Research On Hydrological Frequency Of Rivers In Arid Areas Based On Normal Transformation

Object:Drip irrigation is recognized as one of the most advanced precision irrigation technologies in the world.It has been widely used all over the world for its advantages of water saving,energy saving,increasing production and efficiency.The increasingly scarce water resources make the application of unconventional irrigation water sources fall to the ground.At the same time,the blockage of emitters has become a difficult problem hindering the popularization and application of drip irrigation technology.A large number of experiments have proved that regular flushing of the capillary can conveniently and effectively slow down the blockage of the emitter.At present,the vast majority of drip irrigation systems at home and abroad still use the measure of manual flushing capillary,and the research on automatic flushing valve is still relatively lacking.Methods:Therefore,based on the developed capillary end flushing valve which can be closed automatically and flushed regularly,this thesis explores the response law of the hydraulic performance of four different specifications of automatic flushing valves under three layout modes（C1,C2 and C3）through design tests;On the indoor flushing valve test platform,test the irrigation performance,anti blocking performance and sand particle passing condition of the drip irrigation system of ND-15,FA-40 and FA-80 flushing valves under the sand concentration of 1 g/L and the flushing frequency once a day.Results:The results show that the automatic flushing valve can realize the automation of capillary flushing,simplify the operation process,improve the anti blocking performance of emitters in drip irrigation system and prolong the economic service life of drip irrigation system.The research conclusions are as follows:（1）The flushing duration FD and flushing water quantity FQ have a quadratic function relationship with the inlet pressure H₂ of the flushing valve,and the flushing flow rate FV has a linear relationship with the inlet pressure H₂ of the flushing valve.Connecting the flushing valve after multiple capillary tubes are connected in parallel can reduce the system pressure required for the automatic closing of the flushing valve and improve the applicability of the flushing valve;（2）Flushing can effectively improve the irrigation performance of the emitter:compared with the nonflushing group,the service life of the capillary where FA-40 and FA-80 are located is increased by 32%and 51%.The service life of capillary tube increases with the increase of flushing time FD and flushing flow rate FV.FA-80 has the best flushing effect,and because the automatic flushing valve can flush once after each irrigation,it can better improve the irrigation performance;（3）Flushing can effectively export the sediment deposited in the capillary.The sediment in the capillary where FA-40 and FA-80 are located accounts for only 0.51%and 0.43%of the sediment in the water source.The sediment accumulation rate in FA-80 emitter is only 1/12 of that in ND-15;（4）After the flushing time and flow rate increase significantly,the FA-40 automatic flushing valve can discharge the sediment with larger particle size out of the 48m long capillary during flushing.The distribution range,characteristic particle size and peak particle size of retained sediment in emitters decrease with the increase of flushing velocity;（5）The daily flushing of the automatic flushing valve can greatly reduce the sudden blockage of the emitter caused by bed load sediment.Conclusion:This test comprehensively considers the hydraulic performance and its own anti-clogging performance of the automatic flushing valve at the end of the capillary,the influence on the irrigation performance of the drip irrigation system,the anti-clogging performance and the passage of sand particles,and the evaluation results of the indicators such as the flushing time,the amount of flushing water,the flushing flow rate,the average relative flow rate,the capillary clogging rate,the particle size distribution of the blocked substance,etc.,and the study believes that the automatic rinsing valve at the end of the capillary can discharge most of the sediment out of the 48 m long capillary,and the service life of the capillary is increased by 30%-50%.The optimization of the rising water column can improve the single flushing capacity of the flushometer and reduce the sediment accumulation rate of the cavity on the automatic flushing valve.