Model Development and Loads Analysis of a Wind Turbine on a Floating Offshore Tension Leg Platform

NOTICE The submitted manuscript has been offered by an employee of the Alliance for Sustainable Energy, LLC (ASE), a contractor of the US Government under Contract No. DE-AC36-08-GO28308. Accordingly, the US Government and ASE retain a nonexclusive royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for US Government purposes. 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. BEM blade-element / momentum DEL damage-equivalent load DLC design load cases DOF degree of freedom IEC International Electrotechnical Commision LSS low-speed shaft MIT Massachusetts Institute of Technology PDF probability density function RAO response amplitude operator RMS root mean square TLP tension leg platform iv Executive Summary This report presents results of the analysis of a 5-MW wind turbine located on a floating offshore tension leg platform (TLP) that was conducted using the fully coupled time-domain aero-hydro-servo-elastic design code FAST with AeroDyn and HydroDyn. Models in this code are of greater fidelity than most of the models that have been used to analyze floating turbines in the past— which have neglected important hydrodynamic and mooring system effects. The report provides a description of the development process of a TLP model, which is a modified version of a Massachusetts Institute of Technology design derived from a parametric linear frequency-domain optimization process. The model has been verified using comparisons to frequency-domain calculations in terms of response amplitude operators and probability density functions. Important differences have been identified between the frequency-domain and time-domain simulations, and have generated implications for the conceptual design process. An extensive loads and stability analysis for ultimate and fatigue loads according to the procedure of the International Electrotechnical Commision 61400-3 offshore wind turbine design standard was performed with the verified TLP model. Response statistics, extreme event tables, fatigue …