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.

Finite element hydraulic calculation method and design of thin-wall drip irrigation pipes

In order to improve the accuracy of the hydraulic design of drip irrigation laterals, a finite element method for calculating the energy loss and irrigation uniformity of thin-wall drip irrigation pipes was proposed. The local head loss was determined by the structure of the emitter, working pressure head and lateral wall thickness. The friction head loss along the lateral was calculated by the modified Darcy-Weisbach formula. A computer program was developed to analyze the head loss and uniformity of different drip irrigation pipes. In addition, the results of the proposed method were compared with those of the recommended calculation method in our country′s Technical Specifications for Micro-irrigation Engineering(GB/T 50485—2009). The results showed that the total head loss h_w of the pipeline increased with the increase of the inlet pressure head. With the increase of the emitter spacing, the emitter number and total head loss h_w decreased under the same pressure head and lateral length. The h_w calculated by the technical specifications was much lower than that calculated by this model, when the emitter spacing was large. When the emitter spacing was small, the results of the recommended method were appropriate. When the working pressure was low, the lateral wall thickness had an obvious impact on the irrigation uniformity, which decreased with the increase in wall thickness and the corresponding decrease in cross section. When the emitter nominal flow rate was low, compared with the pressure head, the wall thickness had a low influence on the design maximum lateral length.