Higher-Harmonic Response of a Slender Monopile to Fully Nonlinear Focused Wave Groups

The “ringing” response of a monopile foundation to focused wave groups was investigated in this study. Such responses are of practical interest in the context of offshore wind turbine foundations. Moderately steep transient focused wave groups were generated in a novel numerical wave tank, based on the high-order spectral method, which was verified and in good agreement with published laboratory data. The monopile was simplified into a slender linear elastic cantilever beam to measure the severity of the structural response. The resonant behavior was excited at the triple-wave frequency of the wave loads. The influence of the damping ratio on the ringing response was considered. Different incident wave models and hydrodynamic models were used to predict the wave loads and induced responses over different wave steepness. The wavelet transform was successfully applied to reveal the local characteristics of the wave loads and ringing response.