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Concept design verification of a semi-submersible floating wind turbine using coupled simulations
Location, Date November 2010
Fons Huijs EERA DeepWind’2014, Trondheim, 22 January 2014
page 2
Presentation outline
Tri-Floater design
Simulation approach
Software and numerical model
Simulation results
Conclusions
page 3
Tri-Floater design
Wind turbine NREL 5MW
Hub height above SWL 90 m
Control system ECN
Radius to column centre 36.0 m
Column width 8.0 m
Design draft 13.2 m
Air gap to deck structure 12.0 m
Displacement 3627 t
Catenary mooring lines 3 x 750 m
Chain diameter 100 mm
page 4
Tri-Floater design
operational survival
rated above rated cut-out parked
significant wave height [m] 4.5 4.5 6.5 9.4
wave peak period [s] 7.5 – 10 7.5 – 10 9 – 12 11 – 14
wind velocity at hub [m/s] 11.4 14.0 25.0 42.7
current velocity [m/s] 0 – 0.6 0 – 0.6 0 – 0.6 0 – 1.2
Operational inclination ≤ 10 deg
Operational nacelle acceleration ≤ 3 m/s2
Safety factor mooring line ≥ 1.7
page 5
Simulation approach
Verify design requirements motions and mooring loads
Concept design stage, so minimized computational effort
Simulation duration: 1 hour
Weibull distribution fitted to 50 % highest extremes
Expected maxima determined for 3 hours by extrapolation
Time step and seed dependency studied
page 6
Software and numerical model
AQWA (Ansys) Hydrodynamics (1st and 2nd order)
Mooring
PHATAS (ECN) Rotor aerodynamics
Rotor and tower structural dynamics
Drive-train and control systems
Benchmarked with OC3 spar
Hydrodynamic model validated with model tests
page 7
Software and numerical model
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
heave R
AO
[m
/m]
frequency [rad/s]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
pit
ch
RA
O [
deg
/m]
frequency [rad/s]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
su
rge R
AO
[m
/m]
frequency [rad/s]
page 8
Simulation results
[change lay-out to presentation style]
0 0.5 1 1.50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
frequency [rad/s]
Sx
[m
2s/r
ad]
Floater surge
0 0.5 1 1.50
0.05
0.1
0.15
0.2
0.25
0.3
frequency [rad/s]
Sz
[m
2s/r
ad]
Floater heave
0 0.5 1 1.50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
frequency [rad/s]
S
[deg
2s/r
ad]
Floater pitch
0 0.5 1 1.50
0.005
0.01
0.015
0.02
0.025
0.03
frequency [rad/s]
Sa
z [
m2
/(ra
d*s
)]
Nacelle heave acc. spectra for Vhub 11.4 m/s & Hs 4.5 m
TD sim. Tp 7.5 s
TD sim. Tp 10 s
FD calc. Tp 7.5 s
FD calc. Tp 10 s
0 0.5 1 1.50
0.005
0.01
0.015
0.02
0.025
0.03
frequency [rad/s]
Sa
z [
m2
/(ra
d*s
)]
Nacelle heave acc. spectra for Vhub 11.4 m/s & Hs 4.5 m
TD sim. Tp 7.5 s
TD sim. Tp 10 s
FD calc. Tp 7.5 s
FD calc. Tp 10 s
page 9
Simulation results
0 0.5 1 1.50
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
frequency [rad/s]
Sa
x [
m2
/(ra
d*s
)]
Nacelle surge acceleration
0 0.5 1 1.50
0.005
0.01
0.015
0.02
0.025
0.03
frequency [rad/s]
Sa
z [
m2
/(ra
d*s
)]
Nacelle heave acceleration
0 0.5 1 1.50
0.005
0.01
0.015
0.02
0.025
0.03
frequency [rad/s]
Sa
z [
m2
/(ra
d*s
)]
Nacelle heave acc. spectra for Vhub 11.4 m/s & Hs 4.5 m
TD sim. Tp 7.5 s
TD sim. Tp 10 s
FD calc. Tp 7.5 s
FD calc. Tp 10 s
0 0.5 1 1.50
0.005
0.01
0.015
0.02
0.025
0.03
frequency [rad/s]
Sa
z [
m2
/(ra
d*s
)]
Nacelle heave acc. spectra for Vhub 11.4 m/s & Hs 4.5 m
TD sim. Tp 7.5 s
TD sim. Tp 10 s
FD calc. Tp 7.5 s
FD calc. Tp 10 s
page 10
Simulation results
operational survival
rated above rated cut-out parked
floater inclination [deg]
mean 3.5 2.9 1.7 3.4
3-hour extreme (90%) 7.4 8.5 6.1 11.1
nacelle hor. acceler. [m/s2]
mean 0.7 0.6 0.6 0.8
3-hour extreme (90%) 2.4 2.5 3.0 3.1
page 11
Conclusions
Tri-Floater fulfills design criteria
Low frequency motions are dominant
Wave frequency motions are well predicted by uncoupled frequency domain motion analysis
Such analysis is useful to assess global floater motions in early design stages and optimize the floater design
Coupled simulations are however indispensible in later design stages
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