The initiation of particle movement by wind

摘要: When air blows across the surface of dry, loose sand, a critical shear velocity (fluid threshold, ut), must be achieved to initiate motion. However, since most natural sediments consist range grain sizes, fluid threshold for any sediment cannot defined by finite value but should viewed as which is function size, shape, sorting and packing sediment. In order investigate initiation particle movement wind series wind-tunnel tests was carried out on pre-screened fluvial sands commercially available glass beads with differing mean sizes characteristics. A sensitive laser-monitoring system used in conjunction high speed counter detect initial motion count individual movements. Test results indicate that when slowly increased over smaller or more exposed grains are first entrained drag lift forces either creep (rolling) saltation (bouncing hopping downwind). As continues rise, larger less may also moved drag. On striking saltating impart momentum stationary grains. This impact result rebound original well ejection one into stream at velocities lower than required entrain direct pressure. As result, there cascade effect few varying size initially moving (the range) setting rapidly increasing number Results showed progression from dynamic based movement, can characterized power function, coefficients directly related characteristics