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2006 CIE International Conference on Radar

作者： Ruan Chongji 1 Ding Jianjiang 2 1.Department of Graduate Management Radar Academy Wuhan Hubei 430019 China 2.Division of Scientific Research Radar Academy Wuhan Hubei 430019 China

Based on radar backscattering,a unitary model of radar returns from aircraft rotating parts,such as the propellers of propeller-driven aircrafts and the rotors of helicopters,is derived in detail and modulated characteristics in radar returns are analyzed.The results demonstrate that the modulation induced by the rotating parts of aircraft is relatively invariable,and in some flight conditions can offer additional information for target recognition in air surveillance radar.

关键词： universal model modulated characteristics target recognition air surveillance radar

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Non-negligible factors in low-pressure sprinkler irrigation:droplet impact angle and shear stress

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Journal of Arid Land 2022年第11期14卷 1293-1316页

作者： HUI Xin ZHENG Yudong MUHAMMAD Rizwan Shoukat TAN Haibin YAN Haijun College of Water Resources and Civil Engineering China Agricultural UniversityBeijing 100083China Engineering Research Center of Agricultural Water-Saving and Water Resources Ministry of EducationBeijing 100083China Semi-arid Agriculture Engineering&Technology Research Center of China Shijiazhuang 050051China

Droplet shear stress is considered as an important indicator that reflects soil erosion in sprinkler irrigation more accurately than kinetic energy,and the effect of droplet impact angle on the shear stress cannot be ignored.In this study,radial distribution of droplet impact angles,velocities,and shear stresses were investigated using a two-dimensional video disdrometer with three types of low-pressure sprinkler(Nelson D3000,R3000,and Komet KPT)under two operating pressures(103 and 138 kPa)and three nozzle diameters(3.97,5.95,and 7.94 mm).Furthermore,the relationships among these characteristical parameters of droplet were analyzed,and their influencing factors were comprehensively evaluated.For various types of sprinkler,operating pressures,and nozzle diameters,the smaller impact angles and larger velocities of droplets were found to occur closer to the sprinkler,resulting in relatively low droplet shear stresses.The increase in distance from the sprinkler caused the droplet impact angle to decrease and velocity to increase,which contributed to a significant increase in the shear stress that reached the peak value at the end of the jet.Therefore,the end of the jet was the most prone to soil erosion in the radial direction,and the soil erosion in sprinkler irrigation could not only be attributed to the droplet kinetic energy,but also needed to be combined with the analysis of its shear stress.Through comparing the radial distributions of average droplet shear stresses among the three types of sprinklers,D3000 exhibited the largest value(26.94-3313.51 N/m^(2)),followed by R3000(33.34-2650.80 N/m^(2)),and KPT(16.15-2485.69 N/m^(2)).From the perspective of minimizing the risk of soil erosion,KPT sprinkler was more suitable for low-pressure sprinkler irrigation than D3000 and R3000 sprinklers.In addition to selecting the appropriate sprinkler type to reduce the droplet shear stress,a suitable sprinkler spacing could also provide acceptable results,because the distance from the sprinkler exhibited a highly significan

关键词： center pivot irrigation system water droplet universal model soil erosion water-saving irrigation

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