The focus of this thesis is to implement factor graphs into the problem of detection, classification, and localization (DCL) of underwater objects using active SOund Navigation And Ranging (SONAR). A factor graph is a bipartite graphical representation of the decomposition of a particular function. Messages are passed along the edges connecting factor and variable nodes, on which, a message passing algorithm is applied to compute the posterior probabilities at a particular node. This thesis addresses two issues. In the first section, the formulation of factor graphs for each section of the DCL chain required followed by their closed-form solutions. For the detector, the factor graph determines if the signal is a detection or simply noise. In the classifier, it outputs the probability for the elements in the class. Last, when using a factor graph for the tracker, it gives the estimated state of the object being tracked. The second part concentrates on the application to Continuous Active SONAR (CAS). When using CAS, a bistatic configuration is used allowing for a more rapid update rate where two unmanned underwater vehicles (UUVs) are used as the receiver and transmitter. The goal is to evaluate CAS's effectiveness to determine if the tracking accuracy improves as the transmit interval decreases. If CAS proves to be more efficient in target tracking, the next objective is to determine which messages sent between the two UUVs are most beneficial. To test this, a particle filter simulation is used. / Master of Science

Miniature Autonomous Underwater Vehicles are a major area of research and development today. Because of their size and agility, they are capable of exploring and operating in smaller bodies of water in addition to areas of the ocean that would be out of reach for a larger vehicle. Being autonomous requires that the system must be capable of performing without the need for human supervision, so use of external sensors such as sonar are needed to ensure the safety of the vehicle during missions. However, since all of the onboard instrumentation and external equipment must also be miniature in size, the implementation of a small sonar system is desirable. This thesis contains a brief introduction to sound and sonar, leading into a description of the design and development of a small, inexpensive sonar altimeter. Piezoelectric material is used for transduction in the sonar system while a PIC microcontroller processes the return signals from the water. This altimeter was made to be implemented on a miniature autonomous underwater vehicle developed by the Autonomous Systems and Controls Laboratory at Virginia Polytechnic Institute. In addition to being capable of reporting ocean depths, sonar systems can be used to aid in the navigation of underwater vehicles. A constant altitude controller based on sonar data has been designed, tested, and implemented on the autonomous underwater vehicle. Possibilities for an obstacle avoidance system involving sonar are also discussed in this thesis. / 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

Autonomous underwater vehicles (AUVs) play a vital role in the surveillance and mapping of our oceans, often requiring extensive travel in extreme environments. These data-gathering missions benefit from extended durations, making the minimization of power consumption a key consideration in AUV design. One effective strategy to reduce energy use in AUVs is to implement a variable buoyancy system (VBS) for depth control. The purpose of this work is to design, develop, test, and model a variable buoyancy system to enhance the efficiency and capabilities of a high-speed, long-range AUV. After evaluating various VBS designs, a piston-cylinder buoyancy system was selected and developed. A prototype was produced, featuring two manually controlled piston-cylinder units housed within a cylindrical acrylic shell. This setup was tested at shallow depths, successfully demonstrating the VBS’s ability to achieve depth control and its potential for additional functionalities such as orientation control. A Simulink model of the system was also created to simulate its performance. The results from these simulations were compared to both theoretical calculations and experimental data. This model is then used to establish a framework for the design of a depth controller for the VBS once integrated onto an AUV.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: This thesis presents the design process of the movement control and guidance systems for an automated underwater vehicle (AUV) constructed by the Institute of Maritime Technology in Simon’s Town. The full non-linear mathematical model and simulation environment for the AUV were previously developed in [1]. The design process in this thesis covers an analysis of existing test data and the performance of the current systems in place on the AUV, derivation and analysis of the linear model for the AUV, design of upgraded control and guidance systems, analysis of the new designs including simulation results, practical implementation of the new designs and the results thereof. Over the course of this project a number of flaws were identified in the original control designs and other aspects of the AUV. Most notably, the capability of the AUV is limited owing to its construction, and the current control and guidance methods result in poor movement characteristics. The new control designs are executed through multiple SISO feedback loops, with the most complicated controllers consisting of proportional and integral control. A completely new guidance method was designed which grants theAUVthe ability to track both straight line and circular path segments with no steady state error. These designs were tested in simulation, with results showing good tracking performance, even in the presence of output disturbances. The new designs were implemented on the physical AUV, but testing was limited, with poor results being obtained. The poor test results were caused primarily by the construction of the AUV. / AFRIKAANSE OPSOMMING: Hierdie tesis stel die ontwerpsproses voor vir die bewegingsbeheer- en navigasiestelsels vir ’n outonome duikboot wat gebou is deur die Instituut vir Maritieme Tegnologie in Simonstad. Die volle nie-lineˆere wiskundige model en simulasieomgewing vir die duikboot is voorheen ontwikkel in [1]. Die ontwerpsproses in hierdie tesis behels ’n analise van bestaande toetsdata en van die werksverrigting van die stelsels wat tans op die duikboot ge¨ınstalleer is, die afleiding en analise van ’n lineˆere model vir die duikboot, die ontwerp van verbeterde beheer- en navigasiestelsels, die analise van die nuwe ontwerpe, wat simulasieresultate insluit, die praktiese implementering van die nuwe ontwerpe, en die resultate daarvan. Deur die loop van die projek is ’n aantal tekortkominge ge¨ıdentifiseer in die oorspronklike beheerstelselontwerpe en ander aspekte van die duikboot. Die mees beduidende tekortkominge is dat die vermo¨e van die duikboot beperk word deur die konstruksie daarvan, en dat die huidige beheer- en navigasietegnieke swak bewegingseienskappe lewer. Die nuwe beheerstelselontwerpe is uitgevoer deur ’n aantal enkelintree, enkeluittree terugvoerlusse, waar die mees komplekse beheerders bestaan uit proporsionele en integraalbeheer. ’n Heeltemal nuwe navigasiemetode is ontwerp, wat die duikboot in staat stel om beide reguit lyne en sirkulˆere padsegmente te volg sonder ’n stasionˆere volgfout. Hierdie ontwerpe is getoets in simulasie, waar die resultate goeie volging getoon het, selfs in die teenwoordigheid van uittreeversteurings. Die nuwe ontwerpe is ge¨ımplementeer op die fisiese duikboot, maar beperkte toetse is gedoen, en het swak resultate gelewer. Die swak toetsresultate was hoofsaaklik as gevolg van die konstruksie van die duikboot.

The interest for marine research and exploration has increased rapidly during the past decades and autonomous underwater vehicles (AUV) have been found useful in an increased amount of applications. The demand for versatile platform AUVs, able to perform a wide range of tasks, has become apparent. A vital part of an AUV is its motion control system, and an emerging problem for multipurpose AUVs is that the control performance is affected when the vehicle is configured with different payloads for each mission. Instead of having to manually re-tune the control system between missions, a method for automatic tuning of the control system has been developed in this master’s thesis. A model-based approach was implemented, where the current vehicle dynamics are identified by performing a sequence of excitation maneuvers, generating informative data. The data is used to estimate model parameters in predetermined model structures, and model-based control design is then used to determine an appropriate tuning of the control system. The performance and potential of the suggested approach were evaluated in simulation examples which show that improved control can be obtained by using the developed auto-tuning method. The results are considered to be sufficiently promising to justify implementation and further testing on a real AUV. The automatic tuning process is performed prior to a mission and is meant to compensate for dynamic changes introduced between separate missions. However, the AUV dynamics might also change during a mission which requires an adaptive control system. By using the developed automatic tuning process as foundation, the first steps towards an indirect adaptive control approach have been suggested. Also, the AUV which was studied in the thesis composed another interesting control problem by being overactuated in yaw control, this because yawing could be achieved by using rudders but also by differential drive of the propellers. As an additional and separate part of the thesis, an approach for using both techniques simultaneously have been proposed.

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

Esta tese apresenta um procedimento de identificação experimental de coeficientes hidrodinâmicos de veículos submarinos não tripulados. Apresenta-se o desenvolvimento de uma plataforma experimental para pesquisas em dinâmica, controle e navegação de veículos submarinos. A plataforma experimental inclui: 1) um veículo submarino não tripulado semi-autônomo do tipo estrutura-aberta chamado de LAURS, 2) um sistema multissensorial e multipropulsores para o controle de movimento, e 3) software e arquitetura de controle para a aquisição de dados dos sensores e o controle de movimento. A fim de deduzir as equações do movimento dinâmico do LAURS, apresenta-se a formulação geral das equações hidrodinâmicas não lineares de um veículo submarino com seis graus de liberdade. A partir destas equações gerais acopladas, são deduzidos modelos mais simples para um grau de liberdade (movimento unidirecional) e três graus de liberdade (movimento planar) do veículo. O método de estimação de parâmetros utilizado neste trabalho não requer medidas de aceleração e é baseado na aplicação da técnica dos mínimos quadrados à forma integral das equações dinâmicas do sistema. O procedimento de identificação proposto é baseado na informação dos sensores embarcados. Primeiramente, os coeficientes de arrasto são obtidos a partir de testes de velocidade constante e depois, fixando os coeficientes de arrasto do modelo matemático com estes valores obtidos, são identificados a inércia virtual e os coeficientes de acoplamento a partir de testes de velocidade variável. Nos testes de velocidade variável são aplicadas entradas de força do tipo senoidal. Apresentam-se os valores dos coeficientes hidrodinâmicos para os movimentos de avanço, deriva, arfagem, guinada e caturro do veículo, os quais foram obtidos usando o procedimento de identificação proposto. O desempenho dos modelos dinâmicos identificados é quantitativamente comparado ao movimento do veículo observado experimentalmente. Para o caso dos testes de velocidade constante em avanço e arfagem, foi feita uma comparação dos valores dos coeficientes obtidos usando a abordagem de identificação de sistemas com os dados obtidos a partir dos ensaios de reboque em tanque de provas. Os resultados obtidos validam o procedimento de identificação proposto. Além disso, são apresentados os resultados experimentais obtidos a partir de manobras do tipo zig-zag e é feita uma discussão da identificabilidade de coeficientes de modelos acoplados. Conclui-se que o procedimento de identificação proposto é eficaz na obtenção de valores reais (consistentes com a concepção física do veículo) para os coeficientes hidrodinâmicos de veículos submarinos. A fim de modelar a força hidrodinâmica que atua no veículo em avanço com movimento oscilatório e amplitudes menores do que um comprimento característico, são apresentados os resultados dos ensaios de oscilação forçada usando um mecanismo de movimento planar (MMP). Apresentam-se os valores dos coeficientes de arrasto e de inércia obtidos a partir dos ensaios em avanço no MMP para diferentes números de Keulegan-Carpenter. Os resultados mostram que os coeficientes de arrasto e de inércia para a faixa de velocidades de 0,1 até 0,8m/s dependem fortemente do número de Keulegan-Carpenter e não do número de Reynolds. A partir destes resultados, conclui-se que a amplitude da oscilação do veículo é o principal fator que causa a variação dos coeficientes hidrodinâmicos e não a velocidade do veículo. / In this work, a procedure for experimental identification of hydrodynamic coefficients of unmanned underwater vehicles is presented. At first, the development of a testbed for research on dynamics, control, and navigation of underwater vehicles is presented. This experimental platform includes: 1) a open-frame semi-autonomous unmanned underwater vehicle named LAURS, 2) a multi-sensorial and multi-thruster system for motion control, and 3) software and control architecture for sensor data logging and motion control. In order to derive the LAURS dynamic motion equations, the general formulation of the nonlinear hydrodynamic equations of motion of an underwater vehicle with six degree of freedom is initially presented. From these general coupled equations, simpler formulations with one (unidirectional movement) and three degrees of freedom (planar movement) are derived. The parameter estimation method does not require acceleration measurements and is based on the application of the least squares technique to the integral form of the system dynamic equations. The identification procedure is based on on-board sensor data. First the drag coefficients are obtained from constant velocity tests and afterwards, fixing the drag coefficients in the mathematical model with the obtained values, virtual inertia and coupling coefficients of the vehicle are identified from variable velocity tests. In the tests of variable velocity, sinusoidal force inputs are applied. Values of hydrodynamic coefficients for surge, sway, heave, yaw, and pitch motions are estimated using the proposed identification procedure. Performance of the identified dynamic models is quantitatively compared to the experimentally observed vehicle motion. In the case of constant velocity tests, for the surge and heave motions, comparisons of the hydrodynamic drag coefficient values obtained using the system identification method with data obtained from towing tank tests are presented. Obtained results corroborate for the feasibility of the proposed identification method. Moreover, experimental results obtained from zig-zag maneuvers are presented and the identifiability of coupled dynamic models is discussed. It is possible to conclude that using the proposed method actual hydrodynamic parameters might be estimated. In order to model the hydrodynamic force that acts on the vehicle, in surge motion, with oscillatory movements and with amplitudes that are smaller than or equal to the characteristic length of the LAURS, results of forced oscillation tests in a planar motion mechanism (PMM) are presented. The drag and inertia coefficient values obtained from surge motion tests in the PMM for different Keulegan-Carpenter numbers are presented and discussed. Results illustrates that drag and inertia coefficients, when the vehicle velocity is in the range of 0,1 and 0,8m/s, do not strongly depend on the Reynolds number, however, they are strongly dependent on the Keulegan-Carpenter number. In this context, we can conclude that the oscillation amplitude is the main factor that causes the variation of hydrodynamic coefficients and not the vehicle velocity.

O planeta Terra tem aproximadamente três quartos submersos em água, ainda assim, estima-se que somente são conhecidos 5% dos mares e oceanos. Nas últimas décadas, os AUVs (Autonomous Underwater Vehicles) se converteram em uma ferramenta útil para a exploração dos oceanos por levar a bordo vários equipamentos com um relativo baixo custo de operação. A parte estrutural dos AUVs, usualmente cascas cilíndricas, tem sido estudada. De modo geral, os objetivos desses estudos visam a manter a rigidez e deixar a estrutura mais leve, sob o critério de resistência a flambagem. A falha por flambagem, normalmente, ocorre antes da falha por resistência do material em cascas devido à sua geometria e à influência de imperfeições iniciais. Uma forma de aumentar a rigidez das cascas é o uso de enrijecedores, os quais geralmente são soldados à casca. No entanto, o uso desses enrijecedores em um veículo de pequeno porte diminui o espaço utilizados por diferentes dispositivos e instrumentos do veículo, além de resultar em possíveis inconvenientes na fabricação, tais como aumento do custo e produção de tensões residuais relativas aos processos de soldagem. Portanto, alternativas ao enrijecedor convencional devem ser buscadas para esse tipo de veículo. É possível substituir os enrijecedores convencionais por uma estrutura interna ao vaso de pressão e comum em submersíveis, a prateleira de acomodação da eletrônica. Essa estrutura, chamada aqui de enrijecedores deslizantes, possui cavernas circunferenciais que podem fornecer rigidez à casca e evitar os inconvenientes de redução de volume e de fabricação que os enrijecedores convencionais trazem. No entanto, tal substituição para o aumento de rigidez ainda não foi analisada. Portanto, neste trabalho se propõe analisar o comportamento do enrijecedor deslizante quando utilizado em substituição ao enrijecedor convencional, considerando que ambos fornecem resistência à compressão embora não apresentem as mesmas restrições de graus de liberdade. A análise é feita através de métodos analíticos e numéricos, tipicamente utilizados no estudo de enrijecedores convencionais. / The planet Earth has about three quarters of water, yet it is estimated that only 5% of the seas and oceans are known. In the last decades, the AUVs have become useful tools for the exploration of the oceans by carrying on board several equipment with a relative low cost of operation. The structural part of the AUV\'s, usually cylindrical shells, has been studied as well. In general, the objectives of these studies are to maintain rigidity and to leave the structure lighter, under the criterion of buckling resistance. The buckling failure occurs prior to failure by yielding due to its geometry and the influence of initial shell imperfections. One way to increase the stiffness of the shells is to use stiffeners, which are usually welded to the shell. However, the use of these stiffeners in a small vehicle reduces the space used for different devices and instruments of the vehicle, in addition there are manufacturing drawbacks as residual stresses related to the welding processes. Therefore, alternatives to the conventional stiffener should be sought for this type of vehicle. It is possible to replace conventional stiffeners by an internal structure to the pressure vessel and common in submersibles, the shelf of accommodation of the electronics. This structure, referred to here as sliding stiffeners, has circumferential frame bulkheads that can provide stiffness to the shell and avoid the drawbacks of volume reduction and fabrication that conventional stiffeners bring. However, such substitution for increased rigidity has not yet been analyzed. Therefore, in this work it is proposed to analyze the behavior of the sliding stiffeners when used in substitution of the conventional stiffeners, considering that both provide compressive strength although they do not present the same restrictions of degrees of freedom. The analysis is done by analytical and numerical methods, typical of conventional stiffeners.