Design of microirrigation laterals at minimum cost

Based on the design methods of finite elements and golden-section searches, a method was developed for designing microirrigation laterals at minimum cost. Characteristics of water application uniformity as affected by lateral diameters and lengths were analyzed. When the required average emitter discharge is known, the relationships of water application uniformity, best submain position (paired laterals), and operating pressure head as a function of the lateral diameter and length can be accurately determined using a personal computer. The lateral diameter and length can then be determined from a contour map representing water application uniformity as a function of the lateral diameter and length (computer calculation). The best submain position and operating pressure head for this lateral diameter and length is then determined by computer calculation. This method is suitable for designing microirrigation laterals on both uniformly and nonuniformly sloping fields. Received: 30 May 1997     

An improved method for designing microirrigation submain units

A method was developed for designing microirrigation submain units using the lateral flow rate equation, finite element method, and golden section search. Characteristics of water application uniformity affected by lateral parameters (length and diameter) and submain parameters (length and diameter) were analyzed using computer simulations. The design principle was then implemented based on the simulation results. When the required average emitter discharge, the required water application uniformity, one lateral parameter (length or diameter), and one submain parameter (length or diameter) are given, the optimal values of another lateral parameter, another submain parameter, best submain position (paired laterals), and operating pressure head can be accurately designed using a personal computer. A submain unit designed using this method has a minimal initial cost. This method is suitable for both submain units with uniform lateral lengths (in regular fields) and nonuniform lateral lengths (in irregular fields). Received: 28 May 1996     

Design of microirrigation laterals on nonuniform slopes

A method for designing microirrigation laterals on nonuniform slopes was developed using the finite element method. Six representative nonuniform slope patterns were discussed in detail. The design principle was implemented based on the results of computer simulations. It was found that a single lateral is suitable for Pattern I while paired laterals are better for Patterns II ∼ VI in most cases. The diameter of a single lateral or paired laterals may have two solutions for a required uniformity of water application and the length may have multiple solutions. When the required average emitter discharge, required uniformity of water application, and one parameter (either length or diameter) of a single lateral or paired laterals are given, the unknown parameter, best submain position (paired laterals) and operating pressure head can be accurately designed using personal computers. The design procedures are described. Received: 2 November 1995     

坡地上灌水器流量均等微灌双向毛管设计方法

根据最佳支管位置位于左右两侧毛管最小压力水头相等处的定义,结合能量廓线法推导出确定最佳支管位置的简易计算方法,并提出一种满足允许的最大压力水头和最小压力水头的微灌系统双向毛管设计方法.通过对多种存在条件的模拟计算,确定了最佳支管位置计算公式的最终形式、适用条件及其优化试算方式.利用该方法,能简便快速地设计各种坡地条件下微灌系统(灌水器流量均等)双向毛管.     

Field evaluation of fertigation uniformity as affected by injector type and manufacturing variability of emitters

Fertigation with microirrigation systems is increasing in popularity. Uniformity of fertigation is important for many reasons. Field experiments were conducted to evaluate the effects of injector types and emitters on fertigation uniformity by simultaneously measuring the distributions of water application, solution concentration, and fertilizer applied within a subunit of microirrigation system. Three conventionally used injectors, a water-driven piston proportional pump, a venturi device, and a differential pressure tank, were evaluated with three different emitters. The results indicated that both manufacturing variability of emitters and injector types had a very significant effect on the uniformity of fertilizer applied, while the uniformity of water application was mainly dependent on emitter type. The uniformity of solution concentration was dependent on injection methods. Emitters having a higher manufacturer’s variation produced a more nonuniform distribution of water application and fertilizer applied. For a given emitter type, a differential pressure tank produced considerably higher coefficients of variation (Cv) for water application and fertilizer applied than a proportional pump or a venturi injector because a differential pressure tank released fertilizer in a decreasing rate with time. To obtain a uniform fertigation distribution, an injector that can inject fertilizers in a constant rate is recommended. The relationship between water application uniformity and fertigation uniformity for a microirrigation system was established for different injection methods. Cv for fertilizer applied was very close to water application Cv for a microirrigation system using a proportional pump or a venturi injector as an injection device. However, fertilizer Cv for a differential pressure tank was approximately double of the water application Cv. The injection method and injector performance should therefore be considered in the design of microirrigation systems.     

Hydraulic design procedure for drip irrigation submain unit based on relative flow difference

The combined effects of hydraulic variation and manufacturing variation on the relative flow difference in drip emitters were analyzed for a drip irrigation submain unit. Emitter manufacturing variation is a random variable and follows a normal distribution, which can be expressed by emitter coefficient of manufacturing variation (v) and a random variable (u) following a standardized normal distribution. Emitter flow rate equation can be expressed by two parts: (1) emitter discharge coefficient (k) and discharge exponent (x) determine the flow rate (kh ^x ) from an emitter at pressure head (h) and (2) the unknown random term (uvkh ^x ), taking into account emitter manufacturing variation. Next, the formula for relative flow difference in a drip irrigation submain unit is derived based on (1) hydraulic variations due to head loss and elevation differences and (2) emitter manufacturing variation. A new hydraulic design procedure for drip irrigation submain unit is proposed based on the formula.     

自压滴灌支管灌水单元设计方法

为了解决山地自压滴灌支管灌水单元水力设计问题,以滴头制造偏差、水力偏差和微地形偏差产生的综合流量偏差率作为灌水均匀度衡量标准,计算出支管灌水单元不同压力区允许水压力偏差和最大水压力,根据不同压力区支管水压力递推关系,确定出支管压力偏差分配系数,将支管单元设计转变为支管设计和毛管设计;支管设计采用两阶段设计法,计算出支管各节点水压力,根据该水压力和不同压力区允许最大水压力,对支管进行压力单元的划分,在不同压力区选择不同类型的滴头,使滴头额定工作压力与地形高差提供的工作压力相匹配．研究结果可直接用于山地支管灌水单元设计,计算可在Excel表格中完成,设计方法简单实用．     

Emitter discharge variability of subsurface drip irrigation in uniform soils: effect on water-application uniformity

Emitter discharge of subsurface drip irrigation (SDI) decreases as a result of the overpressure in the soil water at the discharge orifice. In this paper, the variation in dripper discharge in SDI laterals is studied. First, the emitter coefficient of flow variation CV _q was measured in laboratory experiments with drippers of 2 and 4 L/h that were laid both on the soil and beneath it. Additionally, the soil pressure coefficient of variation CV _hs was measured in buried emitters. Then, the irrigation uniformity was simulated in SDI and surface irrigation laterals under the same operating conditions and uniform soils; sandy and loamy. CV _q was similar for the compensating models of both the surface and subsurface emitters. However, CV _q decreased for the 2-L/h non-compensating model in the loamy soil. This shows a possible self-regulation of non-compensating emitter discharge in SDI, due to the interaction between effects of emitter discharge and soil pressure. This resulted in the irrigation uniformity of SDI non-compensating emitters to be greater than surface drip irrigation. The uniformity with pressure-compensating emitters would be similar in both cases, provided the overpressures in SDI are less than or equal to the compensation range lower limit.     

供水水头和灌水器对负压灌溉土壤水运移的影响

研究了不同供水水头（H）（0.5、0、-0.5、-1、-2m）及不同孔径的负压灌水器（3～4、5～6μm）对负压灌溉出水量及土壤水分运移的影响。试验结果表明,不同处理中,湿润锋运移规律相似,湿润体近似为椭球体。当灌溉时间相同时,湿润体体积随供水水头的减小而减小。累计入渗量、最大水平和垂直湿润距离随高程差呈幂函数变化。灌...     

Assessing whole-field uniformity of stationary sprinkler irrigation systems

The procedure established in the literature for the evaluation of stationary sprinkler irrigation systems is limited in space and time since it is based on a sample of precipitation taken around one sprinkler during a given period of the whole irrigation event. This procedure also ignores what happens in the soil after water infiltrates. A model of the drop trajectory and of the water distribution pattern is formulated here for simulating precipitation from single sprinklers. The operating pressure determines sprinkler flow and maximum throw. Wind and evaporation distort the distribution patterns. The water distribution of individual sprinklers is overlapped to generate precipitation over the whole field and to calculate a coefficient of uniformity. Field effective uniformity is then calculated by averaging precipitation over the extension of plant roots or water redistribution within the soil profile. Application of the model has shown the impact of system management and design, field topography and wind on irrigation uniformity. Management factors such as lateral operation time or riser inclination may account for a large part of the field precipitation variations. A rough topography may also reduce uniformity significantly. Wind speed is important when it exceeds 1.8–2 m s^–1. The allowable maximum pressure loss of 20% fixed as a design criterion seems an overly strict limit when other factors may overcome pressure loss as sources of non-uniformity. The sources of non-uniformity have different scales of variation. Large-scale sources, such as lateral operation time or pressure loss, are not dampened by the crop or soil. Sources of smaller-scale variation, such as wind or inclination of the sprinkler riser, are better compensated by the crop and soil. The application of this kind of model to the design and management of sprinkler irrigation systems is discussed. Received: 9 May 1997     

吸力式微润灌水器水力特性试验研究

在参照滴头水力特性检测方法的基础上,从流量变异系数、流量压力关系、水量分布均匀系数等角度研究了吸力式微润灌水器水力特性。结果表明,0.02MPa工作压力下微润灌水器流量变异系数均值为5%,流量变异系数随着压力的增大先减小后增大;流量随着工作压力的增加而明显增大,二者之间具有良好的幂函数关系;水量分布均匀系数在83%～93%之间变化,随工作压力的增加先增大后减小,为了尽可能保证灌水器出流量和灌水均匀,工作压力宜控制在0.018～0.025MPa之间。     

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。     

Multicriteria analysis for design of microirrigation systems. Application and sensitivity analysis

This paper presents a practical application of the DSS MIRRIG for the design of a microirrigation system for a citrus orchard in Algarve (Portugal). Several alternatives were considered using different emitter types (drippers, sprayers, pressure-compensating and non-pressure compensating emitters), different pipe sizes and layouts with and without pressure regulation valves, as well as different pressure head and discharge at the upstream end of the systems. This application is described and the ranking of alternative designs is analysed using the weights given by the farmer to the hydraulic, economic and environmental criteria. An analysis of impacts resulting from selecting different weights is presented aimed at understanding the sensitivity of the model in relation to those criteria. In addition, a sensitivity analysis is performed to test the robustness of the algorithms used for ranking with respect to changes in concordance and discordance threshold values, which show that the values selected by the model are those providing for a more clear ranking of design alternatives.     

淹没出流条件下滴灌灌水器水力性能试验研究

在室内将3种类型的灌水器置于自制水槽中,进行了灌水器的淹没出流试验。试验结果表明:灌水器在淹没出流时的出流规律与自由出流相同,但淹没时的流量略小于对应压力下自由出流的流量,其流量变化率多在10%以内;相比之下,低压时流量变化率比高压时大,即在灌水器额定工作压力(10m)附近,淹没出流对其影响较小。统计特征表明,灌水器淹没后出流更加均匀。不同灌水器类型对淹没与否的敏感程度有所差异,微管灌水器最为明显,其次是内镶式,补偿式变化很小。升降压过程中,降压过程的淹没出流对灌水器的流量变化率均小于升压过程。     

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果进行对比.结果表明：管道总水头损失h_w随入口压力的增大而增大.随着滴头间距的增大,相同管长和压力下滴头个数减少,毛管总水头损失h_w减小;滴头间距较大时,水头损失的规范值远低于本模型计算值,滴头间距较小时,规范推荐的计算结果才较为合理;工作压力较低时,毛管壁厚对灌水均匀度影响较明显,且随着壁厚增大,过水断面减小,均匀度降低;当滴头额定流量较小时,相对于工作压力,壁厚对毛管的极限铺设长度影响较小.     

基于变频恒压控制下的喷微灌单元设计法及应用

利用机电泵加压进行喷微灌过程中,机电泵通常是利用工频电源(50 H z)作恒速运行,无法调节泵的运行特性与管网实际变化的运行状况相适应。在分析变频恒压控制系统原理的基础上,针对喷微灌技术应用中存在的问题,提出了喷微灌系统的单元设计法,对喷微灌系统压力进行分单元、分级控制,极大的提高了灌水均匀度,能够实现适时适量的科学灌水要求,同时具有显著的节水节能效益。     

Critical points: interactions between on-farm irrigation systems and water distribution network

In this work, a new model useful to analyze interactions between the on-farm irrigation system supplied by critical points and the water supply network management was developed. The model evaluates the impacts of changes in the pressure head and demand simultaneity (number of open hydrants at a given time) on the irrigation system and evaluates emitter discharge and uniformity. It also estimates the potential reductions in crop yield due to decreased emission uniformity. The methodology is applied in the Bembézar Irrigation District (Southern Spain). Results show that the additional cost required for providing maximum pressure to the critical field does not offset the increase in crop yield. Hence, an increment from 91.7 to 92.1 % in yield in the critical field would represent increases in energy consumption from 0.15 to 0.17 kWh m^?3 of water. Also, the unit energy cost could be reduced by up to 0.11 kWh m^?3 without implying significant reductions in crop yield. The importance of a good selection of emitters in the critical fields (fields that are supplied by the critical hydrants) was also evaluated.     

Hydraulics of microtube emitters: a dimensional analysis approach

Dimensional analysis is a simple, clear and intuitive method for determining the functional dependence of physical quantities that are of importance to a certain process. Buckingham’s pi theorem is used to derive a dimensionally homogeneous equation for predicting the discharge of the microtube as a function of gravitational acceleration (g), microtube diameter (D), operating pressure head (H) and microtube length (L). Experimental investigations were conducted at College of Agricultural Engineering and Technology, Junagadh, to determine (a) the variation in Q with L, D and H and (b) the coefficients (K, y and z) of the developed model. The L and D of microtube were varied from 5 to 250 cm and 1.2 to 2 mm. The operating pressure was varied from 0 to 1.5 m. The L, H and D combinations selected in the study suit most of the manufacturer’s recommendations for microtube drip irrigation systems. The discharge of microtube decreased with increase in microtube length for particular microtube diameter and operating pressure. The discharge increased with increase in the microtube diameter for a particular operating pressure and microtube length. The values of K, y and z are 4.476, 1 and 0.5, respectively. Goodness of fit and efficiency coefficient reduced with increase in the microtube diameter. The dimensionally homogeneous equation (Eq. 25) developed for all flow regimes can predict discharge with good accuracy for less than 2-mm microtube diameter. The microtube diameter was found to be 1.2 mm based on the dominance of viscous forces over inertial forces.     

低压滴灌施肥条件下温度对滴头堵塞的影响

【目的】探究低压滴灌施肥条件下温度对滴头堵塞的影响。【方法】采用短周期间歇灌水试验方法,考虑温度、运行压力、肥料质量浓度等因素,展开完全随机试验,研究滴头堵塞过程,寻求适宜的加肥质量浓度阈值。【结果】温度越高、运行压力越大、加肥质量浓度越低滴头堵塞风险越小;温度40℃时,运行压力50kPa、加肥质量浓度3g/L的处理具有最高的平均相对流量、均匀度系数以及最低的堵塞率;不同温度下加肥质量浓度阈值不同,温度10、20、30、40℃时加肥质量浓度阈值分别为4、5、7和8g/L。【结论】升高温度、提高运行压力、降低加肥质量浓度能有效降低滴头堵塞风险;升高温度还能提高加肥质量浓度阈值及水流携带固体颗粒的能力,但升高温度对滴头堵塞风险的降低程度随着压力的升高而减弱。     

滴头制造偏差对灌水均匀度及毛管造价的影响

为了阐明滴头制造偏差系数、灌水均匀度、毛管直径及毛管造价的内在联系,降低滴灌系统造价、提高灌水均匀度,通过理论推导结合实证计算的方法,系统分析了不同均匀度条件下滴头制造偏差系数极限值,以及滴头制造偏差系数、毛管直径、允许均匀度等三者的关系,并推导出毛管造价计算公式.结果表明:对于长度为100 m的毛管,当Keller均匀系数( EEU)为0.80时,制造偏差系数从0.05增大到0.07和0.11时,毛管造价分别增大8.7％和37.1％;当滴头制造偏差系数为0.03, EEU由0.80增大到0.85,0.90和0.95时,毛管直径分别增大20％,23.5％和56.5％,毛管造价也相应增大20％,53.8％和207.7％;当滴头制造偏差系数为0.05, EEU由0.80增大到0.85和0.90时,毛管直径则分别增大19.3％和32.8％,毛管造价也分别增大17.1％和71.4％;对于 EEU为0.95时,毛管允许最小流量大于平均流量,管径计算无解.在限定值范围内,滴头制造偏差系数和Keller均匀系数的微小增大将直接导致毛管直径和造价急剧增大;滴灌系统设计应选择制造偏差系数小的滴头及合理的灌水均匀度,以达到降低工程造价的目的.