Experimental And Numerical Simulations Of Sand-bed Collision And Creeping Motion In Aeolian Sand Movement

Aeolian sand movement affects the earth's surface morphology through the formation of dunes and sand ripples on the coast and arid areas.The transport of sand and dust also affects the climate,ecosystems,hydrological cycles,and other parts of the earth system.The collision process between sand particles and the bed surface is an important part of the study of aeolian sand movement.This paper studies the particle-bed collision process through experiments and numerical simulations,and quantitatively characterizes the distribution of the physical quantities of rebound and ejected particles under different impact conditions.The splash function applicable to sand particles is given,and the influence of slope is added to it.In addition,using numerical simulation,the boundaries between creep and reptation movement are given by the change of the distribution pattern of the take-off angle;the boundaries of creeping and saltation movement are given by the variation with height of the particle concentration,and then the motion characteristics of creeping particles are calculated.Finally,using the obtained dividing line,the rotational angular velocities and kinetic energy distributions of the saltation and creeping particles are compared;the mass concentration ratio and horizontal flux ratio between saltation and creeping particles are calculated by combining the distribution of incident speed and incident angle in a stable aeolian sand flow.Main tasks as follows:1.The self-designed particle emission system was used to simulate the bombardment process of natural sand particles and sand bed.Based on the high?speed photography technique,the distribution of the angle,speed,and number of the liftoff particles and its quantitative characterization are obtained,and the splash function of the natural sand particles was given.The mean value of the liftoff physical quantity was calculated from the distribution and compared with the previous results.It was found that the results of the sand grains were qualitatively similar to the substitute materials and simulation results,but quantitatively different.2.By comparing with the experimental results,the parameters in the previous DEM simulations are adjusted to make the simulation results closer to the experimental values.Using the adjusted DEM to simulate the particle-bed process on the slope,the quantitative characterization of the liftoff physical quantity with the slope is obtained.Coupling the results of the slope with the experimental results on the flat ground,the splash function including the influence of the slope is obtained.3.The DEM is used to study the creeping movement based on sand-bed collision.The distribution of the angle,speed,and number of near-surface particles and its quantitative characterizations with incident speed,incident angle,and statistical height are obtained,which meets the needs of scholars when setting different creeping heights.The angular distribution of near-surface particles is used to distinguish creep and reptation particles.The variation with height of the particle concentration is used to distinguish creeping and saltation particles,and the judgments of creep,reptation and saltation movement are given in this paper.Quantitative characterizations of the creeping speed,angle,and number of particles with the incident speed and incident angle are obtained.4.Based on the judgments of creep,reptation and saltation particles,the rotational angular velocity and kinetic energy distribution of saltation and creeping particles are compared,and the energy distribution of incident particles is analyzed.The mass concentration and horizontal flux of saltation and creeping particles are analyzed and calculated as a function of the incident speed and incident angle.Combined with the distribution of incident speed and incident angle in a stable aeolian sand flow,the mass concentration ratio and horizontal flux ratio between saltation and creeping are calculated.