河岸糙率对明渠宽深比影响的研究

Study on the effects of bank roughness on width-depth ratio in open channels

研究了河岸河床相对糙率对明渠宽深比的影响。根据定床渠道、临界渠道和动床渠道3种类型渠道,采用最小能耗率原理,分别构建了宽深比计算的优化模型。结合综合糙率公式,利用条件极值问题优化计算方法,得到了不同类型渠道条件下的宽深比与河岸河床相对糙率之间的定量关系。分析计算结果表明,定床明渠随河岸糙率的增大,宽深比增大;而临界渠道和动床渠道随河岸糙率的增大,宽深比减小。河岸糙率大于河床糙率时,定床渠道为了降低河岸高糙率对流量的影响,从而宽深比增大;而临界渠道和动床渠道,由于河岸糙率大时其抗冲能力大,因而宽深比减小。这些结论可供明渠水力设计时参考。

The effects of bank roughness on width-depth ratio are discussed in this paper. Based on the principle of minimum stream power,the optimization models for calculating the width-depth ratio are constructed for fixed-bed channel,threshold channel,and movable-bed channel,respectively. Combined with Einstein＇s comprehensive roughness equation,the quantitative relations between width-depth ratio and bank relative roughness for different types of channel are derived by using calculation method of conditional extreme value. Results show that for fixed-bed channel the width-depth ratio increases with the increase of bank relative roughness,while for threshold channel and movable-bed channel the width-depth ratio decreases with the increase of bank relative roughness. For fixed-bed channel the width-depth ratio increases for reducing the effect of high bank relative roughness on flow discharge,while for threshold channel and movable-bed channel the width-depth ratio decreases for high bank scour-resistance from high bank relative roughness.