Acoustic Characterization of Wave Energy Converters · 2020. 7. 30. · Sound produced by wave...
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Acoustic Characterization of Wave Energy Converters Brian Polagye and Paul Murphy Department of Mechanical Engineering, University of Washington Acknowledgements The presenters would like to thank the US Department of Energy and NAVFAC for financial support, NWEI and Fred. Olsen for their cooperation with these studies, Sea Engineering for all field operations at WETS, and Jim Thomson for the A-SWIFT precursors and initial Sea Spider. • Scientific Uncertainty Sound produced by wave energy converters may affect marine animals, but the characteristics of these sounds are not well- understood. • Permitting Requirement Acoustic emissions from wave energy converters must not exceed agreed- upon thresholds. Motivations Conclusions and Future Work • Different WEC designs produce distinctly different sounds. • Sounds from individual WECs are unlikely to cause significant environmental harm through acoustic injury. • Next generation of drifters will support acoustic localization through PPS hydrophone synchronization and RTK GPS. • Next generation of bottom packages will support multi- channel hydrophones and be deployed on compliant moorings to minimize and filter flow-noise and self-noise. • Research outcomes are contributing to development of international standards for WEC acoustic characterization. Keith Bethune, Patrick Cross, and Luis Vega Hawai’i Natural Energy Institute, University of Hawai’i Wave Energy Conversion • Wave energy converters (WECs) harness the motion of waves to produce electricity or high-pressure water. • There are over a hundred WEC concepts in active development. • Much like a vessel, multiple mechanisms can produce sound: • Electrical or hydraulic generators/motors, • Mechanical joints, • Mooring systems (e.g., chains, lines), and • Waves breaking over the converter. Study Location: US Navy Wave Energy Test Site WETS Credit: Google Earth • The US Navy Wave Energy Test Site (WETS) is the first grid-connected wave energy test site in the United States. Construction and operations are supported by the DOD Naval Facilities Engineering Command. • Located on the windward side of Oahu within the boundaries of Marine Corps Base Hawai’i. • Moderate wave climate characterized by measurement and modeling. 30 m berth 60 m berth 80 m berth Methods A - SWIFT Drifters Sea Spider Lander Challenges • Masking: Flow-noise, self- noise, and other ambient sources • Temporal duration: Characterize WEC sound over most sea states (>6 months) • Spatial extent: WEC sound may be directional and ensonified area changes with environmental conditions Results: Azura Results: Lifesaver Flow - noise Reduction • Deep-draft point absorber with hydraulic generator (submerged) at 30 m berth developed by Northwest Energy Innovations (US) • Operating at WETS since June 2015 • Characteristic generator tones • Shallow-draft point absorber with rotary generators (top side) at 60 m berth developed by Fred. Olsen (Norway) • Operating at WETS since March 2016 • Broadband acoustic signature Periodogram (A-SWIFT) Spatial Variability (A-SWIFT) Periodogram (A-SWIFT) Spatial Variation (A-SWIFT) Temporal Variation (Sea Spider) as function of significant wave height (H s ) and energy period (T e ) Platform Comparison Met Station GPS OceanSonics icListen HF 1.2 m IMU • Easy to deploy and recover • Fast identification of WEC sound • Enables spatial mapping • Enables persistent observations A-SWIFTs and Waverider at WETS Loggerhead DSG-ST (x3) Unshielded Foam annulus effective, but attenuates f > 1 kHz Foam Thin Plastic f affected by Flow-noise Co-temporal and Co-spatial A-SWIFT flow-noise A-SWIFT self-noise A-SWIFT self-noise A-SWIFT flow-noise WEC and Mooring Bubble Collapse from Breaking Waves A-SWIFT flow-noise A-SWIFT self-noise Generator Tones Distant Mooring Snapping Shrimp Generator Tones Mooring Chain Mechanical “Boom”
Transcript of Acoustic Characterization of Wave Energy Converters · 2020. 7. 30. · Sound produced by wave...
Acoustic Characterization of Wave Energy Converters
Brian Polagye and Paul MurphyDepartment of Mechanical Engineering, University of Washington
AcknowledgementsThe presenters would like to thank the US Department of Energy and NAVFAC for financial support, NWEI and Fred. Olsen for their cooperation with these studies, Sea Engineering for all field operations at WETS, and Jim Thomson for the A-SWIFT precursors and initial Sea Spider.
• Scientific Uncertainty Sound produced by wave energy converters may affect marine animals, but the characteristics of these sounds are not well-understood.
• Permitting RequirementAcoustic emissions from wave energy converters must not exceed agreed-upon thresholds.
Motivations
Conclusions and Future Work• Different WEC designs produce distinctly different sounds.• Sounds from individual WECs are unlikely to cause significant
environmental harm through acoustic injury.• Next generation of drifters will support acoustic localization
through PPS hydrophone synchronization and RTK GPS.• Next generation of bottom packages will support multi-
channel hydrophones and be deployed on compliant moorings to minimize and filter flow-noise and self-noise.
• Research outcomes are contributing to development of international standards for WEC acoustic characterization.
Keith Bethune, Patrick Cross, and Luis VegaHawai’i Natural Energy Institute, University of Hawai’i
Wave Energy Conversion• Wave energy converters (WECs) harness
the motion of waves to produce electricity or high-pressure water.
• There are over a hundred WEC concepts in active development.
• Much like a vessel, multiple mechanisms can produce sound:• Electrical or hydraulic generators/motors,• Mechanical joints,• Mooring systems (e.g., chains, lines), and• Waves breaking over the converter.
Study Location: US Navy Wave Energy Test Site
WETS
Credit: Google Earth
• The US Navy Wave Energy Test Site (WETS) is the first grid-connected wave energy test site in the United States. Construction and operations are supported by the DOD Naval Facilities Engineering Command.
• Located on the windward side of Oahu within the boundaries of Marine Corps Base Hawai’i.
• Moderate wave climate characterized by measurement and modeling.
30 m berth
60 m berth
80 m berth
Methods
A-SWIFT Drifters
Sea Spider Lander
Challenges• Masking: Flow-noise, self-
noise, and other ambient sources
• Temporal duration: Characterize WEC sound over most sea states (>6 months)
• Spatial extent: WEC sound may be directional and ensonified area changes with environmental conditions
Results: Azura
Results: Lifesaver
Flow-noise Reduction
• Deep-draft point absorber with hydraulic generator (submerged) at 30 m berth developed by Northwest Energy Innovations (US)
• Operating at WETS since June 2015• Characteristic generator tones
• Shallow-draft point absorber with rotary generators (top side) at 60 m berth developed by Fred. Olsen (Norway)
• Operating at WETS since March 2016• Broadband acoustic signature
Periodogram (A-SWIFT)Spatial Variability (A-SWIFT)
Periodogram (A-SWIFT)Spatial Variation (A-SWIFT)
Temporal Variation (Sea Spider) as function of significant wave height
(Hs) and energy period (Te)
Platform Comparison
Met Station
GPS
OceanSonics icListen HF
1.2
m
IMU
• Easy to deploy and recover
• Fast identification of WEC sound
• Enables spatial mapping
• Enables persistent observations
A-SWIFTs and Waverider at WETS
Loggerhead DSG-ST (x3)
Unshielded
Foam annulus effective, but attenuates f > 1 kHz
Foam Thin Plastic
f affected by Flow-noise
Co-temporal and Co-spatial
A-SWIFT flow-noise
A-SWIFT self-noise
A-SWIFT self-noise
A-SWIFT flow-noise
WEC and Mooring
Bubble Collapse from Breaking Waves
A-SWIFT flow-noise
A-SWIFT self-noise
Generator Tones
Distant Mooring
Snapping Shrimp
Generator Tones Mooring
Chain
Mechanical “Boom”
