Huang Kai, Hernández-Delfin Dariel, Rech Felix, Dichtl Valentin, Hidalgo Raúl Cruz
Division of Natural and Applied Sciences, Duke Kunshan University, 215306, Kunshan, Jiangsu, China.
Experimentalphysik V, Universität Bayreuth, 95440, Bayreuth, Germany.
Sci Rep. 2020 Feb 21;10(1):3207. doi: 10.1038/s41598-020-59950-z.
Projectile impact into a light granular material composed of expanded polypropylene (EPP) particles is investigated systematically with various impact velocities. Experimentally, the trajectory of an intruder moving inside the granular material is monitored with a recently developed non-invasive microwave radar system. Numerically, discrete element simulations together with coarse-graining techniques are employed to address both dynamics of the intruder and response of the granular bed. Our experimental and numerical results of the intruder dynamics agree with each other quantitatively and are in congruent with existing phenomenological model on granular drag. Stepping further, we explore the 'microscopic' origin of granular drag through characterizing the response of granular bed, including density, velocity and kinetic stress fields at the mean-field level. In addition, we find that the dynamics of cavity collapse behind the intruder changes significantly when increasing the initial speed . Moreover, the kinetic pressure ahead of the intruder decays exponentially in the co-moving system of the intruder. Its scaling gives rise to a characteristic length scale, which is in the order of intruder size. This finding is in perfect agreement with the long-scale inertial dissipation type that we find in all cases.
研究了以不同冲击速度将抛射体撞击由发泡聚丙烯（EPP）颗粒组成的轻质粒状材料的情况。在实验中，使用最近开发的非侵入式微波雷达系统监测侵入体在粒状材料内部的运动轨迹。在数值模拟方面，采用离散元模拟结合粗粒化技术来研究侵入体的动力学以及粒状床的响应。我们关于侵入体动力学的实验和数值结果在数量上相互吻合，并且与现有的关于颗粒阻力的唯象模型一致。进一步地，我们通过在平均场水平上表征粒状床的响应，包括密度、速度和动应力场，来探索颗粒阻力的“微观”起源。此外，我们发现当增加初始速度时，侵入体后方空穴坍塌的动力学发生了显著变化。而且，在侵入体的共动系统中，侵入体前方的动压力呈指数衰减。其标度产生了一个特征长度尺度，该尺度与侵入体尺寸量级相当。这一发现与我们在所有情况下发现的长尺度惯性耗散类型完全一致。
