Concept Design of a Flexible-Hull Unmanned Undersea Vehicle

In recent years, research in the propulsion and maneuvering mechanisms used by fish has demonstrated the utility of biopropulsion for use on undersea vehicles. Despite recent advances in unmanned undersea vehicle (UUV) technology, little progress has been made in improving propulsive efficiency and maneuverability. Most underwater vehicle designs employ a conventional propeller as the main propulsor and shrouded thrusters and/or control fins for maneuvering. Two types of vehicle designs are prevalent: torpedo shaped bodies streamlined for speed and range, or box-shaped bodies designed for maneuvering and station keeping. Unfortunately, most future UUV missions require all of these capabilities: high transit speed, long range/duration, maneuverability and station keeping ability. Thus we look to fish as a potentially optimal UUV design in that they are able to cruise great distances at significant speed, maneuver in tight spaces and accelerate and decelerate quickly. This paper summarizes the relevant design issues and current work in the development of a flexible-hull UUV which propels and maneuvers like a fish. Following the morphology and kinematics of a yellowfin tuna, the Charles Stark Draper Laboratory Vorticity Control UUV (VCUUV) will be the first demonstration of a freely swimming Thunniform (tuna-like motion) robotic vehicle. Simulation of the required kinematics and loads indicate that Thunniform motion can be actuated with a r ind forebody comprising 60% of the total vehicle len~h and four rind links actuating the tail section and caudal fin. Three different actuation concepts were compared by analyzing possible components and arrangements to attain the required loads and mission duration. A recirculating hydraulics concept was chosen for prototyping due to the versatility of the design for study of a variety of swimming speeds and maneuvers. 82 Fish swimming, vorticity control, tuna, unmanned undersea vehicle (UUV). ROV INTRODUCTION Improvements in propulsive efficiency and maneuverability of unmanned undersea vehicles (UUV's) are necessary to achieve the challenging new missions in littoral zone warfare, mine reconnaissance and scientific missions in cluttered environments. Increasingly sophisticated (and power intensive) mission payloads, and the need for greater range and endurance compete for finite energy supplies on board UUV's. Improved propulsive efficiency and energy capacity will directly increase mission time and reduce the launch and recovery overhead. More work may be done in a vehicle deployment: a larger area may be surveyed, or perhaps more time may be spent in one location studying a site of interest. Even modest increases in mission duration will directly improve mission performance. Maneuverability has been a particularly vexing problem for underwater vehicle desig'ners. There are two common actuators for