Damping Performance Analysis Of Semi-active Pendulum TMD Based On Magnetorheological Elastomer

Earthquake disaster is the first group of all disasters,and strong vibration can easily lead to damage or collapse of buildings,resulting in huge casualties and economic losses,so it has been the goal of experts and scholars in the field of earthquake engineering to improve the seismic capacity of structures.With the continuous development of China’s economy science and technology,more and more structures have changed their basic dynamic characteristics during use due to factors such as change of use function,sudden load changes and reinforcement transformation,and the seismic capacity of the structure does not match the original design.Pendulum Tuned Mass Dampers(PTMDs)are widely used in structural vibration control due to their simple construction,ease of design and good damping effect.However,once the PTMD is set,its stiffness and damping characteristics will remain fixed,thus limiting its applicability to situations where the structural frequency changes.Semi-active control in structural vibration control combines the advantages of active and passive control,with the reliability of passive control and the adaptability of active control,and has therefore become the mainstream structural vibration control method.Magnetorheological elastomers(MREs)are a new type of intelligent material whose mechanical properties can vary with the applied magnetic field,and this property makes MREs exhibit controllable damping and stiffness at a macroscopic level.In this paper,a semi-active frequency tunable pendulum tuned mass damper(MRE-PTMD)based on MRE is proposed to address the shortcomings of PTMD,combined with the intelligent adjustable stiffness of magnetorheological elastomer.The main research contents and the main conclusions drawn around the MRE-PTMD are as follows:(1)The design configuration of the MRE-PTMD is proposed,the operating principle of the damper is elaborated,the formulae for calculating the torque and equivalent stiffness provided during the shearing process of the magnetorheological elastomer are derived,and the feasibility of the adjustable frequency of the damper is theoretically verified;subsequently,the equations of motion of the coupled system of the damper and the main structure are established based on the Lagrange equations;finally,the equations of state of the coupled system of the MRE-PTMD and the multi-degree-of-freedom structure are derived in the modal domain,providing a theoretical basis for subsequent research.(2)The design method of the MRE-PTMD is introduced with an example,and the magnetic circuit part of the MRE-PTMD is modelled and analyzed with the electromagnetic simulation software ANSYS Maxwell.The results show that the magnetic circuit of the damper can meet the requirements for the normal operation of the MRE,and the simulation results are consistent with the presumptions;the magnetic induction intensity in the MRE meets the linear relationship with the applied current excitation,and the frequency of the damper is approximately a cubic function of the applied current excitation,which provides a control basis for the subsequent modelling and simulation.(3)A semi-active control strategy for MRE-PTMD is proposed based on the short-time Fourier transform.The performance of passive and semi-active control of a single-degree-of-freedom structural model under seismic excitation before and after frequency variations was numerically simulated using Matlab/Simulink.The seismic reduction effect of MRE-PTMD was examined using the main structural displacements,peak accelerations and the overall root mean square value of the reduction rate as evaluation indicators.The results show that the short-time Fourier transform-based variable frequency control algorithm can track the main structure frequency in real time and quickly adjust the damper frequency to keep it in harmony with the main structure frequency,and that the MRE-PTMD has good damping effect before and after the main structure frequency change,especially after the main structure frequency change compared to the out-of-tune passive MRE-PTMD.(4)The seismic damping performance of MRE-PTMD under near-fault impulsive earthquake is investigated on the example of a five-story structure.The instantaneous frequency of the main structure is identified by tracking the top layer displacement during the simulation,and a numerical simulation model is built in Matlab/Simulink for analysis.The results show that both passive MRE-PTMD and semi-active MRE-PTMD control have damping effect before and after the change of main structure frequency,but the damping effect of both decreases after the change of main structure frequency.Both passive MRE-PTMD and semi-active MRE-PTMD control the peak displacement response of the structure at each level less effectively than the peak acceleration response of each level.The damping effect of both decreases significantly after a change in primary structural frequency,but the semi-active MRE-PTMD has some damping advantage over the dysregulated passive MRE-PTMD.