1 bachynski – centre for ships and ocean structures aero-hydro-servo-elastic analysis of floating...
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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 CeSOS
May 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. NejadWilkinson et al., 2011
Jiang, 2012
Co
ntr
ibu
tio
n t
o f
ailu
re r
ate
(fai
lure
s/t
urb
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
To
p 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
SparTLP
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
FA
Be
ndi
ng
Mom
ent
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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
AY
HEAVE
ROLLPITC
HYA
W-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: control
AeroDyn: aerodynamic forces
Riflex: structural deflections, time stepping