Design and Performance of a TLP Type Floating Support Structure for a 6MW Offshore Wind Turbine

Abstract

The objective of this paper is to present the design and performance of an offshore floating wind turbine support structure and associated station keeping system, for a commercial 6 MW turbine. The results reported in this paper are based on a joint desk study performed by SBM and IFPEN for the development of this new floating support structure concept. The proposed system has been extensively analyzed thanks to time domain simulation software. Time domain models incorporate the wind turbine, the station keeping system, as well as structural components of the floating foundation. The system’s behavior has been assessed for a variety of environment conditions and turbine conditions (operating, idling, fault), resulting in an extensive design load case table. In addition to the nominal system, a number of sensitivities have been investigated to test the system response to various effects: marine growth accumulation on the floating support structure, anchor position tolerance, variations of water level. Results produced during this study show the good performance of the proposed floating wind turbine support structure and components. The proposed arrangement is capable of sustaining 20 years of operation with environment conditions up to the 50-year return period. The motions of the floating support structure are beneficial for the turbine performance, with low inclinations and low nacelle accelerations. As a consequence of these floating support structure’s low motions, the floating offshore wind turbine production is only marginally lower than the production of the same turbine on a fixed offshore foundation in the same environment. Production can occur up to the 50-year joint environment conditions. The work presented in this paper formed part of a design dossier independently reviewed by a certification body to obtain an ‘Approval in Principle‘ for the development of the floating support structure. The study has shown that the floater motion characteristics allow similar turbine production levels to be achieved by a turbine on a fixed offshore foundation, providing support to move of floating offshore energy production.