Feasibility of hydrodynamically activated valves for salp-like propulsion

Using valves to control the direction of internal flow for effective swimming, the jet-propulsion method of sea salp (a barrel-shaped marine invertebrate) provides a promising locomotion mechanism for bio-inspired robots. In this study, we numerically investigate this problem via an axisymmetric fluid–structure interaction model within the immersed-boundary framework. Specifically, we prove that in these systems, it is feasible to use fully passive valves whose opening and closing actions are driven solely by the hydrodynamic load. This finding is going to greatly reduce the complexity of locomotion devices based on this design. Furthermore, we have examined the effect of the design parameters, i.e., the stiffness and inertia, of the valves upon the swimming performance. In general, it is found that stiff and heavy valves increase the swimming speed, whereas soft and light valves decrease the cost of transport.