Propulsive efficiency of underwater vehicles using unsteady propulsors

This study examines the propulsive efficiency of underwater vehicles which are driven by unsteady propulsors. The analysis is focused on vehicles utilizing a novel thruster which expels finite propulsive jets periodically. This analysis also applies to swimming squid and jellyfish (from which the thruster was inspired), and can be extended to any periodic unsteady propulsion. The vehicle trajectory is solved analytically to calculate the exact work output/input and it is observed that with unbounded forcing there is an optimal thruster duty cycle, λ = 0.31, which maximizes propulsive efficiency. This optimal duty cycle is very close to the actual jetting duty cycle observed in steadily swimming squid.