Underwater soft-bodied pulsed-jet thrusters: Actuator modeling and performance profiling

Abstract

A new kind of underwater vehicle is developed by taking inspiration from cephalopods. Its actuation routine is scrutinized\ud via a suitable model. Similar to octopuses and squids, these vehicles consist of an elastic, hollow shell capable of undergoing\ud sequential stages of ingestion and ejection of ambient fluid, which is driven by the recursive inflation and deflation\ud of the shell. The shell actively collapses, and in this way it expels water through a funnel; then it passively returns to the\ud inflated shape, drawing ambient fluid into the cavity. By doing so, a pulsed-jet propulsion routine is performed that enables\ud the vehicle to propel itself in water. Due to their soft nature, the actuation of these vehicles is largely dependent on the\ud subtle management of the elastic response of the shell throughout the propulsion routine. A kinematic model of the actuation\ud mechanism, thoroughly corroborated by experimental validation, is devised which elucidates the relationship between\ud the active (collapse) and passive (refill) stages of the actuation. Upon association with the dynamics of the vehicle, this\ud model permits the derivation of the generic performance profiles of this new kind of vehicle. It is acknowledged that, for\ud given design specifications, an optimal swimming speed exists in coincidence with the coordinated operation between the\ud crank mechanism driving the shell contraction and the onset of elastic energy, which determines the speed of inflation of\ud the shell. These results are invaluable in the definition of rigorous design criteria and derivation of ad-hoc control laws\ud for a new breed of optimized soft-bodied, pulsed-jet, unmanned underwater vehicles

Fundamentals of soft robot locomotion

“…The torpedo-like mantle of the Octopus vulgaris was accurately replicated in [124] by means of a silicone shell, and actuated by a DC motor and cables. Actuation routines, design and control were further investigated to increase the performance of the robot [125][126][127]. Squid jet propulsion inspired the development of a silicone chamber compressed by SMAs [128], whereas multi-nozzle three-dimensional-printed propellers were developed in [129].…”

“…These assets are tightly coupled to the structurally compliant nature of the propelling body, which is one of the core capabilities of soft robots [1]. Experimental evidence of the role of added mass variation in the production of thrust [125] has confirmed that active control of aquatic deformable bodies may pave the way to the design of new kinds of underwater soft robots.…”

Mechanical Construction and Propulsion Analysis of a Rescue Underwater Robot in the case of Drowning Persons

“…Lately, the research has been geared also to the development of marine robotic systems, as some aquatic operations are very difficult for human capabilities or unsafe. A big effort has been aimed at proposing new designs of underwater autonomous vehicles [5], also exploiting bio-inspired principles, such as octopus [6], cephalopod [7], and turtle [8] inspired robots. Sectors like oceanographic science, hydrography mapping, sea exploration, and marine archeology get great benefit from the adoption of unmanned marine robotized vehicles allowing difficult tasks to be tackled like seabed inspection or search and rescue operations [9][10][11][12][13].…”

Can added-mass variation act as a thrust force?

“…The capability to exploit added-mass variation as a potential source of thrust has significant implications in the design [6] and modelling [7], [8] of new kinds of underwater vehicles. To study this phenomenon experimentally we focus on a simple mechanical apparatus, i.e.…”