Water Distribution Model And Parameters Optimization For Sprinkler Irrigation With Pulsating Pressure On Sloping Land

Slope farmland accounts for about 1/3 of the total cultivated land in China,which plays an important role in agricultural production and ensuring food security.However,drought and water shortage lead to low and unstable crop yield in slope farmland.Supplementary irrigation is an important measure to increase and stabilize crop yield.However,due to the existence of the slope,traditional surface irrigation is difficult to implement in sloping farmland.Sprinkler irrigation is one of the most widely used irrigation methods on sloping land,but there are some problems such as poor uniformity of sprinkler irrigation water distribution and low water use efficiency.For this reason,combining with the modern advanced pulsating water pressure supply technology.The water distribution characteristics of sprinkler irrigation with pulsating water pressure on sloping land revealed through experiments.On this basis,the calculation model of water distribution of sprinkler irrigation with pulsating water pressure on sloping land was constructed according to the finite element thought and the principle of water conservation.In order to promote the application of sprinkler irrigation,and provide decision support for the design of sprinkler irrigation system with pulsating water pressure on sloping land,the appropriate parameters were determined by multi-objective optimization method considering system cost and sprinkler irrigation quality.The main research contents and conclusions are as follows:(1)The water distribution and uniformity characteristics of sprinkler irrigation on slope under pulsating water pressure were revealed.Using pulsating water pressure not only does not reduce the water supply capacity of sprinkler,but also plays a positive role in improving the quality of sprinkler irrigation on sloping land.For a single sprinkler,sprinkler irrigation with pulsating water pressure shorten the difference between sprinkler throw radius of uphill and downhill,and reduced difference between the average water application rate of uphill and downhill,and improves the uniformity of water distribution in the spraying area of a single sprinkler.The Christiansen Uniformity Coefficient(CU)value of water distribution for a single sprinkler at pulsating pressure was 6% ～11% higher than that of constant pressure.For multiple sprinklers,sprinkler irrigation with pulsating water pressure decreased the area with low water application rate(<6mm/h),and the average water distribution uniformity increased by 4.06%.Under the 90% confidence level,sprinkler spacing and arrangement had significant effect on sprinkler water application rate,while pulsating pressure amplitude,function type and period had no significant effect on it,and the order of influence was as follows: sprinkler spacing > arrangement > amplitude > function type > period.For the uniformity of sprinkler irrigation on sloping land,sprinkler spacing,arrangement and pulsating pressure amplitude have significant effects on sprinkler uniformity,while pulsating pressure function type and period have no significant effects on sprinkler uniformity.The order of influence is: sprinkler spacing > amplitude > arrangement > function type > period.(2)To slove the problem of difficult to obtain water distribution data of sprinkler irrigation on sloping land,a mathematical model for estimating water distribution pattern of a rotating sprinkler with pulsating pressure on sloping land was established according to the water conservation principle and finite element idea,combined with the coupling relationship between pulsating water pressure period and sprinkler rotation speed,and its accuracy was experimentally verified.The model was applied to study the effects of terrain slope,sprinkler arrangement,sprinkler spacing and average pulsating pressure on water distribution on sloping land.The results showed that with the increase of terrain slope and sprinkler spacing,the area of low water application rate in the spraying area increased,and the uniformity gradually decreased.The suitable slope for this type of sprinkler is less than 11.31 °.The CU value increased with the increase of the average pulsating pressure.However,the increasing rate of uniformity is less than that of the average water pressure,and the effect on improving the sprinkler irrigation uniformity of water distribution is gradually weakened.Sprinklers arranged in equilateral triangle and with the spacing close to R had the best water distribution uniformity,the CU of which was 11.43% and 8.75% higher than that in square and rectangular arrangement,respectively.(3)A multi-objective optimization method for technical parameters of sprinkler irrigation system with pulsating water pressure on sloping land was established.The data envelopment analysis method and the antagonistic cross evaluation were used.Taking technical parameters such as sprinkler arrangement,spacing and pulsating pressure parameters were chosen as input indicators,while output indicators included average water application rate,water application uniformity,initial investment and annual operating cost,an optimization method for sprinkler irrigation technical parameters on sloping land with pulsating water pressure was established.The optimization of technical parameters was carried out on the slope where alfalfa was planted and an area of 100×100 m.If the Rain Bird R5000 sprinkler was used,the technical parameters with the maximum value of cross-evaluation efficiency were optimized as follows: the sprinkler spacing was 8m,the sprinkler layout was square,the average water pressure was 300 k Pa,and the amplitude of water pressure was 50 k Pa.When the above technical parameters are adopted,the average water application rate of sprinkler irrigation system was 10.0 mm/h,water distribution uniformity was 89.7%,initial investment was 33749 yuan,and annual operation cost was5405 yuan.