent decades. Obviously, concluding remarks from the present analysis sound largely satisfactory; this discussion concerns minor standpoints that may relatively contribute to improve the present methodology.

Discussion of “Rapid Prediction of Hydraulic Performance for Emitters with Labyrinth Channels” by Jun Zhang, Wanhua Zhao, and Bingheng Lu

The authors are appreciated for presenting a rapid prediction method of hydraulic performance evaluation for emitters with labyrinth channels. In that procedure, a variable pressure loss coefficient (PLC) was proposed as the evaluation index of an emitter’s hydraulic performance. As a matter of fact, the authors’ previous work (Zhang et al. 2011b) was focused on the same concern with testing the hydraulic performance of specific types of emitters with labyrinth channels. In that procedure (Zhang et al. 2011b), the combined pressure loss coefficient (PLC) was also proposed as an evaluation index which incorporates the effects of frictional and local losses in labyrinth channels. Regarding the same concern, Zhang et al. (2011a) proposed an alternative procedure for testing hydraulic performance of three of the most commonly available high-head in-line drip-tape emitters under different working-head conditions ranging from 0.2 to 10 m, especially for low-head conditions. This analysis (Zhang et al. 2011a) mainly deals with the calculation of the coefficient of manufacturing variation (CV ) and the emitter flow exponent (x), regarding different phases of water pressures. For the design problem of testing emitter hydraulic performance, these three successively published procedures (Zhang et al. 2011a, b, and the paper under discussion) may provide a useful decision support tool for achieving a good design solution among commercially available alternatives with high water application uniformity, and the resulting high irrigation efficiency. With respect to the current problem (testing the emitter hydraulic performance), Qingsong et al. (2010) presented an experimental procedure to simulate the change of emitter flow exponents with different ranges of water pressures examined. The analysis (Qingsong et al. 2010) mainly deals with, first, the calculation of the emitter flow exponent, the average flow velocity, and the Reynold numbers with regarding different phases of water pressures, and then the determination of the best choice among the pressure ranges examined for five types of drip emitters tested. For these purposes, the paper is essentially focused on three research topics: (1) the change of flow exponents with different pressure segments; (2) the relationship between average flow velocities and water pressures, and (3) the relationship between Reynolds numbers and flow exponents. As a useful reference, Yildirim (2010) proposed the backward stepwise procedure for computing three energy loss components; minor friction losses through the path of an integrated in-line emitter, the local pressure losses due to barbed emitter connections, and the pipe friction loss. In that procedure, the mathematical expressions were implemented in a simple Excel spreadsheet to evaluate the relative contribution of each energy loss component; then a combination calculation procedure is used to calculate total energy loss. Two sample designs were evaluated in order to show the relative magnitudes of total friction loss (due to pipe and emitters) emitter local losses, and pipe friction loss for two kinds of the integrated in-line emitters with varying spacing. In order to better understand the present method this discussion calls attention first to the following standpoints which need to be clarified, and then to minor editorial corrections on the paper’s algorithm, which will be presented through the discussion.

Discussion of “Design of Level Basin Irrigation Systems for Robust Performance” by J. Mohan Reddy

The author is appreciated for describing and comparing the simulation results of different methodologies for designing level basin irrigation systems. The three design methods presented in this research are the volume-balance design criterion proposed by the Soil Conservation Service (SCS) of the USDA (1974), the limiting length (LL) design criterion that improves the SCS design procedure (Clemmens et al. 1981; Clemmens and Dedrick 1982; Strelkoff and Katopodes 1977), and the completion-of-advance (CoA) design criterion. To evaluate the performance of a level basin irrigation system, the latter two procedures (LL and CoA) are compared by using a mathematical simulation model (SIRMOD), and the results are shown in Tables 3, 4, and 5 of the paper for three values of Manning roughness coefficient: n 1⁄4 0.04, 0.1, and 0.25, respectively. Essentially, the efficient design techniques of level basin irrigation systems are highly popular because of their significant potential for achieving high application efficiency and improved salinity control. Over the years, three conventional design procedures (SCS, LL, and CoA) have been widely used for basin irrigation design; however, to make a decision on their real performance, systematic knowledge is still required from observations in the field. From this point of view, the paper is very useful and may provide valuable information for irrigation managers and designers in the absence of decent irrigation scheduling. Additionally, the author’s previous work (Reddy and Clyma 1982) primarily concerned the analysis of basin irrigation performance with variable inflow rates. Although concluding remarks in the analysis are sound and satisfactory, this discussion presents the following minor points that may need further clarification.

Discussion of “Assessing Pressure Changes in an On-Demand Water Distribution System on Drip Irrigation Performance—Case Study in Italy” by A. Daccache, N. Lamaddalena, and U. Fratino

2 ðHMÞ 1 � p þ p 1 � p where CV = coefficient of variation; H, M, and P = effects of hydraulics, manufacturer’s variation, and plugging, respectively; and p = percentage of complete plugging. For the case in which the coefficient of variation attributable to hydraulic and manufacturer’s variation is zero [CVðHM Þ¼ 0], the CVðPÞ caused by plugging alone, can be simply expressed as a function of percentage of plugging p

Discussion of “Design of Level Ground Laterals in Trickle Irrigation Systems” by Zayani Khemaies and Hammami Moncef

Theoretical Background of the Paper’s Eq. (16) About the paper’s Eq. (16), Khemaies and Moncef state, “For the design purpose, we shall assume hereinafter that the mean pressure head (hm) is tantamount to the nominal pressure. This statement holds true for the mean (qm) and nominal discharges. Therefore, applying the theorem of the mean value yields hm ¼ 1