明渠冰盖下流动的综合糙率

摘要

The composite roughness of the ice covered flow is a key parameter to determine the relation⁃ship between the flow and water stage. This paper presents a generalized formula for the composite rough⁃ness of ice covered flows by analyzing the relationship among Manning roughness, section-averaged water velocity and wetted perimeter. Based on the generalized formula, the influence of the velocity coefficient a on the composite roughness of the ice covered flows in rectangular channels is studied by considering the distribution of water velocities. Meanwhile, in order to understand the scope of application to them, Ein⁃stein formula, Belokon - Sabaneev formula and Larsen formula are compared with the generalized formula systematically. The results show that for the rectangular open channal with small kreadth-depth ratio b/H, the composite roughness computed by Einstein formula approximate closest to that by the generalized formu⁃la, and the composite roughness obtained by both Belokon- Sabaneev formula and Larsen formula deviate for from that by the generalized formula in many cases.%明渠冰盖下流动的综合糙率 nc是确定冰期水位和流量关系的关键参数，本文根据冰盖区和床面区的边界条件和流量的连续性条件提出了通用的综合糙率公式，研究了冰盖下一般矩形明渠和宽浅明渠流速分布及流速比a对综合糙率 nc的影响，在此基础上，计算分析比较了通用综合糙率公式、Einstein公式、Belokon-Sabaneev公式和 Larsen公式的差异和使用条件，结果表明：对于宽深比 b/H较小的矩形明渠，采用 Belokon-Sabaneev公式将产生很大的计算偏差， Larsen公式只适合宽浅明渠，而Einstein公式是通用综合糙率公式的最好近似，推荐在工程设计中采用。