Meeting Abstract

27.3  Monday, Jan. 4  Mechanics of subsurface swimming of the sandfish Scincus scincus DING, Y*; MALADEN, R; KAMOR, A; GOLDMAN, D; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology dingyang@gatech.edu

Previous work (Maladen et. al, Science, 2009) demonstrated that the sandfish lizard (Scincus scincus) swims within granular media (sand) using axial body undulations without use of limbs and explained the motion with a resistive force theory (RFT) which incorporated measured animal kinematics and an empirical model of granular thrust and drag. Here we use a numerical model of a sandfish moving within an experimentally validated soft sphere molecular dynamics granular media model and experimental x-ray PIV measurements of the velocity field surrounding the sandfish to probe the physics of granular propulsion and to test the assumptions of the RFT including velocity independence of drag due to flow dominated by grain-grain friction, local forces, and non-inertial motion. The numerical model reproduces measured animal kinematics and RFT predictions including the speed-frequency relationship, the independence of wave efficiency on material compaction, and for the latter, the temporally resolved forces and the time averaged thrust to drag ratio on each element. Examination of the granular velocity field surrounding the sandfish in both experiment and simulation reveals that the RFT assumption of force locality is valid because velocities decay rapidly with increasing distance from the body. Particles below the animal are nearly stationary while those above it move rapidly as they refill voids created by body motion. Unlike flow in the vicinity of comparably sized animals in water, vortices are not apparent in the granular flow which confirms that the dynamics are non-inertial.