喷头喷洒雨滴粒径测试的改进研究

色斑法是一种应用广泛的测试雨滴粒径大小的方法。但以往的雨滴率定只考虑色斑直径与雨滴真实粒径的关系,忽略了高度对率定的影响。在大量试验的基础上对数据进行多元回归分析,把高度因素作为影响雨滴粒径测量公式中一个因子。通过数据处理,得到关于高度和色斑直径双因子共同作用下的雨滴粒径的率定公式。并在处理数据过程中对公式的相关性进行了分析,经过与试验数据的比较,发现公式的拟合性好。     

单颗粒液滴飞溅对颗粒起动的影响

通过室内模拟降雨试验,探究单颗粒液滴飞溅对泥沙颗粒起动的影响。试验共设计4种地表坡度（0,15°,25°,35°）及4种粒径的均匀沙（0.098~0.104,0.104~0.5,0.5~0.78,1~1.4 mm）,选取当量直径为4.5 mm的液滴进行模拟试验,同时利用高吸水树脂材料泡发后的水球作为对照组。结果表明,颗粒直径和坡度的变化对颗粒起动的影响较为显著,飞溅子液滴对液滴溅蚀具有重要意义。随着颗粒直径的增大,颗粒的起动逐渐由液滴冲击和子液滴飞溅裹挟共同作用转变为液滴冲击动能传递为主,飞溅携带为辅。当颗粒直径相同时,坡度的增大导致飞溅沙粒不再均衡,斜坡下方的颗粒飞溅量和位移随坡度的增大而增大。坡度越大,下方颗粒溅蚀深度与上方的差距也越大,导致上方颗粒失去支撑,整体失稳垮塌,发生微小滑坡。同种粒径时,树脂水球溅蚀坑的宽深比明显小于相同直径的液滴溅蚀坑,液滴溅蚀量远大于树脂水球直接撞击作用下起动的颗粒量,子液滴的拖曳对颗粒起动具有重要意义。     

雨滴物理特性的粒子成像测量技术研究

雨滴形状、直径、降落速度等是表征雨滴特性的重要物理量。为了获取雨滴物理特性参数,基于粒子成像的瞬态测量可视化技术,研制了降雨环境下拍摄雨滴影像的光路系统和成像系统,开发了雨滴影像的识别、提取、量测等软件系统,设计了一种基于面阵电荷耦合元件的自然降雨成像测量系统。钢珠洒落实验发现该技术观测误差小。外场观测实验发现本次降雨主要以中等粒子为主,雨滴直径和降落速度均值分别为2.00 mm和3.52 m/s。雨滴降落速度可由雨滴直径的线性回归方程表达,且该方程的预测准确度和精度较高。可见,该测量技术可以准确地获取雨滴物理特性参数,为降雨特征和土壤侵蚀研究开辟了新途径。     

黄土区裸露坡地径流养分流失模型的建立与验证

在自然降雨条件下,黄土区坡耕地土壤表层中的养分会随地表径流流失,从而加剧了土壤质量和生产力的下降并造成严重的农业面源污染,使得准确预测黄土区养分随地表径流的流失过程尤为重要。现有的养分流失模型着重于估算长时段的养分流失总量,且未考虑开始产流前入渗水对交换层养分的稀释作用。根据不同降雨时段的养分迁移特性,将整个降雨过程划分为三个阶段:(1)从降雨开始(t₀)至交换层土壤完全饱和(t_sa),(2)从交换层土壤完全饱和(t_sa)至开始产流(t_p),(3)从开始产流(t_p)至降雨结束。在运动波模型近似解析解的基础上建立了综合雨滴击溅、扩散和入渗作用的养分流失近似解析模型;并进行了降雨试验,以率定模型参数和验证模型的可靠性。结果表明:径流及养分的模拟值可与实测值精确匹配(R²> 0.8,纳什效率系数NSE> 0.347)。养分流失模型中的雨滴诱导水分转移速率e_r取值在0.006～0.023 cm·min^–1之间...     

人工模拟降雨系统喷头喷洒雨滴特性测试

利用2D视频雨滴谱仪,对喷头喷洒的雨滴形状、尺寸分布、平均直径和垂直降落速度等进行准确测量,分析了喷嘴直径、工作压力对雨滴平均直径变化趋势的影响,建立了雨滴平均直径与垂直降落速度间的关系模型。结果表明:人工模拟降雨系统下喷头喷洒雨滴的直径范围在0~3 mm;在相同喷嘴直径下,随着工作压力的增大,雨滴平均直径呈下降趋势;在工作压力不变的条件下,随着喷嘴直径的增大,雨滴平均直径会随之增大;通过雨滴平均直径与垂直下落速度间的关系模型,能够较好地预测雨滴的降落速度。     

基于激光粒子探测仪探测结果的Z-I关系分析

[目的]估测高时空分辨率的降水量。[方法]利用翻斗式自动雨量计观测的雨量和雨强对激光粒子探测仪的观测结果进行验证,在确信通过激光粒子探测仪激光带的雨滴数和雨滴直径的基础上,按年、月、主要降水天气类型分别建立雷达反射率因子Z和雨强I、log(Z)-log(I)和雷达回波强度I-Zo的指数关系式。[结果]结果表明,按4种主要降水天气类型建立的Z-I、log(Z)-log(I)和I-Zo的指数关系式拟合率最高,相关系数都在0.96以上,均通过极显著相关性检验,是利用雷达探测的反射率因子(Z)或回波强度(Zo)反演降雨强度的首选。给定回波强度(Zo)后,对应1个最大雨强(Imax)。[结论]利用这种关系,依据雷达探测的回波强度,对预警强降水天气有重要的指示作用。     

黄土区坡耕地细沟间侵蚀和细沟侵蚀的研究

利用人工模拟降雨试验,通过在径流小区上覆盖纱网消除雨滴动能和增加雨滴除落高度来增加雨滴功能,并采用翻耕裸露作对照的试验处理,对黄土区坡耕地细沟间侵蚀和细沟侵蚀过程及其机理进行了研究。结果表明,坡面侵蚀产沙过程可明显的分为四个阶段,即溅蚀,细沟间侵蚀、细沟侵蚀和雨后径流侵蚀阶段。     

Mechanical and hydraulic resistance relations in crust-topped soils

The formation of soil surface crusts leads to increased mechanical and hydraulic resistances. In this study, changes and relationships of both resistances under simulated sprinkle irrigation (or rainfall), and sprinkle followed by flooding, were examined. Results indicated that a silt-loam soil developed a thicker surface crust than a clay soil for any given kinetic energy (KE). Crusts as thick as 3.9 and 2.6 mm formed on the silt-loam and clay soils, respectively. Mechanical resistance, R_m, increased with increasing KE, where the effect was greater in the silt-loam and was attributed to intrinsic resistance and crust thickness. Steady-state infiltration rate (i) was much lower in crusted clay than crusted silt-loam soil. Changes of both R_m, and i closely followed changes in crust thickness (z_c). Thicker crusts showed more resistance against external force than thinner crusts, due to more extended particle interlocking. Obtained functions indicated that the effect of thickness on strength was more significant in the lower range of crust thickness. The effect of z_c on i strongly followed a negative power function for both soils, with higher i in the silt-loam soil.     

Spatial variability of throughfall under a single tree: Experimental study of rainfall amount, raindrops, and kinetic energy

To evaluate the spatial variability of throughfall amount, raindrops, and erosivity under a single canopy during calm meteorological conditions, indoor experiments were conducted using a 9.8-m-tall transplanted Japanese cypress (Chamaecyparis obtusa) and a large-scale rainfall simulator. Drop size distribution, drop velocity, and kinetic energy of throughfall varied spatially under a single canopy as did throughfall amount and rain rate. Compared with throughfall rain rate, the variability was similar in drop size distribution, lower in drop velocity, and higher in kinetic energy. The results suggest that the spatial distribution of throughfall amount was dominated by the canopy shape and position of branches inside the canopy, and thus the spatial distribution was correlated with the radial distance from the trunk. Throughfall amount and rate were lower at the midway point between the trunk and the canopy edge. Throughfall drop size indices (drop size distribution, drop velocity, and unit kinetic energy) varied spatially while did not differ significantly. On the other hand, time-specific throughfall kinetic energy was correlated with the radial distance from the trunk. The dependence the throughfall kinetic energy on the radial distance from the trunk was dominated by the spatial distribution of throughfall amount. The trend in the spatial distribution of throughfall revealed in this study will aid in modelling canopy water processes and in predicting soil erosion on the bare forest floor.