Performance Assessment of a Nonlinear Stiffness Inerter-Based Absorber for Vibration Control of Monopile Offshore Wind Turbines

A Nonlinear stiffness Inerter-Based Absorber (NIBA) is introduced to attenuate the dynamic responses of monopile-supported offshore wind turbines under combined wind and wave loading. A reduced-order dynamic model of a monopile wind turbine incorporating the proposed absorber mounted in the nacelle is developed, where the fore-Aft bending behavior of the tower is idealized as a single rotational degree of freedom. The steady-state response of the nonlinear coupled system subjected to harmonic excitation is obtained using the harmonic balance technique, and the stability characteristics of the resulting periodic solutions are evaluated via Lyapunovs first method. The absorber parameters are determined through an optimization procedure that minimizes the root-mean-square displacement of the tower top. The vibration mitigation capability of the NIBA is then systematically benchmarked against that of a conventional Tuned Mass Damper (TMD) and an optimized linear Inerter-Based Absorber (IBA). The results indicate that the proposed NIBA provides enhanced vibration reduction across a wider frequency bandwidth, achieving reductions of 10.5% and 4.14% in the selected performance metric relative to the TMD and IBA, respectively. Additional time-domain and frequency-domain simulations under realistic stochastic wind and wave excitations further demonstrate that the NIBA consistently yields the largest decreases in both root-mean-square and peak tower-Top displacements, while requiring a smaller maximum absorber stroke, thereby confirming its practical applicability for monopile offshore wind turbine systems.