Underwater gliders are highly efficient, winged autonomous underwater vehicles that propel themselves by modifying their buoyancy and their center of mass. The center of mass is controlled by a set of servo-actuators which move one or more internal masses relative to the vehicle's frame. Underwater gliders are so efficient because they spend most of their time in stable, steady motion, expending control energy only when changing their equilibrium state. Motion control thus reduces to varying the parameters (buoyancy and center of mass) that affect the state of steady motion. These parameters are conventionally controlled through feedback, in response to measured errors in the state of motion, but one may also incorporate a feedforward component to speed convergence and improve performance. In this dissertation, first an approximate analytical expression for steady turning motion is derived by applying regular perturbation theory to a realistic vehicle model to develop a better understanding of underwater glider maneuverability, particularly with regard to turning motions. The analytical result, though approximate, is quite valuable because it gives better insight into the effect of parameters on vehicle motion and stability. Using these steady turn solutions, including the special case of wings level glides, one may construct feasible paths for the gliders to follow. Because the turning motion results are only approximate, however, and to compensate for model and environmental uncertainty, one must incorporate feedback to ensure convergent path following. This dissertation describes the development and numerical implementation of a feedforward/feedback motion control system intended to enhance locomotive efficiency by reducing the energy expended for guidance and control. It also presents analysis of the designed control system using slowly varying systems theory. The results provide (conservative) bounds on the rate at which the reference command (the desired state of motion) may be varied while still guaranteeing stability of the closed-loop system. Since the motion control system more effectively achieves and maintains steady motions, it is intrinsically efficient. The proposed control system enables speed, flight path angle, and turn rate, providing a mechanism for path following. The next step is to implement a guidance strategy, together with a path planning strategy, and one which continues to exploit the natural efficiency of this class of vehicle. The structure of the approximate solution for steady turning motion is such that, to first order in turn rate, the glider's horizontal component of motion matches that of "Dubins' car," a kinematic car with bounded turn rates. Dubins car is a classic example in the study of time-optimal control for mobile robots. For an underwater glider, one can relate time optimality to energy optimality. Specifically, for an underwater glider travelling at a constant speed and maximum flight efficiency (i.e., maximum lift-to-drag ratio), minimum time paths are minimum energy paths. Hence, energy-efficient paths can be obtained by generating sequences of steady wings-level and turning motions. These efficient paths can, in turn, be followed using the motion control system developed in this work. / Ph. D.

Underwater gliders are robust and long endurance ocean sampling platforms that are increasingly being deployed in coastal regions. This new environment is characterized by shallow waters and significant currents that can challenge the mobility of these efficient (but traditionally slow moving) vehicles. This dissertation aims to improve the performance of shallow water underwater gliders through path planning. The path planning problem is formulated for a dynamic particle (or "kinematic car") model. The objective is to identify the path which satisfies specified boundary conditions and minimizes a particular cost. Several cost functions are considered. The problem is addressed using optimal control theory. The length scales of interest for path planning are within a few turn radii. First, an approach is developed for planning minimum-time paths, for a fixed speed glider, that are sub-optimal but are guaranteed to be feasible in the presence of unknown time-varying currents. Next the minimum-time problem for a glider with speed controls, that may vary between the stall speed and the maximum speed, is solved. Last, optimal paths that minimize change in depth (equivalently, maximize range) are investigated. Recognizing that path planning alone cannot overcome all of the challenges associated with significant currents and shallow waters, the design of a novel underwater glider with improved capabilities is explored. A glider with a pneumatic buoyancy engine (allowing large, rapid buoyancy changes) and a cylindrical moving mass mechanism (generating large pitch and roll moments) is designed, manufactured, and tested to demonstrate potential improvements in speed and maneuverability. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. / Microfiche copy available in Archives and Barker. / Vita. / Includes bibliographical references. / by Marc Jeffrey Zeitlin. / M.S.

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains viii, 59 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 51-52).

Thesis (Master of Engineering in Mechanical Engineering)--Cape Peninsula University of Technology, 2018. / Underwater glider wings are the lifting surfaces of unmanned underwater vehicles UUVs depending on the chosen aerofoil sections. The efficiency as well as the performance of an underwater glider mostly depends on the hydrodynamic characteristics such as lift, drag, lift to drag ratio, etc of the wings. Among other factors, the geometric properties of the glider wing are also crucial to underwater glider performance. This study presents an opportunity for the numerical investigation to improve the hydrodynamic performance by incorporating curvature at the trailing edge of a wing as oppose to the standard straight or sharp trailing edge. A CAD model with straight leading edge and trailing edge was prepared with NACA 0016 using SolidWorks 2017. The operating conditions were setup such that the inlet speed varies from 0.1 to 0.5 m/s representing a Reynolds number 27.8 x 10ᵌ and 53 x 10ᵌ. The static pressure at different angles of attack (AOA) which varies from 2 to 16degrees at the increment of 2degrees for three turbulent models (K-Ԑ-standard, K-Ԑ-RNG and K-Ԑ-Realizable), was computed for upper and lower surfaces of the modified wing model using ANSYS Fluent 18.1. Thereafter the static pressure distribution, lift coefficient, drag coefficient, lift to drag ratio and pressure coefficient for both upper and lower surfaces were analysed. The findings showed that the lift and drag coefficient are influenced by the AOA and the inlet speed. If these parameters change the performance of the underwater glider changes as depicted by figure 5.6 and figure 5.7. The hydrodynamics of the underwater glider wing is optimized using the Cʟ/Cᴅ ratio as function of the operating conditions (AOA and the inlet speed). The investigation showed that the optimal design point of the AOA of 12 degrees and a corresponding inlet speed of 0.26m/s. The critical AOA matched with the optimal design point AOA of 12 degrees. It was also observed that Cp varies across the wing span. The results showed the Cp is higher closer to the fuselage while decreasing towards the mid-span and at the tip of the wing. This showed that the wing experiences more stress close to the fuselage than the rest of the wing span which implies that a higher structural rigidity is required close to the fuselage. The results of the drag and lift curves correspond to the wing characteristics typical observed for this type of aerofoil.

Recent efforts in understanding the variability inherent in coastal and offshore waters have highlighted the need for higher resolution sampling at finer spatial and temporal resolutions. Gliders are increasingly used in these transitional waters due to their ability to provide these finer resolution data sets in areas where satellite coverage may be poor, ship-based surveys may be impractical, and important processes may occur below the surface. Since no single instrument platform provides coverage across all needed spatial and temporal scales, Ocean Observation systems are using multiple types of instrument platforms for data collection. However, this results in increasingly large volumes of data that need to be processed and analyzed and there is no current “best practice” methodology for combining these instrument platforms. In this study, high resolution glider data, High Frequency Radar (HFR), and satellite-derived data products (MERRA_2 and ARMOR3D NRT Eddy Tracking) were used to quantify: 1) dominant scales of variability of the central Red Sea, 2) determine the minimum sampling frequency required to adequately characterize the central Red Sea, 3) discriminate whether the fine scale persistency of oceanographic variables determined from the glider data are comparable to those identified using HFR and satellite-derived data products, and 4) determine additional descriptive information regarding eddy occurrence and strength in the Red Sea from 2018-2019. Both Integral Time Scale and Characteristic Length Scale analysis show that the persistence time frame from glider data for temperature, salinity, chlorophyll-α, and dissolved oxygen is 2-4 weeks and that these temporal scales match for HFR and MERRA_2 data, matching a similar description of a ”weather-band” level of temporal variability. Additionally, the description of eddy activity in the Red Sea also supports this 2-4-week time frame, with the average duration of cyclonic and anticyclonic eddies from 2018-2019 being 22 and 27 days, respectively. Adoption of scale-based methods across multiple ocean observation areas can help define “best practice” methodologies for combining glider, HFR, and satellite-derived data to better understand the naturally occurring variability and improve resource allocation.

The gliding petaurids are small sized arboreal and nocturnal marsupials restricted to Australia and the New Guinean region. They have suffered range contractions since European settlement, and most of the species are of conservation concern, either nationally or at a state level. This study applied molecular approaches to investigate several questions involving Petaurus species which may provide valuable insights for their conservation and management of species. The objectives of this study included an examination of phylogenetic and evolutionary relationships among Petaurus species, an assessment of phylogeographic structure within P. breviceps and an investigation of genetic diversity, social structure and mating system of P. breviceps in fragmented habitats. A broad molecular systematics study of the genus Petaurus was first undertaken. Two mitochondrial genes (ND2 and ND4) and a nuclear gene marker (ω-globin) were screened for sequence variation in samples obtained from across the distribution of petaurid species, including Australia, New Guinea and its surrounding islands. Phylogenetic analyses confirmed the monophyly of the genus Petaurus and revealed that, with the exception of P. gracilis, the currently recognised species were associated with divergent mtDNA clades. It also revealed considerable mtDNA diversity within the widely distributed species P. breviceps. The existence of at least seven distinct and divergent mtDNA lineages within P. breviceps was supported, with two lineages located in Australia and at least five lineages in New Guinea. However, the distribution of these evolutionary lineages did not correspond with current morphological subspecies boundaries. Analyses of ω-globin sequence provided support for a number of these distinct populations, suggesting the possible presence of cryptic species within P. breviceps. Molecular analyses also suggested that squirrel gliders, P. norfolcensis, may occur in both South Australia and the Northern Territory, extending the current known range of the species. The presence of P. norfolcensis in SA was further verified by examining museum skins. Population structure and current pattern of gene flow within P. breviceps in Australia was examined further to elucidate phylogeographic structure within the species, and explore potential causes of geographic variation. Evidence for significant phylogeographic structuring across the range of the species in Australia was provided from population genetic (AMOVA) and phylogenetic analyses of both mitochondrial DNA and the ω-globin gene. In particular, there was evidence for the existence of two divergent clades that were distributed over distinct geographical regions. Divergence dates calculated for the two major mtDNA clades suggested that environment and climate changes which occurred during the Pliocene may have facilitated this diversification. Habitat fragmentation is generally considered to be a major factor threatening the viability of forest dependent species such as gliders. Effects of habitat fragmentation were therefore investigated in P. breviceps in the highly disturbed landscape of southeastern South Australia. Genetic mating system and social structure of the species in these fragmented habitats was explored in 13 populations, using nine polymorphic microsatellite loci. Social groups consisted of two to seven gliders, and these were often close relatives, including parents with their offspring. Parentage analyses provided some evidence for a polygamous mating system, with a number of males found to have fathered offspring from multiple female partners. Some direct evidence of inbreeding was also found within a small isolated patch. Genetic diversity within P. breviceps populations was moderate compared to the range reported in other marsupial species. Population structure analyses indicated that gene flow between some patches was restricted. Small patches surrounded by a matrix of pine were more likely to show inbreeding and potentially suffer from inbreeding depression, although further data are required to verify this result. Overall, results suggest that, although the species is still present in these small and isolated patches, it may face threats from a lack of dispersal and inbreeding. Maintaining the size of patches and establishing corridors between isolated populations needs to be considered in conservation and management of species in these fragmented habitats. / http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1295224 / Thesis (Ph.D.) -- School of Earth and Enviromental Sciences, 2007

This paper details a method to compute absolute water velocity profiles from glider-based acoustic Doppler current profiler (ADCP) measurements based on the "shear method" developed for lowered ADCPs. The instrument is a 614-kHz Teledyne RDI ADCP integrated into the body of a Teledyne Webb Research Slocum Glider. Shear is calculated from velocity measurements and averaged over depth intervals to create a dive-averaged shear profile. Absolute velocities are computed by vertically integrating shear profiles yielding relative velocity profiles and then referencing them to dive-average velocity measurements calculated from glider dead-reckoning and GPS. Bottom-track referenced velocities also provide absolute velocities when bottom-tracking is available, and can be applied to relative velocities, producing absolute velocity profiles through linear fitting. Data quality control is based on ADCP percent good measurements. Compass heading bias corrections are applied to the raw ADCP measurements before averaging shear profiles. Comparison between simultaneous, full-water column velocities referenced to dive-average currents and those referenced to bottom-track profiles, resulted in RMS error values of 0.05 m s⁻¹ for both north and east components. During open ocean deployments, the glider ADCP recorded velocities concurrent and proximate to vessel ADCP measurements in waters of similar thermal characteristics. The combined comparison analysis resulted in RMS error values ranging 0.08-0.31 m s⁻¹ and 0.06-0.21 m s⁻¹ for north and east components, respectively. / Graduation date: 2013

Thesis (M.S.)--University of Tennessee, Knoxville, 2004. / Title from title page screen (viewed Sept. 27, 2004). Thesis advisor: R.B. Richards. Document formatted into pages (xi, 83 p. : ill. (some col.)). Vita. Includes bibliographical references (p. 63-65).

The objective of this research is to investigate the techniques and payoffs of integrated aircraft design. Lifting line theory and beam theory are used for the analysis of the aerodynamics and the structures of a composite sailplane wing. The wing is described by 33 - 34 design variables which involve the planform geometry, the twist distribution, and thicknesses of the spar caps, spar webs, and the skin at various stations along the wing. The wing design must satisfy 30 â 31 aeroelastic, structural, aerodynamic, and performance constraints. Two design procedures are investigated. The first, referred to as the iterative, sequential procedure, involves optimizing the aerodynamic design for maximum average cross-country speed at E1 constant structural weight, and then optimizing the the structural design of the resulting wing geometry for minimum weight. This value is then used in another aerodynamic optimization, and the process continues iteratively until the weight converges. The other procedure, the integrated one, simultaneously optimizes the aerodynamic and the structural design variables for either maximum average cross-country speed or minimum weight. The integrated procedure was able to improve the value of the objective function obtained by the iterative procedure in all cases. This shows The objective of this research is to investigate the techniques and payoffs of integrated aircraft design. Lifting line theory and beam theory are used for the analysis of the aerodynamics and the structures of a composite sailplane wing. The wing is described by 33 - 34 design variables which involve the planform geometry, the twist distribution, and thicknesses of the spar caps, spar webs, and the skin at various stations along the wing. The wing design must satisfy 30 â 31 aeroelastic, structural, aerodynamic, and performance constraints. Two design procedures are investigated. The first, referred to as the iterative, sequential procedure, involves optimizing the aerodynamic design for maximum average cross-country speed at E1 constant structural weight, and then optimizing the the structural design of the resulting wing geometry for minimum weight. This value is then used in another aerodynamic optimization, and the process continues iteratively until the weight converges. The other procedure, the integrated one, simultaneously optimizes the aerodynamic and the structural design variables for either maximum average cross-country speed or minimum weight. The integrated procedure was able to improve the value of the objective function obtained by the iterative procedure in all cases. This shows that definite benefits can be gained from taking advantage of aerodynamic/structural interactions during the design process. / Master of Science