Abstract

Cephalopods and jellyfish use large-scale structural deformation to propel themselves underwater, changing their internal volume by 20-50%. This seminar will present recent findings on the internal and external flow dynamics resulting from shapes that change their internal volume and how these findings may be exploited to improve the maneuvering and propulsive efficiency of underwater vehicles and robotic. In the external flow, rapid volume change results in the recovery of large added-mass propulsive forces and the control of boundary layer separation. A shrinking parameter governs the ratio of energy recovered, and sufficiently rapid shrinking was used to power a simple prototype vehicle through a fast-start maneuvers at record breaking acceleration. In the internal flow, the large added-mass variation over a volume-pulsation cycle leads to a net thrust with similar magnitude to the net jet momentum. The large internal added-mass also dominates the inertia of the freely swimming system, which was exploited to in a flexible robotic system which resonates to increase it’s speed and propulsive efficiency.