Vibration Mitigation Performance Of Electromagnetic Inertial Mass Dampers For Stay Cables

Bridge stay cables are susceptible to excessive vibration suffered from the external excitation due to their low inherent damping.However,the vibration mitigation performance of a classical viscous damper(VD)on stay cable is still limited.An electromagnetic inertial mass damper(EIMD)is a novel passive damper with high vibration control performance and is composed of an inerter element and electromagnetic damping element in parallel.To date,the vibration mitigation performance of the EIMD for stay cables has been rarely investigated.Regarding this problem,this thesis systematically studies the control performance of the EIMD on the stay cable,which mainly includes research work and innovative achievements stated as follows:(1)A nonlinear and a linearized mechanical model of the EIMD are proposed.Considering the friction and parasitic damping existed in the damper,the nonlinear mechanical model of the EIMD is proposed.Base on the equal energy dissipation rule,the friction damping can be equivalent to a viscous damping,and then the linearized mechanical model is derived in further.The mechanical models are validated by a series of dynamic tests on a full-scale EIMD prototype.(2)The design formulas of the optimal parameters of the EIMD for stay cables are derived.Base on the Krenk theoretical analysis model of cable-damper system,the relationship between the modal damping ratio and the EIMD parameters is obtained,and then the optimal parameter design formulas of the stay cable-EIMD system are derived.The modal damping ratios of the system are also calculated using the Newton iteration method,which are compared with those predicted by the theoretical formulas.The comparison results have illustrated the high-fidelity of the theoretical design formulas,and the applicable range of the formulas is identified in terms of the inertance of the EIMD.The theoretical analysis result has also demonstrated that the EIMD can enhance the damping performance for stay cables,of which the modal damping ratios are five times larger than those of classical VD at least.(3)The EIMD control performance on a super-long stay cable of the Stonecutters Bridge in Hong Kong is investigated via numerical simulation.The difference numerical model of the cable-EIMD system is established.The vibration mitigation performance of the system in the first six modes was analyzed systematically under the harmonic excitation and buffeting force,respectively.The numerical results demonstrate that the EIMD can achieve better damping performance than the classical VD in both lower and higher modes under the harmonic excitation.Numerical results show that the control performance of the EIMD for stay cables is superior to the classical VD under buffeting vibration.(4)The control performance of the EIMD on the stay cable is investigated systematically by conducting a full scale experiment.This experimental study has analyzed the effects of the inertances and damping coefficients on the modal frequencies,damping ratios and modal shapes of the stay cable,and investigated the vibration reduction mechanism of the EIMD for stay cables.In addition,the finite difference model of the cable-EIMD system is established.The correspondingly numerical results are obtained through complex modal eigenvalue analysis,which matches well with the experimental results.The experimental results illustrate that the EIMD with suboptimal parameters can achieve the control performance about two times better than the classical VD.