A national laboratory of the U.S. Department of Energy Office of Energy Efficiency & Renewable Energy National Renewable Energy Laboratory Innovation for Our Energy Future Dynamics Modeling and Loads Technical Report NREL/TP-500-41958 Analysis of an Offshore November 2007 Floating Wind Turbine J.M. Jonkman NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 Dynamics Modeling and Loads Technical Report NREL/TP-500-41958 Analysis of an Offshore November 2007 Floating Wind Turbine J.M. Jonkman Prepared under Task No. WER7.5001 National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov 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 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Available electronically at http://www.osti.gov/bridge Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831-0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:[email protected] Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800.553.6847 fax: 703.605.6900 email: [email protected] online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste 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 Acronyms and Abbreviations Abbr. = abbreviation ADAMS® = Automatic Dynamic Analysis of Mechanical Systems ARGOSS = Advisory and Research Group on Geo Observation Systems and Services A2AD = ADAMS-to-AeroDyn BEM = blade-element / momentum BVP = boundary-value problem CM = center of mass COB = center of bouyancy DAC = disturbance-accommodating control DLC = design load case DLL = dynamic link library DOE = U.S. Department of Energy DOF = degree of freedom DOWEC = Dutch Offshore Wind Energy Converter project DU = Delft University 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 shear FAST = Fatigue, Aerodynamics, Structures, and Turbulence FEA = finite-element analysis FFT = fast Fourier transform F2T = frequency-to-time GDW = generalized dynamic-wake GE = General Electric HAWT = horizontal-axis wind turbine IEA = International Energy Agency IEC = International Electrotechnical Commission JONSWAP = Joint North Sea Wave Project metocean = meteorological and oceanographic MIMO = multiple-input, multiple-output v MIT = Massachusetts Institute of Technology MSL = mean sea level NACA = National Advisory Committee for Aeronautics NASA = National Aeronautics and Space Administration NAME = Naval Architecture and Marine Engineering NFESC = Naval Facilities Engineering Service Center NREL = National Renewable Energy Laboratory NSS = normal sea state NTM = normal turbulence model NWTC = National Wind Technology Center OCS = offshore continental shelf OC3 = Offshore Code Comparison Collaborative O&G = oil and gas OWC = oscillating water column PI = proportional-integral PID = proportional-integral-derivative PSD = power spectral density PSF = partial safety factor RAM = random access memory RAO = response amplitude operator RECOFF = Recommendations for Design of Offshore Wind Turbines project RNG = random-number generator SAR = synthetic aperture radar SDB = shallow-drafted barge SISO = single-input, single-output SML = SWIM-MOTION-LINES SVD = singular-value decomposition SWL = still water level TFB = tower feedback TLP = tension leg platform TMD = tuned-mass damper UAE = Unsteady Aerodynamics Experiment VIV = vortex-induced vibration WAMIT® = Wave Analysis at MIT WGN = white Gaussian noise WindPACT = Wind Partnerships for Advanced Component Technology project w.r.t. = with respect to vi Nomenclature A = amplitude of a regular incident wave Ad = discrete-time state matrix ai = component of the undisturbed fluid-particle acceleration in Morison’s equation in the direction of the ith translational degree of freedom of the support platform Aij = (i,j) component of the impulsive hydrodynamic-added-mass matrix a XE r = three-component acceleration vector in Kane’s equations of motion for the center th of mass (point Xr) of the r system rigid body in the inertial frame (frame E) ARadiation = added inertia (added mass) associated with hydrodynamic radiation in pitch A0 = water-plane area of the support platform when it is in its undisplaced position Aξ = amplitude of the platform-pitch oscillation Bd = discrete-time input matrix Bij = (i,j) component of the hydrodynamic-damping matrix BRadiation = damping associated with hydrodynamic radiation in pitch BViscous = damping associated with hydrodynamic viscous drag in pitch CA = normalized hydrodynamic-added-mass coefficient in Morison’s equation CB = coefficient of the static-friction drag between the seabed and a mooring line CD = normalized viscous-drag coefficient in Morison’s equation Cd = discrete-time output