圆形喷灌机末端出流多口系数的研究

对以往圆形喷灌机输水管出流多口系数的计算公式进行了分析。圆形喷灌机输水管上除了第一个出水口与中心支轴中心线的距离外,其余出水口之间的距离均相等,在此条件下,提出了圆形喷灌机末端出流不为零时输水管多口系数的计算公式。该公式计算精度高,适用范围广。     

多孔管的变径设计

要保证孔口压力差不超过允许范围条件下，一条多孔管可由两种管径不同的管段组成，即采用变径法设计。本文考虑了影响多孔管沿程压力的因素，导出了各种地形坡度下变径设计计算公式。这一方法可供喷灌及微灌工程设计参考。     

多孔管允许最大长度的计算

导出了不同地面坡度的多孔管允许最大长度公式，这一成果可用于喷灌及微灌工程的规划设计。     

An approach for simulating the hydraulic performance of irrigation laterals

A new method for simulating lateral hydraulics in laminar or turbulent flow has been developed. The outflow is considered as a discrete variable and the friction head losses are calculated using the Darcy–Weisbach equation with an equivalent friction factor. Local head losses are also computed by applying equivalent coefficients that can be dependent on Reynolds number. Considering these premises, a compact expression that is valid for any type of regime has been deduced for calculating global head losses along any lateral stretch. The proposed method is useful to workout the hydraulic computation of laterals with the inlet segment at full or fractional outlet spacing, and complex laterals when a different pipeline diameter, slope, flow regime or emitter gap have to be considered.     

线源滴灌土壤湿润均匀性的影响因素试验研究

线源滴灌设计中,滴灌管出流均匀性与土壤湿润均匀性有本质不同,前者仅仅是后者必要的基础,但是要保证线源滴灌土壤湿润均匀性,还需要考虑滴头间距、滴头流量、滴水量和土壤质地的差别。对影响线源滴灌土壤湿润均匀性的主要因素进行了试验研究。试验中所用土壤为沙土和沙壤土;滴头间距为30 cm和50 cm;滴头流量为0.3~4 L/h;滴水量为10~25 L不等。试验表明,沿滴灌管方向的土壤湿润均匀度取决于湿润区的交汇程度,而湿润区的交汇程度又取决于土壤湿润区水平运移宽度和滴头间距。沙土沿滴灌管方向的土壤湿润均匀度随滴水量的增大而显著增大,沙壤土的相应指标则随滴头流量的增大而增大。土壤湿润均匀度随滴头间距的增大而减小。线源滴灌设计时,粘粒含量较少的土壤应该有一定的设计湿润深度和较小的滴头间距才能保证其湿润均匀度满足设计要求。研究结论对完善滴灌技术设计理论有帮助。     

多孔管沿程压力分析

针对目前多孔管沿程水头损失计算方法存在的问题,推导出了一个新的多孔管沿程水头损失近似计算公式。利用导出的公式,分析了多孔管沿程的压力变化,这无论是对喷、滴灌工程的规划设计,还是对多孔管水力特性的进一步研究都是有益的。     

Characterization of the microtube emitters used in a novel micro-sprinkler

The microtube is a simple and cheap emitter that was widely used throughout the world in the early days of drip irrigation. Its length can be adjusted according to the pressure distribution along the lateral line and the discharge from the microtube can be adjusted by its length. This not only counters the pressure loss due to pipe friction but also makes it suitable for undulating and hilly conditions, where pressure in the lateral line varies considerably according to the differences in elevation. This is the major problem facing the designer, i.e., emitter flow changes as the acting pressure head changes. In this study, a novel micro-sprinkler system is proposed that uses microtube as the emitter and where the length of the microtube can be varied in response to pressure changes along the lateral to give uniformity of emitter discharges. The objective of this work is to develop and validate empirical and semi-theoretical equations for the emitter hydraulics. Laboratory testing of two microtube emitters of different diameter over a range of pressures and discharges was used in the development of the equations relating pressure and discharge, and pressure and length for these emitters. The equations proposed will be used in the design of the micro-sprinkler system, to determine the length of microtube required to give the nominal discharge for any given pressure. The semi-theoretical approach underlined the importance of accurate measurements of the microtube diameter and the uncertainty in the estimation of the friction factor for these tubes.     

Total energy loss assessment for trickle lateral lines equipped with integrated in-line and on-line emitters

The accurate evaluation for the pressure head distribution along a trickle (drip) irrigation lateral, which can be operated under low-pressure head, dictates to precisely determine the total energy (head) losses that incorporate the combined friction losses due to pipe and emitters and, the additional local losses, sometimes called minor losses, due to the protrusion of emitter barbs into the flow. In routine design applications, assessment of total energy losses is usually carried out by assuming the hypothesis that minor losses can be neglected, even if the previous experimental studies indicated that minor losses can become a significant percentage of total energy losses as a consequence of the high number of emitters (with reducing the emitter spacing) installed along the lateral line. In this study, first, simple mathematical expressions for computing three energy loss components—minor friction losses through the path of an integrated in-line emitter, the local pressure losses due to emitter connections, and the major friction losses along the pipe—are deduced based on the backward stepwise procedure, which are quickly implemented in a simple Excel spreadsheet, to rapidly evaluate the relative contribution of each energy loss component to the amount of total energy losses. An approximate combination formulation is finally proposed to evaluate total energy drop at the end of the lateral line. For practical purpose, two design figures were also prepared to demonstrate the variation of total friction losses (due to pipe and emitters) with emitter local losses, and the variation of pipe friction losses with emitter minor friction losses, versus different emitter spacing ranging from 0.2 to 1.5 m, and various total number of emitters, regarding two kinds of the integrated in-line emitters. Comprehensive comparison test covering two design applications for different kinds of integrated in-line and on-line emitters indicated that the present mathematical model is simple, can be easily adaptable, but sufficiently accurate in all design cases examined, in comparison with the alternative procedures available in the literature.     

Computer evaluation of sprinkler irrigation uniformity

Summary A method for evaluating the water application rate (WAR) and uniformity coefficient (Cu) of overlapping irrigation sprinklers is given for realistic field conditions which includes wind drift of the sprinkler spray. The method requires as input — the geometry of the sprinkler arrangement, trajectories of water drops from the sprinkler nozzle as calculated by the equations of motion and the WAR distribution (discharge) profile of a single sprinkler experimentally observed under windless conditions. Wind direction with respect to the main sprinkler line is shown to have a small effect on Cu and is assumed to be parallel to the main line. Results show that the effect of wind drift of sprinkler spray on Cu can be neglected for wind velocities less than 1 ms^–1 (Fig. 8). Analysis of simulated discharge profiles (Table 1) shows that the maximum value of the uniformity coefficient was obtained with triangular sprinkler discharge profiles at low values of spacing, changing to trapezoidal profiles as the spacing increases (Figs. 8 and 9). The effect of nozzle pressure on WAR was evaluated for the pressure range between 294 and 490 kPa and an optimum layout of overlapping sprinklers, designed to minimize the effect of wind drift and nozzle pressure on the uniformity of WAR distribution, is presented.Notation C _D air drag coefficient of water drop - Cu uniformity coefficient - D diameter of water drop - d _k reference k-th water drop - incremental scanning distance at a certain size matrix - g acceleration of gravity - h _pm mean value of water application rate (mean value of WAR) - h (x, y) WAR at points P (x, y) - h _o (k, n) WAR at points P _o (k, n) - h _p (l, m) WAR at cross points of a certain size matrix covering the unit area for calculation of Cu - i row index number (see Fig. 3) - j column index number (see Fig. 3) - K Kàrmán's constant - k index number of water drop, d _k - L number of scanning points along main line - l index number of scanning point along main line - M number of scanning points along the line perpendicular to main line - m index number of scanning point along the line perpendicular to main line     

薄壁内镶贴片式滴灌带有限元水力计算方法及设计

为了提高滴灌系统水力设计的准确性,基于有限元原理,提出一种计算薄壁内镶贴片式滴灌带能量损失和灌水均匀度的方法,局部水头损失根据贴片式滴头结构、管内压力和管道壁厚确定,沿程水头损失通过改进Darcy－Weisbach公式编写计算机程序,分析了不同滴灌带的水头损失及均匀度变化规律,并与《微灌工程技术规范》中推荐计算方法的结...     

以灌水量均等为目标的喷灌支管设计方法

在传统的喷灌支管设计中,支管上各喷头等间距布置,但是沿支管灌水量不相等。为此提出一种实现沿支管灌水量相等,但允许喷头间距变化的支管设计方法。采用这种设计方法可以提高喷灌灌水均匀度,并且能在不增加用水量和不均加能耗的情况下,增加支管灌溉面积。最后给出一个算例,说明这种方法的计算过程及应用效果。     

Center-pivot uniformity analysis with variable container spacing

Evaluation procedures for determining water application uniformity under center-pivot sprinkler systems have been documented in various technical publications. The so-called “catch cans” (open containers) are placed along one or more radial legs from the center of the field to obtain sample water application measurements, from which standard performance indices can be calculated. All of the published procedures for calculating indices such as the coefficient of uniformity (CU) and distribution uniformity (DU) are based on equal radial spacing of the containers, but in practice some evaluators choose to decrease the spacing toward the outer end of the leg, whereby more measurement samples are taken at locations which represent larger relative fractions of the total irrigated area. It is also common to have inadvertently non-uniform container spacing when one or more tip over during the test, or when avoiding placing a container along a wheel track at a tower. Modified equations and procedures are presented herein to correctly account for variable container spacing, along with spreadsheet macros to perform the calculations.     

Application of a hydraulic model for testing management decisions at distributary level

Summary This study was conducted on the Lagar Distributary of Gugera Branch of Lower Chenab Canal, Punjab, Pakistan. A computer model MISTRAL was adopted for evaluating management options. The study showed that the model can be used as a decision support tool for prioritizing management options. The model suggests that under current physical conditions of this distributary the combination of rotation between the distributaries and along the distributary canals can improve the equity of water discharge. For example, in case of Lagar Distributary the discharge of tail outlets can be increased threefold by introducing rotation between the tail of the distributary and an offtaking minor canal. A small decrease in the discharge of the minor would result from adopting this option. A combination of rotations between this and neighboring distributaries and along the Lagar itself can increase the discharge of tail outlets up to seven times. The results of the model indicate that operational changes can improve the discharge of tail outlets to some extent, but the improvement of physical conditions of the distributary is needed to achieve equity conditions, as specified in the design.     

An improved Lewis-Milne equation for the advance phase of border irrigation

Summary The Lewis-Milne (LM) equation has been widely applied for design of border irrigation systems. This equation is based on the concept of mass conservation while the momentum balance is replaced by the assumption of a constant surface water depth. Although this constant water depth depends on the inflow rate, slope and roughness of the infiltrating surface, no explicit relation has been derived for its estimation. Assuming negligible border slope, the present study theoretically treats the constant depth in the LM equation by utilizing the simple dam-break wave solution along with boundary layer theory. The wave front is analyzed separately from the rest of the advancing water by considering both friction and infiltration effects on the momentum balance. The resulting equations in their general form are too complicated for closed-form solutions. Solutions are therefore given for specialized cases and the mean depth of flow is presented as a function of the initial water depth at the inlet, the surface roughness and the rate of infiltration. The solution is calibrated and tested using experimental data.Abbreviations a (t) advance length - c mean depth in LM equation - c _f friction factor - c _h Chezy's friction coefficient - g acceleration due to gravity - h(x, t) water depth - h ₀ water depth at the upstream end - i() rate of infiltration - f(x, t) discharge - q₀ constant inflow discharge - S _f energy loss gradient or frictional slope - S₀ bed slope - t time - u(x, t) mean velocity along the water depth - x distance - Y() cumulative infiltration - (t) distance separating two flow regions - infiltration opportunity time     

低比转速叶轮叶片数的选择准则

离心叶轮叶片数的正确选择是提高叶轮水力性能的重要措施.通过考查国外最新速度系数法设计资料和分析影响叶轮流道脱流和园盘摩擦损失的多种因素,提出了与传统观点相反的结论：增加低比转速离心叶轮叶片,并不是改善叶轮水力性能的有效途径,在合理选定叶片包角、叶轮出口宽度及优化叶轮直径的条件下,适当降低低比转速叶轮叶片数,对提高叶轮水力效率、消除离心泵的特征曲线的驼峰都有重要意义.这一新观点为设计人员正确确定低比转速叶轮叶片数提供了重要参考.     

稻谷的摩擦带电特性研究

谷物的摩擦带电特性是谷物电特性之一。对其进行深入研究对谷物加工有着重要的意义。本研究对3个品种的稻谷进行了不同含水率、不同摩擦材料和不同摩擦速度的摩擦带电特性研究。从机理方面解释了稻谷摩擦带电的成因。确定了影响稻谷摩擦带电的主要因素。研究表明,稻谷的摩擦带电与稻谷含水率、摩擦速度、稻谷的介电常数以及摩擦材料等因素有关。     

流量呈梯形分布的微灌变径管道水力设计方法

在微灌水力设计中，坡地上的田块多是不规则的，因而管道的沿程出流量的分布也是不规则的。过去对于这种类型的管道水力设计方法研究甚少。为便于设计，有必要对其水力参数进行简化计算，寻求一套较系统的等距、非等出流的水力设计方法。     

Velocity profile modeling in rectangular and compound open-channel cross sections

A 3-D hydraulic model was developed for computing velocity profiles, surface velocity coefficients, and discharge under steady, uniform flow conditions for rectangular and compound open-channel cross sections. Reynolds-averaged Navier–Stokes equations, Reynolds stress equations, and kinetic energy and dissipation equations were applied in the model using the finite-volume method with the k–ε turbulence model. Many previously unpublished approaches to solving the numerical details of this type of hydraulic model are presented herein. Four different sets of Reynolds stress equations (one using the Boussinesq hypothesis and three algebraic stress models of varying complexity) were tested. Only one of the four stress models was successful in predicting the depression of the maximum stream-wise velocity below the water surface. The model was verified using data collected at the Utah Water Research Laboratory. A companion paper (Marjang and Merkley in Irrig Sci, 2009, in press) describes the application of this model to the calculation of surface velocity coefficients for the float method to estimate discharge in rectangular and compound irrigation canals.     

液体射流泵内部流动分析:Ⅱ理论计算参数确定

推导了射流泵理论模型方程中计算参数与断面几何和流动参数的关系,利用数值模拟结果,确定了理论模型中的计算参数,分析了理论计算参数随流量比的变化规律．结果表明:反力分布系数c1与吸入面积比c在最优工况近似相等,而随着流量比偏离最优工况,两者偏差增大;利用c值代替c1值不会导致理论计算结果显著误差;工作流体速度一定条件下,动量修正系数k1不随流量比变化而变化,近似为常数;k2随流量比变化呈双曲线形状,随着流量比增大,逐渐趋近于1;喷嘴流速系数1、吸入管路流速系数4为常数;扩散管入口断面流速分布均匀性对扩散管流速系数3值有重要影响;喉管流速系数2及喉管入口收缩段流速系数5随流量比增加而线性减少,是影响理论计算结果的主要参数．理论计算结果与试验结果吻合较好,验证了计算参数确定方法的可行性和理论模型的可靠性．     

梯形渠道机翼形量水槽试验

基于Hager对圆锥筒及圆柱体量水槽测流原理分析,推求出梯形渠道机翼形量水槽在自由出流时的流量理论计算公式,指出流量校正系数可由相对水头确定.选择6种收缩比进行了一系列室内模型试验,并根据试验数据建立了相对流量与相对水头的无量纲关系式.结果表明,相对流量与相对水头具有良好的相关关系,流量计算最大相对误差为±3.5%,该量水槽临界淹没度可达0.90,控制断面收缩比为0.372～0.585时可得到较好的量水效果.