Post on 17-Apr-2018
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Dynamic Analysis of Floating Wind Turbines Erin Bachynski, PhD candidate at CeSOS erin.bachynski@ntnu.no May 28, 2013
www.cesos.ntnu.no CeSOS – Centre for Ships and Ocean Structures
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
TLP Semi-submersible Spar
We need to understand floating wind turbine behavior so that we can bring the cost down
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Spar • Deep draft, heavy ballast at the
bottom • Small diameter at the water
level • Small, slow motions (+) • Straightforward installation (+) • Requires large water depth (-)
• Analysis challenge: mooring
system
Image: Statoil
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Semi-Submersible • Stability from large
waterplane moment of inertia
• Relatively large motions (-) • Straightforward installation
(+) • More flexible w.r.t. water
depth (+)
• Analysis challenge: large columns and heave plates, structural response of the braces
Image: Principal Power
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Tension Leg Platform (TLP)
• Stability from tension legs, implying motions as an inverted pendulum • Small motions (+) • Flexible w.r.t. water depth (+) • Smaller steel weight (+) • Small footprint area on seabed (+) • Challenging installation (-)
• Analysis challenges: elastic coupling
between tower/platform/tendons, high-frequency forcing and response
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Source: NREL/Wind power today, 2010.
structural dynamics
hydrodynamics
aerodynamics control
-complex -tightly coupled -nonlinear -time domain -long term periods -transient (faults)
Integrated aero-hydro-servo-elastic analysis
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Simo-Riflex-AeroDyn • Nonlinear time domain coupled
code (Riflex: MARINTEK) • Single structural solver • Aerodynamic forces via DLL • Advanced hydrodynamics
(Morison, 1st and 2nd order potential, ringing) (Simo: MARINTEK)
• Control code (java) for normal operation and fault conditions
• Good agreement with DTU Wind’s HAWC2 (land-based and spar, including fault)
SIMO: wave forces
Java: control AeroDyn:
aerodynamic forces
RIFLEX: structural deflections, time stepping Ormberg, H. & Bachynski, E. E. Global analysis of floating wind turbines: Code development,
model sensitivity and benchmark study. 22nd International Ocean and Polar Engineering Conference, 2012, 1, 366-373
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Aerodynamics
Image: J. de Vaal, 2012
Image: J. de Vaal, 2012
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Ormberg, H. & Bachynski, E. E. Global analysis of floating wind turbines: Code development, model sensitivity and benchmark study. 22nd International Ocean and Polar Engineering Conference, 2012, 1, 366-373
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Control system
• Serves to – regulate rotor rotation
speed – regulate power output – protect structure
• Actions – Change generator torque – Change blade pitch
0
100
200
300
400
500
600
700
800
900
0
5
10
15
20
25
0 5 10 15 20 25
Thru
st
Rot.
Spee
d, B
l.Pitc
h, P
ower
Wind Speed (m/s)
Blade Pitch (deg) Power (MW) Rotor Speed (RPM) Thrust (kN)
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Blade pitch mechanism failures
PhD candidates at CeSOS studying the effects of
control system failures on different platforms : Z. Jiang, M. Etemaddar, E. Bachynski, M. Kvittem, C. Luan, A. R. Nejad
Wilkinson et al., 2011
Jiang, 2012
Con
trib
utio
n to
failu
re ra
te (f
ailu
res/
turb
ine/
yr) (
%)
Pitc
h sy
stem
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
-200 -150 -100 -50 0 50 100 150 200-1.5
-1
-0.5
0
0.5
1
1.5x 10
4
Tow
er T
op B
MY
, kN
m
TLP, EC 5
time - TF, s
BC
What happens if one blade stops pitching?
Shut down turbine quickly
Fault occurs
Continue operating with faulted blade
TLP, U=20m/s, Hs = 4.8m, Tp = 10.8s
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Comparison of controller fault effects on different platforms
Spar TLP
Semi-Sub 1 Semi-Sub 2
Bachynski, E. E.; Etemaddar, M.; Kvittem, M. I.; Luan, C. & Moan, T. Dynamic analysis of floating wind turbines during pitch actuator fault, grid loss, and shutdown Energy Procedia, 2013 . (Accepted for publication)
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Environmental/ Fault Conditions
Fault Definition
A No fault
B Blade seize
C Blade seize + shutdown
D Grid loss + shutdown
EC U (m/s) Hs (m) Tp (s)
Turb. Model
Faults # Sims. Sim. length* (s)
1 8.0 2.5 9.8 NTM A, B, C, D 30 16 min. 2 11.4 3.1 10.1 NTM A, B, C, D 30 16 min.
3 14.0 3.6 10.3 NTM A, B, C, D 30 16 min.
4 17.0 4.2 10.5 NTM A, B, C, D 30 16 min.
5 20.0 4.8 10.8 NTM A, B, C, D 30 16 min.
6 49.0 14.1 13.3 NTM A (idling) 6 3 hours
7 11.2 3.1 10.1 ETM A 6 3 hours
* Simulation length after 200s initial constant wind period
Max. thrust
50 yr. storm
Ext. turb.
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
No fault Blade seize Blade seize + shutdown Grid loss + shutdown Storm condition Extreme turbulence at rated speed
Tow
er T
op F
A Be
ndin
g M
omen
t
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Hydrodynamics
• Large volume structures: potential flow – First order – Second order (sum- and
difference-frequency) – Third order (ringing)
• Slender structures: Morison’s equation
hydrodynamics
aerodynamics control
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Hydrodynamics: Morison vs. Potential Flow for FWTs • Semi-submersible:
– Morison’s equation compares well to potential flow if one chooses the coefficients carefully and integrates to the instantaneous free surface
• TLPWTs: – For medium and large diameters,
Morison’s equation gives larger forcing at high frequencies compared to potential flow
– Small diameters: Morison’s Equation works well
0 0.5 1 1.5 2 2.5 30
1
2
3
4
5
6
7x 10
4
F 5/ ζ, k
Nm
/m
ω, rad/s
P1+V (sim)M (sim)P1 (theory)M inertia (theory)
Large difference at pitch/bend natural frequency
Kvittem, M. I.; Bachynski, E. E. & Moan, T. Effects of hydrodynamic modelling in fully coupled simulations of a semi-submersible wind turbine. Energy Procedia, 2012, 24, 351-362
Bachynski, E. E. & Moan, T. Hydrodynamic Modeling of Tension Leg Platform Wind Turbines 32nd International Conference on Ocean, Offshore and Arctic Engineering, 2013
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Hydrodynamics: Ringing forces on TLPWTs • Ringing: transient response at
frequencies higher than the wave frequency
• Third order diffraction loads • Wave loads by FNV formulation1
(long-wave approximation, sum-frequency components only, bandwidth limitation in interacting waves)2
520 530 540 550 560 570-2
-1
0
1
2
3x 10
F x, kN
520 530 540 550 560 570-2
-1
0
1
2x 10
5
MFA
, kN
m
Time, s
520 530 540 550 560 5704000
6000
8000
10000
12000
14000
T 1, kN
P1+V, Turbine OnP1+V, Turbine OffP2+V+FNV, Turbine OnP2+V+FNV, Turbine Off
W
ave
Forc
e To
wer
Bas
e B
endi
ng
Dow
nwin
d Te
nsio
n D=14 m, Hs = 8.71 m, Tp =10 s
1) Faltinsen, O. M.; Newman, J. N. & Vinje, T. Nonlinear wave loads on a slender vertical cylinder. Journal of Fluid Mechanics, 1995, 289, 179-198
2) Johannessen, T. B. Nonlinear Superposition Methods Applied to Continuous Ocean Wave Spectra.Journal of Offshore Mechanics and Arctic Engineering, 2012, 134, 011302-1-011302-14
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Structural Modeling
• Flexible beam elements (tower, blades, mooring system)
• Rigid hull • Global model – simplified generator • Blades: complex cross-section!
structural dynamics hydrodynamics
aerodynamics control
Aerodynamic axes
Principal bending axes Center of mass
Shear center
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Design and Analysis of TLPWTs
• Design comparisons – Parametric design study of TLPWTs – Combined wind and wave energy platforms
• Analysis alternatives – Can a frequency-domain analysis be used? – Can Morison’s equation be used? – Are second order potential flow effects important? – How do different ringing force models affect the results?
• Extreme conditions – How likely are we to lose tension in a storm? – What happens if the wind turbine controller fails? – What happens when the wind and waves come from different
directions?
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
TLPWT Parametric Design Study:
• Variations in: – Diameter – Water Depth – Pontoon Radius – Ballast Fraction
5 baseline designs:
45 resulting designs 7 environmental conditions
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 5000 10000 15000
Ft (k
N)
Displacement (m3)
TLPWT 1 TLPWT 2 TLPWT 3 TLPWT 4 TLPWT 5 MIT/NREL UMaine GLGH IDEAS Crozier
Bachynski, E. E. & Moan, T. Design Considerations for Tension Leg Platform Wind Turbines Marine Structures, 2012, 29, 89-114
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Parametric Design Study Results • Changes in diameter, pontoon radius, and ballast affect
both stiffness and mass – complex results! • Tendon tension variation decreases with pretension, but
tower bending decreases with increased ballast • Cost increases with displacement • A design with three pontoons, large pontoon radius, and
mid-range (4000 to 7000 tonnes) displacement may be reasonable
Res
pons
es
Parameters
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Concluding remarks
• Floating wind turbines present complex, unanswered design and analysis challenges
• Numerical simulations require coupled aero-hydro-servo-elastic tools and expertise
• A wide variety of environmental and operational conditions must be considered
• In our studies of floating wind turbines at CeSOS we hope to provide insights that can help inform designers and regulatory bodies
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Thank you !
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
References • Bachynski, E. E.; Etemaddar, M.; Kvittem, M. I.; Luan, C. & Moan, T.
Dynamic analysis of floating wind turbines during pitch actuator fault, grid loss, and shutdown. Energy Procedia, 2013. (Accepted for publication)
• Bachynski, E. E. & Moan, T. Design Considerations for Tension Leg Platform Wind Turbines Marine Structures, 2012, 29, 89-114
• Bachynski, E. E. & Moan, T. Hydrodynamic Modeling of Tension Leg Platform Wind Turbines. 32nd International Conference on Ocean, Offshore and Arctic Engineering, 2013
• Bachynski, E. E. & Moan, T. Linear and Nonlinear Analysis of Tension Leg Platform Wind Turbines.The 22nd International Ocean and Polar Engineering Conference, 2012
• Bachynski, E. E. & Moan, T. Point Absorber Design for a Combined Wind and Wave Energy Converter on a Tension-Leg Support Structure. 32nd International Conference on Ocean, Offshore and Arctic Engineering, 2013
• Faltinsen, O. M.; Newman, J. N. & Vinje, T. Nonlinear wave loads on a slender vertical cylinder. Journal of Fluid Mechanics, 1995, 289, 179-198
• Jiang, Z.; Karimirad, M. & Moan, T. Steady State Response of a Parked Spar-type Wind Turbine Considering Blade Pitch Mechanism Fault. The 22nd International Ocean and Polar Engineering Conference, 2012
• Johannessen, T. B. Nonlinear Superposition Methods Applied to Continuous Ocean Wave Spectra.Journal of Offshore Mechanics and Arctic Engineering, 2012, 134, 011302-1-011302-14
• Jonkman, J.; Butterfield, S.; Musial, W. & Scott, G. Definition of a 5-MW Reference Wind Turbine for Offshore System Development. NREL/TP-500-38060, National Renewable Energy Laboratory, 2009
• Jonkman, J. & Matha, D. A Quantitative Comparison of the Responses of Three Floating Platforms European Offshore Wind 2009 Conference and Exhibition, 2009
• Kvittem, M. I.; Bachynski, E. E. & Moan, T. Effects of hydrodynamic modelling in fully coupled simulations of a semi-submersible wind turbine. Energy Procedia, 2012, 24, 351-362
• Ormberg, H. & Bachynski, E. E. Global analysis of floating wind turbines: Code development, model sensitivity and benchmark study. 22nd International Ocean and Polar Engineering Conference, 2012, 1, 366-373
• Wilkinson, M.; Harmann, K.; Spinato, F.; Hendriks, B. & van Delft, T. Measuring Wind Turbine Reliability - Results of the Reliawind Project. European Wind Energy Conference (EWEA 2011), 2011