| Center pivot irrigation systems have good characteristics of high automation level, large control area, and strong adaptability. The center pivot irrigation systems are suitable for large-scale, intensive agricultural production and pastoral area irrigation. However, there are problems such as improper design and operation and poor irrigation quality in application of the center pivot irrigation systems in China. Theoretical analysis and field evaluation were conducted to investigate effects of sprinkler type, system travel speed, and environment parameter on hydraulic performance. Moreover, a software, called SCECP (Sprinkler Configuration and Evaluation of Center Pivot), was modified. And optimal design of the hydraulic performance was conducted. Main work and results are as follows:(1) Theoretical analysis of the hydraulic performance of the center pivot irrigation systems was conducted. Field evaluations of the hydraulic performance of a system were conducted under five system travel speeds. System length is 97.3 m, system discharge is 25.16 m3/h, and system inlet pressure is 200 kPa. The results showed that coefficient of water application uniformity (CUH) ranged from 75.3% to 80.3% and from 62.5% to 72.8% for the R3000 and D3000 sprinklers, respectively. Uniformity coefficient of soil water content (CUHs) ranged from 86.3% to 93.1% for the two types of sprinklers. And CUHs was averaged at 91%, whereas CUH was averaged at 73%. Moreover, CUH decreased as the system travel speed increased. Water application rates at the typical radial positions along the lateral were higher for the D3000 sprinklers than for the R3000 sprinklers. Runoff depth decreased as the system travel speed increased. As for all test schemes, average values of WDEL for the R3000 and D3000 sprinklers were 6.5% and 4.0%, respectively. Considering the influencing degrees of factors on WDEL, wind speed is uppermost, later for air temperature, last for relative humidity.(2) A software was modified for use in sprinkler configuration and performance evaluation of the center pivot irrigation systems. The modifications were focused on module of selection of the end gun, module of analysis of the water application rate and database development. Performance of six center pivot irrigation systems in the typical regions of China were evaluated. The results indicated that relative errors between measured and theoretical travel speeds of outmost tower were averaged at 2.3%, indicating that these systems were in relatively good operating condition. The relative errors between measured and theorical average water application depths were averaged at-2.1%. CUH of the six systems ranged from 44.4%-89.9%. The analyzed reasons that CUH of some systems were lower than design standard, included improper selection or operation of pump, lack of pressure regulating valve, and improper sprinkler configuration. Sprinkler package configuration of one system with poor water application uniformity was optimized with the help of the modified software, and CUH increased about 15%.(3) Effects of the system length, the system discharge, and the system travel speed on the water application uniformity were simulated and analyzed. Considering the influencing degrees of factors on the water application uniformity, the system length is uppermost, later for the system discharge, last for the system travel speed. When the system length was constant, maximum and mean water application rate along the lateral both increased as the system discharge increased. The longer the system, the more area where the water application rate was higher than the allowable application rate, and surface storage and runoff might be more likely to occur. |
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