Integrated Dynamic Analysis of Floating Offshore Wind Turbines

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Integrated Dynamic Analysis of Floating Offshore
Wind Turbines

• B. Skaare1, T. D. Hanson1, F.G. Nielsen1, R.
  Yttervik1, A.M. Hansen2, K. Thomsen23, T. J.
  Larsen2
• Norsk Hydro OE Research Centre
• Risø National Laboratory
• Presently Siemens Wind Power
• Presented by Finn Gunnar Nielsen

EWEC2007 Milan, Italy 7-10 May 2007
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Background Hywind Deep-water floating offshore
wind turbine

• Challenge existing solutions by combining
  technologies
• Offshore floater technology from OG industry.
• Best available offshore wind turbines.

Case studied Turbine power 5
MW Draft hull 120 m Nacelle
height 81 m Rotor diameter
123 m Water depth 200700
m Displacement 8100 t Mooring
3 lines
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Hywind technical development

• Theory and computer codes.
• Engineering studies.
• Production and installation studies.

• Model test for verification.
• Next step
• Full scale demo version.

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Power curve
Simplified wind turbine model.
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Thrust curve
Simplified wind turbine model.
Constant Power
Maximum Power
Negative slope gt Negative damping contribution
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SIMO/RIFLEX/HAWC2 Integration

• HAWC2 (RISØ)
• Wind turbine loads and dynamics Interface
• SIMO / RIFLEX (MARINTEK)
• SIMO Rigid body dynamics in waves and current.
• RIFLEX Slender flexible body dynamics in waves
  and current

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SIMO/RIFLEX/HAWC2 Integration Testing
Comparison of motions in the coupling node in
simulations with SIMO/RIFLEX/HAWC2 (a) and
SIMO/RIFLEX (b). Waves Hs 5 m, Tp 12 s, 50
deg offset angle relative to the x-axis. No wind
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HYWIND Model Scale Experiments

• Motivation
• Validate results from numerical analysis.
• Demonstrate system behaviour
• Included
• Wind, waves
• Mooring
• Various control algorithms for rotor speed and
  blade pitch control
• Scale 1/47

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Recalculations of Model Scale Experiments

• Used SIMO / RIFLEX / HAWC2
• Implemented model test data for
• Mean wind speed and turbulence intensity
• Wave spectrum
• Floater and mooring model
• Aerodynamic model (NACA44XX blade profile)
• Control strategies

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Control Strategies

• Estimated relative wind velocity was obtained
  from thrust force measurements.
• Rotor speed and blade pitch angle of the turbine
  was controlled
• Below rated wind speed
• Control for maximum possible power (variable
  rotor speed, constant blade pitch angle)
• Above rated wind speed
• Conventional control
• Control for constant power (Constant rotor speed,
  variable blade pitch angle)
• Conventional control with active damping
• Control for constant power and tower pitch
  damping. (Constant rotor speed, variable blade
  pitch angle)

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Estimation of Relative Wind Speedquasistatic
assumption
The relative wind velocity is given from
where
where is the rotor thrust force
is the density of air D is the rotor diameter
is the rotor speed in RPM J is the advance
number given by the surface in the figure
(1)
(2)
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Estimation of Relative Wind Speed
Example of estimated wind speed for simulation a
test Hs 9m, Tp 13s, Umean19.49m/s,
Tint0.1265.
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Recalculations of Model Scale Experimentsfree
decay tests
Conventional Control Active Damping Constant
wind 17 m/s . No waves.
Conventional Control Constant wind 17 m/s. No
waves.
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Recalculations of Model Scale Experimentsirregul
ar wave tests.
Conventional Control Active Damping Mean wind
17 m/s. Hs 5m. Tp 12s
Conventional Control Mean wind 17 m/s. Hs 5m. Tp
12s
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Summary and conclusions

• A system for integrated analysis of floating
  offshore wind turbines has been developed
• The Floating offshore wind turbine HYWIND has
  been model tested with control of rotor speed and
  blade pitch angle.
• The integrated computer program RIFLEX /SIMO
  /HAWC2 has been validated towards the model test
  results.
• Very good correspondence between experimental and
  numerical results are obtained.
• The negative damping of the platform pitch motion
  at above rated wind speeds is efficiently
  compensated by use of an active damping
  algorithm.
• The integrated computer tool will be applied in
  further optimization of HYWIND

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