High-frequency resonance of bottom-fixed monopile-supported offshore wind turbines under nonlinear waves

This study presents a high-fidelity hydroelastic framework for analyzing the nonlinear dynamic response of monopile-supported offshore wind turbines (OWTs) under wave excitation. Nonlinear wave loads were computed using the potential flow theory in conjunction with the weak-scattering assumption, in which hydrodynamic forces were obtained by integrating the pressure over the wetted surface. A coupled boundary element–finite element method (BEM–FEM) was developed to resolve structural responses efficiently. The model is validated using nonlinear wave diffraction simulations around a vertical cylinder. The computed wave loads were benchmarked against physical experiments, analytical solutions, frequency-domain models, and fully nonlinear potential flow results, demonstrating excellent agreement and confirming model reliability. The validated framework was used to assess the third-harmonic resonance of a bottom-fixed National Renewable Energy Laboratory 5-MW OWT. Parametric studies revealed that the resonance response is highly sensitive to the wave amplitude, frequency, and structural damping. The results provide important insights into the nonlinear resonance mechanisms and offer practical guidance for the fatigue-resistant and safe design of OWT in extreme marine environments.