Offshore wind turbines are a leading renewable energy technology with significant potential to support the drive for a low-carbon economy. As the availability of shallow water sites declines, floating offshore wind turbine (FOWT) technologies can play a leading role in accessing deep water sites. This paper investigates design and global performance of a semi-submersible floating offshore wind turbine system.

Existing design concepts of floating support structures and station keeping systems for FOWT’s are mostly developed based on experience from the offshore oil and gas industry, which has witnessed almost 70 years of designing and operating numerous floating offshore structures. This paper first introduces a new semi-submersible FOWT system developed by the authors for the application in South China Sea. The system consists of 8MW wind turbine, supporting tower, semi-submersible platform structure, station keeping mooring lines, and dynamic cable. The principal dimensions of the platform and ballast setting are iteratively designed for the better global performance in terms of response amplitude operator. The FOWT system also covers the layout of mooring lines and the configuration of dynamic cable. The semi-submersible FOWT system is designed to meet the requirement for natural periods recommended by the guidance notes from ABS.

The time domain fully coupled aero-hydro-servo-elastic response of the floating wind turbine is investigated by using the FEA program of OrcaFlex. The turbine takes the form of a conventional three-bladed rotor, with variable-speed and variable blade-pitch control capabilities. The turbine object in OrcaFlex is used to model the generator, gearbox, hub, blades and associated control systems. The environmental conditions in South China Sea are used in the dynamic analysis. The load case matrix covers 1-yr operating, 10-yr, and 100-yr extreme conditions. The time history of generator power is presented for the illustration of the regulation facilitated by the blade controller. The results include generator power, vessel offset, heave motion, heel angle, and maximum tension of mooring lines. For the 100-yr tropical environmental condition, the wind turbine is parked. The air gap especially at the tip of blades is examined for the extreme parked condition.

This paper finally summarizes the findings from the design and global performance of the semi-submersible floating offshore wind turbine system.

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