HYDRAULIC ANALYSIS OF LOOPED MICROIRRIGATION SUBMAIN UNITS USING THE FINITE ELEMENT METHOD

摘要

Looped pipe networks are commonly used in water delivery systems due to their improved performance and reliability. Some irrigation systems (e.g., subsurface drip irrigation systems) are often designed as looped systems. The proper design of the submain units can significantly affect investment cost and crop yield. Therefore, the hydraulic performance of looped submain units should be explored. This article presents a comprehensive finite element based formulation for hydraulic analysis of looped microirrigation submain units. The proposed equations are solved iteratively using Gaussian elimination, and the results correlated well with experiment data. A custom computer software program was developed to implement the method for large irrigation submain units. The data obtained show that a looped submain unit can achieve better water application uniformity when compared with a branched system. On the condition of satisfying certain design criteria (EU > 0.8), the looped submain unit can be much larger with a slight increase in total cost. It may also be possible to use a smaller pipe diameter with lower cost when the submain unit size is determined. Uniformity of the looped submain unit is relatively insensitive to changes in the flow exponent (x), indicating that lower-cost, non-pressure-compensating emitters could be used. The optimal system design usually relates to a trade-off between reliability and cost, considering that a looped microirrigation submain unit seems to be a suitable alternative to a branched system.