1. Verification and Validation of Offshore Wind Modeling Tools through IEA Wind Tasks 23 and 30 IEA Wind TEM# 76: "Floating Offshore Wind Plants“ April 28, 2014 Amy Robertson, Ph.D. Senior Engineer, NREL NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

2. IEA Wind TEM #76 2 National Renewable Energy Laboratory Offshore Wind Turbines (OWTs) are designed using aero-hydro-servo-elastic codes They need to be verified and validated to assess their accuracy, and give confidence in their usefulness to users IEA Wind Tasks 23 and 30 were developed to address this issue IEA Wind Task 23 and 30 Background

3. IEA Wind TEM #76 3 National Renewable Energy Laboratory Verification and Validation Verification = Assurance that the code is a faithful representation of a mathematical model –Achieved through code-to-code comparisons Validation = Assurance that the code represents observed real-world physical behavior –Achieved through comparisons of simulated response data to experimental data (code-to-data comparisons)

4. IEA Wind TEM #76 4 National Renewable Energy Laboratory IEA Wind Task 23 : Subtask 2 of this task was called the Offshore Code Comparison Collaboration (OC3) –Ran from 2005 to 2009 IEA Wind Task 30: Offshore Code Comparison Collaboration Continuation (OC4) –Continues work of OC3 project, examining more systems –Ran from 2010 to 2013 IEA Wind Task 30 Extension: Offshore Code Comparison Collaboration Continuation with Correlation (OC5) –New focus on validation rather than verification –Running from 2014-2017 Spar Concept by SWAY IEA Wind Tasks 23 and 30

5. IEA Wind TEM #76 5 National Renewable Energy Laboratory Assess simulation accuracy & reliability Train new analysts how to run codes correctly Investigate capabilities of implemented theories Refine analysis methods Identify further R&D needs Discuss modeling strategies Develop suite of benchmark models & simulations Run simulations (load cases) & process results Compare & discuss results Activities Objectives OC3/OC4 Objectives & Activities

6. IEA Wind TEM #76 6 National Renewable Energy Laboratory OC3/OC4 Phases OC3 ran from 2005 to 2009: –Phase I: Monopile + Rigid Foundation –Phase II: Monopile + Flexible Foundation –Phase III: Tripod –Phase IV: Floating Spar Buoy OC4 ran from 2010 to 2014: –Phase I: Jacket –Phase II: Floating semisubmersible

7. IEA Wind TEM #76 7 National Renewable Energy Laboratory Load Cases 1.X – System Identification Full-system flexibility Eigenanalysis – compare frequencies Free decay – frequencies and damping 2.X – Rigid Rigid turbine Aerodynamics without hydro: –Steady & turbulent winds Hydrodynamics without aero: –Regular & irregular waves 3.X – Onshore Wind Turbine Flexible tower, drivetrain, & rotor Rigid substructure Aero-servo-elastics without hydro: –Steady & turbulent winds 4.X – Inverted Pendulum Flexible support structure Rigid tower top Hydro-elastics without aero: –Regular & irregular waves 5.X – Full-System Dynamics Full-system flexibility Full aero-hydro-servo-elastics: –Steady winds with regular waves –Turbulent winds with irregular waves Damage Scenarios –Flooding –Mooring loss

8. IEA Wind TEM #76 8 National Renewable Energy Laboratory Output Parameters

9. IEA Wind TEM #76 9 National Renewable Energy Laboratory OC3/OC4 Participants & Codes SIMPACK-AeroDyn 3Dfloat ADAMS-AeroDyn-HydroDyn ADCoS-Offshore-(ASAS) ANSYS-WaveLoads BHawC Bladed (Multibody) CAST CHARM3D DeepC DeepLinesWT FAST-AeroDyn-HydroDyn FAST-AeroDyn-NASTRAN FLEX5-(Poseidon) HAWC and HAWC2 Hydro_GAST OrcaFlex OPASS+FAST RIFLEX-Coupled SESAM Simo+(Riflex+AeroDyn) SIMPACK+HydroDyn SWT UOU+FAST Wavec2Wire WAMSIM

10. IEA Wind TEM #76 10 National Renewable Energy Laboratory Aero-Hydro-Servo-Elastic Capabilities

11. IEA Wind TEM #76 11 National Renewable Energy Laboratory OC4 Phase II Results - Semi Eigenanalysis

12. EWEA Offshore Wind Conference 12 National Renewable Energy Laboratory For both ME and PF approaches, mean drift loads need to be considered. Platform Surge Motion (m) OC4 Phase II Results - Semi Regular Waves

13. EWEA Offshore Wind Conference 13 National Renewable Energy Laboratory Extension of the OC4 project – additional 4 years Three phases – examining three different systems Compare simulation results to physical response data OC5 – Simulation Tool Validation Monopile - Tank Testing Semi - Tank Testing Jacket/Tripod – Open Ocean

14. 14 STEP 1: Create a model of the system STEP 2: Choose data sets for comparison STEP 3: Calibrate the model STEP 4: Validate the model o Obtain system design information o Develop a specification document of the design for participants (participants will help modify/improve this document) o Participants will then develop a model of the structure based on the specification document within their modeling tool of choice o Create a list of available datasets, including specifics on wind/waves o Group will down-select data sets to be used for calibration and validation o Select measurement channels to be used for comparisons o Calibration will be done as a group. o Run structural-only cases, and calibrate model properties (mass/stiffness) using natural frequencies, structural damping rations, mooring force-disp. o Run steady wind-only cases, and calibrate airfoil coefficients using rotor performance (power, torque, thrust) o Run wave-only cases, and calibrate hydrodynamic coefficients using free- decay tests, current-only tests, and wave-only tests o Simulate model for a variety of cases with increasing complexity (if available): wind-only, wave-only, and then wind/wave o Do not use datasets used for calibration o Compare simulated response to that of the measurements o Discuss differences between participant results and tests OC5 Validation Process

15. EWEA Offshore Wind Conference 15 National Renewable Energy Laboratory Coordination & Meetings E-mail coordination Meetings –Net-meetings held every 1-2 months –Physical meetings held 1-2 times per year IEA Wind Task 23 and 30 SharePoint website: –http://oc4.collaborationhost.nethttp://oc4.collaborationhost.net –Hosted by NREL –Includes meeting presentations, minutes, model and load case descriptions, and simulation results –Anonymous account available: o Login: anonymous@oc4.collaborationhost.netanonymous@oc4.collaborationhost.net o Password: changeit2 –Certain directories open only to IEA Wind Task 30 members

16. EWEA Offshore Wind Conference 16 National Renewable Energy Laboratory Next OC5 Physical Meeting Friday, June 13 th, 9:00-5:00 Venue for OMAE conference (Palace Hotel in San Francisco, CA) First in-person meeting of OC5 project Introduce work for Phase I of project Doodle Poll to find out how many will be coming –http://doodle.com/sbsq9zbis6qnh4tnhttp://doodle.com/sbsq9zbis6qnh4tn –Observers welcome to attend

17. IEA Wind TEM #76 17 National Renewable Energy Laboratory Code-to-code comparisons have agreed well Differences caused by variations in: –Model fidelity –Aero-, hydro-, & structural-dynamic theories –Model discretization –Numerical problems –User error Many code errors have been resolved Engineers equipped with modeling experience Verification is critical to advance offshore wind New validation work will further highlight the applicability of different modeling approaches Spar Concept by SWAY Semi-submersible Concept Conclusions

18. Thank You! Amy Robertson +1 (303) 384 – 7157 Amy.Robertson@nrel.gov NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

19. EWEA Offshore Wind Conference 19 National Renewable Energy Laboratory Timeline

20. IEA Wind TEM #76 20 National Renewable Energy Laboratory Design of interest is identified –NREL 5 MW –Variety of support structures Information needed to model system is developed by operating agents and shared with participants A set of simulations (load cases) is defined to assess system behavior –Stepped approach Participants build model in code of choice and run load cases Simulated response behavior is compared between the codes Discussions on reasons for differences: –Modeling errors –Modeling approach Conclusions are drawn: –Advantages/disadvantages of modeling approaches –Future needs for modeling tools OC3/OC4 Approach

21. IEA Wind TEM #76 21 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 Comparisons: –Each participant models design in code of choice –Participants run load cases –Results (loads/motions) compared –Identify mistakes, influence of modeling choice, discussions OC3/OC4 Approach REpower 5M Wind Turbine