Designing a Hybrid Retraction System for a Wave Energy Capture Device
Project Site: Trex Enterprises
Mentor: Ned Davis, Dee Symonds & Michael Engelmann
Ocean waves contain significant energy, and they can provide a more reliable and continuous source of renewable energy than the sun or wind. A wave energy capture (WEC) device has been developed by Trex Enterprises to power ocean-based instruments and sensors. A generator is housed in the WEC device that is suspended just below a buoy and connected by a long cable to an anchor. Upward wave motion actuates the generator by extending the cable between the WEC device and the anchor, but the cable must be retracted during downward wave motion. The original design relied on a passive mechanical spring system, but it could not adjust its response to specific wave periods or heights, and it was also prone to fatigue failure. We have designed an active motorized retraction system that provides a more reliable mechanism and that can respond electronically to a variety of wave heights and periods. A Hall Effect sensor detects the rotation of the main shaft, and a comparator observes the overload on the motor, indicating upward wave motion. Microcontrollers process signals from the sensor and comparator to initiate and stop the retraction motor. A passive spring has been retained in our design to reduce the load on the active retraction motor; the shared load also reduces spring fatigue and improves reliability. We anticipate that testing will reveal a substantial increase in performance and life span of the WEC device when this hybrid retraction system is used, compared to the spring-only design.