| As one of the important mechanized irrigation equipment utilized in the modern agricultural water-saving irrigation and precision irrigation, center pivot and lateral move irrigation systems which have well-known advantages such as high irrigation quality, powerful versatility and complete automation, have been playing an increasingly role in agricultural reconstruction and development of West China. The main objectives of this dissertation were to investigate water distribution uniformity of center pivot and lateral move irrigation systems, based on the variable rate technology.The main research contents included six parts as follows:(1) Based on analyzing the current hydraulic models, a new analytical mathematical formula for the friction factor of a center pivot system with end flow was developed. Compared well with other well-known formulas and validated by field test, the new equation is more accurate and universal than the previous equations. By ways of theoretical and experimental research on the discharge coefficient of low pressure sprinklers normally used in center pivot and lateral move systems, a proper scope of discharge coefficients and an optimum coefficient value were put forward.(2) Based on studying the key techniques of improving the uniformity of chemigation duing the short time as the center pivot's starting and stopping, mathematical equations for calculating the time of chemical filling with the complete lateral and the amount of net water applied by each sprinkler between the time interval of the first sprinkler beginning to apply chemical and the last one beginning to apply were proposed in this paper. And the effect of start/stop time and right position of each tower on the uniformity of chemigation was discussed. In the end, a proper procedure of operating a center pivot system was presented.(3) Simulating the moving properties of towers when the alignment angle between two adjacent towers changes, the results showed that as the alignment angle decreases, the numbler of intermittent movement increases distinctly and the uniformity in travel path can be improved slightly. The moving distance of tower is relative to the timer percentage and has no relations to the alignment angle and cycle time of ihe movement.(4) It was the first time that the effect of cycle time on water distribution uniformity in travel path was discussed using a graphic method. Compared the simulated uniformity coefficient with the measured value, the results indicated that as the cycle time decreases, the uniformity in travel path can be improved delicately.(5) Series of mathematical models of water distribution uniformity of center pivot and lateral move systems moving continuously and intermittently were developed, and a computer program for selecting the sprinkler and nozzling along the lateral and calculating application water depth was presented based on the tested performance data of low pressure sprinklers. According to comparing the simulated water distribution and the measured one under the same conditions, the results showed the primary factoraffecting the water distribution uniformity is the water application distribution of singled sprinkler, other factors in turn are sprinkler spacing, cycle time of timer, alignment angle etc. In the end, an optimal sprinkler spacing for D3000 type and PZ type, two main sprinklers normally mounted on center pivot and lateral move systems, was put forward, respectively.(6) It was the first time to advance a newly general idea and principle of electrical drive motors operating with variable frequency. A field experiment was conducted on a modified lateral move system with variable frequency motors. Compared the measured water distribution with the measured one on the same lateral move system with the conventionally electrical drive power, the results indicated that the newly drive method can acquire the same high uniformity coefficients as those by the normally electrical drive power.
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