Nonlinear-memoryless-amplification behavior of bi-directional prestressed TMD for integrated vibration control of offshore wind turbine

An improved pendulum tuned mass damper with nonlinear cable tension, known as the prestressed tuned mass damper (PSTMD), has been proposed and investigated for mitigating excessive vibrations of offshore wind turbines (OWTs) across a frequency range. Unlike conventional nonlinear TMDs constructed with nonlinearity springs or dampers, the nonlinearity in the PSTMD originates from the geometric properties of its prestressing cables. This study extends the development of the device to a bi-directional PSTMD, considering the distinct nonlinear-memoryless-amplification (NMA) behavior for integrated vibration control in an OWT system, by means of the theoretical analysis and numerical simulation approaches. A mathematical model is derived to describe the nonlinear tensile forces of the cables in the bi-directional PSTMD, and a dynamical nonlinear model of the OWT with proposed PSTMD is established to account for aero-hydrodynamic loadings. NMA dynamic behavior under harmonic loads is examined via using the Newton–Raphson algorithm to explore the integrated vibration control of bi-directional PSTMD under wind–wave loads. Numerical simulations are conducted to demonstrate the effectiveness of the nonlinear bi-directional PSTMD in suppressing vibrations of the OWT system under both harmonic and wind–wave excitations. The analysis results indicate that the bi-directional PSTMD, considering the NMA behavior, effectively mitigates the frequency detuning phenomenon at the natural frequency of the OWT system. Furthermore, the study reveals that this approach offers significant advantages in vibration mitigation compared to a linear system.