小行星II上的跳弹：低速掠射撞击衬底粒度的实验室试验的灵敏度
Ricochets on Asteroids II: Sensitivity of laboratory experiments of low velocity grazing impacts on substrate grain size
摘要：
我们比较了低速的影响，跳弹具有相同的冲击速度和冲击角度到颗粒介质具有相似的体积密度，孔隙率和摩擦系数，但不同的平均粒径。抛射体直径与平均颗粒长度的比值范围从我们的粗砂介质中的4到我们的细砂中的50。使用高速视频和荧光标记，我们测量的比率，前到后的影响水平和垂直速度分量，我们称之为恢复系数，和偏转角所造成的影响，在水平面上。恢复系数是敏感的平均粒度的比率与水平速度分量的两倍大，我们的粗砾石，我们最好的沙子。这意味着，系数流体静力学，阻力和升力，在经验力的法律，是敏感的平均晶粒尺寸。对粒度最敏感的系数是升力系数，在我们的粗介质和最细介质之间，升力系数减小3倍。偏转角在较粗的介质中是最大的，其大小大约取决于晶粒尺寸的3/2次方。这种缩放与通过与单个颗粒碰撞发生动量转移的模型相匹配。在今后关于撞击粒状小行星表面的物体群的模型中，应考虑撞击力学对基底大小分布的依赖性。
英文摘要：
We compare low velocity impacts that ricochet with the same impact velocity and impact angle into granular media with similar bulk density, porosity and friction coefficient but different mean grain size. The ratio of projectile diameter to mean grain length ranges from 4 in our coarsest medium to 50 in our finest sand. Using high speed video and fluorescent markers, we measure the ratio of pre- to post-impact horizontal and vertical velocity components, which we refer to as coefficients of restitution, and the angle of deflection caused by the impact in the horizontal plane. Coefficients of restitution are sensitive to mean grain size with the ratio associated with the horizontal velocity component about twice as large for our coarsest gravel as that for our finest sand. This implies that coefficients for hydro-static-like, drag-like and lift-like forces, used in empirical force laws, are sensitive to mean grain size. The coefficient that is most strongly sensitive to grain size is the lift coefficient which decreases by a factor of 3 between our coarsest and finest media. The deflection angles are largest in the coarser media and their size approximately depends on grain size to the 3/2 power. This scaling is matched with a model where momentum transfer takes place via collisions with individual grains. The dependence of impact mechanics on substrate size distribution should be considered in future models for populations of objects that impact granular asteroid surfaces.
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