| The research on variable-rate sprinklers was one of the main contents of China National High-tech Program(No.2006AA100211) "Light-duty Irrigated System for variable irrigation".Variable irrigation is the key technology in the precision irrigation, and variable-rate sprinkler is one of the ways to accomplish variable irrigation. There has been lots of researches variable-rate sprinklers both from home and abroad, but according to the existing products, the common variable-rate sprinklers have the disadvantage of complicated structure, unreliable performance and so on. The design of the existing variable-rate sprinkler is to add an variable-rate device to the strike sprinkler. The variable-rate device adjust the structural parameter to accomplish the variable-rate spray. The undesirable irrigation uniformity was a common problem for those variable-rate sprinkler. In order to improve the irrigation uniformity of the variable-rate sprinkler, a new kind of variable-rate sprinkler with a pressure and flow rate adjusting device and a nozzle-changeable device was put forward in this dissertation. The pressure and flow rate adjusting device was utilized to adjust the working pressure of the sprinkler and the nozzle-changeable device was used to change the discharge area. By regulation the two factors synchronized, the water distribution uniformity of the variable-rate sprinkler will be improved. Meanwhile, this dissertation also studied the water distribution of the variable-rate sprinkler applied in slope land with small angle. The results showed that this kind of sprinkler can slove the water distribution problem caused by the factor of the terrain. The main research contents and results were as follows:1. Proposed here two indexes which were spray shape and water distribution uniformity to evaluate hydraulic performance of variable-rate sprinkler. And analyzed the influence of the throw radius caused by working pressure, nozzle area and trajectory angle. By calculating instantaneous application rate, it is indicated that the irrigation uniformity will go bad when change single factor to accomplish variable-rate irrigation.2. Based on equal nozzle area theory, non-circle nozzles with four different shapes were designed and their hydraulic characteristics were compared through experiments. The result indicated that for the star shaped nozzle, the range rarely decrease and the tendency of the water distribution under different pressure were of the same. The hydraulic characteristics was compared between the star shaped nozzle and the circle nozzle. The result showed that water distribution of the star-shaped nozzle were better than that of the circle nozzle.3.Variable-rate sprinkler BPY series with nozzle-regulator were designed. This kind of sprinkler use a pressure and flow rate adjusting device to adjust the working pressure, and a nozzle-changeable device to change the discharge area. By regulation of these two factors synchronized, the water distribution uniformity of the variable-flow rate sprinkler will be improved. Through feasibility analysis on this sprinkler, the relation among nozzle area, the range and the working pressure was obtained. The result indicated that, when the spray shape is square, the range of the working pressure for BPY20 is 0.54 to 1, and for BPY30 is 0.57 to 1, for BYP with nozzle-regulator is 0.46 to 1.When the spray shape is triangle, the range of the working pressure for BPY30 is 0.33 to 1, and for BPY20 is 0.21 to 1, for BYP with nozzle-changeable device is 0.21 to 1.The variable-rate sprinkler with nozzle-changeable device could accomplish given spray area under a smaller range of pressure.4. Three kinds of nozzle-changeable device with different orifice areas for the sprinklers BPY20 and BPY30 were designed respectively. Impact of the nozzle-regulators to the stress introduced on the spring, the discharge coefficient of the sprinkler, the shape factor, and the throw radius were tested. It was obtained that:the premium radius of the orifice for the nozzle-regulator in BPY20 is D=6mm, for BPY30, it was D=7mm. The hydraulic performance of the variable-rate sprinkler with nozzle-regulator was measured. By compared with that of the star-shaped variable-rate sprinkler, the variable-rate sprinkler with nozzle-regulator provided better anticipated areas so that the water distribution uniformity was improved. 5. Based on the kinetic equations of the rain drops,a mathematic model for the transformation from the water distribution pattern on a flat ground to that on a sloping land was derived. Through the comparison between the field test and calculation data, it was found that:among 5°-20°, obtains from the transformation model were in good consistence with that from test. Based on the transformation from the water distribution data on the flat groud, a large amount of data on the sloping land were acquired to provide an experimental basis for the study of irriagtion on the sloping land.6. According to the water distribution model, the impact of slopes on the hydraulic performance was invesgated. For the sprinkler on the slopes of 5°-20°, the variable-rate sprinkler can help to solve the problem of non-uniform distribution caused by the terrain conditions on an upslope or an downslope. The variable-rate sprinkler suitable to the slope of 10°was designed and the hydraulic performance in field operation was tested. The test indicated that:the variable-rate sprinkler will solve the problem of long range, high sprinkler intensity on the upslope and short range, low sprinkler intensity on the downslope. |
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