AN EXPERIMENTAL-STUDY OF MULTIPLE GRAIN-SIZE EJECTA PRODUCED BY COLLISIONS OF SALTATING GRAINS WITH A FLAT BED
AN EXPERIMENTAL-STUDY OF MULTIPLE GRAIN-SIZE EJECTA PRODUCED BY COLLISIONS OF SALTATING GRAINS WITH A FLAT BED
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DOI：
10.1111/j.1365-3091.1995.tb00401.x
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发表时间：
1995-08-01
期刊：
影响因子：
3.5
通讯作者：
MCEWAN, IK
中科院分区：
文献类型：
--
作者：
RICE, MA;WILLETTS, BB;MCEWAN, IK
碰撞数据来自于三种大小的沙粒的彩色高速胶片，这些沙粒在总颗粒种群的床上跳跃。随着河床逐渐被侵蚀，每一部分都被标记上了颜色，颗粒与表面碰撞时喷射出的每种尺寸的比例被记录在许多胶片上。结果证实了先前的发现，即V-3/V-1等于0。5:0。6， V-n/V-1等于0。随着晶粒尺寸的减小，回弹角增大。弹射颗粒的大小、撞击器的大小、弹射速度和角度以及每次碰撞的弹射次数都要进行检查。此外，还观察到晶粒参数随时间的变化。对于细粒冲击器，喷射速度一般随喷射粒径的减小而增加，但对于粗粒和中粒冲击器，细粒冲击速度不遵循这一趋势。喷射角度一般在40度到60度之间，粗颗粒的平均喷射角度比细颗粒要浅。每次碰撞的弹射次数随着撞击器尺寸的减小而增加。粗颗粒比细颗粒以较低的速度和较浅的角度喷射的一般趋势将导致晶粒尺寸的分选。弹射颗粒碰撞时的前动量损失与弹射颗粒的前动量损失和弹射颗粒的数量之间的相关性不强。跳跃颗粒的大部分前进动量被转移到爬行颗粒上。床层的组成和几何形状被认为是影响跃迁云演化的重要因素。
Collision data are presented from coloured high-speed films of three size fractions of sand grains saltating over a bed of the total grain population. Each fraction was colour tagged and the proportion of each size ejected by grains colliding with the surface was recorded on a number of films taken as the bed was progressively eroded. The results confirm earlier findings that V-3/V-1 congruent to 0 . 5-0 . 6, V-n/V-1 congruent to 0 . 08 and the rebound angle increases with decreasing grain size. Ejected grains are examined in relation to their size, the impactor size, ejection speed and angle and the number of ejecta per collision. In addition, changes in grain parameters are observed with time. For fine impacters, ejection speeds generally increase with a decrease in ejecta size, but the fine fraction does not follow this trend for the coarse and medium impacters. Ejection angles are typically between 40 degrees and 60 degrees, with coarse grains having shallower mean angles than fine ejecta. The number of ejections per collision increases with a decrease in particle size for each impactor size. The general tendency for coarse particles to be ejected at lower speeds and shallower angles than fine particles will lead to sorting of the grain sizes. There is poor correlation between the forward momentum loss of the saltating grains at collision and bath the forward momentum of the ejected grains and the number of ejected grains. Much of the forward momentum of the saltating grains is transfered to creeping grains. The composition and geometry of the bed are considered to be important factors in the evolution of the saltation cloud.