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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 CeSOSerin.bachynski@ntnu.noMay 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