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Abstract-Hydrokinetic turbines, also known as marine current turbines, have the potential to be a major component of the world's renewable energy portfolio. Improving the efficiency of turbines is critical to making this technology more widespread and cost-effective. This work focused on raising power output for a given turbine blade design and flow speed through the addition of a straight-diffusing shroud. A shroud works by lowering pressure at the turbine outlet and thereby accelerating the flow through the turbine. The performance (measured by the power coefficient, CP) of a shrouded horizontal axis hydrokinetic turbine was studied experimentally in a tow tank at the United States Naval Academy. Two different shroud designs were built and tested, and performance was compared to the bare turbine. Both shrouds featured the same diffuser angle (20 0 ) but different area ratios, cross-sectional shapes, and tip gaps. The second shroud design was optimized using numerical flow simulation data, and resulted in a 21% increase in power output compared to the bare turbine. Both shroud designs lowered the stall speed of the turbine and allowed operation at lower tip speed ratios.

The Sensor Hosting Autonomous and Remote Craft (SHARC) Wave Glider system is an autonomous surface vehicle widely used for long-duration at-sea data collection and acoustic monitoring. The system is manufactured by Liquid Robotics Inc. (LRI) and consists of two components (1) a surface float housing sensors, batteries, solar panels, and communication systems, and (2) a submerged propulsor (glider) containing six hinged hydrofoils. A third component, a submerged body housing additional sensors, may be towed behind the propulsor. While system launch is relatively straight forward, recovery of the system is challenging and incurs high risk. Challenges include (1) the Wave Glider system contains multiple components, (2) forward motion of the system cannot easily be arrested, and (3) the ship conducting recovery operations often has a high freeboard. Need for an improved recovery system is desired, particularly for the United States Naval Oceanographic Office (NAVOCEANO), as current recovery methods require personnel in small boats or swimmers in the water to control the vehicle and attach lifting lines. These procedures are hazardous to both personnel and equipment and are limited to low sea states. This project, conducted by a team of five undergraduate students and two advisers, designed and evaluated multiple alternatives as viable recovery solutions. Based on design and operational requirements, the final proposed solution is two-part. The first is a remotely actuated inflatable lift bag attached to the stern of the submerged propulsor that will halt forward movement when inflated; and the second is a vertical cable loop mounted on the surface float to facilitate lifting of the float, propulsor and towed payloads. The proposed solution was demonstrated to be feasible and met all design requirements, with an emphasis on simplicity.

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