枝状管网水力瞬变工况的试验与数值模拟     

石喜  吕宏兴  朱德兰  孙斌  曹彪 《排灌机械工程学报》2013,31(5):406-412

采用试验并结合特征线法(MOC)对带有一个分支管管网阀门关闭时产生的水锤压力及波动规律进行了研究,试验采用压力传感器监测水锤压力波动、角位移传感器测定阀门的关闭时间及关闭规律,结果表明:MOC方法能较好地预测管网阀门关闭产生的最大水锤压力值,管网监测点计算与试验值相对误差小于13％,但MOC方法计算所得压力波的衰减比较缓慢,而试验得到的压力波衰减很快,是由于在计算中使用的恒定流摩阻所致;在此基础上对5种阀门关闭方案产生的瞬变流动进行了数值计算,表明管路末端2个阀门同时关闭时管网中产生的水锤压力最大,在实际工程中应避免阀门同时关闭的操作;管网最大水锤压力随关阀时间的延长而减小,当阀门关闭时间一定时,采用曲线关闭规律产生的最大水锤压力比直线关闭规律产生的要小,而采用两阶段直线关闭规律产生的最大水锤压力压力小于线性关闭的,对于实际工况中的两阶段关闭应通过延长第一阶段关闭时间以减小最大水锤压力．  相似文献   

Effects of deficit irrigation with saline water on spring wheat growth and yield in arid Northwest China     

Jing JIANG 《干旱区科学》2013,5(2):143-154

Field experiments were conducted in 2008 and 2009 to study the effects of deficit irrigation with saline water on spring wheat growth and yield in an arid region of Northwest China. Nine treatments included three salinity levels s1, s2 and s3 (0.65, 3.2, and 6.1 dS/m) in combination with three water levels w1, w2 and w3 (375, 300, and 225 mm). In 2008, for most treatments, deficit irrigation showed adverse effects on wheat growth; meanwhile, the effect of saline irrigation was not apparent. In 2009, growth parameters of w1 treatments were not always optimal under saline irrigation. At 3.2 and 6.1 dS/m in 2008, the highest yield was obtained by w1 treatments, however, in 2009, the weight of 1,000 grains and wheat yield both followed the order w2 > w1 > w3. In this study, spring wheat was sensitive to water deficit, especially at the booting to grain-filling stages, but was not significantly affected by saline irrigation and the combination of the two factors. The results demonstrated that 300-mm irrigation water with a salinity of less than 3.2 dS/m is suitable for wheat fields in the study area.  相似文献   

Measuring cotton water status using water-related vegetation indices at leaf and canopy levels   总被引：1，自引：0，他引：1  

QiuXiang YI  AnMing BAO  Yi LUO  Jin ZHAO 《干旱区科学》2012,4(3):310-319

Drought is one of the major environmental threats in the world. In recent years, the damage from droughts to the environment and economies of some countries has been extensive, and drought monitoring has caused widespread concerns. Remote sensing has a proven ability to provide spatial and temporal measurements of surface properties, and it offers an opportunity for the quantitative assessment of drought indicators such as the vegetation water content at different levels. In this study, sites of cotton field in Shihezi, Xinjiang, Northwest China were sampled. Four classical water content parameters, namely the leaf equivalent water thickness (EWT leaf ), the fuel moisture content (FMC), the canopy equivalent water thickness (EWT canopy ) and vegetation water content (VWC) were evaluated against seven widely-used water-related vegetation indices, namely the NDII (normalized difference infrared index), NDWI 2130 (normalized difference water index), NDVI (normalized difference vegetation index), MSI (moisture stress index), SRWI (simple ratio water index), NDWI 1240 (normalized difference water index) and WI (water index), respectively. The results proved that the relationships between the water-related vegetation indices and EWT leaf were much better than that with FMC, and the relationships between vegetation indices and EWT canopy were better than that with VWC. Furthermore, comparing the significance of all seven water-related vegetation in- dices, WI and NDII proved to be the best candidates for EWT detecting at leaf and canopy levels, with R 2 of 0.262 and 0.306 for EWT leaf-WI and EWT canopy -NDII linear models, respectively. Besides, the prediction power of linear regression technique (LR) and artificial neural network (ANN) were compared using calibration and validation dataset, respectively. The results indicated that the performance of ANN as a predictive tool for water status measuring was as good as LR. The study should further our understanding of the relationships between water-related vegetation indices and water parameters.  相似文献   

无功补偿新技术及其装置运行管理     

郭金刚 《农业科技与装备》2012,(7):44-45,48

为提高配电网功率因数和降低有功损耗,概述无功功率对电网安全运行的影响,在详细介绍无功补偿新技术及其装置运行管理的基础上,提出合理制定电网无功补偿方案的可行性建议。  相似文献   

2011-2015年河南省农业机械总动力的预测   总被引：1，自引：0，他引：1  

李建伟  梁爱琴  田辉 《农机化研究》2012,34(6):47-50

农业机械总动力是衡量农业机械化水平的一项重要指标。对河南省农业机械总动力进行预测,将为农业机械化部门制定合理的发展规划提供一定的理论支持,同时也为农机企业了解未来市场需求状况提供一定的参考。以1991-2010年间的河南省农业机械总动力统计数据为基础,利用BP神经网络建立了河南省农业机械总动力的预测模型。该模型采用3层BP神经网络,输入层、隐含层和输出层的神经元数目分别为5,13和1。隐含层和输出层的激励函数分别为正切型与对数型Sigmoid函数。采用分步预测的思想,利用自适应学习速率训练方法对该网络进行了训练,获得了该模型中各层之间的连接权值和各层神经元的阈值。利用该模型对现有数据进行了仿真预测,结果表明,该模型具有较高的预测精度。在此基础上,对河南省"十二五"期间的农业机械总动力进行了预测,并给出了预测数据。  相似文献   

农网长距离线路应用串补技术的理论研究与仿真     

任艳杰  朴在林  赵玉林 《农机化研究》2012,34(7):224-227

众所周知,引起线路电压的损失主要由两部分组成:一是线路电阻引起的电压损失;二是线路电抗引起的电压损失。目前,由于农网很多线路送电距离长、导线截面大等原因,导线的电抗远大于线路电阻。因此,研究降低线路电抗上的压降损耗是当前关注的热门课题。为此,针对某农网66kV系统存在因线路长、电抗大而造成沿线各负荷点电压水平低、沿线线路损耗大等问题,对其采用串联补偿技术进行了探讨。经理论分析与软件仿真,证明了该技术用于农网长距离线路改善电压质量的可行性,为提高电能质量、降低线路损耗和保证农网的安全稳定运行提出了一个新的思路。  相似文献   

基于混合WSN的智能灌溉远程SCADA系统     

张增林  郁晓庆  拓延生 《节水灌溉》2012,(1):57-60

采用Citect组态软件、无线传感器网络（WSN）、和GPRS模块,开发设计了一套分布式精确灌溉的闭环远程SCADA（Supervisory Control And Data Acquisition）系统。该系统主要由上位机、灌溉监控器、WSN、GPRS无线通讯模块和灌溉阀门系组成。其中,无线传感器网络采用地上和地下的混合拓扑结构,灌溉控制器通过土壤水分含量调控区域面积内的灌水量;远程监控中心采用Citect组态软件实现数据、人机界面管理,并可以通过web发布来实现高层次的监控。测试和试验过程中,数据采样间隔设定为30min,选用4组WSN节点,分别测得深度为5cm和35cm处的土壤温度、含水量,测试结果与普通灌溉相比可节水约20％。该系统实现了灌溉的在线自动监控和作物的精量灌溉,创新性的建立了一种地上、地下混合结构的无线传感器网络模型,为进一步研究奠定了基础。  相似文献   

利用流媒体技术实现机械制造实习网络教学     

黄克 《湖南农机》2012,39(3):183-184

文章从介绍流媒体技术出发,介绍了流媒体技术与网路视频如何实现有效融合,以提高便重于动手实践的机械制造实习教学效果,希望为广大工程院校提高机械制造实习课程教学效果提高一些技术借鉴.  相似文献   

信息网络机房的接地保护技术研究     

郑敏 《湖南农机》2012,(5):28-29

接地技术对于实现气象系统信息网络机房的人员和信息设备的有效保护,确保信息网络机房的数据安全、稳定、可靠等都具有十分重要的意义与价值。文章在理清接地技术的含义及其重要价值的基础上,分析了接地技术的分类,探讨了接地保护技术的设计及实现方案。  相似文献   

应对未来城市发展的创森理念与技术   总被引：2，自引：2，他引：0  

刘滨谊 《中国城市林业》2012,10(6):1-4

通过分析未来城市发展需求,提出城市森林是继承与构建城市自然生态系统的主体、是城市绿化的高级阶段的思想;预测未来城市形态,提出以生态绿化空间为主体的未来城市空间"网状结构"以及从绿肺扩展为绿脉的观念和构建生态绿地网络的技术;从城市现阶段发展启动出发,根据实践案例,提出城市"生态-文化区"(ECD)概念以及点、带结合的ECD网络空间技术。    相似文献