OC3: Benchmark Exercise of Aero-elastic Offshore Wind
Turbine CodesJ A Nichols and T R Camp, Garrad Hassan and Partners Ltd.
J Jonkman and S Butterfield, NREL
T Larsen and Anders Hansen, Risø
J Azcona, A Martinez and X Munduate, CENER
F Vorpahl and S Kleinhansl, CWMT
M Kohlmeier, T Kossel and C Böker, Leibniz University of Hannover
D Kaufer, SWE University of Stuttgart
Outline
• Background and partners
• Objectives
• Project phases and approach
• Phase III: offshore tripod
• Results
• Future work
Background and PartnersThe Offshore Code Comparison Collaboration (OCCC) has been coordinated within the IEA Wind Annex XXIII by the National Renewable Energy Laboratory (NREL).
Project group consists of research bodies, universities and partners from industry. Phase III includes contributions from:
• National Renewable Energy Laboratory (NREL) (USA)• Endowed Chair of Wind Energy of the Universität
Stuttgart (D)• Garrad Hassan (UK)• Risø National Laboratory (DK)• National Renewable Energies Center (CENER) (ESP). • Fraunhofer Centre for Wind Energy and Maritime
Engineering (D)• Leibniz University of Hannover (D)
Simulation tools:• Bladed, Flex5, FAST, HAWC2, ADCoS, WaveLoads and ANSYS
Objectives
• Establishment of a suite of benchmark simulations to test new codes and for training of new analysts
• Identification and verification of code capabilities and limitations of implemented theories
• Investigation and refinement of applied analysis methodologies
• Investigation on the accuracy and reliability of results obtained by simulations to establish confidence in the predictive capabilities of the codes
• Identification of further research and development needs
Project Phases
Phase I
Phase II
Phase III
Phase IV
Approach
• At each stage simulations are selected to highlight different areas of interest
• To start with, only basic models are used
• Then more features are added
• This facilitates identifying the differences between the different codes
Basic Structure
Wind Loads Wave Loads
Full simulation
Dynamics
Static Simulation
Phase III: Offshore Tripod
• Significant jump in complexity from monopile substructure.
• Statically indeterminate
• Loads influenced by relative deflection of members
Modelling – wave loads
• Importance of modelling the structure near the sea surface in detail
• Without a fine discretisation, sharp jumps are seen in load signals
-4000.0000
-3500.0000
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-1000.0000
-500.0000
0.0000
0 5 10 15 20 25 30 35
Time [s]
Shea
r F
orce
[kN
m]
Upwind leg axial shearforce (coarsediscretisation)
Upwind leg axial shearforce (finediscretisation)
Axia
l Fo
rce (
kN)
Modelling – overlapping members
• It is important to take account of the overlapping regions when structure members join at nodes
• In this case, the volume which could be double-counted would be 8% of the total volume below sea level having a significant effect on buoyancy and wave loads.
Modelling – shear deflection
• Bernoulli-Euler theory only considers pure bending of a beam.
• One side is compressed while the other is stretched.
• In real beams, there is some shear deformation of the material.
• This becomes important once relative deflection of joined members becomes important.
x
MP
MPl
EI
lx 6)4(
12
2
l
2
12
lGA
EI
S
Modelling – shear deflection
Results - Eigenanalysis
0.0000
0.5000
1.0000
1.5000
2.0000
2.5000
3.0000
1st T
ower
For
e-Aft
1st T
ower
Side
-to-S
ide
1st D
rivet
rain
Tor
sion
1st B
lade
Collec
tive
Flap
1st B
lade
Asym
met
ric F
lapwise
Pitc
h
1st B
lade
Asym
met
ric F
lapwise
Yaw
1st B
lade
Asym
met
ric E
dgew
ise P
itch
1st B
lade
Asym
met
ric E
dgew
ise Y
aw
2nd
Tower
For
e-Aft
2nd
Tower
Side
-to-S
ide
2nd
Blade
Collec
tive
Flap
2nd
Blade
Asym
met
ric F
lapwise
Pitc
h
2nd
Blade
Asym
met
ric F
lapwise
Yaw
CENER FASTNASTRAN Natural Frequency (Hz)
CENER Bladed Natural Frequency (Hz)
CWMT ADCoS Natural Frequency (Hz)
GH Bladed Natural Frequency (Hz)
GH Bladed (Timoshenko) Natural Frequency (Hz)
LUH WaveLoadsANSYS Natural Frequency (Hz)
Risoe HAWC2 Natural Frequency (Hz)
Risoe HAWC2_BE Natural Frequency (Hz)
SWE FLEX5Poseidon Natural Frequency (Hz)
Results – Output Locations
12
3
4
5
6
12
3
4
5
6
Results – bending moments due to wave loads
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-10000
-5000
0
5000
10000
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
-700
-600
-500
-400
-300
-200
-100
0
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
-10000
-8000
-6000
-4000
-2000
0
2000
4000
6000
8000
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
-3000
-2500
-2000
-1500
-1000
-500
0
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
-1500
-1450
-1400
-1350
-1300
-1250
-1200
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
-1800
-1600
-1400
-1200
-1000
-800
-600
-400
-200
0
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
1 2
3 4
5 6
-15000
-10000
-5000
0
5000
10000
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
-700
-600
-500
-400
-300
-200
-100
0
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
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-8000
-6000
-4000
-2000
0
2000
4000
6000
8000
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
-3000
-2500
-2000
-1500
-1000
-500
0
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
-1500
-1450
-1400
-1350
-1300
-1250
-1200
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
-1800
-1600
-1400
-1200
-1000
-800
-600
-400
-200
0
5 10 15
Simulation Time (s)
Ben
ding
Mom
ent (
kNm
))
1 2
3 4
5 6
Results – shear forces due to wave loads
-100
-50
0
50
100
150
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-200-150-100
-500
50100150
200250300
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-20
0
20
40
60
80
100
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-20
-10
0
10
20
30
40
50
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-60
-40
-20
0
20
40
60
80
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-15000
-10000
-5000
0
5000
10000
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
1 2
3 4
5 6
-100
-50
0
50
100
150
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-200-150-100
-500
50100150
200250300
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-20
0
20
40
60
80
100
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-20
-10
0
10
20
30
40
50
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-60
-40
-20
0
20
40
60
80
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
-15000
-10000
-5000
0
5000
10000
5 10 15
Simulation Time (s)
She
ar F
orce
(kN
)
1 2
3 4
5 6
Results – axial forces due to wave loads
-7103
-7102
-7102
-7101
-7101
-7100
-7100
-7099
-7099
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-4500
-4000
-3500
-3000
-2500
-2000
-1500
-1000
-500
0
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-1200
-1000
-800
-600
-400
-200
0
200
400
600
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-3500
-3000
-2500
-2000
-1500
-1000
-500
0
500
1000
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-6000
-5000
-4000
-3000
-2000
-1000
0
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-7250
-7240
-7230
-7220
-7210
-7200
-7190
-7180
-7170
-7160
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
1 2
3 4
5
6
-7103
-7102
-7102
-7101
-7101
-7100
-7100
-7099
-7099
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-4500
-4000
-3500
-3000
-2500
-2000
-1500
-1000
-500
0
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-1200
-1000
-800
-600
-400
-200
0
200
400
600
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-3500
-3000
-2500
-2000
-1500
-1000
-500
0
500
1000
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-6000
-5000
-4000
-3000
-2000
-1000
0
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
-7250
-7240
-7230
-7220
-7210
-7200
-7190
-7180
-7170
-7160
5 10 15
Simulation Time (s)
Axi
al F
orce
(kN
)
1 2
3 4
5
6
Motion of the dynamic support structure
-0.035
-0.030
-0.025
-0.020
-0.015
-0.010
-0.005
0.000
0.005
0.010
5 10 15
Simulation Time (s)
Tow
er T
op D
ispl
acem
ent (
m))
-0.005
-0.004
-0.003
-0.002
-0.001
0.000
0.001
0.002
0.003
0.004
0.005
5 10 15
Simulation Time (s)
Mea
n S
ea L
evel
Dis
plac
emen
t (m
))
Future Work
• Phase IV beginning
• Floating spar-buoy structure
• Stretching the limits of existing wind turbine
codes
• Involvement of codes used by oil and gas companies to model offshore structures
Conclusions
• Identification of important issues for space-frame offshore support structures.
• Encouragement for the development of existing codes to incorporate these features.
• Establishment of baseline load calculations and results for new codes to be tested against.
• A number of engineers are now equipped with experience of modelling offshore structures with greater knowledge of the factors which influence loading results.
