Browsing by Author "Wolek, Artur"

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    Design and testing of a pneumatically propelled underwater glider for shallow water
    Wolek, Artur; Gode, Tejaswi; Woolsey, Craig A.; Quenzer, Jake; Morgansen, Kristi A. (Virginia Center for Autonomous Systems, 2015-10-28)
    This report details the design and testing of a pneumatically propelled underwater glider. The vehicle was designed as a platform for motion control experimentation, and to explore the use of novel actuator designs to improve performance in shallow water and significant currents. The glider’s pneumatic buoyancy engine is capable of rapidly inflating an elastomeric bladder to 5 liters. (This displacement is an order of magnitude greater than that of legacy buoyancy engine designs.) The buoyancy engine was shown to operate reliably at 25 m depth. However, the compressibility of the bladder and associated change in tank weight (from exhausting air with each dive) presented significant challenges in trimming the vehicle. The attitude of the glider is controlled by translating and rotating a semi-annular mass. Because of the geometry of this mechanism, the glider is not restricted to a range of roll attitudes (i.e. the glider has unlimited roll authority and can “flip over”). By flipping over the glider may employ asymmetric hydrodynamic surfaces while preserving the same flow-relative geometry during both descents and ascents. Such asymmetric hydrodynamic surfaces (e.g. cambered hydrofoils, dihedral, wing twist) may be used to improve efficiency and performance. The ability to operate in both upright and inverted orientations requires reducing the contribution of the rigid body (minus the moving mass) to the bottom heaviness of the vehicle. A moving acoustic long-baseline ranging system was developed to position the glider while it was underway. The performance of this system was characterized experimentally in terms of ping success rate for various transducer geometries and depths in a shallow-water, rocky bottom lake.
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    Optimal Paths in Gliding Flight
    Wolek, Artur (Virginia Tech, 2015-05-28)
    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.