Comparative Analysis of Horizontal Self-Burrowing Strategies Using Full-Scale DEM-MBD Co-Simulations

In a companion paper, we demonstrated the capability of a coupled discrete element method (DEM)-multi-body dynamics (MBD) framework in simulating self-burrowing behavior in granular media. In this paper, the same framework was calibrated by running direct shear tests and then used to systematically compare various horizontal self-burrowing strategies. The robot of interest has a minimalistic, modular design and mainly consists of a pair of cylinders with or without a cone or auger tip. The robot could achieve extension-contraction movement, and tips have options to rotate. A series of burrowing strategies were simulated: cyclic extension-contraction of the cylinders without a tip, with a static or rotating cone tip, or with a static or rotating auger tip. The rotation of the tip was only activated when the cylinders extended. It was found that without a tip, the kinematics is symmetric in time, and the robot does not have net translation with time. With a tip, the robots all burrowed horizontally due to the fact that the combinations of asynchronous extension-contraction and rotational motions break the kinematic symmetry. The burrowing speed is highest for the case with a rotating auger tip and is lowest for the case with a static cone tip. A net upward force (lift) was also found during the horizontal movement of the robot, which caused the robot to deviate from the planned trajectory and tend to move upward.