Sea Technology

DEC 2012

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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The Coastal Glider is prepared for deployment. (Bottom) Naval Undersea Warfare Center scientists retrieve the Coastal Glider offshore Greenland. includes the installation of a dedicated science computer and improved communications and survivability. Glider Components Rated to 200 meters depth, the Coastal Glider is capable of self-ballasting from fresh- to ocean water and has a variable speed capability to handle nearshore currents up to 2 knots. During initial design stages, potential users requested a maximum speed up to 5 knots, but the general consensus was that 2 knots would be suffcient. Buoyancy Engine. The requirement for adaptive ballasting meant that the buoyancy engine (BE) volume be at least 3 percent of the vehicle volume. After the glider's hydrodynamic design was completed, it was determined that a 2 percent variation was needed. Thus, the BE volume of 5 liters represents 5 percent of the vehicle volume. Several types of BE drive mechanisms were investigated. The simplest mechanism for driving the BE is a ballscrew arrangement. Ball screws, however, are subject to being back driven if there is no locking mechanism or locking current. These options would add excessively to the complexity or the power consumption, so the ball drive was eliminated. Alternatively, an Acme drive could have generated the necessary high drive forces without the back-drive issue, but its effciency is very low. For these reasons, a hydraulic system was selected. Hydro-Leduc's (Azerailles, France) Model PB32.5 microhydraulic pump was investigated, as it had been successfully used in profling buoys and other gliders. The best effciency point 34 st / DECEMBER 2012 www.sea-technology.com of this pump occurs at an operating pressure of 34.5 megapascals. This is signifcantly higher than the 2-megapascal water pressure at the maximum depth of 200 meters. A reverse-amplifer BE system was designed so that, at maximum depth, the BE pump operates at the best effciency point. Coupling the pump to a high-effciency DC motor resulted in a BE effciency of 70 percent. Pitch and Roll System. The pitch and roll components were selected such that a single mass (the battery) could be used for both pitch and roll control. This was accomplished by selecting a high-effciency commercial off-the-shelf (COTS) linear actuator for the pitch system with an integral linear potentiometer for position feedback. This actuator was connected to an adaptor plate, which was in turn connected to the battery mass. The linear actuator is equipped with an integral slip clutch to prevent damage in case it is overdriven. The battery mass was designed so the center of gravity of the battery was 2 centimeters below the glider's centerline. The layout of other components was designed so the glider's center of gravity rested on its centerline. The roll actuator is also a COTS DC motor, which is mounted on the adaptor plate and, thus, moves with the battery mass. The roll system is connected

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