With increasing demand on energy, and efforts towards protecting the environment, renewable energy has gained significant attention in recent years. Among the renewable energy resources, wind energy has been regarded as the most promising renewable, clean, and reliable energy resource, thus has become an important player in the world's energy market.
Since offshore wind fields have good features such as high steady wind speeds, and offshore wind farms can be sited such that noise and aesthetic inconveniences to the public are minimized, more and more floating wind turbines are being developed. Tension Leg Platform (TLP) –type wind turbines have good motion characteristics, namely relatively small heave/roll/pitch motions, making their efficiency of power generation very similar to those of land-based wind turbines; thus they have become very attractive candidates for offshore wind farm developments.
A three-column TLP with a 5 MW wind turbine has been developed for a water depth of 50 m. The TLP wind turbine is designed for quayside integration with the fully commissioned wind turbine at construction yard to avoid costly and high-risk offshore assembly. The fully integrated platform is wet towed to the installation site to eliminate the need to mobilize expensive crane vessels for offshore installation.
The wind turbine was modeled using FAST (Fatigue, Aerodynamics, Structures, and Turbulence), a publicly available program that models aero-elasticity and mechanical properties of wind turbine systems, developed by the National Renewable Energy Laboratory (NREL). The hydrodynamic coefficients of the TLP were computed using WAMIT and coupled with the FAST code to simulate aeroservo-hydro-elastic responses.
Platform motions; accelerations at nacelle; mooring tensions; eigen frequencies of tower; fore-aft shear, side-to-side shear, and vertical forces at tower base; side-to-side bending,fore-aft bending, and yaw moments at tower base; electric power generated. These are the major results analyzed and discussed in 50-yrp and 100-yrp environmental conditions. Key features of the wind turbine global responses due to hydrodynamic-aerodynamic coupled effects have been presented and highlighted.