Northwest National Marine Renewable Energy Center (NNMREC)
Estimating the Acoustic Impact of a Tidal Energy Project Chris Bassett, Jim Thomson, and Brian Polagye University of Washington Mechanical Engineering 161st Meeting of the Acoustical Society of America Seattle, WA May 24, 2011 NNMREC Tidal Energy Basics Power Technology requires strong currents (> 1 m/s) Power density ~ V3
Siting Clean Current Estuaries Race with Rocks, BC tidal ranges large 3.5 m,shallow ~65 kW (< 80 m) for MCT Relatively Strangford, UK operational reasons 14x2 m, 1200 kW Ideally near load center
Devices early development Cross-flow and horizontal-axis Pile and gravity foundations Generators & gear boxes Verdant Power New York, East River 5 m, 33 kW NNMREC Tidal Energy Technology OpenHydro 6m turbine: Direct-drive permanent magnet generator
Gravity foundation No yaw mechanism Cut-in speed ~ 0.7 m/s OpenHydro 10 m Bay of Fundy Turbine (Source: OpenHydro) NNMREC Site Information Tripod Deployments Proposed pilot project Admiralty Inlet, Washington Primary inlet to Puget Sound Depth ~ 60 m
Urban waterway NNMREC Stationary Hydrophone Measurements Autonomous hydrophone (16 GB capacity) 80 kHz sampling 1% duty cycle for 3 months Records 7 sec. every 10 min. NNMREC
Ambient Noise Significant variability associated with anthropogenic noise (Example spectra) (All data) Ship Bedload Transport Average Conditions Quiet Mean SPL (0.02 30 kHz) 119 dB re 1PaPa
NNMREC Pseudosound Pseudosound due to turbulent pressure fluctuations Recorded above 20 Hz above 0.3 m/s Masks low frequency ambient noise Removed from ambient noise analysis Ongoing work with flow shields NNMREC Estimated Source Level
Broadband SL (0.02 3 kHz): Operating at peak power output (14 rpm) 154 dB per turbine Measurements by the Scottish Association of Marine Sciences (SAMS) (Source: OpenHydro) NNMREC Implication for Received Levels SONAR Equation:
Broadband Levels 0 RL = SL 15log(r) r Broadband SL: Operating at peak power output (14 rpm) 2 turbines Incoherent sources NNMREC Implication for Received Levels
Artificial time series with ambient SPLs and RLs from turbines added in to 70% of recordings. Assume limited spatial variability in ambient noise levels. Broadband Received Levels Calculated for multiple distances assumed to be equidistant from sources Turbine impact is relatively
small except locally NNMREC Comparison to Other Sources Puget Sound urban waterway with many anthropogenic sources NNMREC Conclusion Insufficient source data are currently available Complex environments suitable for tidal energy are difficult to study
Noise impacts will likely be local context is important NNMREC Thank You This material is based upon work supported by the Department of Energy, Snohomish County PUD, the National Science Foundation. Field Engineers Joe Talbert and Alex DeKlerk Captain Andy Reay-Ellers
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