147.2  Monday, Jan. 7  Influence of Deformation Geometry on Sand-swimming Performance HATTON, R. L.*; DING, Y.; CHOSET, H.; GOLDMAN, D. I.; Oregon State University; Georgia Institute of Technology; Carnegie Mellon University; Georgia Institute of Technology Ross.Hatton@oregonstate.edu

Many animals move within granular media such as desert sand. Studies of an undulatory sand-swimmer, the sandfish lizard, showed that the grains around the organism form a frictional fluid in which inertial effects are small and kinematics dominate. To examine the kinematics of swimming in granular media (GM) we have adapted, from our work in robotics, a geometric model for swimming in viscous fluids. This model relates the net displacement induced by a stroke to an area integral in the stroke parameters. It also gives rise to a visualization that allows us to better understand the performance of the system, whether it be an animal or a robot. For each component direction – forward, lateral, and rotational – this visualization can be viewed as a graph of a function or a “terrain map.” A closed loop in this space represents a cyclic motion, i.e. a stroke. If a stroke encompasses a large positive “mountain” or deep negative “valley,” then it accrues positive or negative displacement, respectively, in its component direction. If the stroke encloses as much positive as negative area, then it produces no displacement; it has enclosed a self-canceling region.

Previously, we demonstrated the principles of the geometric approach on a reduced system, the three-link swimmer. Here, we extend them to continuous systems that can still be modeled by two internal degrees of freedom. In particular, we look at traveling waves of body curvature. The resulting visualizations highlight both the fundamental similarities between various modes of swimming and the differences in their effectiveness.