This paper examines a new type of thruster which, similar to squid and jellyfish, generates propulsive forces by cyclically ingesting and expelling jets of water. The thrust output of this device depends greatly on the nature of the expelled jet, with greater output occurring for jets which form a single coherent vortex ring rather than a vortex ring with a trailing wake. The average thrust output as well as the jetting efficiency are maximized with respect to the thruster's nozzle diameter and jet velocity program. The appropriate constraints of the problem are defined including a dynamic constraint to ensure that the propulsive jet forms a single vortex ring. It is shown that the average thrust output under these constraints reaches a maximum when the nozzle radius is set to a critical value, and that using an orifice nozzle decreases propulsive efficiency at low Reynolds numbers.

A new type of underwater thruster was designed to provide high-accuracy, low-speed maneuvering to underwater robots. Located internal to the vehicle surface, these thrusters have a minimal effect on the forward-drag profile of the vehicle. These thrusters, whose inspiration comes from the natural propulsion of cephalopods and jellyfish, generate control forces by successive ingestion and expulsion of jets of water from a cavity mounted in the hull of the vehicle. The jetting process has no net mass flux but results in a positive momentum flux. A time-dependent thrust model was developed, which predicted the thruster dynamics as a function of time, actuation frequency, and thruster-driving parameters. A linear transfer-function model was developed to approximate both the thruster and vehicle dynamics, which led to maneuver categorization into three regimes:Cruising,Docking, andTransition. The predicted frequency response was verified through hybrid simulation to be accurate for predicting general trends and cutoff frequency.

A new type of underwater thruster is studied which is inspired by the natural locomotion of squid and other cephalopod. The thruster is similar to synthetic jet actuators used for flow control studies, but operates on different length and frequency scales. A hybrid simulation experiment has been designed to test the performance of this thruster in a static environment, under dynamic, unsteady driving signals. The hybrid simulation implements actual thrust production on a virtual vehicle model and attempts to control the trajectory of that vehicle. It was determined that this type of thruster being controlled with a basic PD control algorithm demonstrates excellent position tracking in a wide range of maneuvers. The thruster showed that it could produce controlling forces accurately on several scales of thrust. However, the maneuvering system was subject to an appreciable position overshoot at high vehicle oscillation frequencies, due to unmodeled thruster settling time.

Similar to propulsion techniques employed by squid and other cephalopod, a new type of thruster was designed which utilized pulsatile jet propulsion to generate controlling forces. The thrust production from this device was characterized in a static environment and seen to be well approximated by a simple fluid slug model. A linear transfer function model was derived to describe the transient dynamics of this thruster and a virtual vehicle simulation was developed to test the thruster with unsteady driving signals to verify this model. Due to the extremely non-linear nature of underwater vehicle environments we developed a scaling system to classify regimes of maneuvers and characterize their dynamics independently. Within the hybrid simulation environment, using a simple proportional derivative control algorithm, a thruster/controller was designed and observed to provide sufficient control over the vehicle performing large scale maneuvers. However, some additional compensation may be required for accurate small scale maneuvers which require minimal overshoot.