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Modelling of Noise Effects of Operational Offshore Wind Turbines - Noise Transmission Through Various Foundation

Types

Dr. Mark-Paul Buckingham

Presentation Outline

Xi Introduction Background Offshore Wind turbine modelling Site specific acoustic propagation

model example (tidal) Q & A

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

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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

Sample Clients

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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

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

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.

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

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

Near-Field Modelling

3D emission signature

Directional structural-acoustic interaction

Simulated characteristics of wind turbine

Frequency-dependent variable excitation

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

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

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

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

Structural Domain Boundary Conditions

Seabed Roller Boundary

Variable Excitation

Bedrock Fixed Constraint

Acoustic Boundary Conditions

Reflective BoundaryCylindrical Wave

Radiation

Structural-Acoustic Interaction

Mesh Optimisation

Interconnecting face mesh optimisation

Mesh element size optimisation

Mesh optimisation for numerical accuracy and computational efficiency

Off-shore foundations

Cavity filled with dense sand

Sediment Layer

Bedrock

Gravity Base Jacket Monopile

Underwater Sound Field – Offshore Wind Foundations

Gravity Base: 200 Hz Jacket: 360 Hz Monopile: 120 Hz

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Sound Pressure Level Results: 15 ms-1

GS 1 GS 2 GS 3

P S P and S

Directional underwater sound field: offshore wind farm

Comparison sound fields for foundation types

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)

Far field models – Wenz curves

Marine species hearing threshold

0.01 0.1 1 10 100 10000

20

40

60

80

100

120

140

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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

Frequency (kHz)

Aud

itory

Thr

esho

ld (d

B re

1 µ

Pa)

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).

Audiograms

Composite Audiograms of mammal species

Off-shore wind turbines

Far field models – ambient contour

Far field models – ambient comparison

Far field models – Minke Hearing Threshold

Far field models – minke response (min)

Far field models – minke response (max)

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.

 

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.

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

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

Acoustic output of turbine

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

Far-field beam trace model

Slice through 3-D sound field

SPL at any point in 3-D sound field

Masking by background noise

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)

0.01 0.10 1.00 10.00 100.00 1000.000

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100

120

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Kastelein,etal,2002 - harbour porpoise (B)Andersen, 1970 - harbour porpoise (B)Popov, et al, 1986 - harbour porpoise (AEP)Composite HP

Frequency (kHz)

Aud

itory

Thr

esho

ld (d

B re

1 µ

Pa)

Audiograms of harbour porpoise

Detect and collision avoidance - porpoise

Detect and collision avoidance - porpoise

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)

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

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

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