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Influence of wind coherence on the response of a floating wind turbine Marte Godvik, Statoil Research & Technology

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Page 1: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Influence of wind coherence on the response of a floating wind turbine Marte Godvik, Statoil – Research & Technology

Page 2: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Background I

Hywind development

• Hywind Demo – Karmøy:

− 1 turbine of 2.3MW with rotor diameter of 82m

• Hywind Scotland project:

− 5 turbines of 6MW with rotor diameter of 154m

• Future large commercial parks of multi-MW turbines

• New challenges:

− Wind farm wakes

− Large rotor diameter

• Acceptable yaw motions vs acceptable mooring line tensions

2

=> increased yaw motions

Page 3: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Courtesy of Vattenfall Wind Power

Background II

Wind models

3

• Wind models for simulation and calculation of loads are given by

the wind industry standards:

− Small vs large rotors

− Fixed vs floating turbines

Page 4: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Simulation of loads and responses

Turbulent wind and wake models

• Turbulent wind models:

− Kaimal spectrum and exponential coherence model (TurbSim):

• Spectral densities and coherence explicitely given

− Mann model (DTU Mann64 generator):

• Three-dimensional velocity spectral tensor and coherence tensor

• Wake models:

− Effective turbulence:

• Scales the ambient turbulence according to park configuration

− Dynamic Wake Meandering (DWM) models (Hawc2):

• Wakes, superimposed on free turbulent wind, consist of

wind speed deficit, meandering and microscopic turbulence

4

Courtesy DTU

Courtesy DTU

Page 5: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Simulation of loads and responses

Ex: Hywind with large rotor

5

• SIMA tool:

− Simulation and Engineering Analysis of Marine Operations and

Floating Systems with wind turbine module

− Fully integrated model comprising turbine, tower, substructure,

mooring and controller

• Wind boxes are pre-generated

Page 6: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Ex: Hywind with large rotor

TI and wind models on mooring fatigue

6

Mann

ambient TI

DWM wake

Kaimal

effective TI

Relative fatigue life

[-]

2.5

1.9

1.9

• Relative fatigue life of mooring configuration for the floater in different wind models

(maximum values over lines and bridles):

1. Fatigue life of the mooring configuration is quite sensitive on TI level

2. DWM model yields higher fatigue life than effective TI (NB! Mann model)

3. Kaimal model yields higher fatigue life than Mann model

𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝑓𝑎𝑡𝑖𝑔𝑢𝑒 𝑙𝑖𝑓𝑒 =

𝐹𝑎𝑡𝑖𝑔𝑢𝑒 𝑙𝑖𝑓𝑒 𝑖𝑛 𝑋

𝐹𝑎𝑡𝑖𝑔𝑢𝑒 𝑙𝑖𝑓𝑒 𝑖𝑛 𝑀𝑎𝑛𝑛 𝑒𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑇𝐼

Page 7: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Ex: Hywind with large rotor

Wind coherence on response

7

The different models co-spectrum of points across a large rotor differ for low frequencies

Tension – bridle 1

Mooring line 3

Yaw motion

0 0.05 0.1 0.15 0.2 0

Frequency [Hz]

Sp

ectr

um

- b

ridle

1

Effective TI - Mann

Effective TI - Kaimal

0 0.05 0.1 0.15 0.2 0

1

Frequency [Hz]

Spectr

um

- m

ooring lin

e 3

Effective TI - Mann

Effective TI - Kaimal

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

0

Frequency [Hz] S

pectr

um

- y

aw

Effective TI - Mann

Effective TI - Kaimal

Bridle response

Mooring line

response

Yaw motion

1

1

Page 8: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Ex: Hywind with large rotor

Yaw response

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• Max, min and mean values for yaw response of 1 h simulations for 36 load cases

0 5 10 15 20 25 30 35

Wind speed [m/s]

Ya

w [

de

g]

Comparison - yaw motion

Effective TI - Mann - mean

Effective TI - Kaimal - mean

Effective TI - Mann - max

Effective TI - Kaimal - max

Effective TI - Mann - min

Effective TI - Kaimal- min

0 5 10 15 20 25 30 35 -

Free wind speed [m/s]

Ya

w [

de

g]

Comparison - yaw motion

Effective TI - mean

Ambient TI - mean

Effective TI - max

Ambient TI - max

Effective TI - min

Ambient TI- min

0 5 10 15 20 25 30 35

Free wind speed [m/s] Y

aw

[d

eg

]

Comparison - yaw motion

Effective TI - mean

Meandering wake - mean

Effective TI - max

Meandering wake - max

Effective TI - min

Meandering wake- min

Page 9: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Wind coherence on response

Concluding remarks

• For Hywind with large rotor low frequent wind coherence is important

for the yaw response and the mooring line fatigue

• As different wind models yield different loads, validated models are

needed to reduce uncertainty

• In particular, focus should be on:

− Coherence for low frequencies

− Site specific vs standardized models

− Atmospheric stability conditions

− Dynamic meandering wakes

• The solutions are to be found in measurement

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Page 10: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

JIP – Validation of Turbulence Models

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Phase 1: Existing measurements

Page 11: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Influence of wind coherence on a floating

wind turbine

Marte Godvik

Principal Researcher

[email protected]

Tel: +4797140760 www.statoil.com

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Page 12: Offshore wind - Sima tool; floating wind turbine motion … Stavanger...Floating Systems with wind turbine module − Fully integrated model comprising turbine, tower, substructure,

Simulation of loads and responses

SIMA windturbine software

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• Simulation and Engineering Analysis of Marine Operations and

Floating Systems (SIMA) with wind turbine module

• Fully integrated model comprising turbine, tower, substructure,

mooring and controller

• Static analysis, coupled time domain analysis and eigenvalue

analysis

• Wind boxes are pre-generated