微灌系统灌水均匀系数合理取值研究
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摘要
微灌灌水均匀度是微灌工程规划设计中的一项重要参数，直接决定了微灌系统灌溉质量的优劣。本文首先提出了微灌毛管局部水头损失计算方法，在此基础上应用步进法水力学解析原理，建立了考虑水力、制造和微地形偏差的微灌均匀系数计算模型，同时建立了灌水量和作物产量的函数关系，分析了支管单元系统年费用的计算方法，通过数值模拟方法，模拟了不同微灌支管单元的均匀系数和产投比（作物产值与系统年费用比值），并以均匀系数为决策变量，以产投比最大为目标函数，构建了适宜于不同作物的微灌均匀系数优化模型。通过上述研究，主要得到以下结论：
（1）毛管局部水头损失hj由灌水器流量q、灌水器插头断面面积A1、灌水器个数N及毛管内径D决定；局部水头占沿程水头损失的比例与灌水器流量q、灌水器插头断面面积A1、灌水器个数N成正比关系，与毛管内径D和灌水器间距Se成反比关系。
（2）在灌水小区不同参数情况下，局部水头占沿程水头损失的比值变化范围较大，本文数据分析中最低可达到0.02，最大可达到1.10，在某些极端情况下，会出现局部水头损失大于沿程水头损失的现象。在计算毛管局部水头损失时，不能仅按照规范中要求的占沿程水头损失的10%-20%估算，否则将造成较大误差，使得实际均匀度偏离要求的均匀度，建议通过本文推导的计算公式推算毛管局部水头损失。
（3）产投比随均匀系数的增大先增大后减小，存在一个极大值。以西瓜为例，经过分析得到最优均匀系数为0.78。当均匀系数大于合理取值范围（0.73-0.83）时，其微小地增加会引起产投比的急剧下降。均匀系数由0.83增长到0.93，产投比降低了58.57%，因此，微灌工程设计中不能一味追求高的灌水均匀系数，否则会造成经济上的不合理。
（4）灌水器制造偏差、微地形偏差和支管入口压力等因素对均匀系数均有影响，通过对影响因素与均匀系数的关系分析，建议灌水器生产过程中，将制造偏差系数控制在0.00-0.10范围内。对于微压滴灌系统或者当支管入口压力较小时，建议微地形偏差系数Sz不大于0.01m。对于微地形偏差不大于0.09m的平坦地形，建议支管入口压力取值在6m以下，但对于灌水器设计工作水头或灌水器最小工作水头的精确合理取值，还需要进一步的系统的优化设计。
（5）开发了均匀系数优化设计与分析软件，该软件能够针对不同作物选取合理均匀系数取值，并进行基于步进法的灌水器流量与压力推算，作物产量与系统年费用的模拟。可用于分析管网参数对均匀度及产投比的影响。并生成AutoCAD设计图及文本文档。
Uniformity is an important criterion to measure the irrigation quality of micro-irrigationsystem. Also it’s a key parameter in the procedure of micro-irrigation system design. In orderto get the reasonable micro-irrigation uniformity for different plants, this paper firstlyproposed the equation for emitter local head loss calculation, on the basis of which,established the uniformity calculation model considering hydraulic, manufacturer andmicro-topography deviation through hydraulics analytical theory of forward step method,analyzed the relationship between irrigation water amount and yield. On the same time, theuniformity and output-input ratio(the ratio of output and irrigation annual investment) fordifferent submain unit was simulated, moreover, regarding uniformity as decision variable,the maximum output-input ratio as objective function, micro-irrigation uniformityoptimization model for different plants was established. Through the above research, theconclusion are listed as follows:
(1) The effecting factors of lateral local head loss were emitter flow rate, emitter plugsection area, emitter number and lateral diameter. Lateral local head loss was withproportional relation to emitter number, emitter plug section area and emitter flow rate andwith inverse relation to lateral diameter.
(2) The proportion of lateral local head loss to frictional loss changed from0.02to1.10,which was determined by emitter plug section area, number, flow rate, spacing and diameter.In some extreme cases, the local head loss was larger than the frictional head loss. Therefore,in micro-irrigation design, using Eq.(2-4) to calculate local head loss was recommended.
(3) The output-input ratio increased and then decreased when uniformity increased.There was a maximum value for output-input ratio. Taking watermelon as example, thereasonable uniformity is0.78, a tiny increase in uniformity would cause a sharp decline ofoutput-input ratio when it was beyond reasonable value range. When uniformity increasedfrom0.83to0.93, the output-input ratio would decreased by58.57%. Therefore, blindlypursuit high irrigation uniformity was not acceptable in micro-irrigation otherwise wouldcause the economic loss.
(4) Emitter manufacture variation, micro-topography deviation and manifold inletpressure effected the uniformity and output-input ratio dramatically. Through the analysis ofrelationship between uniformity and effecting factors, the emitter manufacture variation coefficient should be controlled in the range of0.00-0.10. The micro-topography deviationcoefficient should not be larger than0.10for micro-pressure drip irrigation or when themanifold inlet pressure is small. Manifold inlet pressure could be lower than6m when fieldslope is smaller than0.09cm. The exact optimized value of manifold inlet pressure should beexplored further.
(5) The software for micro-irrigation aid design was developed, which can select theoptimized value of uniformity for different plant, calculate the pressure and flow rate of eachemitter, calculate the crop yield and system investment, generate the pipe line layout diagram.
（1）毛管局部水头损失hj由灌水器流量q、灌水器插头断面面积A1、灌水器个数N及毛管内径D决定；局部水头占沿程水头损失的比例与灌水器流量q、灌水器插头断面面积A1、灌水器个数N成正比关系，与毛管内径D和灌水器间距Se成反比关系。
（2）在灌水小区不同参数情况下，局部水头占沿程水头损失的比值变化范围较大，本文数据分析中最低可达到0.02，最大可达到1.10，在某些极端情况下，会出现局部水头损失大于沿程水头损失的现象。在计算毛管局部水头损失时，不能仅按照规范中要求的占沿程水头损失的10%-20%估算，否则将造成较大误差，使得实际均匀度偏离要求的均匀度，建议通过本文推导的计算公式推算毛管局部水头损失。
（3）产投比随均匀系数的增大先增大后减小，存在一个极大值。以西瓜为例，经过分析得到最优均匀系数为0.78。当均匀系数大于合理取值范围（0.73-0.83）时，其微小地增加会引起产投比的急剧下降。均匀系数由0.83增长到0.93，产投比降低了58.57%，因此，微灌工程设计中不能一味追求高的灌水均匀系数，否则会造成经济上的不合理。
（4）灌水器制造偏差、微地形偏差和支管入口压力等因素对均匀系数均有影响，通过对影响因素与均匀系数的关系分析，建议灌水器生产过程中，将制造偏差系数控制在0.00-0.10范围内。对于微压滴灌系统或者当支管入口压力较小时，建议微地形偏差系数Sz不大于0.01m。对于微地形偏差不大于0.09m的平坦地形，建议支管入口压力取值在6m以下，但对于灌水器设计工作水头或灌水器最小工作水头的精确合理取值，还需要进一步的系统的优化设计。
（5）开发了均匀系数优化设计与分析软件，该软件能够针对不同作物选取合理均匀系数取值，并进行基于步进法的灌水器流量与压力推算，作物产量与系统年费用的模拟。可用于分析管网参数对均匀度及产投比的影响。并生成AutoCAD设计图及文本文档。
Uniformity is an important criterion to measure the irrigation quality of micro-irrigationsystem. Also it’s a key parameter in the procedure of micro-irrigation system design. In orderto get the reasonable micro-irrigation uniformity for different plants, this paper firstlyproposed the equation for emitter local head loss calculation, on the basis of which,established the uniformity calculation model considering hydraulic, manufacturer andmicro-topography deviation through hydraulics analytical theory of forward step method,analyzed the relationship between irrigation water amount and yield. On the same time, theuniformity and output-input ratio(the ratio of output and irrigation annual investment) fordifferent submain unit was simulated, moreover, regarding uniformity as decision variable,the maximum output-input ratio as objective function, micro-irrigation uniformityoptimization model for different plants was established. Through the above research, theconclusion are listed as follows:
(1) The effecting factors of lateral local head loss were emitter flow rate, emitter plugsection area, emitter number and lateral diameter. Lateral local head loss was withproportional relation to emitter number, emitter plug section area and emitter flow rate andwith inverse relation to lateral diameter.
(2) The proportion of lateral local head loss to frictional loss changed from0.02to1.10,which was determined by emitter plug section area, number, flow rate, spacing and diameter.In some extreme cases, the local head loss was larger than the frictional head loss. Therefore,in micro-irrigation design, using Eq.(2-4) to calculate local head loss was recommended.
(3) The output-input ratio increased and then decreased when uniformity increased.There was a maximum value for output-input ratio. Taking watermelon as example, thereasonable uniformity is0.78, a tiny increase in uniformity would cause a sharp decline ofoutput-input ratio when it was beyond reasonable value range. When uniformity increasedfrom0.83to0.93, the output-input ratio would decreased by58.57%. Therefore, blindlypursuit high irrigation uniformity was not acceptable in micro-irrigation otherwise wouldcause the economic loss.
(4) Emitter manufacture variation, micro-topography deviation and manifold inletpressure effected the uniformity and output-input ratio dramatically. Through the analysis ofrelationship between uniformity and effecting factors, the emitter manufacture variation coefficient should be controlled in the range of0.00-0.10. The micro-topography deviationcoefficient should not be larger than0.10for micro-pressure drip irrigation or when themanifold inlet pressure is small. Manifold inlet pressure could be lower than6m when fieldslope is smaller than0.09cm. The exact optimized value of manifold inlet pressure should beexplored further.
(5) The software for micro-irrigation aid design was developed, which can select theoptimized value of uniformity for different plant, calculate the pressure and flow rate of eachemitter, calculate the crop yield and system investment, generate the pipe line layout diagram.
引文
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SL103-1995.微灌工程技术规范.北京:中国计划出版社
白丹.1992.多孔管沿程压力分析.农业机械学报,23(3):49～55
白丹.1995.微灌田间管网的混合整数规划模型.农业机械学报,26(1):45～49
白丹.1996.树状给水管网的优化.水利学报,(11):52～55
陈渠昌,郑耀泉.1994.灌水器局部损失水头的估算.内蒙古水利,(04):420～423
陈渠昌,郑耀泉.1995.微灌工程设计灌水均匀系数的选定.农业工程学报,11(2):128～132
范兴科,吴普特,牛文全,张林,王芳.2008.低压滴灌条件下提高系统灌水均匀度的途径探讨.灌溉排水学报,27(1):18-20
方永忠.1996.生成树变换法求输配水系统最短供水路线.中国给水排水,(4):10～14
傅琳.1998.微灌技术发展中的问题:节水灌溉.北京.中国农业出版社
胡笑涛,康绍忠,马孝义.2000.地下滴灌灌水均匀度研究现状及展望.干旱地区农业研究,18(2):115～117
李宝珠.2007.微灌工程干管环状管网模式研究.[硕士学位论文].杨凌:西北农林科技大学
李久生,尹剑锋,张航.2010.滴灌均匀系数对土壤水分和氮素分布的影响.农业工程学报,26(12):27～33.
李久生,尹剑锋,张航.2011.滴灌均匀系数和施氮量对白菜生长及产量和品质的影响.农业工程学报,27(1):36～43
李久生.1996.喷灌均匀系数对作物产量影响的模拟研究.农业工程学报,12(4):102～106.
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