In previous work we presented design and manufacturing rules for optimizing the energy density of piezoelectric bimorph actuators through the use of laser-induced melting, insulating edge coating, and features for rigid ground attachments to maximize force output, as well as a prestacked technique to enable mass customization. Here we adapt these techniques to bending actuators with four active layers, which utilize thinner material layers. This allows the use of lower operating voltages, which is important for overall power usage optimization, as typical small-scale power supplies are low-voltage and the efficiency of boost-converter and drive circuitry increases with decreasing output voltage. We show that this optimization results in a 24%-47% reduction in the weight of the required power supply (depending on the type of drive circuit used). We also present scaling arguments to determine when multi-layer actuator are preferable to thinner actuators, and show that our techniques are capable of scaling down to submg weight actuators.

We demonstrate that shape-changing or morphing fins provide a new paradigm for improving the ability of vehicles to maneuver and move rapidly underwater. An ingenuous solution is employed by fish to accommodate both the need for stability of locomotion and the ability to perform tight maneuvers: Retractable fins can alter the stability properties of a vehicle to suit their particular goals. Tunas, for example, are large fish that are fast swimmers and yet they need rapid turning agility to track the smaller fish they pursue; they have perfected the use of their dorsal and ventral fins to ensure stability when retracted and rapid turning when erected. Although fish employ unsteady propulsors rather than propellers, we show that engineering rigid-hull underwater vehicles can also exploit similar solutions. We explore the basic flow mechanisms and design considerations of employing morphing fins to alter the stability and maneuvering qualities of vehicles and apply unsteady forces and moments under active control. We also show results from maneuvering simulations and experiments on a model of an underwater vehicle.

Underwater Vehicles generally have control fins located only near their aft end, for making controllable changes in directions. This design allows for stability of control; however, the turns are typically large in comparison to the vehicle body length. Some bony fish, such as tuna, on the other hand, have deployable ventral and dorsal fins located towards the front of their body, in addition to their other fins. Their deployable fins allow them to modulate their hydrodynamic behavior in response to their environment. Tunas keep these fins retracted during steady cruising, and then deploy them during rapid maneuvers. However, the details of these hydrodynamic effects are not well understood. To investigate this phenomena, using a REMUS 100 as a model, a pair of vertical fins was added at different hull positions, to investigate the effects of fin location on the horizontal plane hydrodynamics, through: stability parameters, nonlinear simulation, and towing tank experiments. Depending on the added fin location, the stability of the vehicle changed, thereby affecting the maneuverability. As fins were placed further forward on the vehicle, maneuverability increased, with effects tapering off at 0.2 BL ahead of the vehicle's center of buoyancy. This investigation explored how rigid underwater vehicles could benefit from added fins, without drastically changing the design of current vehicles.