李保如泥沙起动流速公式修正研究

Modifications to Li Baoru’s sediment incipient velocity formula

现代水力学中近壁层流层厚度可反映边壁摩阻特性,是影响细颗粒泥沙起动的重要因素。李保如泥沙起动流速公式考虑到泥沙颗粒所处边界的水力学差异及近壁层流层对细颗粒泥沙的'隐蔽'影响,将细颗粒的摩擦系数f处理为近壁层流层厚度对细颗粒泥沙'隐蔽'作用的综合影响系数,但由于当时缺乏黏性细颗粒泥沙的试验资料,导致公式在黏性细颗粒泥沙起动流速的走向上表现不佳。本文仍采用原作者的物理图形,只是将摩擦系数f的函数由近壁层流层厚度对细颗粒泥沙'隐蔽'影响项与重力作用项两项组成,进一步将前者表示为'近壁层流层厚度δ与泥沙粒径D之比'即δ/D的指数形式,并在推导δ/D的表达式时直接用曼宁公式表示谢才系数C而引入糙率n,经过实测起动流速资料分别确定指数与系数后,即得出新的泥沙起动流速公式。利用大量实测资料验证表明,尽管不去考虑概念难以判明且难以定量描述的黏结力及附加下压力的复杂影响,且也不考虑流速沿水深的分布计算公式如何表达,但只要合理考虑近壁层流层厚度对细颗粒泥沙起动的影响,同样能够建立出同时适用于黏性及散粒体泥沙的起动流速公式。

Considering the fact that fine sediment may hide beneath viscous sublayers,and the difference existing between solidness and fluidity,Li Baoru believed that viscous sublayer thickness occupies a vital function in fine sediment incipient motion.Li Baoru also believed that the incipient coefficient can be considered as a function of sediment diameter and viscous sublayer thickness.Li Baoru’s sediment incipient velocity formula is acquired upon the combination with the measured sediment incipient velocity data.However,the incipient velocity values of extremely fine sediment computed by this formula,is smaller compared to real values.In view of that,in this paper,by altering the function of the incipient coefficient,a modified version of Li Baoru’s sediment incipient velocity formula is obtained on the basis of the measured data of sediment incipient velocity.The values of the sediment incipient velocity calculated by the adapted formula correspond well with the assessed data beneath the same depth.Furthermore,using qualitative and quantitative analysis,the modified version of Li Baoru’s sediment incipient velocity formula,reflecting the effect of viscous sublayer thickness,is attested to be a unified formula of incipient velocity which can be applied to both fine and coarse sediment.