Abstract
The Fred. Olsen Lifesaver, a point-absorber wave energy converter, was deployed at the US Navy Wave Energy Test Site in Kaneohe, HI (USA) from March 2016 to April 2017. A combination of free-drifting and stationary measurements were used to characterize its acoustic signature over a range of sea states. Comparisons are made between co-spatial and cotemporal observations that investigate temporal trends and identify sound originating from the test area. Initial free-drifting surveys suggested limited sound originating from the Lifesaver, but relatively high-amplitude, episodic sound originating from the mooring system. Because these observations were contaminated with flow-noise and self-noise, a refinement to compliantly couple the drifting hydrophone to its surface expression was implemented, providing good agreement with stationary observations. During a subsequent survey, sound from the power take-off could be identified, as well as a damaged bearing producing a characteristic warble. Such observations reinforce the ability of acoustic monitoring to provide condition health monitoring for marine energy systems. The episodic nature of sound around the Lifesaver motivates future classification algorithm development to discriminate between sound produced by the wave energy converter and sound produced by the other sources (e.g., moorings, marine mammals).