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Influence of wind coherence on the response of a floating wind turbine Marte Godvik, Statoil – Research & Technology
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
Courtesy of Vattenfall Wind Power
Background II
Wind models
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• Wind models for simulation and calculation of loads are given by
the wind industry standards:
− Small vs large rotors
− Fixed vs floating turbines
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
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Courtesy DTU
Courtesy DTU
Simulation of loads and responses
Ex: Hywind with large rotor
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• 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
Ex: Hywind with large rotor
TI and wind models on mooring fatigue
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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
Ex: Hywind with large rotor
Wind coherence on response
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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
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
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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JIP – Validation of Turbulence Models
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Phase 1: Existing measurements
Influence of wind coherence on a floating
wind turbine
Marte Godvik
Principal Researcher
Tel: +4797140760 www.statoil.com
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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