9. Modeling and Analysis of Offshore Floating Wind Turbines

Offshore wind reserves vast amount of energy that could be effectively tapped to meet the demand for a greener global energy portfolio. To date, only a small fraction of offshore wind resources has been accessed worldwide, partially due to the deepwater constraints and relevant development costs. Compared with bottom-fixed wind turbines, floating wind turbines are less proven technically but more cost-effective in deep waters. A floating offshore wind turbine usually requires two additional components than does a land-based wind turbine: a floating platform and a station-keeping system. These two elements add to the system complexity. Advanced numerical analysis tools are important to the design in that they can be used to accurately capture the dynamic behavior of floating wind turbines. This chapter elaborates on two aspects for the spar platform, which is a proven support structure for floating wind turbines. First, a method is developed to account for sophisticated dynamics of the mooring system. This method is an improvement compared to the quasi-static approach, which simplifies the mooring system to six degrees of freedom (DOF). Both the slender geometry and the hydrodynamic loads contributing to the nonlinear dynamical behaviors are accurately evaluated for the mooring system of the spar platform. Second, the chapter introduces state-of-the-art dynamic analyses, including dynamic responses, design standards, and fault conditions of floating wind turbines. The mechanism and consequences of pitch system fault and shutdown are presented in details.