Snake Swimming Hydrodynamics, Biomechanics, and Maneuverability

Snakes are anguilliform swimmers, they move through water by propagating a traveling wave of increasing amplitude along their body length. Their relatively simple body shape, swimming style, and high maneuverability has made them a popular model in robotics. Yet it is important to understand how snakes achieve swimming efficiency and maneuverability to successfully extend these qualities into robotics. As a snake swims its body pushes against the surrounding water, therefore, its undulation is the source of both its propulsion and drag force. We use digital defocusing particle tracking velocimetry to measure the movement of the surrounding fluid, thus revealing a foot print of its movement. By reconstructing the velocity field we are able to identify shed vortices and directly calculate parameters such as hydrodynamic impulse and kinetic energy. We use these results, incorporated with the snake’s swimming kinematics, to explore differences in swimming efficiency between different snakes with different morphological characteristics. Snakes are also highly maneuverable. They often change direction or stabilize in the water column by coiling, tying and turning their bodies. In doing so they are solving a mathematically difficult problem: how to maximize torque while minimizing the moment of inertia. We will explore how snakes shift their moment of inertia throughout a turn and consider how the timing of vortex shedding allows them to accomplish this goal.