Nonlinear Hydrostatic Restoring Characteristics of a Spar Floating Wind Turbine

Floating wind turbine technologies have worldwide applications. Regarding the wind turbine floater stability, there are three principal design philosophies: ballast-, buoyancy- and mooring-stabilized. Although linear hydrostatic stiffness coefficient has been applied in most hydro-aero-elastic codes, accurate calculation of the nonlinear hydrostatic restoring forces is important for the floating stability evaluation and load. This study selects a 5-megawatt spar floating wind turbine as a representative floater. The nonlinear hydrostatic stiffness coefficient for different heeling angles is analytically calculated and compared against those obtained by a hydrodynamic software, and an excellent match is shown. A sensitivity study is carried out to consider the uncertainties in the hydrostatic stiffness due to varying geometry and weight distribution. The present results can be applied in the time-domain simulations for floating wind turbines.