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Estimating the Acoustic Impact of a Tidal Energy Project
Chris Bassett, Jim Thomson, and Brian PolagyeUniversity of Washington
Mechanical Engineering
161st Meeting of the Acoustical Society of AmericaSeattle, WA May 24, 2011
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Tidal Energy Basics
Power Technology requires strong currents (> 1 m/s) Power density ~ V3
Siting Estuaries with large tidal ranges Relatively shallow (< 80 m) for
operational reasons Ideally near load center
Devices – early development Cross-flow and horizontal-axis Pile and gravity foundations Generators & gear boxes
MCTStrangford, UK14x2 m, 1200 kW
Clean CurrentRace Rocks, BC3.5 m, ~65 kW
Verdant PowerNew York, East River5 m, 33 kW
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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)
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Site Information
Tripod Deployments
Proposed pilot project Admiralty Inlet, Washington
Primary inlet to Puget Sound
Depth ~ 60 m
Urban waterway
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Stationary Hydrophone Measurements
Autonomous hydrophone (16 GB capacity)
80 kHz sampling 1% duty cycle for 3 months Records 7 sec. every 10 min.
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Ambient Noise
Mean SPL (0.02 – 30 kHz) 119 dB re 1μPa
Significant variability associated with anthropogenic noise
(Example spectra) (All data)
Bedload Transport
Ship
AverageConditions
Quiet
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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
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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)
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Implication for Received Levels
Broadband Levels SONAR Equation:
RL = SL – 15log(r) – α r
0
Broadband SL: Operating at peak
power output (14 rpm) 2 turbines Incoherent sources
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Implication for Received Levels
Broadband 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.
Calculated for multiple distances assumed to be equidistant from sources
Turbine impact is relatively small except locally
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Comparison to Other Sources Puget Sound urban waterway with many anthropogenic sources
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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
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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