Fluid inerter for optimal vibration control of floating offshore wind turbine towers

This paper proposes the use of a tuned mass damper fluid-inerter (TMDFI) for vibration control of spar-type floating offshore wind turbine towers. The use of an inerter in parallel with the spring and damper of a tuned mass damper (TMD) is a relatively new concept. The ideal inerter has a mass amplification effect on the classical TMD leading to greater vibration control capabilities. Previous work by the authors has shown that inerter based TMDs have great potential in vibration control of floating offshore wind turbines where enhanced vibration mitigation can be achieved using a relatively lighter device than classical TMDs. However, this previous work was based on the assumption of an ideal inerter that assumes the use of a mechanical flywheel type inerter. Mechanical inerters have some inherent disadvantages due to their complexity in design and high cost of maintenance. The use of a fluid inerter can alleviate these disadvantages as its design is rather simple and it comes with very low maintenance. Such devices have been proposed and investigated in the literature, however, their applicability in vibration control of floating wind turbines has not been investigated by researchers. The optimal design of a TMDFI is presented in this paper. It has been shown that optimization of a TMDFI is a six-dimensional non-linear optimization problem whose solution hyperplane contains multiple local minima. A systematic way has been developed in this paper, avoiding the use of metaheuristic search techniques, to optimize the damper while providing greater insight into the damper properties that offers a set of guidance to the designer. Numerical results demonstrate impressive vibration control capabilities of this new device under various stochastic wind-wave loads. It has been shown that the fluid-inerter performs as well as the ideal mechanical inerter. The considerable advantages of a TMDFI over the classical TMD demonstrated in this paper makes it an exciting candidate for vibration control. © 2022 The Author(s)