Hydroelasticity effects on wave-induced loads and fatigue accumulation for a flexible offshore structure in irregular seas

Offshore wind turbine foundations consist of slender cylindrical members whose fatigue life and ultimate strength are strongly influenced by wave-structure interactions. Accurate design requires consideration of hydroelastic effects, which are often neglected in rigid-body analyses. This study employs a fully coupled computational fluid dynamics–finite element (CFD-FEM) framework to examine the hydroelastic response of a top-fixed flexible cylinder in irregular waves. The model solves the incompressible Navier-Stokes equations with nonlinear structural dynamics and is validated against experimental measurements of free-surface elevation, hydrodynamic forces, and structural accelerations. Results show that structural flexibility redistributes the spectral energy of wave-induced loads, introducing nonlinear coupling between the wave excitation and structural modes. The acceleration spectrum features a dominant peak at approximately three times the wave frequency and a secondary resonance near the first wet natural frequency. Statistical and fatigue analyses reveal that flexibility amplifies high-order force components and increases cumulative fatigue damage by about 78% compared with a rigid configuration. These findings highlight the importance of incorporating hydroelasticity in fatigue and reliability assessments of offshore wind turbine support structures.