Theoretical And Experimental Study Of Structural Vibration Control Based On Eddy Current Dampers

Permanent magnet Eddy Current Dampers is a new speed-type passive energy-consuming device in civil engineering.Recently,Professor Chen Zhengqing in Hunan University has invented a new type of Eddy Current Tuned Mass Damper（ECTMD）based on a plate-type Eddy Current Damping unit and invented a variety of ball screws with high energy density Type axial eddy current damper（BS-ECD）by integrating the ball screw with a plate-type eddy current damping unit.From the point of view of mechanical properties,BS-ECD is a nonlinear velocity-type damper,and its damping force mathematical model is significantly different from tradition al velocity-type dampers such as oil dampers.Therefore,it is necessary to systematically analyze its vibration control performance and perfect its parameter design method.On the other hand,ECTMD has the advantages of high start-up sensitivity,good damping linearity,and easy adjustment and it can be made into a small tuned mass damper（TMD）suitable for wind tunnel experiments to investigate the bridge vortex-induced vibration control by using TMD.In this paper,starting from the needs of vibration control in civil engineering structure,the BS-ECD’s vibration reduction effect on general SDOF structures subjected to different excitation,and on cable’s multi-modal vibration control is analyzed through theoretical analysis and numerical simulation.Then,by using sectional model wind tunnel experiments,the vortex-induced vibration（VIV）control theory based on ECTMD is studied.The main content and research results of the paper are as follows:（1）The energy dissipation formula and equivalent damping ra tio of BS-ECD under harmonic load are derived.Then,the BS-ECD’s damping force curve and hysteresis curve are compared with nonlinear viscous fluid damper under the same equivalent damping ratio,which reveals the energy consumption characteristics of BS-ECD.Using displacement amplification factor,damping force-frequency response function,and load transfer rate as evaluate criterion,the vibration control effect of BS-ECD and nonlinear viscous fluid dampers on SDOF structures subjected to harmonic excitation is compared and analyzed,revealing the influence of BS-ECD design parameters on its vibration control performan ce.（2）The equivalent damping ratio formula of BS-ECD under seismic load is derived.Taking structural displacement response and acceleration response,damper control force,and energy consumption as evaluate criterion,the control performance of dimensionless design parameters such as equivalent damping ratio,critical velocity,and the apparent mass of BS-ECD on seismic response of SDOF structure are systematically studied through structural seismic time history response analysis and response spectrum analysis.Finally,the parameter design method of BS-ECD under seismic load is established after comparing it with the nonlinear viscous liquid damper.（3）In the framework of equivalent linearization theory,based on the equivalent linear damping coefficient formula of BS-ECD,the relationship between the cable’s dimensionless additional modal damping ratio and the design parameters of BS-ECD is derived.Taking the minimum value of the additional damping ratio of the first several modes of cables reaching maximum as the optimization criterion,the parameter optimization design method of BS-ECD is established.Finally,the sensitivity of the cable’s additional modal damping ratio to the variation of the optimal parameter deviation and displacement am plitude of the damper is clarified.（4）A small-scale ECTMD suitable for wind tunnel experiment of bridge sectional model is developed.Based on this,the wind tunnel experiment of TMD control performance for vertical VIV of bridge is carried out.Taking equivalent damping ratio,bridge VIV displacement amplitude and TMD working stroke length as control indexes,the influence of TMD design parameters such as mass ratio,frequency ratio and damping ratio on control effect is studied.Based on the experiment results,the existing TMD control theory and parameter design method in bridge vortex-induced vibration are compared,and the TMD parameter design principle of bridge vortex vibration control is proposed.