Unveiling the role of self-propulsion intensity in the ascent dynamics of an intruder in granular media

Self-propulsion intruders in granular media are relevant to both engineering applications, such as powder mixing blades, and natural systems, like sand-swimming lizards. The dynamics of self- propulsion intruders in particles, particularly under non-preset displacements, have received relatively little attention. In this study, we realized a self-propulsion cylindrical intruder using an eccentric rotor module and experimentally investigated its ascent in granular media under various vibration conditions. Our combined experimental and discrete element method simulation results show that the ratio of force amplitude to frequency effectively defines the self-propulsion intensity. This work elucidates the linear correlation between the intruder's ascent rate and self-propulsion intensity, and reveals the mechanism behind its upward motion. We further propose a model based on mass flow rate that describes the dynamics of the ascent, with experimental results in good agreement. This work offers a new perspective for understanding self-propulsion behavior in granular systems and provides theoretical support for the design of bio-inspired locomotion mechanisms.