Performance Assessment Of MRE,Variable Stiffness Isolator,and Its Smart Vibration Isolation/Reduction Systems

Nowadays,the characteristics of engineer structures are as follows:the diversification of the constructing model and the super bigness of constructing scale.Meanwhile,huge progresses have been made in the researches and applications of smart materials and smart strutures.Health monitoring systems using distributed optical fiber sensors,SMA actuators,MRF/ERF dampers,and piezoelectric sensors have been proposed,studied and manufactured.With the characters of self-sensing,self-adaptive and self repairing,smart materials and strutures have shown huge protential in engineering structure applications.As a novel smart material,MRE has shown continuous,accurate and quike responding tunable shear modulus,which is poromising to be made into smart control systems.Starting from this background,the research has followed the three main contents:MRE’s properties,MRE device its mechanical model,MRE devices’ applications and thier effectiveness.The research has conducted a series of simulations and experiments,and proposed the method to build the constitutive model of MRE,the mechanical model of MRE devices,and the simulation model of structures installed with MRE devices step by step.The primary research work and conclusions of this thesis are comprised of five aspects as follows:(1)MREs have been fabricated and dynamic tests,shear tests and magnetoconductivity tests have been carried out.It is proved that MREs have three dynamic properties:magnetorheological effects,nonlinearity and viscoelasticity.(2)The drawbacks of the existing constitutive models of MRE were discussed based on the material tests data.Then the revised Bouc-Wen model and its parameter optimization algorithm have been proposed.It is proved that the proposed model can accurately resemble and predict the dynamics of MRE.Besides,the hysteresis loop character based parameter optimization algorithm has been proved to be effective to find the stable solution to quantify the dynamic properties of MRE.(3)The disadvantage of existing MRE isolators have been discussed,and a new type of MRE variable stiffness conical isolator using separate coils and substitutes have been proposed.Mechanical model of the proposed device has been built based on the proposed constitutive model,basic mechanical equations and electromagnetic finite element analysis.Experiments were carried out to verify the effectiveness of the device and the accuracy of the mechanical model.At last,modifications were carried out based on the nonlinear 3D electromagnetic finite element analysis to better predict the variable stiffness of MRE devices.It is proved that the proposed mechanical model is both accurate and concise enough and it is proved that the proposed device save 66%MRE,50%copper and 75%energy to generate control force compared to existing MRE devices.(4)The design procedure and the control algorithm of the MRE isolation system have been proposed on the basis of the mechanical model.The corresponding isolation system for a relic display case and a 4-story masonry structure have been designed and simulated in Simulink.After simulation,the structure shake table tests were carried out to verify the isolation effectiveness.It is shown that the isolation effectiveness satisfy the design objective when following the design code based design procedure.The simulations and the shake table test have shown about 10%decrease in isolators’deformation.(5)The design procedure and the control algorithm of the MRE variable stiffness TMD system have been proposed on the basis of the mechanical model.The simulation model of a constructing bridge tower installed with MRE variable stiffness TMD has been built and the natural frequency tracking control algorithm has been proposed.Simulation were carried out to estimate the effectiveness of the TMD systems and shake table tests were conducted to verify the effectiveness of the design procedure and the accuracy of the simulations.It is proved that the design procedure has the ability to design proper variable stiffness TMD system,and the stiffness tunable TMD system can improve the effectiveness by 10%～30%.