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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

erin.bachynski@ntnu.no

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

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

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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

% 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