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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