Thrust depletion at high pulsation frequencies in underactuated, soft-bodied, pulsed-jet vehicles

In this paper we examine the passive stage in the propulsive cycle of a soft-bodied, pulsed-jet, underwater vehicle and its effect on the resultant thrust. This vehicle consists of an elastic shell which propels itself via the discontinuous expulsion and ingestion of finite slugs of ambient water, resulting in a pulsated routine. The activation routine involves the collapse of the elastic shell via cable transmission and its subsequent passive inflation driven by the elastic energy stored in the strained shell walls. Earlier analysis by the authors have found that the thrust generated at each pulsation depends massively on the resilience of the elastic material which composes the shell. In order to improve the design of these vehicle it is thus necessary to characterize the dynamic behaviour of the elastic shell during its stage of inflation by resorting to a coupled potential flow-elastodynamics model. The results enable to better parametrize the thrust model so far employed for this kind of vehicles and in this way achieve a more rigorous description of the vehicle dynamics for design and control purposes.