Xi Engineering Consultants will share their expertise in this field and discuss their latest research on the noise effects of operational offshore wind turbines on marine species that commonly occur in the Irish Sea.

1. Modelling of Noise Effects of Operational Offshore Wind
Turbines - Noise Transmission Through Various
Foundation Types
1
Dr. Mark-Paul Buckingham

2. Presentation Outline
 Xi Introduction
 Background
 Offshore Wind turbine modelling
 Site specific acoustic propagation
model example (tidal)
 Q & A

3. 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:
 Offshore and Onshore wind
 Tidal stream turbines
 Superconductor industries
 Health and occupational safety
 Residential planning and construction
 Military

4. What We Do & Why
Expert in the Science of Vibration:
 Survey
 Analysis & Diagnosis
 Design Validation
 System Modelling
 Solution Implementation
 Commission & Test
 Operational Service & Monitor
Our Client concerns:
 Environmental Impact
 Performance degradation
 Structural fatigue
 Groundborne vibration
 Health & Safety noise
 Industrial process reliability
4

5. Sample Clients

6. Applications in Marine Renewable Energy
• Holistic system modelling for
improved reliability
• Minimise device costs
• Minimise O&M requirements
• Design of condition monitoring
systems
• Test data analysis & diagnosis
• Acoustic predictions for EIA
- Installation & operation
• Mitigation for tonal emissions
OFFSHORE WIND
TIDAL ENERGY CONVERTERS
WAVE ENERGY CONVERTERS
INSTALLATION NOISE
6

7. Introduction
 Operational noise from marine renewables energy devices affects the marine
environment
 Operational noise is of concern to regulatory bodies involved in the consent of
renewable energy devices with respect to its impact on marine species.
 Collision avoidance
 Behavioural response
 Injury
 Impact on other sectors that use the marine environment, e.g. military

8. Introduction
 There is little information to allow estimates of their operational noise once they in the
marine environment
 We use the dynamics of turbines to model their acoustic output providing information to
marine biologists and regulatory bodies
 The acoustic output can also be used by manufactures and developers to optimise their
devices and array layouts.

9. Structure of the Marine Scotland project
1. Noise sources in turbines
2. Near-field FEM model of a generic
turbine
3. Far-field beam trace model of an array
of turbines
4. Use of far-field model output
5. Assessment against Key species

10. Noise Impacts
The key potential impacts of operational turbine noise on marine species are:
 Disturbance or physiological effects as a result of underwater noise arising
from operational offshore wind turbines.
 Potential longer term avoidance of the development area by marine mammals
 Potential reduction of the feeding resource due to the effects of
noise, vibration, and habitat disturbance on important prey species

11. Near-Field Modelling
 3D emission signature
 Directional structural-
acoustic interaction
 Simulated characteristics of
wind turbine
 Frequency-dependent
variable excitation

12. Tower Geometry
 REPower 6MW
 Rotor Diameter 126 m
 Tower Height 75 m
 Total of 29 independent tower
pieces and three tower angles
 Nacelle drive train components
 Transmission Ratio 1:97

13. Acoustic Domain
 Cylindrical domain for radial
spreading
 50 m depth for jacket and gravity
base
 30 m depth for monopile
 Domain radius of 40 m
 Surface probe for SPL calculation
Surface Probe

14. Noise Source – Drive train and its geometry
 Rotational imbalances
 Blade pass
 Gear meshing in gearbox
 External grid
 Electromagnetic effects
between poles and stators in
the generator

15. Vibration drivers – rotation dependent
 Gear meshing
 Three stage gear box
 Include multiples of gear-
meshing (harmonics)
 Correct geometry position
and orientation of
excitation forces
 Vibration pathway include
isolation mounts

16. Structural Domain Boundary Conditions
Seabed Roller
Boundary
Variable Excitation
Bedrock Fixed
Constraint

17. Acoustic Boundary Conditions
Reflective
BoundaryCylindrical Wave
Radiation
Structural-Acoustic
Interaction

18. Mesh Optimisation
 Interconnecting face mesh
optimisation
 Mesh element size optimisation
 Mesh optimisation for numerical accuracy and computational efficiency

19. Off-shore foundations
Cavity filled with
dense sand
Sediment
Layer
Bedrock
Gravity Base Jacket Monopile

20. Underwater Sound Field – Offshore Wind Foundations
Gravity Base: 200 Hz Jacket: 360 Hz Monopile: 120 Hz

21. Sound Pressure Level Results: 15 ms-1
GS 1 GS 2 GS 3
P S P and S
21

22. Directional underwater sound field: offshore
wind farm

23. Comparison sound fields for foundation types

24. Masking by background noise
 Compare modelled sound field to
background noise
 Site measurement
 Scottish Association of Marine
Science (Dr Ben Wilson)
 Loughborough University (Dr
Paul Lepper)
 Wenz curve sea state 6 and
shallow water (Wenz 1962)

25. Far field models – Wenz curves

26. Marine species hearing threshold
0
20
40
60
80
100
120
140
160
180
0.01 0.1 1 10 100
AuditoryThreshold(dBre1µPa)
Frequency (kHz)
Grey seal - Ridgeway & Joyce
(1975) (AEP)
Harbour seal (composite from Gotz
and Janik, 2010)
Harp seal (Terhune &
Ronald, 1972) (B)
Harbour seal (Kastelein, et
al., 2009) (B)
Composite seal

27. Audiograms
Audiograms of fish: eels based on Jenko, et al. (1989), shad based on
Mann, et al. (2001), Atlantic salmon based on Hawkins and Myrberg (1983)
and sea trout based on Horodysky, et al. (2008).

28. Audiograms
Composite Audiograms of mammal species

29. Off-shore wind turbines

30. Far field models – ambient contour

31. Far field models – ambient comparison

32. Far field models – Minke Hearing Threshold

33. Far field models – minke response (min)

34. Far field models – minke response (max)

35. Conclusions
 Wind turbines founded on monopiles emit high noise into the marine
environment at low frequency (<500 Hz). Monopiles are ~10 dB louder than
equivalent gravity bases and ~50 dB louder than equivalent jackets at low
frequency.
 At high frequencies (>500 Hz) jackets emit higher noise levels than gravity
bases or monopiles. However, the sound pressure level produced by all three
foundation types at high frequency is close to or below the ambient background
noise.
 The SPL emitted by all three foundation types during normal operation is not
sufficient to cause chronic injury unless particularly sensitive species, such as
porpoise, remained within 10s of meters of a foundation for over an hour.
 Noise levels from operating windfarms are likely to be audible to marine
mammals, particularly under scenarios where wind speeds increase.

36. Conclusions
 Jacket foundations appear to generate the lowest marine mammal impact
ranges when compared to gravity and monopile foundations.
 Low-frequency specialists minke whales are most likely to be affected and are
predicted to respond to the wind farm out to ranges of up to ~18 km.
 Seal species (harbour and grey) and bottlenose dolphins were not considered
to be at risk of displacement from the operational turbines.
 The predicted onset PTS ranges indicate that it is unlikely that any of the
marine mammal species considered would experience auditory injury as a
result of operational wind farm noise.
 Atlantic salmon and European eels can detect monopiles at greater ranges
than gravity bases, while they do not sense jackets in the far-field. Shad and
sea trout do not sense any of the foundation types in the far-field.

37. Far-field model of a tidal turbine array
 Hypothetical array between
Colonsay and Jura off the
west coast of Scotland
 An array of 6 generic 1MW
tidal turbines

38. Near-field FEM of a generic 1 MW turbine
 Gear-meshing at:
 25 Hz
 150 Hz
 700 Hz
 The model has a two way
coupling between surface
acceleration and acoustic
pressure
 The variation in pressure and
sound pressure level outside
the turbine can therefore be
calculated

39. Acoustic output of turbine

40. Far-field beam trace model
 Use the SPL from the near-
field model as a source term in
a beam trace model
 Gaussian beam trace model
AcTUP, produced by CMST at
Curtin University, Australia.
 Model radial vertical sections
from each turbine and compile
in Matlab
 Each radial section uses a
source term relative to the
same radial position in the
near-field model

41. Far-field beam trace model

42. Slice through 3-D sound field

43. SPL at any point in 3-D sound field

44. Masking by background noise

45. Hearing threshold of marine species
 Compare modelled sound
field to audiograms of
marine species
 Determine range that marine
species can detect turbine
and avoid collision
 Sea Mammal Research Unit
Ltd, St Andrew University
(Dr Cormac Booth, Dr
Stephanie King)
0
20
40
60
80
100
120
140
0.01 0.10 1.00 10.00 100.00
AuditoryThreshold(dBre1µPa)
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

46. Detect and collision avoidance - porpoise

47. Detect and collision avoidance - porpoise

48. Potential behaviour response and injury
 Determine 3-D m-weighted
sound field (Southall et al.
2007)
 Behavioural response
 Use to calculate SEL and
possibility of injury
 Harbour and grey seal
 75 Hz to 75 kHz (Southall
et al. 2007)

49. Other uses
 Array layout optimisation:
 Avoid acoustic barriers
 Optimisation of turbine design to
avoid problematic tones
 Frequency matching
 Information for other marine
sectors and stakeholders

50. Conclusion
 Three dimension sound field modelled using
a combination of near-field FEM and far-field
beam trace models
 Estimate the acoustic output of production-
models before they are installed in arrays
 Comparison to ambient noise measurements
and audiograms
 Provides developers, marine scientist and
consenting bodies with information to allow
the safe installation of tidal turbine arrays

51. Further Details & Contact
If you’d like to discuss any aspects of this presentation in greater detail, please
contact us:
Dr Mark-Paul Buckingham Xi Engineering Consultants Ltd
152 Morrison Street
Email: mp@xiengineering.com Edinburgh
Tel.: 0131 247 7580 EH3 8EB