泥沙起动条件分析及推移质输沙率公式

基于床面均匀泥沙颗粒相对位置关系,确定了瞬时作用流速及有效作用高度,建立了平坡泥沙起动条件与床面泥沙暴露度的关系。从理论上分析得到,泥沙跃移起动要求水流条件最高,滚动起动及滑动起动取决于泥沙颗粒的暴露角,且暴露角θ不随拖曳力系数C_D和上举力系数C_L的变化而变化。当暴露角θ小于42.8°时,泥沙更易于滚动起动;当暴露角θ大于42.8°时,泥沙更易于滑动起动。在此基础上,推导出了考虑两种起动模式的起动全概率公式,建立了床面推移质单宽输沙率公式。通过经典的推移质输沙率实测资料验证及误差计算表明,公式结构合理,计算精度较高,对于高、中、低输沙率都具有较好的适用性。

Analysis of sediment incipient conditions and bed load transport formula

The instantaneous acting velocity and effective acting height were determined based on the relative position of sediment particles on the river bed. The relationship between the incipient conditions of sediment,and the sediment exposure on the bed surface was established. Result shows that the saltation incipient motion requires the highest flow conditions. Incipient motion by rolling and sliding is depended on the exposure angle of sediment particles. The exposure angle θ does not change with the drag coefficient C_D and lift coefficient C_L.When the exposure angle θ is less than 42. 8°,a sediment particle is easier to rolling;when the exposure angleθ is greater than 42. 8°,the sediment is more likely to sliding. On this basis,the bed load total threshold probability formula considering two incipient modes was deduced,and the bed load transport formula was established. The validation and error calculation of the classical measured data of bed load transport rate show that the formula is reasonable in structure and accuracy to apply for high,medium and low sediment transport rate.