跃移泥沙颗粒起跳时间的特性分析

Analysis on characteristics of take-off time of saltation particles

跃移是推移质泥沙颗粒运动的主要形式之一,跃移颗粒的运动特性是影响推移质输沙率的重要参数,但目前对跃移泥沙颗粒的起跳时间研究相对较少。本文利用高速摄影技术,对不同粒径泥沙起跳过程进行了系列的试验研究,后期采用RGB颜色映射函数获得灰度图,通过逐帧批处理获取颗粒的运动轨迹,直接得到了泥沙颗粒的起跳时间大小。试验结果表明,在本文试验的水沙条件下,泥沙颗粒的起跳时间呈现偏态分布,随着水流作用流速与特征沉速之比从0.3增大至0.7,起跳时间的变化趋势不显著。在此基础上,利用Gilbert和岗恰洛夫两家输沙率实测资料反算出了起跳时间的大小,并与韩其为公式进行了对比。结果表明:起跳时间的试验实测值与反算值均能够与理论计算值相吻合,在证明理论正确性和试验结果合理性的同时,阐明了随着水流作用流速与特征沉速之比Vbω的进一步增大,起跳时间呈现逐渐变小的变化趋势。

Saltation is one typical form of bedload transport.Characteristics of saltation particles are impor⁃tant parameters which affect the bedload transport rate,but there are relatively few studies on the take-off time of saltation.In this study,a series of experiments on the take-off process of sediment with different particle sizes are carried out by using high-speed photography technology.Grayscale image was obtained by RGB color mapping function,and the particle trajectory was collected by batch processing.Furthermore,the take-off time of bed particles can be calculated.Results show that the distribution of take-off time is al⁃ways abnormal under different flow and sediment condition tested in the present study.With the increasing of the ratio of flow velocity to characteristic settling velocity from 0.3 to 0.7,the change trend of take-off time is not significant.Furthermore,the take-off time is inversely calculated by using the measured data of Gilbert and Gangchalov sediment transport rate,and compared with Han Qiwei's theory.Both the experimen⁃tal observation and inverse calculation value of take-off time can be consistent with the theoretical calcula⁃tion,which not only proves the correctness of the theory and the rationality of the experimental results,but also clarifies that the take-off time shows a decreasing trend with the further increasing of the ratio of flow velocity to characteristic settling velocity.