Dynamics Modeling and Loads Analysis of an Offshore Floating Wind Turbine

TLDR: In this paper, the authors describe the development, verification, and application of a comprehensive simulation tool for modeling coupled dynamic responses of offshore floating wind turbines, which is used to simulate the dynamic response of wind turbines.

Abstract: This report describes the development, verification, and application of a comprehensive simulation tool for modeling coupled dynamic responses of offshore floating wind turbines.

Figures

Table 7-2. Pitch-to-Feather Sensitivity of Aerodynamic Thrust to Blade Pitch

Figure 6-3. Time histories from sea-based simulation number 101 in DLC 1.4

Table 5-2. Definition of Wind and Wave Models

Table 3-2. Distributed Blade Structural Properties

Table 3-4. Distributed Blade Aerodynamic Properties

Table 3-9. Sensitivity of Aerodynamic Power to Blade Pitch in Region 3

Full text

A
national laboratory of the U.S. Department of Energ
y
Office of Energy Efficiency & Renewable Energ
y
National Renewable Energy Laboratory
Innovation for Our Energy Future
Dynamics Modeling and Loads
Analysis of an Offshore
Floating Wind Turbine
J.M. Jonkman
Technical Report
NREL/TP-500-41958
November 2007
NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337

National Renewable Energy Laborator
y
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Operated for the U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy
by Midwest Research Institute • Battelle
Contract No. DE-AC36-99-GO10337
Technical Report
NREL/TP-500-41958
November 2007
Dynamics Modeling and Loads
Analysis of an Offshore
Floating Wind Turbine
J.M. Jonkman
Prepared under Task No. WER7.5001

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Acknowledgments
I would like to thank many individuals for the successful completion of this project. Without
their advice and help, I could not have completed a work of this scope.
First, I would like to thank my Ph.D. committee for evaluating this work: Professor Mark Balas,
formerly of the University of Colorado and now with the University of Wyoming; Professors
Carlos Felippa and Lucy Pao of the University of Colorado; Dr. Michael Robinson of the
National Renewable Energy Laboratory; and Professor Paul Sclavounos of the Massachusetts
Institute of Technology. Special thanks go to my advisor, Professor Mark Balas, for his
guidance and support of this work, and to Professor Paul Sclavounos, for educating me in marine
hydrodynamics.
Thank you to Dr. Robert Zueck and Dr. Paul Palo of the Naval Facilities Engineering Service
Center for giving me insight into the dynamics and modeling of mooring systems.
I would also like to thank Dr. Jon Erik Withee of the U.S. Navy for initiating the study of
offshore floating wind turbines at the Massachusetts Institute of Technology, and Kwang Lee for
continuing in that effort and verifying the output of SWIM. I am also grateful to Libby Wayman
for modifying SWIM to output the frequency-dependent solutions of the radiation and diffraction
problems, for developing a floating platform concept, and for providing me with data that I could
use to validate my own models.
Thank you also to Torben Larsen of Risø National Laboratory and the Technical University of
Denmark for introducing me to the importance of the role that a variable blade-pitch-to-feather
control system can play in offshore floating wind turbines.
I would also like to thank Ian Edwards of ITI Energy for sponsoring the loads-analysis activities
and Professor Nigel Barltrop and Willem Vijfhuizen of the Universities of Glasgow and
Strathclyde for developing the ITI Energy barge and mooring system concept.
Big thanks go to several of my colleagues at the National Renewable Energy Laboratory’s
National Wind Technology Center. I thank George Scott for processing the reference-site data
from the Waveclimate.com service, and Bonnie Jonkman for assisting me in developing the
scripts needed to generate the WAMIT
®
geometric-data input files. I thank Marshall Buhl for
developing the scripts used to run the loads analysis and for assisting me in processing the loads-
analysis data. Thank you to Dr. Gunjit Bir for assisting me in examining the system instabilities
and to Lee Jay Fingersh and Dr. Alan Wright for their guidance and advice in my controls-
development activities. Thanks also to Kathleen O’Dell, Rene Howard, Janie Homan, Bruce
Green, and Bonnie Jonkman for editing this work to make it much more readable. Thank you
also to Walter Musial and Sandy Butterfield for leading the offshore wind energy program and to
Dr. Robert Thresher and Dr. Michael Robinson for directing the National Wind Technology
Center and for giving me the time and resources needed to work on this project.
I would like to thank my family and friends for their gracious support and encouragement
throughout this effort—I couldn’t have completed the project without your help.
iii

This work was performed at the National Renewable Energy Laboratory in support of the U.S.
Department of Energy under contract number DE-AC36-99-GO10337 and in support of a
Cooperative Research and Development Agreement (CRD-06-178) with ITI Energy.
iv

Frequently asked questions

Q1. What are the contributions in "Dynamics modeling and loads analysis of an offshore floating wind turbine" ?

In this paper, the authors present the results of their analysis examining the influence of conventional blade-pitch control systems on the pitch damping of the wind turbine plus floating barge system. 

Q2. What are the future works in "Dynamics modeling and loads analysis of an offshore floating wind turbine" ?

Possibilities include streamlining the shape of the barge to allow surface waves to more easily pass by ( i. e., as in a spar-buoy concept ), shifting the CM closer to the COB through ballast ( i. e., as in a spar-buoy concept ), or introducing tauter mooring lines ( i. e., as in a TLP concept ). 

Q3. What is the meaning of the word 'ecd'?

= extreme coherent gust with direction change ECN = Energy Research Center of the Netherlands EOG = extreme operating gust equiripple = equalized-ripple ESS = extreme sea state ETM = extreme turbulence model EWM = turbulent extreme wind model EWS = extreme wind shearFAST = Fatigue, Aerodynamics, Structures, and Turbulence FEA = finite-element analysis FFT = fast Fourier transform F2T = frequency-to-timeGDW = generalized dynamic-wake GE = General ElectricHAWT = horizontal-axis wind turbineIEA = International Energy Agency IEC = International Electrotechnical CommissionJONSWAP 

Q4. What is the name of the project?

The vast deepwater wind resource represents a potential to use offshore floating wind turbines to power much of the world with renewable energy. 

Q5. What are the main points of the paper?

Design modifications for reducing the platform motions, improving the turbine response, and eliminating the instabilities are suggested. 

Q6. What is the meaning of the word 'wind turbine'?

The coupling between the wind turbine response and the barge-pitch motion, in particular, produced larger extreme loads in the floating turbine than experienced by an equivalent land-based turbine. 

Q7. Who is grateful to me for modifying SWIM?

I am also grateful to Libby Wayman for modifying SWIM to output the frequency-dependent solutions of the radiation and diffraction problems, for developing a floating platform concept, and for providing me with data that The authorcould use to validate my own models. 

Q8. What is the meaning of the term 'dynamic analysis'?

Many floating wind turbine concepts have been proposed, but dynamics models, which account for the wind inflow, aerodynamics, elasticity, and controls of the wind turbine, along with the incident waves, sea current, hydrodynamics, and platform and mooring dynamics of the floater, were needed to determine their technical and economic feasibility. 

Q9. What is the purpose of this article?

These suggestions are aimed at obtaining costeffective designs that achieve favorable performance while maintaining structural integrity. 

Q10. Who is the author of this article?

Special thanks go to my advisor, Professor Mark Balas, for his guidance and support of this work, and to Professor Paul Sclavounos, for educating me in marine hydrodynamics. 

Q11. Who initiated the study of offshore floating wind turbines?

I would also like to thank Dr. Jon Erik Withee of the U.S. Navy for initiating the study of offshore floating wind turbines at the Massachusetts Institute of Technology, and Kwang Lee for continuing in that effort and verifying the output of SWIM. 

Q12. What is the meaning of the acronym?

I would like to thank my family and friends for their gracious support and encouragement throughout this effort—I couldn’t have completed the project without your help.iiiThis work was performed at the National Renewable Energy Laboratory in support of the U.S. Department of Energy under contract number DE-AC36-99-GO10337 and in support of a Cooperative Research and Development Agreement (CRD-06-178) with ITI Energy.ivAcronyms and AbbreviationsAbbr. = abbreviation ADAMS® = Automatic Dynamic Analysis of Mechanical Systems ARGOSS = Advisory and Research Group on Geo Observation Systems and Services A2AD = ADAMS-to-AeroDynBEM