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This work investigates the possibility of mitigating the wind-wave exerted vibration of floating offshore wind turbines using a nonlinear energy sink (NES). The vibration mitigation of floating wind turbines using passive linear control strategies have been intensively investigated, however, the effectiveness of the linear absorbers only works in a narrow frequency band, resulting in limited vibration suppression performance. The NES comprising a mass, a damper and a cubic stiffness element has the ability to mitigate vibrations in a broadband frequency range, which has been adopted in multiple engineering structures with significant performance benefits identified. In this paper, taking spar-buoy floating wind turbines as prototype structure, a simplified model with a NES mounted in nacelle subjected to wind and wave loads is presented. The harmonic balance method is then employed to analyse its nonlinear responses to the influence of NES parameters, together with the pseudo-arc-length method. The optimum NES parameter values are subsequently identified. Results show that the performance improvement can be up to 74.2% and 14.0%, respectively, comparing to that with no absorber and the TMD. Furthermore, to demonstrate the vibration suppression ability of the optimised NES in more realistic spar-buoy wind turbines, Orcaflex-the world's leading package for the dynamic analysis of offshore systems, is adopted as the simulation tool. The spar-buoy wind turbine as well as the NES are established in Orcaflex and it is demonstrated that the performance benefits with the NES preserve under various loading conditions. • Absorber design methodology of the nonlinear energy sink (NES) for the floating offshore wind turbines is proposed. • The harmonic balance method combined with the pseudo-arc-length method is used to analyse system's nonlinear responses. • Orcaflex is adopted as the simulation tool, with the spar-buoy wind turbine and the NES established in it. • The proposed NES outperforms an optimised TMD in a wide range of frequency for the wind turbine vibration mitigation under various loading conditions. [ABSTRACT FROM AUTHOR]

Tuned mass dampers (TMDs), in which a reaction mass is attached to a structural system via a spring-parallel-damper connection, are commonly used in a wide range of applications to suppress deleterious vibrations. Recently, a mass-included absorber layout with an inerter element, termed the tuned mass damper inerter (TMDI), was introduced, showing significant performance benefits on vibration suppression. However, there are countless massincluded absorber layouts with springs, dampers and inerters, which could potentially provide more preferred dynamic properties. Currently, because there is no systematic methodology for accessing them, only an extremely limited number of massincluded absorber layouts have been investigated. This paper proposes an approach to identify optimum vibration absorbers with a reaction mass. Using this approach, a full class of absorber layouts with a reaction mass and a pre-determined number of inerters, dampers and springs connected in series and parallel, can be systematically investigated using generic Immittance-Function-Networks. The advantages of the proposed approach are demonstrated via a 3 d.f. structure example. [ABSTRACT FROM AUTHOR]

This paper proposes a new method, the structure-immittance approach, for designing the passive vibration absorbers consisting of inerters, dampers and springs. When considering possible configurations for these elements broadly, one of two exist approaches may be taken, either a structure-based or an immittance-based approach. Both methods have their advantages and disadvantages. In this paper, the new approach combines the advantages of the existing ones. It can both consider a full set of absorber layouts together (the advantage of immittance-based approach), and restrict the complexity, topology and element values of the candidate layouts (the advantage of structure-based approach). The structural immittances covering a full set of possible networks with one damper, one inerter and at most one spring are derived and applied to a civil engineering study. This demonstrates the advantages of the new methodology in being able to identify the optimum configurations for different element constraints. [ABSTRACT FROM AUTHOR]

This paper investigates the use of a two-terminal vibration suppression device in a building. The use of inerter-spring-damper configurations for a multi-storey building structure is considered. The inerter has been used in Formula 1 racing cars and applications to various systems such as road vehicles have been identified. Several devices that incorporate inerter(s), as well as spring(s) and damper(s), have also been identified for vibration suppression of building structures. These include the tuned inerter damper and the tuned viscous mass damper. In this paper, a three-storey building model with a two-terminal absorber located at the bottom subjected to base excitation is studied. The brace stiffness is also taken into consideration. Four optimum absorber layouts, in terms of how spring, damper and inerter components should be arranged, for minimising the maximum relative displacements of the building are obtained with respect to the inerter's size and the brace stiffness. The corresponding parameter values for the optimum absorber layouts are also presented. Furthermore, a real-life earthquake data is used to show the advantage of proposed absorber configurations. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Summary: This paper investigates the use of two two‐terminal vibration suppression devices in a building and assesses the performance benefits over those achieved using a single device. The inerter‐combined configurations for a multi‐storey building structure are considered. The inerter is a two‐terminal device, with the property that the applied force is proportional to the relative acceleration across its terminals. In this paper, a five‐storey building model with two absorbers of the same kind subjected to base excitation is studied, where one is located between ground and the first floor and the other is between the first and second floors of the building. Three passive suppression layouts, two dampers, two tuned inerter dampers, and two tuned viscous mass dampers are considered. The optimal configurations for minimising the maximum interstorey drifts of the building are obtained with respect to the inerter's size and the damping boundary. The corresponding parameter values are also presented. For the sake of comparison, the single device mounted between the ground and first floor is also considered. Finally, with specific inertance and damping values, the frequency response is provided to show the potential advantage of the proposed optimal configurations. It is demonstrated that the optimal configurations with a pair of devices are more effective than the optimal single device with equal total inertance and the same total damping boundary. The approach demonstrated in this paper is applicable to the investigation of using more than two devices for multistorey buildings. [ABSTRACT FROM AUTHOR]