Ascent dynamics of self-propulsion intruder and the effects on granular rheology

The study of the motion behavior of self-propulsion intruders in granular materials is of significant importance in the fields of robotics and biomimetics. This study experimentally investigates the ascent behavior of self-propulsion intruders in a quasi-two-dimensional granular system and, through discrete element method simulations, reveals the underlying mechanisms of the intruder's ascent and its mesoscopic impact on the granular media. The results show that the excitation force induces local fluidization of the particles and generates a flow that compresses the space beneath the intruder. This flow is the primary cause of the intruder's ascent. Based on these findings, we propose a simplified model to describe the intruder's ascent trajectory, which reveals a strong correlation between the rising rate and the ratio of excitation force amplitude to frequency (J = F/f). J is positively correlated with the equivalent buoyancy. The relationship between J and the drag coefficient in the model suggests that a smaller J may cause fluctuations in the volume fraction, thereby increasing the resistance experienced by the intruder. This study provides a novel perspective and guidance for research on intruder models and the field of robotics manufacturing.