Oral: Impact of Intruder Spacing on Intrusion and Drag on Granular Slopes

Drag forces during low-velocity intrusion into granular media were previously modeled as the sum of forces on plate elements covering the intruder-granular interface. [Li et al. 2013] However, recent studies with adjoining intruders revealed an increase in drag force, suggesting that a restricted range of motion of grains caused by intruders may contribute to such increases. We investigate how intruder spacing affects force response during vertical intrusion and horizontal plowing under varying granular stability. Usingflatplates(5 cm wide, 1 mm thick) in a poppy-seed bed, we performed constant-speed (1.4 cm/s) experiments at various bed slopes, increasing the angle to just below the repose point (~32°) where the bed instability begins. Results confirm a peak-then-plateau drag trend with increasing spacing during intrusion. In plowing, drag rises with spacing due to larger shearing surfaces, as shown by particle image velocimetry (PIV). Furthermore, vertical drag remains consistent across slopes, while plow drag decreases by nearly 50% near the angle of repose. These findings indicate that plowing is highly sensitive to granular stability, while vertical intrusion is not. The insights gained could improve the understanding of granular-rigid body interactions and aid in designing robot feet with enhanced locomotion on sandy terrain.