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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Aero-Hydro-Servo-Elastic Analysis of Floating Wind Turbines with Tension Leg Moorings
Erin Bachynski, PhD candidate at [email protected] 15, 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
Floating wind turbine concepts studied at CeSOS
TLPSemi-submersibleSpar
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
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 (-)
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
TLPWT Design
MIT-NREL TLPWT (Matha, 2009)Shimada, 2011 Moon, 2010Botta, 2009
• Displacement – Increases cost– Decreases risk of slack
• Pontoon radius– Increases stability– Increases hull loads
• Tendons
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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
Challenges:-complexity-tight coupling-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
Aerodynamics
J. de Vaal, 2012
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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
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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
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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 faultBlade seizeBlade seize + shutdownGrid loss + shutdownStorm conditionExtreme turbulence at rated speed
Tow
er T
op F
A B
endi
ng 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-frequency
• Slender structures: Morison’s equation
• Tension-moored structures: ringing forces (3rd order)
hydrodynamics
aerodynamics control
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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
structural dynamicshydrodynamics
aerodynamics control
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
TLPWT Parametric Design Study:
Pitch
Tower Base Bending
Line Tension• Diameter • Water Depth• Pontoon Radius• Ballast Fraction
• 45 resulting designs• 7 environmental conditions
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
Concluding remarks• TLP 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
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www.cesos.ntnu.no Erin Bachynski – Centre for Ships and Ocean Structures
TLPWT + 3 Point Absorbers• Preliminary results indicate no
significant change in power output for WEC or WT by combining
• Reduced tendon tension variation (5-10%) and motions
LINE T
ENSIO
NSU
RGESW
AYHEA
VEROLL
PITCH
YAW
-30 %
-25 %
-20 %
-15 %
-10 %
-5 %
0 %
5 %
10 %
EC1EC2EC3
% C
hang
e in
Sta
ndar
d De
viati
on
% difference calculated as [(TLPWTWEC) – TLPWT]/TLPWT
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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 HAWC2 (land-based and spar, including fault)
SIMO: wave forces
Java: controlAeroDyn:
aerodynamic forces
Riflex: structural deflections, time stepping