行政院國家科學委員會專題研究計畫成果報告:泥砂顆粒啟動之滾動與抬起機率研究

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 two threshold conditions identified herein enable us to precisely define the probabilities of entrainment in the rolling and lifting modes. The lifting probability increases monotonously with the dimensionless shear stress θ, consistent with the earlier results yet displaying improved agreement with the experimental data. The maximum value of rolling probability, with a magnitude of 0.25, occurs at 15 . 0 ≈ θ . For 05 . 0 < θ (or 6 . 0 > θ ), 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 entrainment probability. The rolling and lifting probabilities are further linked to two separate criteria for incipient motion. The results reveal that a consistent probability corresponding to the critical state of sediment entrainment cannot be found.