Buoyancy driven underwater gliders, which locomote by modulating their buoyancy and their attitude with moving mass actuators and inflatable bladders, are proving their worth as efficient long-distance, long-duration ocean sampling platforms. Gliders have the capability to travel thousands of kilometers without a need to stop or recharge. There is a need for the development of methods for hydrodynamic modeling. This thesis aims to determine the hydrodynamic parameters for the governing equations of motion for three autonomous underwater vehicles. This approach is two fold, using data obtained from computational flight tests and using a semi-empirical approach. The three vehicles which this thesis focuses on are two gliders (Slocum and XRay/Liberdade), and a third vehicle, the Virginia Tech Miniature autonomous underwater vehicle. / Master of Science

There are benefits to the use of internal actuators for rotational maneuvers of small-scale underwater vehicles. Internal actuators are protected from the outside environment by the external pressure hull and will not disturb the surrounding environment during inspection tasks. Additionally, internal actuators do not rely on the relative fluid motion to exert control moments, therefore they are useful at low speed and in hover. This paper describes the design, fabrication and testing of one such autonomously controlled, internally actuated underwater vehicle. The Internally Actuated, Modular Bodied, Untethered Submersible (IAMBUS) can be used to validate non-linear control strategies using internal actuators. Vehicle attitude control is provided by three orthogonally mounted reaction wheels. The housing is a spherical glass pressure vessel, which contains all of the components, such as actuators, ballast system, power supply, on-board computer and inertial sensor. Since the housing is spherically symmetric, the hydrodynamics of IAMBUS are uncoupled (e.g. a roll maneuver does not impact pitch or yaw). This hull shape enables IAMBUS to be used as a spacecraft attitude dynamics and control simulator with full rotational freedom. / Master of Science

The process developed herein uses a Multiple Objective Genetic Optimization (MOGO) algorithm. The optimization is implemented in ModelCenter (MC) from Phoenix Integration. It uses a genetic algorithm that searches the design space for optimal, feasible designs by considering three Measures of Performance (MOPs): Cost, Effectiveness, and Risk. The complete synthesis model is comprised of an input module, the three primary AUV synthesis modules, a constraint module, three objective modules, and a genetic algorithm. The effectiveness rating determined by the synthesis model is based on nine attributes identified in the US Navy's UUV Master Plan and four performance-based attributes calculated by the synthesis model. To solve multi-attribute decision problems the Analytical Hierarchy Process (AHP) is used. Once the MOGO has generated a final generation of optimal, feasible designs the decision-maker(s) can choose candidate designs for further analysis. A sample AUV Synthesis was performed and five candidate AUVs were analyzed. / Master of Science

A methodology for the design of small autonomous underwater vehicle propulsion systems has been developed and applied to the Virginia Tech 690 AUV. The methodology is novel in that it incorporates fast design level codes capable of predicting the viscous effects of low Reynolds number flow that is experienced by small, slow turning propellers. The methodology consists of determining the minimum induced loss lift distribution for the propeller via lifting line theory, efficient airfoil sections for the propeller via a coupled viscous-inviscid flow solver and optimization, brushless DC motor identification via ideal motor theory and total system efficiency estimates. The coupled viscous-inviscid flow solver showed low Reynolds number flow effects to be of critical importance in the propeller design. The original Virginia Tech 690 AUV propulsion system was analyzed yielding an experimental efficiency of 26.5%. A new propeller was designed based on low Reynolds number airfoil section data yielding an experimental efficiency of 42.7%. Finally, an entirely new propulsion system was designed using the methodology developed herein yielding a predicted efficiency of 57-60%. / Master of Science

The Virginia Tech Trawl-Resistant Self-Mooring Autonomous Underwater Vehicle (TRSMAUV) is designed to reside on the seafloor for extended periods of time. The TRSMAUV shape allows for deployment in areas where trawl fisheries are conducted. TRSMAUV is a two stage vehicle. The ingress vehicle is the delivery device, and it is constructed from two symmetric halves. The top half contains the ingress vehicle propulsion system and control surfaces. The bottom half is the trawl-resistant mooring package. A smaller vehicle, the egress vehicle, is housed within the bottom ingress half and provides the guidance, navigation and control algorithms for the TRSMAUV. This report covers the general design elements of the TRSMAUV, the detail design of several prototypes, the results of the field trials, and the next steps that will be taken to build the final vehicle. / Master of Science

Approved for public release; distribution is unlimited / This thesis centers around actual field operations and post-mission analysis of data acquired using a REMUS AUV operated by the Naval Postgraduate School Center for Autonomous Underwater Vehicle Research. It was one of many platforms that were utilized for data collection during AOSN II, (Autonomous Oceanographic Sampling Network II), an ONR sponsored exercise for dynamic oceanographic data taking and model based analysis using adaptive sampling. The vehicle's ability to collect oceanographic data consisting of conductivity, temperature, and salinity during this experiment is assessed and problem areas investigated. Of particular interest are the temperature and salinity profiles measured fromlong transect runs of 18 Km. length into the southern parts of Monterey Bay. Experimentation with the REMUS as a mine detection asset was also performed. The design and development of the mine hunting experiment is discussed as well as its results and their analysis. Of particular interest in this portion of the work is the issue relating to repeatability and precision of contact localization, obtained from vehicle position and sidescan sonar measurements. / Lieutenant, United States Navy

Este trabalho trata do controle dos movimentos de um Veículo Submersível Autônomo (VSA). Veículos submersíveis são difíceis de controlar devido à alta não linearidade de seus modelos, ao forte acoplamento de movimentos, ao desconhecimento de certas dinâmicas, às incertezas do próprio modelo, devido a distúrbios externos impostos pelo ambiente e devido ao ruído de sensores. A dificuldade de controle pode ser exacerbada quando o veículo é subatuado. Para realização deste trabalho foi escolhido um VSA do tipo torpedo, cujo modelo matemático disponível na literatura foi devidamente modificado para garantir uma melhor descrição de seus movimentos em seis graus de liberdade (6-GL). O modelo foi então validado através de simulações numéricas. Para a síntese dos controladores utilizou-se uma técnica de controle avançada. Mais especificamente, utilizou-se a abordagem do controle H1 para sistemas multivariáveis. Assim foram obtidos controladores centralizados capazes de superar o problema do forte acoplamento de movimentos. Técnicas de controle avançado permitem também considerar as informações disponíveis sobre perturbações, incertezas, ruídos e diferentes tipos de entrada já na fase de síntese, o que permite obter controladores com desempenho adequado numa ampla faixa de operação. Neste trabalho, em particular, a técnica da Sensibilidade Mista foi escolhida para a síntese de controladores robustos. Nesta abordagem, formatam-se algumas funções de malha fechada ligadas a sensibilidade do sistema buscando garantir estabilidade e desempenho robusto para o sistema controlado. Usando a mesma técnica de controle desenvolveu-se ainda um controlador de dois graus de liberdade (2-GL), apropriado para aplicação no problema de guiagem, onde procura-se seguir trajetórias tridimensionais. Os controladores desenvolvidos foram testados em simulações numéricas, produzindo-se uma grande quantidade de resultados. A análise destes resultados revela o poder e flexibilidade das técnicas escolhidas. / This work focuses the motion control of an Autonomous Underwater Vehicle (AUV). Underwater vehicles are difficult to control due to high non-linearities of its model, coupling between dynamics, unknown dynamics, model uncertainties, disturbances and sensor noises. Difficulty is greater, when the system is subactuated. In this work, a mathematical model of a torpedo-like AUV available in the bibliography was chosen and refined, leading to a six degree of freedom (6-DOF) model. The model was further analyzed and validated by a number of numerical simulations. Advanced approaches were used for the synthesis of controllers. Speciffically, a H1 approach for multivariable systems was used. Thus, a centralized controller was developed, able to avoid the problem of high coupling between the variables. This advanced approach is also able to use informations about perturbations, uncertainties, noises and different types of input signals in the synthesis stage, leading to controllers with better performance in a large operation bandwidth. In this work, a Mixed Sensitivity approach was employed. This control approach is based on the shapping of well known closed-loop sensitivity functions, seeking to achieve stability and performance robustness. Using a similar technique, a controller with two degree of freedom (2-DOF) was also synthesised, to tackle the guidance problem tracking of 3-D trajectories was then fully achieved. The controllers developed were tested in a number of numerical simulations. Analyses of results reveals the power and flexibility of the employed techniques.

This thesis discusses the use of a cooperative multiple robot system as applied to distributed tracking and sampling of a boundary edge. Within this system the boundary edge is partitioned into subsegments, each allocated to a particular robot such that workload is balanced across the robots. Also, to minimize the time between sampling local areas of the boundary edge, it is desirable to minimize the difference between each robot’s progression (i.e. phase) along its allocated sub segment of the edge. The paper introduces a new distributed controller that handles both workload and phase balancing. Simulation results are used to illustrate the effectiveness of the controller in an Autonomous Underwater Vehicle (AUV) under ice edge sampling application. Successful results from experimentation with three iRobot(R) Creates are also presented.

The objective of the master’s thesis work is to investigate how an autonomous underwater vehicle (AUV) should act in an underwater tunnel environment. The thesis proposes sensors, control strategies, mission statement, among others, required for tunnel assignments. A behavior-based control (BBC) strategy has been developed to control the AUV. The BBC is used in the middle level of the vehicle control, i.e. the reactive control system which describes how the AUV navigates through a tunnel, while other events are considered. The control strategy has also been separated into two parts, and these are: controlling the AUV’s heading and controlling the AUV to a desired distance from the tunnel wall. To be able to evaluate the performance of the system, a graphical user interface (GUI) has been developed. The GUI enables the operator to change control settings during simulations. Two proposed control strategies are presented with simulated results. / Syftet med examensarbetet är att undersöka hur en autonom undervattensfarkost (AUV) bör agera i en undervattenstunnel miljö. Avhandlingen föreslår sensorer, reglerstrategier, uppdragsbeskrivning med mera som krävs för tunneluppdrag. En beteendebaserad (behavior-based) reglerstrategi har utvecklats för att styra AUV:n. Reglerstrategin används i mellersta nivån i farkostens reglering, det vill säga den reaktiva regleringen som beskriver hur farkosten ska styra genom en tunnel samtidigt som andra händelser beaktas. Reglerstrategin har även delats upp i två delar: reglering av AUV:ns kurs och reglering av AUV:n till ett önskat avstånd från tunnelns vägg. För att kunna verifiera funktionaliteten av systemet så har även ett grafiskt användargränssnitt utvecklats. Gränssnittet möjliggör att man kan ändra reglerparametrar under en simulering. Två föreslagna reglerstrategier presenteras med tillhörande resultat.

Adaptive path planning of an autonomous marine vehicle (surface or subsurface) in the role of a communication and navigation aid (CNA) for multiple autonomous underwater vehicles (AUVs) for survey missions is studied. This path planning algorithm can be run before deployment, based on the planned paths of the survey AUVs, or underway, based on information transmitted by the survey AUVs. The planner considers the relative depth of the CNA and survey AUVs (not previously done) allowing the CNA to better aid survey AUVs that maintain a set distance over the ocean floor while surveying. Results are presented from simulations and in-water trials for both pre-deployment and underway planning modes, the latter being preferred since it can adapt to the survey AUV path during the mission. The necessity of bounding the distance between the CNA and any survey AUV in order to bound survey AUV position error is also described.