Studying the Kinetics of a Self-propelled Cruiser in 2D Granular Media under Gravity

We propose a cruiser able to move in a granular medium made of nearly 50-50 bidisperse dissipative particles under gravity. The cruiser has a circular shape with a square indentation on its edge. By shifting and then ejecting granular particles entering its indent-region facing a given direction, the cruiser gains thrust to push itself forward in the same direction, which can be either perpendicular or parallel to gravity. Using molecular dynamics (MD) simulations, we identify three universal phases during one particle-ejection process: 1) acceleration by the ejection thrust, 2) deceleration by the compressed particles ahead and 3) relaxation with the decompressed particles. We also confirm that the cruising capability improves with increasing the particle-ejection strength and with decreasing the interference from gravity.