Performance Test On Multi-stage Coil Magnetorheological Damper And Its Application In Structural Vibration Mitigation

Structural vibration control technology has been studied for more than four decades,a lot of achievments have been made and successfully applied in different kinds of engineering structures.As a representative semi-active control device,magnetorheological damper has received extensive attention from scholars both at home and abroad.Magnetorheological damper is a kind of damping device which is developed by using the fast reversible rheological characteristics of magnetorheological fluid under magnetic field,which has the advantages of large damping force,.low low energy consumption,quick response,and good control effect and so on,and more precison structural vibration control can be achieved under seismic excitation due to the adjustable damping force under different currents.Though a lot of research has been studied and gratifying achievements have been made in the aspects of design of magnetorheological damper,mathematical model,semi-active control strategy,shaking table test and dynamic analysis of controlled structure,many problems still exists and need further study,espacilly the research about the multi-stage coil magnetorheological damper.The coils are parallel connected with each other,and the damping force characteristics and energy dissipation capacity differs when different combinations of coils are enegized,and a new semi-active control strategy can be proposed based on the characteristics of multi-stage coil magnetorheological damper,which is simple,convenient,and can improve the influence of time delay caused by the conventional multi-state control strategy,as well as simplify the design of the controller.Thus,conducting performance test on multi-stage magnetorheological damper and its application in structural vibration control is of great significance.In this dissertation,method combining experimental study,theoretical analysis and numerical simulation is adopted to systematically study the mechanical property of multi-stage coil magnetorheological damper,mathematical model,elasto-plastic time history analysis of controlled structure and optimization analysis.The main work is as follows:(1)Performance test on multi-stage coil magnetorheological damperConducting performance test on multi-stage coil magnetorheological damper under different currents,displacement amplitudes and excitation frequencies when different coil combination(one coil,three coils and five coils)are applied current,to study the varing law of damping characteristics of the magnetorheological damper with respect to current,displacement amplitude and excitation frequency,as well as the energy dissipation capacity.(2)Micro mathematical model of magnetorheological fluidFrom the micro aspective,the chain mechanism of ferromagnetic particles in magnetorheological fluid under the magnetic field is analyzed based on the magnetic dipole theory,the stability of single chain and two-chain structure is discussed,and the compact-two column micro model of magnetorheological fluid is proposed to calculate the yield shear stress of magnetorheological fluid.(3)Magnetic analysis of multi-stage coil magnetorheological damperThe finite element model of multi-stage coil magnetorheological damper is established,magnetic field distribution is simulated when each coil is applied current,and the Gauss function is adopted to fit the simulation results,finally the calculation formula is obtained to calculate the magnetic induction intensity of each effective damping gap when different combination of coils are energized;theoretical analysis of the magnetic field distribution of the multi-stage coil magnetorheological damper according to the Ampere circuital theorem,and the simplified formula for calculating the average magnetic induction intensity of the effective damping gaps is deduced,which provide a basis to establish the mathematical model of multi-stage coil magnetorheological damper.(4)Mathematical model of multi-stage coil magnetorheological damperBased on the micro mathematical model of magnetorheological fluid and the magnetic analysis of the damper,the micro-macro model of multi-stage coil magnetorheological damper is finally established by adopting the quasi-static model of magnetorheologic damper,which can be used to calculate the damping force of multi-stage coil magnetorheological damper when different combinations of coils are applied current and provide a basis for the dynamic analysis of magnetorheological damping structure.(5)Elasto-plastic dynamic analysis of the controlled structure with magnetorheological damperBased on the space frame model,the dynamic analysis program for uncontrolled space frame structure and controlled structure with magnetorheological damper is developed using MATLAB,in which the threefold line stiffness retrograde model is employed to simulate the stiffness retrograde characteristics of the member when elasto-plastic deformation is produced.The displacement and acceleration responses of the controlled and uncontrolled structure are calculated and analyzed under different seismic waves.(6)Optimization analysis of structure with magnetorheological dampersLocation optimization analysis of magnetorheological damper under different objective functions and different number of dampers is conducted based on the Genetic Algorithm,the optimization placement of magnetorheological damper is obtained.A new control strategy is also proposed based on the characteristics of multi-stage coil magnetorheological damper,the proposed control strategy is simple and convenient,which reduces the influence of time delay of the conventional multi-stage control strategy effectively and simplify the design of the controller.Innovations of this dissertation are as follows:(1)The micro mathematical model of magnetorheological fluid is proposed based on the magnetic dipole theory,which can be used to calculate the yield shear stress of magnetorheological fluid under different influencing factors;(2)Based on the micro model of magnetorheoligcal fluid and the magnetic field analysis of multi-stage coil magnetorheological damper,the mathematical model of multi-stage coil magnetorheological damper is proposed through the fluid mechanics analysis of the magnetorheological damper;(3)The elasto-plastic dynamic analysis program of the uncontrolled and controlled structure with magnetorheological damper are developed,based on which the placement optimization analysis is conducted,a new control strategy is also proposed based on the characteristics of multi-stage coil magnetorheological damper,which is simple and convenient.