科研之友
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摘要
A discrete element model (DEM) is developed for investigation of the dynamic behavior of sand grains, in which the motion of individual grains is considered. The DEM has been used for simulating 9000 grains' motion blown by wind, resulting in ripples and saltating paths. Exchange between saltation and creep along the surface is also calculated, which is helpful for revealing the intrinsic mechanism of ripple formation. A critical event in the trajectory of sand grain saltating in the air is its interaction with the surface. As another application of DEM, the numerical experiment of a sand bed impacted by a single grain traveling at 8 ms(-1) and 11.5degrees is performed to quantitatively evaluate the splash process. A normalized Maxwellian distribution function f (v(y)) = a.v(y)(c) . exp (-b, nu(y)(d)) is proposed for the vertical velocity distribution of splashed grains, where the parameters a, b, c, and d can be regressed from the vertical velocity component of saltating grains. Generally, the vertical velocity of saltating grains fits the Maxwellian function well, with the correlation coefficients larger than 0.8. The result also shows that the restitution and surface friction coefficients of grains have negligible influence on the Maxwellian function. Therefore, the DEM can simulate sand movement and offer more detailed information as to what happens inside the flow, which could be applied in a wider suitable range in comparison with previous models.
