CIVINS / Approved for public release; distribution is unlimited / The utility of present Autonomous Underwater Vehicles (AUVs) is limited by their on-board energy storage capability. Research indicates that rechargeable batteries will continue to be the AUV power source of choice for at least the near future. Thus, a need exists in both military and commercial markets for a universal, industry-standard underwater AUV recharge system. A novel solution using a linear coaxial wound transformer (LCWT) inductive coupling mounted on the AUV and a vertical docking cable is investigated. The docking cable may be deployed from either a fixed docking station or a mobile "tanker AUV". A numerical simulation of the simplified system hydrodynamics was created in MATLAB and used to evaluate the mechanical feasibility of the proposed system. The simulation tool calculated cable tension and AUV oscillation subsequent to the docking interaction. A prototype LCWT coupling was built and tested in saltwater to evaluate the power transfer efficiency of the system. The testing indicated that the surrounding medium has little effect on system performance. Finally, an economic analysis was conducted to determine the impact of the proposed system on the present military and commercial AUV markets. The recharge system creates substantial cost-savings, mainly by reducing support ship requirements. An effective AUV recharge system will be an important element of the Navy's net-centric warfare concept, as well as a valuable tool for commercial marine industries. / Lieutenant Commander, United States Navy

In the interest of enhancing the capabilities of autonomous underwater vehicles US Naval Operations, controlling vehicle position to follow depth contours presents exciting potential for navigation. Use of a contour tracking control algorithm in lieu of preprogrammed waypoint navigation offers distinct advantages within new challenges. The difficult nature of this problem lies in the non-trivial connection between the necessary corrective action and the feedback error used in traditional control methods. Stated simply, modern vehicle control algorithms separate horizontal and vertical plane navigation. The autonomous vehicle senses heading error and applies rudder to steer the vehicle to a desired heading. Simultaneously, the vehicle might sense altitude and apply stern plane angles to maintain a safe height above ground. This thesis research examines the new problem of sensing depth and altitude in the vertical plane while steering the vehicle horizontally to find a specified bathymetry contour. While more remains to understand, this research proves the existence of a solution and suggests similar approaches may facilitate tying vehicle navigation to other indirect sensors. This thesis presents two contour tracking control algorithms and examines the performance of each by simulating the response of the REMUS underwater vehicle to ideal and real-world bathymetry models.

The US Navy is developing Seaweb undersea acoustic networking technology to enable distributed autonomous ocean sensors. An Unmanned Undersea Vehicle (UUV) can operate as a mobile node among the grid in the conduct of its own mission, using the fixed nodes as navigation reference points. The fixed grid provides a cellular communications infrastructure for command & control and data telemetry. In turn, the UUV can support the fixed grid by physically redistributing large quantities of data throughout the network or for breaching the sea surface and acting as a mobile gateway node, communicating via satellite to a command center ashore. Assimilating UUVs as network nodes significantly enhances undersea network capability, expanding the available concepts of operations. This thesis concerns the use of the fixed undersea network as a means to track the UUV and anticipates routine operations of mobile nodes in the context of fixed grids. This work is also a fundamental step toward advanced operations of fully mobile networks in the form of collaborative swarms.

With the Global War on Terrorism (GWOT) taking place in full force, autonomous vehicles have become a major asset to government forces. Expansion of single vehicle technology to multiple vehicle technology is required in order for the United States to stay ahead of its adversaries in the GWOT and other technological fields (such as oceanography). Multiple vehicle technology has been explored by many different institutions in the recent past (Leonard, 2001 and Kucik, 2003). Expansion of this technology will lead to greater autonomy and robustness amongst the vehicles. This thesis presents a simulation of a "follow the leader" behavior for multiple Autonomous Underwater Vehicles (AUVs). The follower vehicle incorporates the use of forward-looking sonar to track the leader vehicle. This process will free up bandwidth between acoustic modems; allowing data transfer to occur with greater efficiency. Hydrodynamic coefficients are used to develop steering equations that model REMUS through a track of specified waypoints similar to a real-world mission track. A two-dimensional forward looking sonar model with a 120 [degree] horizontal scan and a 110 meter radial range is modeled to track the leader vehicle. Resulting bearing and range between the two vehicles is incorporated as control for positioning the follower vehicle.

CIVINS / This thesis presents a simulation of autonomous underwater vehicle navigation using a single transponder to create a virtual long baseline (VLBL). Similarly to LBL systems, ranges in a VLBL are calculated between the vehicle and the transponder, but the vehicle position is determined by advancing multiple ranges from a single transponder along the vehicles dead reckoning track. Vehicle position is then triangulated using these successive ranges in a manner analogous to a 'running fix' in surface ship navigation. Navigation data from bottom survey operations of an underwater vehicle called the Autonomous Benthic Explorer (ABE) were used in the simulation. The results of this simulation are presented along with a discussion of the benefits, limitations, and implications of its extension to real-time operations. A cost savings analysis was also conducted based both on the idea that a single surveyed beacon could be deployed for underwater navigation and on the further extension of this problem that the 'single beacon' used for navigation could be located on the ship itself. / Contract number: N62271-97-G-0026. / CIVINS / US Navy (USN) author.

Autonomous underwater vehicle navigation is a complex problem of state estimation. Accurate navigation is made difficult due to a lack of reference navigation aids or use of the Global Positioning System (GPS) that could establish the vehicles position. Accurate navigation is critical due to the level of autonomy and range of missions and environments into which an underwater vehicle may be deployed. Navigational accuracy depends not only on the initialization and drift errors of the low cost Inertial Motion Unit (IMU) gyros and the speed over ground sensor, but also on the performance of the sensor fusion filter used. This thesis will present the method by which an Extended Kalman Filter (EKF) was tuned after installation of an IMU in the ARIES Autonomous Underwater Vehicle. The goal of installing the IMU, analyzing the navigational results and tuning the EKF was to achieve navigational accuracy in the horizontal plane with a position error of less than one percent of distance traveled when compared to GPS. The research consisted of IMU installation and software modifications within the vehicle to fully realize the design goal. Data collection and analysis was conducted through field experiments and computer simulation. A significant result of this work was development of a pseudo-adaptive algorithm to vary the measurement noise values in selected channels to for a desired response in the filter and improve accuracy and precision in the state estimates.

One day fully autonomous AUV's will no longer require human interactions to complete its missions. To make this a reality, the AUV must be able to safely navigate in unfamiliar environments with unknown obstacles. This thesis builds on previous work conducted at NPS's Center for AUV Research to improve the autonomy of the REMUS class of AUVs with an implemented FLS. The first part of this thesis deals with accurate path following with the use of look-ahead pitch calculations. With the use of a SIMULINK model, constraints surrounding obstacle avoidance path planning are then explored, focusing on optimal sensor orientation issues. Two path planning methods are developed to address the issues of a limited sonar field of view and uncertainties brought on by an occlusion area. The first approach utilizes a pop-up maneuver to increase the field of view and minimize the occlusion area, while the second approach creates a path with the addition of a spline. Comparing the two methods, it was concluded that spline addition planner provided a robust optimal obstacle avoidance path and along with the look-ahead pitch controller completes the design of a "back-seat driver" to improve REMUS's survivability in an unknown environment. / US Navy (USN) author.

Thesis (M.S.M.E.)--University of Delaware, 2006. / Principal faculty advisor: Xinyan Deng, Dept. of Mechanical Engineering. Includes bibliographical references.

Thesis (M.S. in Operations Analysis)--Naval Postgraduate School, June 2004. / Thesis advisor(s): Arnold H. Buss. Includes bibliographical references (p. 123-124). Also available online.

Thesis (M.S. in Applied Science (Robotics))--Naval Postgraduate School, September 2003. / Thesis advisor(s): Don Brutzman, Anthony Healey, Douglas P. Horner. Includes bibliographical references (p. 177-181). Also available online.