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泥沙起动是水沙相互作用的结果,受水流结构、泥沙级配和排列方式等随机因素的影响,泥沙起动充满随机性.泥沙颗粒在床面随机排列对起动的影响,常通过颗粒间相互隐蔽系数或暴露度反映.本文在精细模拟大颗粒泥沙间绕流作用的基础上,重点研究了泥沙随机排列所产生的垂向暴露度和纵向暴露度对起动的影响.研究发现:泥沙颗粒所处位置的不同,使其在相邻颗粒间的暴露度不同,则泥沙颗粒所受周围水流绕流作用不同,该泥沙颗粒起动的难易程度就有所不同.针对该问题,本文研究取得了如下进展:1)以力矩平衡作为起动的临界状态,建立反映局部绕流影响的大粒径泥沙(卵石)滚动起动模型;2)推求出了反映绕流及泥沙随机排列影响的双向相对暴露度概率分布函数;3)得到了考虑双向暴露度影响的泥沙起动流速公式.
Sediment start is the result of water-sand interaction, which is influenced by random factors such as water flow structure, sediment grading and arrangement, etc. The sediment start is full of randomness. The mutual concealment coefficient or the exposure degree between particles is reflected.This paper focuses on the effect of vertical exposure and longitudinal exposure caused by the random arrangement of silt on the starting on the basis of finely simulating the flow around large particles of sediment. It is found that the different positions of sediment particles make them have different exposure between adjacent particles, so that the sediment particles flow around the surrounding water flow is different, the ease of starting the sediment particles is different. In order to solve this problem, the following progresses have been made in this dissertation: (1) The moment equilibrium is taken as the starting critical state, and a large-size sediment (pebble) roll start model that reflects the influence of local flow around is established; (2) And the probability distribution function of the two-way relative exposure which is affected by the random arrangement of sediment. (3) The formula of sediment flow velocity considering the effect of bidirectional exposure is obtained.