1. IEA Wind Task 23 OC3: Phase IV Results Regarding Floating Wind Turbine Modeling
NREL – Jason Jonkman
MARINTEK – Ivar Fylling
Risø-DTU – Torben Larsen
GH – James Nichols
Anders Hansen
LUH – Martin Kohlmeier
IFE – Tor Anders Nygaard
Acciona – Javier Pascual Vergara
UMB – Karl Jacob Maus
Daniel Merino
NTNU – Madjid Karimirad
POSTECH – Wei Shi
Zhen Gao
Hyunchul Park
Torgeir Moan
Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by the Alliance for Sustainable Energy, LLC

2. Floating Challenges & Phase IV Model
Low frequency modes:
Influence aerodynamic damping & stability
Large platform motions:
Coupling with turbine
Complicated shape:
Radiation & diffraction
Moorings
Statoil supplied data for 5-MW Hywind conceptual design
OC3 adapted spar to support the NREL 5-MW turbine:
Rotor-nacelle assembly unchanged
Tower & control system modified
Challenges
OC3-Hywind
OC3-Hywind Model

3. Aero-Hydro-Servo-Elastic Capabilities

4. Phase IV Load Cases

5. Output Parameters & Results Legend
Drivetrain & Generator
Loads & Operation
7 Outputs
Rotor Blade
Loads & Deflections
13 Outputs
Tower
Loads & Deflections
15 Outputs
Environment
Wind & Waves
4 Outputs
Mooring System
Fairlead & Anchor Tensions & Angles
12 Outputs
Platform
Displacements
6 Outputs
Output Parameters (57 Total)
Results Legend

6. Full-System Eigenanalysis

7. Free Decay
Free Decay in Platform Surge
Free Decay in Platform Pitch

8. Hydro-Elastic Response with Regular Waves

9. Hydro-Elastic Response with Irregular Waves

10. Aero-Hydro-Servo-Elastic Response with Regular Waves

11. Aero-Hydro-Servo-Elastic Response with Irregular Waves

12. Aero-Hydro-Servo-Elastic
“Effective RAOs”

13. Unresolved Issues of OC3 Phase IV
Close agreement was not achieved by all codes:
What was the reason?
The ”effective RAO” load case was somewhat ”academic”:
What response charateristic is more relevant?
Alternative suggested by IF — RAOs could be derived from irregular time series & cross spectra between excitation & response
The stochastic response statistics & spectra are sensitive to simulation length:
What length would be more appropriate?
How can we eliminate start-up transients from the comparisons?

14. Limitations of OC3 Phase IV
OC3-Hywind platform was considered as a rigid body; no hydro-elastic effects
OC3-Hywind platform is simple in shape; only a single member
Hydrodynamic radiation & diffraction was negligible in the OC3-Hywind spar buoy
Sea current was never considered
Few sea states were tested; larger waves may be interesting
The relative importance of 2nd versus 1st order hydrodynamics was never assessed
The relative importance of dynamic versus quasi-static mooring models was never assessed
The influence of platform motion on rotor aerodynamics was never looked at in detail

15. 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 the Alliance for Sustainable Energy, LLC

16. Background OWTs are designed using aero-hydro-servo-elastic codes
The codes must be verified to assess their accuracy

17. OC3 Activities & Objectives
The IEA Offshore Code Comparison Collaboration (OC3) is an international forum for OWT dynamics code verification
Discuss modeling strategies
Develop suite of benchmark models & simulations
Run simulations & process results
Compare & discuss results
Assess simulation accuracy & reliability
Train new analysts how to run codes correctly
Investigate capabilities of implemented theories
Refine applied analysis methods
Identify further R&D needs
Activities
Objectives

18. OC3 Approach & Phases Approach Phases All inputs are predefined:
NREL 5-MW wind turbine, including control system
Variety of support structures
Wind & wave datasets
A stepwise procedure is applied:
Load cases selected to test different model features
OC3 ran from 2005 to 2009:
Phase I – Monopile + Rigid Foundation
Phase II – Monopile + Flexible Found’tn
Phase III – Tripod
Phase IV – Floating Spar Buoy
3-year follow-on project recently initiated:
Phase V – Jacket
Phase VI – Floating semisubmersible
Approach
Phases

19. Semisubmersible Concept
Summary
OC3 aims to verify OWT dynamics codes
Simulations tested a variety of OWT types & model features
Code-to-code comparisons have agreed well
Differences caused by variations in:
Model fidelity
Aero- & hydrodynamic theory
Model discretization
Numerical problems
User error
Future work will consider offshore jacket & semisubmersible
Verification is critical to advance offshore wind
Spar Concept by SWAY
Semisubmersible Concept