Noise from offshore wind turbines and effects on the ...
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Noise from offshore wind turbines and
effects on the marine environment Dr. Brett Marmo and Dr Iain Roberts
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Introduction
Offshore wind farms produce noise that enters the marine
environment.
This noise can be heard by marine species and it may affect
their behaviour
Marine Scotland are the regulatory authority for building wind
farms in Scottish waters and must consider their
environmental impact
Turbines are placed on a variety of foundations – how does
this affect noise output and environmental impact?
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Xi Engineering Consultants
Xi are based in Edinburgh and have clients
throughout Europe and North America
Our focus is vibration. We have provided vibration
solutions to many sectors including:
Onshore wind and tidal stream turbines
Oil and gas
Superconductor industries
Health and occupational safety
Residential planning and construction
Military
Xi are COMSOL Certified Consultants
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Modelling strategy
Model vibration using coupled solid-shell
domains in the structural mechanics
module
The foundation is surrounded by an
acoustic domain which is coupled to the
structural domain.
The COMSOL model gives the near-field
sound-field
Use the near-field as a source-term in a
gausian beam trace model to extrapolate
to the far field
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Foundation types
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Noise Source – Drive train
Rotational imbalances
Blade pass
Gear meshing in gearbox
External grid
Electromagnetic effects
between poles and stators in
the generator
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Vibration drivers – rotation dependent
Gear meshing
Three stage gear box
Gear meshing at:
25 Hz
80 Hz
360 Hz
Include multiples of gear-
meshing (harmonics)
Correct geometry
position and orientation
of excitation forces
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Off-shore foundations
Cavity filled with dense sand
Sediment Layer
Bedrock
Gravity Base Jacket Monopile
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Sound Pressure Level Results
Gravity Base: 200 Hz Jacket: 360 Hz Monopile: 120 Hz
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Far field models – horizontal section
Use near-field results as
source term in ray trace
model
Model vertical sections at
different angular positions
Collate results to produce
a wind farm of 16 turbines
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Far field models – vertical section
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Comparison of foundation types
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Foundation type and species hearing threshold
0
20
40
60
80
100
120
140
160
180
0.01 0.1 1 10 100 1000
Au
dit
ory
Th
resh
old
(d
B r
e 1
µP
a)
Frequency (kHz)
Grey seal - Ridgeway & Joyce(1975) (AEP)
Harbour seal (composite fromGotz and Janik, 2010)
Harp seal (Terhune & Ronald,1972) (B)
Harbour seal (Kastelein, et al.,2009) (B)
Composite seal
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How far away can a seal hear the wind farm
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Hearing threshold of marine species
0
20
40
60
80
100
120
140
0.01 0.10 1.00 10.00 100.00 1000.00
Au
dit
ory
Th
resh
old
(d
B r
e 1
µP
a)
Frequency (kHz)
Kastelein,etal,2002 -harbour porpoise (B)
Andersen, 1970 -harbour porpoise (B)
Popov, et al, 1986 -harbour porpoise (AEP)
Composite HP
Audiograms of harbour porpoise
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How far away can a porpoise hear the wind
farm
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Conclusion
The modelling approach provided information on how
foundations affect the environment
It is not possible to measure this directly in the field
This information is helping inform government policy on the
installation of offshore wind farms
The noise produced by wind farms was found to be within the
hearing of marine mammals but at a level too low to cause
harm