泥沙颗粒床面暴露度的理论分析及应用

Theoretical analysis on relative exposure degree of bed particle and its applications

床面泥沙暴露度是影响床面泥沙起动和输移的重要因素之一,目前在理论层面如何合理描述其影响尚未形成清晰的认识。本文在已有研究的基础上,针对非均匀沙,提出了新的暴露度计算公式,建立了床面泥沙暴露度与泥沙粒径之间的函数关系。基于该公式,推导得到了包涵暴露度影响的单颗粒滚动和跃移运动参数的理论表达式,通过与跃移距离和跃移高度的实测数据对比发现,计算值能够与实测值相吻合。为了进一步验证公式的正确性,在运动参数的基础上,推导得到了推移质输沙率公式,计算了均匀沙输沙率、非均匀沙分组输沙率和总输沙率。通过与实测数据的对比发现,计算值与实测值之间的相对误差均在可接受范围内。同时,计算结果表明,在相同的水流条件下,不同暴露度下的分组输沙率可以相差十几倍,由此说明了床面泥沙暴露度对非均匀沙输移的影响十分显著。

Sediment relative exposure degree plays a significant role in non-uniform sediment movement and transport.There has been no clear understanding of how to reasonably describe the effect of sediment relative exposure degree theoretically so far.In this study,a new formula for relative exposure degree is proposed,which is the function of particle size.Based on this formula,theoretical formulas of movement parameters for rolling and saltation particles with consideration of the effect of relative exposure degree are derived.Good agreements with experimental data for saltation height and distance are obtained.In order to verify the present theory,the bedload transport rate in groups and total transport rate for non-uniform sediment are calculated,which show that the relative error is within the acceptable range.Results also show that the bedload transport rate in groups varies more than ten times for particles of different sizes under the same flow condition,which implies that the effect of sediment relative exposure degree is very impor⁃tant.