Preliminary development of a novel catamaran floating offshore wind turbine platform and assessment of dynamic behaviours for intermediate water depth application

Abstract

This paper presents the preliminary development of a novel catamaran Floating Offshore Wind Turbine (FOWT) concept and a numerical assessment of its dynamic characteristics subject to operational conditions when operating in 150 m water depth. A numerical tool, F2A, which couples FAST and ANSYS AQWA numerical tools via a Dynamic Link Library (DLL) is used to conduct efficient aero-hydro-servo-elastic simulations. The tool enables fully coupled time-domain simulations to predict the hydrodynamic loads, mooring tensions (using AQWA) and aero-elastic loads (using FAST) which is required for the complete evaluation of a FOWT's dynamic behaviour and performance. A verification study is conducted by comparing the catamaran FOWT's inherent characteristics against the ITI Energy barge FOWT. Furthermore, validation of the numerical results is achieved through comparisons with published results of similar models. More specifically, performance indicators of wind turbine platforms including dynamic responses, stability, and power production under operational conditions. It has been observed that the catamaran concept has significantly reduced responses (22% and 7% reduction in F-A tower-base bending moment and rotor thrust, respectively) and improved stability (50% reduction in pitch response (RAO)) compared to the barge. The catamaran concept offers steady production in a full range of operation conditions. This research confirms that a catamaran floating support platform offers a viable alternative to existing support FOWT concepts for application in intermediate water and provides greater insight into the behavior of barge-type FOWT concepts.