Collapse Behavior of Onshore and Spar-Floating Wind Turbine Towers During Blade Pitch Malfunction

Blade pitch control is one of the most important control systems for a wind turbine: blade pitch controller malfunction can lead to increased vertical bending moment at the tower base, which may result in structural failure. This study investigated the collapse behavior mechanism at the tower root due to an extreme event of blade pitch malfunction for onshore and spar-floating wind turbines. An aero-hydro-elastoplastic coupled analysis tool previously developed and validated by one of the authors was utilized to capture the structural response at the tower root in elastic and plastic regions. Three strength models—(i) SM-01, (ii) SM-02, and (iii) SM-03—were selected to demonstrate the collapse behavior mechanism of onshore and spar-floating 5 MW wind turbines in a time-series simulation. The damage in the plastic region, termed the collapse extent, was evaluated at the collapsing section. Moment–rotational angle relationships are discussed under the same wind conditions. The tower vibrations were found to dominate the structural response of the onshore wind turbine, whereas the tower vibrations and floater response dominate the spar-floating wind turbine response during the failure event. The collapse extent of the spar-floating wind turbine was found to be 8 times larger than the onshore wind turbine under the same wind conditions. Furthermore, simulations were carried out for the spar-floating wind turbine to understand the effect of incoming waves on the collapse behavior: the collapse extent increases as the wave amplitude and period increase under the same wind conditions.