Yang Ding, University of Southern California
601 Pao Yue-Kong Library
Locomotion within granular media like sand, soil and debris that display both solid and fluid-like behavior is challenging and not well understood. I will summarize our efforts to understand the swimming of the sandfish lizard in sand. High speed x-ray imaging showed that the 10 cm-long sandfish swims at 2 body-lengths/sec within sand by propagating an undulatory traveling wave down the body. We developed an empirical resistive force model with granular forces measured from experiments. The model correctly predicts the animal’s wave efficiency (ratio of forward speed to wave speed) as approximately 0.5. The model also explains the muscle activation pattern observed on sandfish and solved a long-standing puzzle of undulatory swimmers. The empirical model agrees with a more detailed numerical simulation: a multi-segment model of the sandfish coupled to a multi-particle discrete element method (DEM) simulation of the granular medium. The principles discovered helped the development of a sand-swimming physical model (a robot) which, like in our empirical and multi-particle numerical models, swims fastest using the preferred sandfish wave pattern.