Analysis and experimental study on dynamic characteristics of an integrated quasi-zero stiffness isolator

The dynamic performance of an integrated quasi-zero stiffness (IQZS) isolator which is constructed by a single elastic structure is investigated in this study. This prototype exhibits the characteristics of the best simplicity, high reliability and without friction by using the minimum number of elements. For completeness, the static properties of the IQZS isolator are provided at first. And then, the dynamic behavior is analyzed and the frequency response under harmonic excitation is derived by using an equivalent mechanical model. Frequency response curves (FRCs) are obtained by using the harmonic balance method (HBM) under force excitation condition. Moreover, the dynamic performance of the nonlinear isolator supporting a lumped mass is investigated by using force transmissibility, which are derived by modelling and compared with an equivalent linear system with the same design parameter values. The isolation performance of the nonlinear isolator outperforms the linear counterpart for providing a larger isolation range. The effects of system parameters on the transmissibility are also examined. At last, the comparison between the analytical and experimental results under force excitation shows that the analytical model of the IQZS isolator is accuracy in terms of force transmissibility. The calculation results discussed may provide a theoretical basis for designing this class of IQZS isolator in engineering practice.

Nonlinear viscoelastic oscillations of single-mass system at power excitation

Nonlinear oscillations of single-mass system at force excitation of vibration connected with fixed base by weightless viscoelastic spring are considered. To take into account the rheological properties of the spring material, the Boltzmann-Volterr principle was used. Mathematical models of the problem in question are obtained, which are described by nonlinear integro-differential equations. A solution method based on the use of quadrature formulas has been developed and a computer program has been compiled on its basis, the results of which are reflected in the form of graphs. Influence of nonlinear and rheological properties of spring on amplitude and phase of mass oscillations is investigated.

Response of an Annular Tuned Liquid Damper Equipped With Damping Screens

Annular tuned liquid dampers (TLDs) may be installed in slender structures with limited floor space, in which people and utilities must pass through the core, such as a wind turbine or observation tower. This study investigates an annular-shaped TLD equipped with damping screens. A linearized equivalent mechanical model capable of capturing the fundamental sloshing mode response of an annular TLD is presented. An experimental shake table testing program is completed to assess the performance of the model. Thirty-six frequency sweep tests consisting of various TLD configurations, excitation amplitudes, and excitation directions are completed. Good agreement is observed between the linearized equivalent mechanical model and experimental wave heights, sloshing forces, and energy dissipated per cycle that have been filtered to include only the fundamental sloshing mode response. The model is also observed to be in good agreement with experimental data for different excitation directions. The model is coupled to a generalized structure to investigate the response of a structure equipped with an annular TLD. The annular TLD is found to reduce the response of a generalized offshore wind turbine structure undergoing harmonic force excitation. The annular TLD provides performance comparable to an optimal linear tuned mass damper (TMD) with the same properties for a range of force excitation amplitudes.