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IEA Wind Task 23 OC3:Phase IV Results Regarding Floating Wind Turbine Modeling
Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by the Alliance for Sustainable Energy, LLC
EWEC 2010 2 National Renewable Energy Laboratory
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-MWHywind conceptual design
• OC3 adapted spar to support the NREL 5-MW turbine:– Rotor-nacelle assembly unchanged– Tower & control system modified
Ch
alle
ng
esO
C3-
Hyw
ind
OC3-Hywind Model
EWEC 2010 3 National Renewable Energy Laboratory
Aero-Hydro-Servo-Elastic Capabilities
FAST Bladed ADAMS HAWC2 3Dfloat Simo SESAM / DeepC
Code Developer NREL GH MSC + NREL
+ LUH Risø-DTU IFE-UMB MARINTEK DNV
OC3 Participant NREL + POSTECH GH NREL + LUH Risø-DTU IFE-UMB MARINTEK Acciona + NTNU
Aerodynamics ( BEM or GDW )
+ DS ( BEM or GDW )
+ DS ( BEM or GDW )
+ DS ( BEM or GDW )
+ DS ( BEM or GDW ) BEM None
Hydrodynamics Airy+ + ME,
Airy + PF + ME ( Airy+ or Stream )
+ ME Airy+ + ME,
Airy + PF + ME Airy + ME Airy + ME Airy + PF + ME Airy+ + ME,
Airy + PF + ME
Control System (Servo) DLL, UD, SM DLL DLL, UD DLL, UD, SM UD DLL None
Structural Dynamics (Elastic) Turbine: FEMP + ( Modal / MBS ), Moorings: QSCE
Turbine: FEMP + ( Modal / MBS ), Moorings: UDFD
Turbine: MBS, Moorings: QSCE,
UDFD
Turbine: MBS / FEM, Moorings: UDFD
Turbine: FEM, Moorings: FEM, UDFD
Turbine: MBS, Moorings: QSCE,
MBS
Turbine: MBS, Moorings: QSCE,
FEM
Airy+ – Airy wave theory +) with free surface corrections BEM – blade-element / momentum DLL – external dynamic link library DNV – Det Norsk Veritas DS – dynamic stall
GDW – generalized dynamic wake FEMP – finite-element method P) for mode preprocessing only MBS – multibody-dynamics formulation ME – Morison’s equation MSC – MSC Software Corporation
PF – linear potential flow with radiation & diffraction
QSCE – quasi-static catenary equations SM – interface to Simulink® with MATLAB® UD – implementation through user-defined
subroutine available UDFD – implementation through user-defined force-
displacement relationships
EWEC 2010 4 National Renewable Energy Laboratory
Phase IV Load Cases
EWEC 2010 5 National Renewable Energy Laboratory
Output Parameters (57 Total)
Rotor BladeLoads & Deflections13 Outputs
Drivetrain & GeneratorLoads & Operation
7 Outputs
TowerLoads & Deflections
15 Outputs
EnvironmentWind & Waves4 Outputs
PlatformDisplacements6 Outputs
Mooring SystemFairlead & Anchor
Tensions & Angles12 Outputs
Output Parameters & Results Legend
Results Legend
EWEC 2010 6 National Renewable Energy Laboratory
Full-System Eigenanalysis
EWEC 2010 7 National Renewable Energy Laboratory
Free Decay
Free Decay in Platform Surge
Free Decay in Platform Pitch
EWEC 2010 8 National Renewable Energy Laboratory
Hydro-Elastic Responsewith Regular Waves
EWEC 2010 9 National Renewable Energy Laboratory
Hydro-Elastic Responsewith Irregular Waves
EWEC 2010 10 National Renewable Energy Laboratory
Aero-Hydro-Servo-Elastic Responsewith Regular Waves
EWEC 2010 11 National Renewable Energy Laboratory
Aero-Hydro-Servo-Elastic Responsewith Irregular Waves
EWEC 2010 12 National Renewable Energy Laboratory
Aero-Hydro-Servo-Elastic“Effective RAOs”
EWEC 2010 13 National Renewable Energy Laboratory
• 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?
Unresolved Issues of OC3 Phase IV
EWEC 2010 14 National Renewable Energy Laboratory
• 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
Limitations of OC3 Phase IV
Thank You for Your Attention
Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by the Alliance for Sustainable Energy, LLC
Jason Jonkman, Ph.D.+1 (303) 384 – [email protected]
EWEC 2010 16 National Renewable Energy Laboratory
• OWTs are designed using aero-hydro-servo-elastic codes• The codes must be verified to assess their accuracy
Wind Turbine & Support StructureApplied Loads
External Conditions
Soil
Hydro-dynamics
Aero-dynamics
Waves & Currents
Wind-InflowPower
GenerationRotor
Dynamics
Substructure Dynamics
Foundation Dynamics
Drivetrain Dynamics
Control System
Soil-Struct. Interaction
Nacelle Dynamics
Tower Dynamics
Background
EWEC 2010 17 National Renewable Energy Laboratory
• 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
Act
ivit
ies
Ob
ject
ives
OC3 Activities & Objectives
The IEA Offshore Code Comparison Collaboration (OC3) is an international forum for OWT dynamics code verification
EWEC 2010 18 National Renewable Energy Laboratory
• 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
Ap
pro
ach
Ph
asesOC3 Approach & Phases
EWEC 2010 19 National Renewable Energy Laboratory
• 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 windSpar Concept by SWAYSemisubmersible Concept
Summary