We study the dynamics of an intruder moving through a fluidized granular medium in three dimensions ($d=3$). The intruder and grains have both translational and rotational degrees of freedom. The energy-dissipation mechanism is solid friction between all pairs of particles. We keep the granular system fluidized even at rather high densities by randomly perturbing the linear and angular velocities of the grains. We apply a constant external force of magnitude $F$ to the intruder and obtain its steady-state velocity $V_s$ in the center-of-mass frame of the grains. The $F-V_s$ relation is of great interest in the industrial processing of granular matter and has been the subject of most experiments on this problem. We also obtain the mobility, which is proportional to the inverse viscosity, as a function of the volume fraction $\varphi$. This is shown to diverge at the jamming volume fraction. For $\varphi$ below the jamming fraction, we find that $V_s\sim F$ for small $F$ and $V_s\sim F^{1/2}$ for large $F$. The intruder shows diffusive motion in the plane perpendicular to the direction of the external force.

中文翻译：

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摩擦颗粒流体中的入侵者动力学：分子动力学研究

我们研究了入侵者在流化颗粒介质中的三个维度的动态变化（$d=3$）。入侵者和谷物都具有平移和旋转自由度。耗能机制是所有成对颗粒之间的固体摩擦。通过随机扰动颗粒的线速度和角速度，即使在相当高的密度下，我们也能保持颗粒状系统的流体化。我们施加恒定大小的外力$F$ 进入入侵者并获得其稳态速度 $V_s$在谷物的质心框架中。的$F-V_s$这种关系在颗粒物的工业加工中引起了极大的兴趣，并且已经成为该问题上大多数实验的主题。我们还获得了与反粘度成正比的迁移率，它是体积分数的函数$\varphi$。这显示出在阻塞体积分数处发散。对于$\varphi$ 低于干扰分数，我们发现 $V_s〜F$ 小 $F$ 和 $V_s〜F^{\mathrm{1个}/2}$ 大 $F$。入侵者在垂直于外力方向的平面上显示出扩散运动。