Dynamic analysis of offshore wind turbine in clay considering soil–monopile–tower interaction

• Soil stiffness degradation is more at higher wind speed, which increases responses.
• Static p–y curves in offshore monopile design leads to underestimation in design.
• Non-consideration of dynamic analysis may lead to unplanned resonance condition.
• Rotor frequency has dominant role than blade passing frequency.
• Magnitude of wave load has vital role in design than resonance from wave frequency.

A comprehensive study is performed on the dynamic behavior of offshore wind turbine (OWT) structure supported on monopile foundation in clay. The system is modeled using a beam on nonlinear Winkler foundation model. Soil resistance is modeled using American Petroleum Institute based cyclic p–y and t–z curves. Dynamic analysis is carried out in time domain using finite element method considering wind and wave loads. Several parameters, such as soil–monopile–tower interaction, rotor and wave frequencies, wind and wave loading parameters, and length, diameter and thickness of monopile affecting the dynamic characteristics of OWT system and the responses are investigated. The study shows soil–monopile–tower interaction increases response of tower and monopile. Soil nonlinearity increases the system response at higher wind speed. Rotor frequency is found to have dominant role than blade passing frequency and wave frequency. Magnitude of wave load is important for design rather than resonance from wave frequency.