Theoretical And Experimental Study On Seismic Control Performance Of Magnetic Bi-stable Nonlinear Energy Sink

The nonlinear energy sink(NES)is a passive control technology of additional substructure,which is different from the traditional tuned mass damper(TMD)technology.Its control principle is by setting an additional substructure with strong nonlinear stiffness characteristics,and using the intrinsic resonant characteristics of the nonlinear system to make the dynamic response of substructure to the primary structure through the internal resonance capture,so a large amount energy of the primary structure is absorbed by substructure and dissipated.NES not only maintains the passive characteristics,but also has the technical potential of expanding control bandwidth,improving robustness and control effect.It has important research and application prospects in seismic reduction of civil engineering.In order to study a new NES with strong non-linear restoring force and better seismic control performance,A Magnetic Bi-stable Nonlinear Energy Sink is proposed to achieve efficient passive seismic response control of structures.The research is carried out by combining numerical simulation with experimental research.The specific innovations and work include:(1)The analytical model of magnetic force of rectangular magnet is established by equivalent magnetic charge method,and the analytical expression of non-linear interaction force between two magnets is obtained.A new type of non-linear energy well with smooth negative stiffness and double potential well characteristics is proposed by utilizing the essential non-linear restoring force relationship of the interaction between permanent magnets and by reasonably choosing the size and layout of magnets.Magnetic Bi-stable Nonlinear Energy Sink(NES)is used to control the seismic response of structures.(2)For the typical analysis model,the numerical parameters of MNES,cubic NES and TMD control devices are optimized by using impulse loads,and the differences in the performance of the optimized control methods are investigated.The results show that the control performance of magnetic NES is better than that of the existing cubic NES,and the robustness of MNES to the dynamic characteristics of the main structure is better than that of TMD.The robustness of MNES to the variation of the peak value of ground motion is equal to that of TMD.(3)The power spectrum is constructed by using numerical wavelet transform,and the control mechanism of MNES is analyzed in time-frequency domain.The analysis results show that magnetic NES can produce more significant and sustained resonance behavior in broad-frequency domain for the main structure in the process of earthquake action,so that the device can play a better seismic performance.This wide-band internal resonance characteristic,especially the capture behavior of instantaneous sub-harmonic internal resonance,is insensitive to the change of the fundamental frequency of the main structure,so its vibration control performance has strong robustness.(4)The influence of friction damping on the control performance of MNES is studied,including the peak value of ground motion records and the friction coefficient.The results show that the control performance of frictional MNES is almost the same as that of viscous MNES.Friction-magnetic NES still maintains good seismic control performance and robustness in a certain range of variation of peak ground motion and friction coefficient.(5)Taking the Guangzhou TV Tower benchmark model as an engineering example,the response characteristics of the MNES control system under short and long ground motions are studied,and the wavelet power spectrum of the response process is constructed to comprehensively analyze the time-frequency effect of earthquake motions on the super-high-rise MNES system.The results show that the response of super-high-rise structures is significantly increased by long-period ground motions.The MNES designed with the optimal parameters can control the short-period and long-period seismic responses,and the control performance has good robustness to the predominant period of ground motions.(6)The MNES device model is designed and manufactured.The reciprocating performance test and parameter correlation test of the device model are carried out.The theoretical model error is corrected by numerical identification technology.On this basis,the model shaking table test of MNES vibration reduction control system is carried out.The results show that the numerical simulation and experimental results are in good agreement,the accuracy of numerical simulation and the rationality of theoretical analysis are verified.Under the condition that the actual parameters of the model deviate from the theoretical design values,magnetic NES still performs well in shock absorption control performance.It has strong robustness.