Browsing by Author "Gode, Tejaswi"
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- Design and testing of a pneumatically propelled underwater glider for shallow waterWolek, 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.
- Long Basline Ranging Acoustic Positioning SystemGode, Tejaswi (Virginia Tech, 2015-04-30)A long-baseline (LBL) underwater acoustic communication and localization system was developed for the Virginia Tech Underwater Glider (VTUG). Autonomous underwater vehicles, much like terrestrial and aerial robots require an effective positioning system, like GPS to perform a wide variety of guidance, navigation and control operations. Sea and freshwater attenuate electromagnetic waves (sea water is worse due to higher conductivity) within very few meters of striking the water surface. Since radio frequency communications are unavailable, many undersea systems use acoustic communications instead. Underwater acoustic communication is the technique of sending and receiving data below water. Underwater acoustic positioning is the technique of locating an underwater object. Among the various types of acoustic positioning systems, the LBL acoustic positioning method offers the highest accuracy for underwater vehicle navigation. A system consisting of three acoustic 'beacons which are placed on the surface of the water at known locations was developed. Using an acoustic modem to excite an acoustic transducer to send sound waves from an underwater glider, the range measurements to each of the beacons was calculated. These range measurements along with data from the attitude heading and reference system (AHRS) on board the glider were used to estimate the position of the underwater vehicle. Static and dynamic estimators were implemented. The system also allowed for underwater acoustic communication in the form of heartbeat messages from the glider, which were used to monitor the health of the vehicle.