Froude scaling of rotating intrusion drag in microgravity regolith.

Abstract

Rotational intrusion into granular media is crucial for small body sampling but remains less studied than its non-rotational counterpart. Using a GPU-accelerated discrete element method, we investigate the resistance of a rotating cylindrical penetrometer as a function of the Froude number. Unlike quasi-static intrusion, which creates a stagnant zone ahead of the intruder, rotation disrupts this structure, inducing shear dilation both in front of and around the intruder. This results in a thin, highly mobilized layer of particles, causing the slope of the force-depth to decrease following a negative power-law relationship with increasing Froude number. As rotation intensifies, the rate of resistance reduction slows, and sliding friction becomes negligible, while rolling and torsional resistances remain significant. Furthermore, introducing cohesion shifts the granular medium's response from plastic to elasto-plastic, significantly altering the force-depth relationship and leading to resistance saturation. A brief gravity scan shows that weaker gravity modestly increases the depth-dependence of relative resistance and amplifies the influence of rotation. These findings enhance the understanding of rotational intrusion mechanisms under micro-gravity.