初速度对运动物体在颗粒介质中阻力的影响

采用分子动力学模拟方法研究物体从二维颗粒介质底部上升过程的动力学行为．研究发现，物体在上升过程中所受到的阻力与物体的初速度有关．当物体的初速度较小时，黏性系数随着初速度增加而减小，等效阻力则逐渐增加；而当初速较大时，黏性系数随着初速度增加反而逐渐增加，而等效阻力则逐渐减少，甚至可转变成等效推力．

Effects of the Initial Velocity on the Drag Force of a Projectile in Granular Medium

We study the dynamic behavior of a projectile going up from the bottom of a two-dimensional granular medium by molecular dynamic simulations. We find that the drag force of the projectile in the rising process can be well described by adding a viscous damping and a bulk frictional force. The viscous coefficient decreases with the increase of initial velocity, but the bulk frictional force gradually increases when the initial velocity is small. However, when the initial velocity is large, with the increasing of it, the viscous coefficient increases, but the bulk frictional force gradually decreases, even transforms into an equivalent thrust force.