Probabilistic description of grain resistance from simultaneous flow field and grain motion measurements

摘要

Experiments were carried out using a mobile gravel bed placed in a tilting flume witha modified particle image velocimetry (PIV) system. Individual grain movements weresurveyed using data from time series of images. Near-bed velocity flow fieldmeasurements were made simultaneously above the same area of the sediment surface byapplying cross-correlation techniques to the collected plan view images. Statistics of grainmotions were collected through a semiautomatic procedure. Significant changes in theflow field were observed in the proximity of the entrained or deposited particles. A strongcorrelation is shown between the changes in the local streamwise and lateral velocityand the movement of the grains. The theory of Grass is revisited and developed based onthe experimental results. The probability distribution of individual grain resistance hasbeen derived from the statistics of the near-bed velocity field and of the entrainment risk.