The nature of saltation and of ‘bed-load’ transport in water

机械 湍流 推移质 推力 消散 流速 打滑(空气动力学) 悬移质 地质学 岩土工程 泥沙输移 物理 流量(数学) 热力学 沉积物 古生物学
作者
R. A. Bagnold
出处
期刊:Proceedings of the Royal Society of London [Royal Society]
卷期号:332 (1591): 473-504 被引量:489
标识
DOI:10.1098/rspa.1973.0038
摘要

Owing to observational difficulties the distinction between a ‘suspended’ load of solids transported by a stream and a ‘ bed-load ’ has long remained undefined. Recently, however, certain critical experiments have thrown much light on the nature of bed-load transport. In particular, it has been shown that bed-load transport, by saltation, occurs in the absence of fluid turbulence and must therefore be due to a separate dynamic process from that of transport in suspension by the internal eddy motion of a turbulent fluid. It has been further shown that the forward motion of saltating solids is opposed by a frictional force of the same order as the immersed weight of the solids, the friction coefficient approximating to that given by the angle of slip. The maintenance of steady motion therefore requires a predictable rate of energy dissipation by the transporting fluid. The fluid thrust necessary to maintain the motion is shown to be exerted by virtue of a mean slip velocity which is predictable in the same way as, and approxim ates to, the terminal fall velocity of the solid. The mean thrust, and therefore the transport rate of saltating solids, are therefore predictable in terms of the fluid velocity close to the bed, at a distance from it, within the saltation zone, of a ‘centre of fluid thrust’ analogous to the ‘centre of pressure’. This velocity, which is not directly measurable in water streams, can be got from a knowledge of stream depth and mean flow velocity. Thus a basic energy equation is obtained relating the rate of transporting work done to available fluid transporting power. This is shown to be applicable to the transport both of wind-blown sand, and of water-driven solids of all sizes and larger than that of medium sand. Though the mean flow velocity is itself unpredictable, the total stream power, which is the product of this quantity times the bed shear stress, is readily measurable. But since the mean flow velocity is an increasing function of flow depth, the transport of solids expressed in terms of total stream power must decrease with increasing flow depth/grain size ratio. This considerable variation with flow depth has not been previously recognised. It explains the gross inconsistencies found in the existing experimental data. The theoretical variation is shown to approximate very closely to that found in recent critical experiments in which transport rates were measured at different constant flow depths. The theory, which is largely confirmed by these and other earlier experiments, indicates that suspension by fluid turbulence of mineral solids larger than those of medium sands does not become appreciable until the bed shear stress is increased to a value exceeding 12 times its threshold value for the bed material considered. This range of unsuspended transport decreases rapidly, however, as the grain size is reduced till, at a certain critical size, suspension should occur at the threshold of bed movement.
最长约 10秒,即可获得该文献文件

科研通智能强力驱动
Strongly Powered by AbleSci AI
更新
PDF的下载单位、IP信息已删除 (2025-6-4)

科研通是完全免费的文献互助平台,具备全网最快的应助速度,最高的求助完成率。 对每一个文献求助,科研通都将尽心尽力,给求助人一个满意的交代。
实时播报
卓若之完成签到 ,获得积分10
刚刚
苯二氮卓完成签到,获得积分10
1秒前
温暖完成签到 ,获得积分10
3秒前
mojomars完成签到,获得积分10
3秒前
时尚雨兰完成签到,获得积分0
4秒前
一叶知秋完成签到,获得积分10
6秒前
叶123完成签到,获得积分10
7秒前
量子星尘发布了新的文献求助10
8秒前
Minicoper发布了新的文献求助10
8秒前
背书强完成签到 ,获得积分10
9秒前
淡然以柳完成签到 ,获得积分10
11秒前
dolabmu完成签到 ,获得积分10
14秒前
崔崔完成签到 ,获得积分10
18秒前
SYLH应助xcxc采纳,获得10
19秒前
wp4455777完成签到,获得积分10
20秒前
十一完成签到,获得积分10
20秒前
ru完成签到 ,获得积分10
22秒前
慧木完成签到 ,获得积分10
22秒前
WW完成签到 ,获得积分10
23秒前
小高同学完成签到,获得积分10
24秒前
轻轻1完成签到,获得积分10
27秒前
28秒前
大橙子发布了新的文献求助10
32秒前
iuhgnor完成签到,获得积分10
35秒前
可夫司机完成签到 ,获得积分10
38秒前
yang完成签到,获得积分10
40秒前
一1完成签到 ,获得积分10
42秒前
jiaolulu完成签到,获得积分10
42秒前
量子星尘发布了新的文献求助10
44秒前
爆米花应助LiZhao采纳,获得10
44秒前
轻轻完成签到,获得积分10
47秒前
Orange应助jiaolulu采纳,获得10
47秒前
xcxc完成签到,获得积分10
49秒前
water应助科研通管家采纳,获得50
49秒前
49秒前
默存完成签到,获得积分10
52秒前
风中的金鱼完成签到 ,获得积分10
54秒前
橙汁完成签到,获得积分10
55秒前
普鲁卡因发布了新的文献求助10
58秒前
cora完成签到 ,获得积分10
1分钟前
高分求助中
【提示信息,请勿应助】关于scihub 10000
Les Mantodea de Guyane: Insecta, Polyneoptera [The Mantids of French Guiana] 3000
徐淮辽南地区新元古代叠层石及生物地层 3000
The Mother of All Tableaux: Order, Equivalence, and Geometry in the Large-scale Structure of Optimality Theory 3000
Handbook of Industrial Diamonds.Vol2 1100
Global Eyelash Assessment scale (GEA) 1000
Picture Books with Same-sex Parented Families: Unintentional Censorship 550
热门求助领域 (近24小时)
化学 材料科学 医学 生物 工程类 有机化学 生物化学 物理 内科学 纳米技术 计算机科学 化学工程 复合材料 遗传学 基因 物理化学 催化作用 冶金 细胞生物学 免疫学
热门帖子
关注 科研通微信公众号,转发送积分 4038128
求助须知:如何正确求助?哪些是违规求助? 3575831
关于积分的说明 11373827
捐赠科研通 3305610
什么是DOI,文献DOI怎么找? 1819255
邀请新用户注册赠送积分活动 892655
科研通“疑难数据库(出版商)”最低求助积分说明 815022