1. A Quantitative Comparison of Three Floating Wind Turbines
AWEA Offshore Wind Project Workshop
December 2-3, 2009
Jason Jonkman, Ph.D.
Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle

2. Offshore Wind Technology
Onshore
Shallow Water
0m-30m
Transitional
Depth
30m-60m
Deepwater 60m+

3. Floating Wind Turbine Pioneers
Developer
StatoilHydro, Norway
Blue H, Netherlands
Principle Power, USA
SWAY, Norway
Platform
“Hywind” spar buoy with catenary moorings
Tension-leg concept with gravity anchor
“WindFloat” semi-submersible with catenary moorings
Spar buoy with single taut tether
Wind Turbine
Siemens 2.3-MW upwind, 3-bladed
Gamma 2-bladed, teetering, yaw-regulated
Coordinating with suppliers for 5-MW+ units
Swivels downwind
Partnering with Multibrid
Status
$78M demonstration project in North Sea
First PoC installed in Summer 2009
Plans to license technology
Deployed PoC system with 80-kW turbine in Italy in summer 2007
Receiving funding from ETI for UK-based projects
Extensive numerical modeling
Tested in wave tank
Planning demonstration projects

4. Floating Wind Turbine Concepts
+ relative advantage
0 neutral
– relative disvantage
TLP
Spar
Barge
Pitch Stability
Mooring
Ballast
Buoyancy
Natural Periods + –
Coupled Motion
Wave Sensitivity
Turbine Weight
Moorings
Anchors
Construction & Installation
O&M
Design Challenges
Low frequency modes:
Influence on aerodynamic damping & stability
Large platform motions:
Coupling with turbine
Complicated shape:
Radiation & diffraction
Moorings, cables, & anchors
Construction, installation & O&M

5. Modeling Requirements
Coupled aero-hydro-servo-elastic interaction
Wind-inflow:
Discrete events
Turbulence
Waves:
Regular
Irregular
Aerodynamics:
Induction
Rotational augmentation
Skewed wake
Dynamic stall
Hydrodynamics:
Diffraction
Radiation
Hydrostatics
Structural dynamics:
Gravity / inertia
Elasticity
Foundations / moorings
Control system:
Yaw, torque, pitch

6. Coupled Aero-Hydro-Servo-Elastics

7. Floating Concept Analysis Process
Use same NREL 5-MW turbine & environmental conditions for all
Design floater:
Platform
Mooring system
Modify tower (if needed)
Modify baseline controller (if needed)
Create FAST / AeroDyn / HydroDyn model
Check model by comparing frequency & time domain:
RAOs
PDFs
Run IEC-style load cases:
Identify ultimate loads
Identify fatigue loads
Identify instabilities
Compare concepts against each other & to onshore
Iterate on design:
Limit-state analysis
MIMO state-space control
Evaluate system economics
Identify hybrid features that will potentially provide the best overall characteristics

8. Three Concepts Analyzed
NREL 5-MW on
OC3-Hywind Spar
NREL 5-MW on
ITI Energy Barge
NREL 5-MW on
MIT/NREL TLP

9. Sample MIT/NREL TLP Response

10. Normal Operation: DLC 1.1-1.5 Ultimate Loads Blade Root Bending Moment
Low-Speed Shaft Bending Moment
Yaw Bearing Bending Moment
Tower Base Bending Moment

11. Floating Platform Analysis Summary
MIT/NREL TLP
Behaves essentially like a land-based turbine
Only slight increase in ultimate & fatigue loads
Expensive anchor system
OC3-Hywind Spar Buoy
Only slight increase in blade loads
Moderate increase in tower loads; needs strengthening
Difficult manufacturing & installation at many sites
ITI Enery Barge
High increase in loads; needs strengthening
Likely applicable only at sheltered sites
Simple & inexpensive installation

12. Ongoing Work & Future Plans
Assess roll of advanced control
Resolve system instabilities
Optimize system designs
Evaluate system economics
Analyze other floating concepts:
Platform configuration
Vary turbine size, weight, & configuration
Verify simulations further under IEA OC3
Validate simulations with test data
Improve simulation capabilities
Develop design guidelines / standards
Spar Concept by SWAY
Semi-Submersible Concept

13. Thank You for Your Attention
Jason Jonkman, Ph.D.
+1 (303) 384 – 7026
Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle

14. Summary of Selected Design Load Cases from IEC61400-1 & -3
Design Load Case Table
Summary of Selected Design Load Cases from IEC & -3

15. Normal Operation: DLC 1.2 Fatigue Loads Side-to-Side Fore-Aft In-Plane
Out-of-Plane
Side-to-Side
Fore-Aft 0°
90°
Blade Root Bending Moments
Low-Speed Shaft Bending Moments
Yaw Bearing Bending Moments
Tower Base Bending Moments

16. DLC 6.2a Side-to-Side Instability
Idling:
DLC 6.2a Side-to-Side Instability
Aero-elastic interaction causes negative damping in a coupled blade-edge, tower-S-S, & platform-roll & -yaw mode
Conditions:
50-yr wind event for TLP, spar, & land-based turbine
Idling + loss of grid; all blades = 90º; nacelle yaw error = ±(20º to 40º)
Instability diminished in barge by wave radiation
Possible solutions:
Modify airfoils to reduce energy absorption
Allow slip of yaw drive
Apply brake to keep rotor away from critical azimuths

17. Idling: DLC 2.1 & 7.1a Yaw Instability
Aero-elastic interaction causes negative damping in a mode that couples rotor azimuth with platform yaw
Conditions:
Normal or 1-yr wind & wave events
Idling + fault; blade pitch = 0º (seized), 90º, 90º
Instability in TLP & barge, not in spar or land-based turbine
Possible solutions:
Reduce fully feathered pitch to allow slow roll while idling
Apply brake to stop rotor