Rolling and Lifting Probabilities for Sediment Entrainment
Journal
Journal of Hydraulic Engineering
Journal Volume
129
Journal Issue
2
Start Page
110
End Page
119
ISSN
0733-9429
Date Issued
2003-01-01
Author(s)
Wu, Fu-Chun
DOI
10.1061/(ASCE)0733-9429(2003)129:2.110
Abstract
This study addresses the rolling and lifting probabilities for sediment entrainment by incorporating the probabilistic features of the turbulent fluctuation and bed grain geometry. The lognormally distributed instantaneous velocity and uniformly distributed initial grain position, along with a relation between lift coefficient and particle Reynolds number, are used to extend the theoretical formulation of the entrainment probabilities in smooth-bed flows. The two threshold conditions identified herein enable us to precisely define the probabilities of entrainment in the rolling and lifting modes. The results obtained in this study coincide well with the published data. The lifting probability increases monotonously with the dimensionless shear stress θ, which is consistent with the earlier results yet displays improved agreement with the experimental data. The maximum value of rolling probability, with a magnitude of 0.25, occurs at θ ~0.15. For θ<0.05 (or θ>0.6), the rolling (or lifting) probability makes up more than 90% of the total entrainment probability and thus can be used as an approximation to the total probability of entrainment. The proposed rolling and lifting probabilities are further linked to the two separate criteria for incipient motion to explore the critical entrainment probabilities. The results reveal that a consistent probability corresponding to the critical state of sediment entrainment cannot be found. 2003.
Subjects
Drag coefficient
Entrainment
Lift coefficients
Probability distribution
Sediment
Type
journal article