Smith, Samuel M.

Maneuvering thrusters can provide small underwater vehicles with the ability to dynamically control position at low speeds. However, the successful implementation of these thrusters requires an understanding of their dynamic response, as well as a design which meets the specified design requirements. This thesis experimentally investigates the design and dynamic performance of small diameter tunnel thrusters for two small autonomous underwater vehicles. A systematic series of dynamic experiments were conducted with three working tunnel thruster prototypes that fulfill the operating and design constraints of these vehicles. The results from these experiments are shown to provide an accurate representation of the overall performance and thrust capability of the thrusters tested. Experimental data is compared with simulations utilizing a recently proposed thruster model, and the ability of the model to predict the dynamic response is discussed.

Recent successes in Autonomous Underwater Vehicle (AUV) technology have generated demand for broader, more general use of these vehicles, along with demand for longer, more complicated missions. However, AUVs are becoming more complex, and hence more difficult to program, test and maintain. A discrete event system would provide conditional execution for mission management, failure detection, and resource allocation techniques. The goal of this thesis is to provide a convenient formalism for discrete event systems that reduces the apparent complexity of the system while maintaining its robust capabilities. The chosen formalism allows the convenient representation of hierarchies of concurrent hierarchical state machines. The formal semantics of the model are discussed, along with complete data structures and algorithms. As an example, a complete design of the navigator state machine is provided.

Having the ability to dock an Autonomous Underwater Vehicle (AUV) can significantly enhance the operation of such vehicles. In order to dock an AUV, the vehicle's position must be known precisely and a guidance algorithm must be used to drive the AUV to its dock. This thesis will examine and implement a low cost acoustic positioning system to meet the positioning requirements. At-sea tests will be used as a method of verifying the systems specifications and proper incorporation into the AUV. Analyses will be run on the results using several methods of interpreting the data. The second portion of this thesis will develop and test a fuzzy logic docking algorithm which will guide the AUV from a location within the range of the sonar system to the docking station. A six degree of freedom simulation incorporating the Ocean Explorer's hydrodynamic coefficients will be used for the simulation.

The purpose of this thesis is to investigate the ability of using piping networks as a communication channel using power line communication transceivers. Two ways by which a piping network is able to propagate waves are investigated. The first wave propagation method is through the pipe shell. Using structural waves and PZT type transducers, data packets are sent and received through the propagation of structural waves in the pipe shell. However, because of the dispersive behavior of quasi flexural radial waves, the data packets are distorted. The second wave propagation method explored is acoustic waves in the enclosed fluid. The data packets are sent and received along the piping network using three types of hydrophones. The reliability of this method depends mostly on the sensitivity of the hydrophones.

Autonomous underwater vehicle (AUV) missions are generally of a multi-tasked nature, i.e., there are usually several criteria which need to be met concurrently during the course of a mission. An example is the bottom altitude tracking mission proposed by the University of South Florida. They have developed a bottom classification and albedance package (BCAP) which will be used to record data to ground-truth oceanographic satellites. Two criteria needed for this mission are vehicle safety and motion stability of the recording sensors. This thesis will respectively compare the results of three bottom altitude tracking controllers: a linear modification of an existing depth controller, a TSK fuzzy logic controller, and a behavior based decision controller. Aspects analyzed for meeting the criteria were the ability of the auv to avoid collisions with bottom, the ability of the auv to maintain a desired altitude above the sea floor, and the ability of the auv to keep the amount of blur in a picture taken by a downward looking camera under one pixel. From simulation and real world testing, final results indicate the behavioral based decision controller was proven to be the most robust and the only controller tested to be able to handle multi-criteria.

The development of a Flight Control System for a non-linear six degree of freedom model of an Autonomous Underwater Vehicle is described. Heading, pitch and depth are regulated by three independent Fuzzy Logic Controllers (FLCs). Numerical methods are used to tune rule bases to control tables that are based on the minimum time characteristics of the model. Setpoint errors are eliminated using fuzzily constrained integrators. A scheme to vary control policy with forward speed is also detailed. System stability is evaluated using cell-to-cell mapping. A variable structure fuzzy heading controller is designed for an unstable non-linear model of an Unmanned Underwater Vehicle. Scheduling of scaling parameters accommodates changes in forward speed as predicted by thruster RPM and angular distance turned. This FLC combines bang-bang and linear type control to respond more rapidly and robustly than a gain scheduled linear PID controller.

Any Autonomous Underwater Vehicle (AUV) software system is expected to be dynamic due to changes in mission goals, addition of new hardware, implementation of new algorithms, etc. Thus, for a successful AUV program, it is important to have a carefully and properly designed software architecture that is flexible enough to accommodate future changes. The AUV program in the Ocean Engineering Department of Florida Atlantic University has undergone significant development over the past one and a half years to achieve a flexible software system. This flexible architecture should also help in performing diverse kinds of AUV missions with minimal reconfiguration. The focus of this thesis work is to perform m evaluation of the past and present software systems used in our AUVs, and to describe the implementation details that were necessary for the migration of the past software system to a newer, more flexible and powerful software architecture. Another purpose of the thesis is also to describe the design philosophy behind the new architecture and its impact on the AUV program.

The Morpheus, the latest generation of AUV developed at Florida Atlantic University was designed to be as modular as possible, and to handle longer, more complicated missions. The software must now reflect this improvement: it should be as dynamic as possible, must adapt to the different missions and emphasize flexibility and scalability. It must allow for complex behaviors, failure detection and handling and multiple cooperative missions. On the other hand, the new high-level controller has to remain accessible to the non expert user. To achieve these goals, a new architecture, based on the Convenient Hierarchical Autonomous State Machine formalism, was implemented using Python. The system is modeled as a set of concurrent processes communicating through shared memory to accommodate a variety of sensor payloads from one mission to the next. New control tools can be integrated dynamically into the architecture in the form of modules implementing new behaviors.

This report highlights important aspects of previous work with the Ocean Explorer (OEX) autonomous underwater vehicle (AUV) docking system as a background. This includes short baseline navigation, the Tracking Controller, Mechanical aspects of the dock, and results of testing of the docking system for the OEX Details of the Morpheus AUV are then given along with the major concerns faced in trying to adapt the OEX dock to the Morpheus. Using computer simulation, the reaction of the Morpheus when it impacts the dock is explored and the results of at sea testing (the collision of the vehicle and the dock) is discussed. A stinger strength analysis of the docking components is included and finally, suggestions for future work including modifications of the existing dock as well as another docking scheme are presented.

This project consisted of a feasibility study to ascertain whether or not an inexpensive acoustic modem for an Autonomous Underwater Vehicle (AUV) could be developed using low cost commercially available products. Our AUV's at Florida Atlantic University currently use LonWorks for their internal control networks, so we have plenty of experience with their parts. The LonWorks Power Line Transceivers are capable of generating a signal that can be sent to a transducer for communication through the water. The PLT-30 Power Line Transceiver generates a direct sequence spread spectrum signal (DSSS) that offers many useful operating features; such as anti-jam, interference rejection and covert communications, low intercept probability, and most importantly, multipath protection. After numerous tests, however, the system was incapable of establishing reliable acoustic communications. We conclude that the PLT-30 Power Line Transceiver use as an underwater acoustic modem is not a viable approach. As an alternative method, communication through an electric current field was tested in a salt-water pool. The initial test produced a 100% success rate.