This thesis explores the feasibility of using morphing rudders in autonomous underwater vehicles (AUVs) to improve their performance in complex current environments. The modeling vehicle in this work corresponds to the Florida Atlantic University's Ocean EXplorer (OEX) AUV. The AUV nonlinear dynamic model is limited to the horizontal plane and includes the effect of ocean current. The main contribution of this thesis is the use of active rudders to successfully achieve path keeping and station keeping of an AUV under the influence of unsteady current force. A constant ocean current superimposed with a sinusoidal component is considered. The vehicle's response is analyzed for a range of current frequencies. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

Thesis: Ph. D. in Mechanical and Oceanographic Engineering, Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 117-135). / A fundamental problem in autonomous underwater robotics is the high latency between the capture of image data and the time at which operators are able to gain a visual understanding of the survey environment. Typical missions can generate imagery at rates hundreds of times greater than highly compressed images can be transmitted acoustically, delaying that understanding until after the vehicle has been recovered and the data analyzed. While automated classification algorithms can lessen the burden on human annotators after a mission, most are too computationally expensive or lack the robustness to run in situ on a vehicle. Fast algorithms designed for mission-time performance could lessen the latency of understanding by producing low-bandwidth semantic maps of the survey area that can then be telemetered back to operators during a mission. This thesis presents a lightweight framework for processing imagery in real time aboard a robotic vehicle. We begin with a review of pre-processing techniques for correcting illumination and attenuation artifacts in underwater images, presenting our own approach based on multi-sensor fusion and a strong physical model. Next, we construct a novel image pyramid structure that can reduce the complexity necessary to compute features across multiple scales by an order of magnitude and recommend features which are fast to compute and invariant to underwater artifacts. Finally, we implement our framework on real underwater datasets and demonstrate how it can be used to select summary images for the purpose of creating low-bandwidth semantic maps capable of being transmitted acoustically. / by Jeffrey W. Kaeli. / Ph. D. in Mechanical and Oceanographic Engineering

Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2005. / Includes bibliographical references (leaves 78-79). / The initial water impact of a free-falling object is primarily related to the fluid forces on the wetted surface of the object. The shape-dependent added-mass coefficients express the fluid forces integrated over the body, and thus physically represent the additional inertia of water accelerated with the body. The field of hydrodynamic impact has been primarily concerned with estimating the added-mass coefficients of various types of bodies for different water impact types, such as seaplane landings, torpedo drops, and ship slamming. In this study, a numerical model has been constructed to estimate the hydrodynamic impact loads of a REMUS dropped in free-fall from a helicopter in a low hover. Developed by von Alt and associates at Woods Hole Oceanographic Institution, the REMUS (Remote Environmental Monitoring UnitS) is a small, man-portable, torpedo shaped Autonomous Underwater Vehicle (AUV) that is normally operated from small boats for a variety of scientific, industrial, and military applications. Finite-element method software and computer aided drafting tools were used to create a simplified model of REMUS without fins, propeller, or transducers. / (cont.) This axisymmetric REMUS model was cut by a flat free surface at various pitch angles and submergence values, and a panel mesh of the wetted surface of the vehicle was created using an automatic mesh generator. Surface boundary conditions are enforced for the free surface by reflecting the body panels using the method of images. Each panel mesh was evaluated for its added- mass characteristics using a source collocation panel method developed by Dr. Yonghwan Kim, formerly of the Vortical Flow Research Laboratory (VFRL) at the Massachusetts Institute of Technology. Experimental impact tests were conducted with a specially-instrumented test vehicle to verify the initial impact accelerations. / by Stephen Michael Roe. / S.M.

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2015. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. Vita. / Includes bibliographical references (pages 203-213). / The capabilities of autonomous underwater vehicles (AUVs) and their ability to perform tasks both autonomously and adaptively are rapidly improving, and the desire to quickly and efficiently sample the ocean environment as Earth's climate changes and natural disasters occur has increased significantly in the last decade. As such, this thesis proposes to develop a method for single and multiple AUVs to collaborate autonomously underwater while autonomously adapting their motion to changes in their local environments, allowing them to sample and track various features of interest with greater efficiency and synopticity than previously possible with preplanned AUV or ship-based surveys. This concept is demonstrated to work in field testing on multiple occasions: with a single AUV autonomously and adaptively tracking the depth range of a thermocline or acousticline, and with two AUVs coordinating their motion to collect a data set in which internal waves could be detected. This research is then taken to the next level by exploring the problem of adaptively and autonomously tracking spatiotemporally dynamic underwater fronts and plumes using individual and autonomously collaborating AUVs. / by Stephanie Marie Petillo. / Ph. D.

Thesis: M.S., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1979 / Bibliography: leaves 38-39. / by Michio Takahashi. / M.S. / M.S. Massachusetts Institute of Technology, Department of Mechanical Engineering

Thesis: Ph. D., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 153-156). / One of the long term goals of Autonomous Underwater Vehicle (AUV) minehunting is to have multiple inexpensive AUVs in a harbor autonomously classify hazards. Existing acoustic methods for target classification using AUV-based sensing, such as sidescan and synthetic aperture sonar, require an expensive payload on each outfitted vehicle and expert image interpretation. This thesis proposes a vehicle payload and machine learning classification methodology using bistatic angle dependence of target scattering amplitudes between a fixed acoustic source and target for lower cost-per-vehicle sensing and onboard, fully autonomous classification. The contributions of this thesis include the collection of novel high-quality bistatic data sets around spherical and cylindrical targets in situ during the BayEx'14 and Massachusetts Bay 2014 scattering experiments and the development of a machine learning methodology for classifying target shape and estimating orientation using bistatic amplitude data collected by an AUV. To achieve the high quality, densely sampled 3D bistatic scattering data required by this research, vehicle broadside sampling behaviors and an acoustic payload with precision timed data acquisition were developed. Classification was successfully demonstrated for spherical versus cylindrical targets using bistatic scattered field data collected by the AUV Unicorn as a part of the BayEx'14 scattering experiment and compared to simulated scattering models. The same machine learning methodology was applied to the estimation of orientation of aspect-dependent targets, and was demonstrated by training a model on data from simulation then successfully estimating the orientations of a steel pipe in the Massachusetts Bay 2014 experiment. The final models produced from real and simulated data sets were used for classification and parameter estimation of simulated targets in real time in the LAMSS MOOS-IvP simulation environment. / by Erin Marie Fischell. / Ph. D.

Thesis (S.M.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 111-112). / Over the past 20 years, underwater vehicle technology has undergone drastic improvements, and vehicles are quickly gaining popularity as a tool for numerous oceanographic tasks. Systems used on the vehicle to alter buoyancy, or variable buoyancy (VB) systems, have seen only minor improvements during the same time period. Though current VB systems are extremely robust, their lack of performance has become a hinderance to the advancement of vehicle capabilities. This thesis first explores the current status of VB systems, then creates a model of each system to determine performance. Second, in order to quantitatively compare fundamentally different VB systems, two metrics, [beta]m and [beta]vol, are developed and applied to current systems. By determining the ratio of performance to size, these metrics give engineers a tool to aid VB system development. Finally, the fundamental challenges in developing more advanced VB systems are explored, and a couple of technologies are investigated for their potential use in new systems. / by Harold Franklin Jensen III. / S.M.

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Sonars are used extensively for underwater sensing and recent advances in forward-looking imaging sonar have made this type of sonar an appropriate choice for use on Autonomous Underwater Vehicles. The images received from these sonar do however, tend to be noisy and when used in shallow water contain strong bottom reflections that obscure returns from actual targets. The focus of this work was the investigation and development of post-processing techniques to enable the successful use of the sonar images for automated navigation. The use of standard image processing techniques for noise reduction and background estimation, were evaluated on sonar images with varying amounts of noise, as well as on a set of images taken from an AUV in a harbour. The use of multiple background removal and noise reduction techniques on a single image was also investigated. To this end a performance measure was developed, based on the dynamic range found in the image and the uniformity of returned targets. This provided a means to quantitatively compare sets of post-processing techniques and identify the “optimal” processing. The resultant images showed great improvement in the visibility of target areas and the proposed techniques can significantly improve the chances of correct target extraction. / AFRIKAANSE OPSOMMING: Sonars word algemeen gebruik as onderwater sensors. Onlangse ontwikkelings in vooruit-kykende sonars, maak hierdie tipe sonar ’n goeie keuse vir die gebruik op ’n Outomatiese Onderwater Voertuig. Die beelde wat ontvang word vanaf hierdie sonar neig om egter raserig te wees, en wanneer dit in vlak water gebruik word toon dit sterk bodemrefleksies, wat die weerkaatsings van regte teikens verduister. Die fokus van die werk was die ondersoek en ontwikkeling van naverwerkings tegnieke, wat die sonar beelde bruikbaar maak vir outomatiese navigasie. Die gebruik van standaard beeldverwerkingstegnieke vir ruis-onderdrukking en agtergrond beraming, is geëvalueer aan die hand van sonar beelde met verskillende hoeveelhede ruis, asook aan die hand van ’n stel beelde wat in ’n hawe geneem is. Verdere ondersoek is ingestel na die gebruik van meer as een agtergrond beramings en ruis onderdrukking tegniek op ’n enkele beeld. Hierdie het gelei tot die ontwikkeling van ’n maatstaf vir werkverrigting van toegepaste tegnieke. Hierdie maatstaf gee ’n kwantitatiewe waardering van die verbetering op die oorspronklike beeld, en is gebaseer op die verbetering in dinamiese bereik in die beeld en die uniformiteit van die teiken se weerkaatsing. Hierdie maatstaf is gebruik vir die vergelyking van verskeie tegnieke, en identifisering van die “optimale” verwerking. Die verwerkte beelde het ’n groot verbetering getoon in die sigbaarheid van teikens, en die voorgestelde tegnieke kan ’n betekenisvolle bedrae lewer tot die suksesvolle identifisering van obstruksies.

O presente trabalho vem propor um estudo numérico qualitativo de um modelo hidro-elástico para simulação das vibrações induzidas por vórtices (VIV) em cabos submersos. O modelo é composto de um sistema acoplado de equações que descrevem tanto a estrutura quanto o fluido. A estrutura é modelada através de um oscilador elástico clássico e discretizada através de um método de massas concentradas. O fluido é considerado através de osciladores discretos baseados em modelos fenomenológicos com equação de Van der Pol ou Ginzburg-Landau. O acoplamento entre os dois ocorre na direção transversal ao escoamento local através da força de sustentação. O estudo foi feito para verificar quais tipos de comportamentos de resposta podem ser obtidos através do uso dos modelos fenomenológicos e, também, avaliar o potencial de tais modelos no ciclo de projeto na indústria atual, com foco na indústria petrolífera. Esta adequabilidade ao uso em projeto leva em conta, em primeiro lugar, a qualidade das respostas, mas também leva em conta a viabilidade da execução de simulações numéricas em tempo apropriado. Assim, um modelo numérico foi desenvolvido para permitir a integração, no domínio do tempo, deste sistema hidro- elástico. Esta integração é feita através de um método explícito de Euler e permite tratar não-linearidades dos osciladores elástico e fluido. Um conjunto de situações foi simulado numericamente, incluindo configurações verticais e também configurações em catenária. As simulações indicam alto grau de acoplamento entre os osciladores, o que leva a ressonância entre ambos na maior parte dos casos. Com relação ao comportamento do oscilador estrutural em si, foi possível observar fenômenos interessantes tais como lock-in e travelling waves, além do terceiro harmônico da vibração transversal detectado em alguns experimentos reportados em literatura. Com relação à adequabilidade do uso do modelo em projeto, considera-se que isto seja possível dada a relativa rapidez das simulações e aos resultados promissores que ainda podem ser melhorados. / The present work proposes a qualitative numerical study of a hydro-elastic model in order to simulate vortex-induced vibrations in submerged cables. The model is composed of a coupled system of equations describing the structure and the fluid. The structure is modeled through a classical elastic oscillator and discretized using a lumped mass approach. The fluid is modeled through discrete oscillators based on phenomenological models using Van der Pol or Ginzburg- Landau type equations. The coupling between these two oscillators is carried by the lift force. The study was carried in order to verify which response behavior can be obtained by using such phenomenological models and also, to evaluate their potential to be used in the offshore industry. In order to accomplish that, the model must provide reliable answers and must allow fast responses when it comes to simulation time. In this sense, a numerical model was developed to allow the time domain integration of this hydro-elastic model. The numerical integration is performed by a simple explicit Euler algorithm and allows dealing with non-linearities of both oscillators, elastic and fluid. A set of conditions was numerically simulated, including top tensioned risers and catenary. Simulations indicate a high level of coupling between the two oscillators and thus resonance is achieved in most part of the cases. With respect to the structural oscillator analysis, it was possible to observe interesting phenomena such as lock-in, travelling waves and also the third harmonic observed in some experiments and reported in the literature. Regarding the feasibility of the model usage in the daily offshore industry life, it seems possible once the model generally runs fast and some promising results were achieved.

O presente trabalho vem propor um estudo numérico qualitativo de um modelo hidro-elástico para simulação das vibrações induzidas por vórtices (VIV) em cabos submersos. O modelo é composto de um sistema acoplado de equações que descrevem tanto a estrutura quanto o fluido. A estrutura é modelada através de um oscilador elástico clássico e discretizada através de um método de massas concentradas. O fluido é considerado através de osciladores discretos baseados em modelos fenomenológicos com equação de Van der Pol ou Ginzburg-Landau. O acoplamento entre os dois ocorre na direção transversal ao escoamento local através da força de sustentação. O estudo foi feito para verificar quais tipos de comportamentos de resposta podem ser obtidos através do uso dos modelos fenomenológicos e, também, avaliar o potencial de tais modelos no ciclo de projeto na indústria atual, com foco na indústria petrolífera. Esta adequabilidade ao uso em projeto leva em conta, em primeiro lugar, a qualidade das respostas, mas também leva em conta a viabilidade da execução de simulações numéricas em tempo apropriado. Assim, um modelo numérico foi desenvolvido para permitir a integração, no domínio do tempo, deste sistema hidro- elástico. Esta integração é feita através de um método explícito de Euler e permite tratar não-linearidades dos osciladores elástico e fluido. Um conjunto de situações foi simulado numericamente, incluindo configurações verticais e também configurações em catenária. As simulações indicam alto grau de acoplamento entre os osciladores, o que leva a ressonância entre ambos na maior parte dos casos. Com relação ao comportamento do oscilador estrutural em si, foi possível observar fenômenos interessantes tais como lock-in e travelling waves, além do terceiro harmônico da vibração transversal detectado em alguns experimentos reportados em literatura. Com relação à adequabilidade do uso do modelo em projeto, considera-se que isto seja possível dada a relativa rapidez das simulações e aos resultados promissores que ainda podem ser melhorados. / The present work proposes a qualitative numerical study of a hydro-elastic model in order to simulate vortex-induced vibrations in submerged cables. The model is composed of a coupled system of equations describing the structure and the fluid. The structure is modeled through a classical elastic oscillator and discretized using a lumped mass approach. The fluid is modeled through discrete oscillators based on phenomenological models using Van der Pol or Ginzburg- Landau type equations. The coupling between these two oscillators is carried by the lift force. The study was carried in order to verify which response behavior can be obtained by using such phenomenological models and also, to evaluate their potential to be used in the offshore industry. In order to accomplish that, the model must provide reliable answers and must allow fast responses when it comes to simulation time. In this sense, a numerical model was developed to allow the time domain integration of this hydro-elastic model. The numerical integration is performed by a simple explicit Euler algorithm and allows dealing with non-linearities of both oscillators, elastic and fluid. A set of conditions was numerically simulated, including top tensioned risers and catenary. Simulations indicate a high level of coupling between the two oscillators and thus resonance is achieved in most part of the cases. With respect to the structural oscillator analysis, it was possible to observe interesting phenomena such as lock-in, travelling waves and also the third harmonic observed in some experiments and reported in the literature. Regarding the feasibility of the model usage in the daily offshore industry life, it seems possible once the model generally runs fast and some promising results were achieved.