| Earthquake is a kind of natural disaster that seriously threatens the safety of human life and property.How to improve the seismic capacity of flexible structure,and reduce losses caused by earthquakes,has always been a research hotspot in the field of structural engineering.With the continuous development and innovation of flexible structures,the strict aseismic fortification standard puts forward higher requirements for structural isolation.Due to its fixed structure and performance parameters,traditional passive isolation bearing has limited effect on the attenuation of random and changeable ground motion,which cannot meet the development requirements of high performance,multifunction and intelligence of engineering structure.Intelligent material and structure possess the characteristics of "self-perception,self-adaptation and self-repair",showing their broad application prospects in the field of engineering isolation.As one of cuttingedge intelligent materials,magnetorheological elastomer(MRE)stands out as its superior magnetic-controlled performance.MRE-based device possesses tunable characteristics of stiffness and damping,which can not only isolate the vibration energy,but also realize the role of limitation and energy-consumption.Therefore,smart device and system based on MRE are expected to be applied in flexible structural field,so as to protect people's life and property safety.At present,some breakthroughs have been made in the application of MRE in the field of seismic isolation engineering,but there are still some key problems need to be solved.Firstly,there exist difficult excitation and long time-delay problems in MRE application,which would lead to the system's big energy consumption and low control precision.Secondly,current research of MRE device mainly focus on a form design of device structure and magnetic circuit analysis,which seriously lack the object-oriented design and optimization theory.On the one hand,the advantages of smart control of MRE cannot be maximized;on the other hand,it is difficult to popularize MRE device from experimental research to engineering application.Thirdly,the magnetic-induced timedelay phenomenon and dynamic model with low precision of MRE applied device,would make the control effect of isolation system uncertain,which may easily reduce or even deteriorate the performance of designed controller.Fourthly,there are few research on the exprimental control of MRE isolation under random seismic wave excitation in domestic,and mainly confined to numerical simulation,while the actual experimental control study,especially the experimental study of MRE isolation system considered time delay,needs to be further investigated.Centering on the above key scientific issues and takes light steel frame structure as the isolation application object,systematic research on MRE material,device and control is carried out in this thesis,and the main contents are summarized as follows:(1)In order to solve the mutually conditioned bottleneck problem of excitation and energy consumption,time-delay and control accuracy,a multi-component micro/nano composite MRE material with high performance is developed.Firstly,based on the particle modification method,a novel petaloid CIP@Fe Ni particle is synthesized.By utilizing multiple magnetic particles combined into elastomer,MRE materials with high magnetorheological effect and rapid response under weak magnetic field are developed.Secondly,three characterization systems,such as magnetic dynamic mechanical properties,magnetic response time characteristics,and long time dynamic response characteristics of MRE materials are established.By which,the magnetorheological properties and response time performance of MREs are tested and analyzed effectively.Lastly,based on the microscopic mechanical mechanism,a model of macroscopic electromagnetic-force coupling response mechanism of MRE is established,and the response time of MRE is effectively identified.(2)Aiming at the problem that the structural developing of MRE devices is difficult to match with the practical application demand,,an object-oriented design and optimization theory is proposed.Firstly,theoretical analysis and design of the core component and the overall configuration of MRE iaolstion bearing(MRE-IB)are realized,according to the requirements of application object and seismic design conditions.Secondly,combined with the electromagnetic performance of MRE and magnetic circuit design criteria,multi-objective optimization system of the geometry and performance of MRE-IB is established,so as to achieve three optimization objectives of superior magnetic-controllable performance,low power consumption and fast response time.Lastly,the efficient and accurate solution of the optimal problem of MRE-IB is realized through the joint programming of genetic algorithm and finite element method.Then the MRE-IB is manufactured and assembled,and a verification test system is built to analyze and verify the optimization results.(3)To solve the problem of magnetic-induced time delay problem of MRE device,and on the basis of conventional mechanical properties characterization.The theory of static and dynamic response time characteristics of device is built and the method of response measurement is formed,based on the.Firstly,based on the optimized MRE-IB,the vibration transfer characteristics and force-displacement characteristics of MRE-IB are characterized by excitation sweep method and ellipse method,respectively.Then based on the theoretical model,the variation rules of the natural frequency,equivalent stiffness and equivalent damping of the bearing are obtained.Secondly,the magnetostatic/dynamic response time characteristics of MRE-IB,including current,magnetic field and force responses,are studied,so as to further evaluate the time-delay of MREIB.Lastly,the cause and composition of response time of each physical field in the device are analyzed,and some effective suggestions for improving the response speed are given.(4)Aiming at the problem of the difficulty in accurate modeling of MRE device under different working conditions,BP and NARX neural network modeling strategies based on genetic algorithm and particle swarm optimization(PSO)algorithm are designed to effectively describe the forward and reverse dynamics characteristics of MRE-IB.Firstly,based on the dynamic mechanical test data of MRE-IB,the Bouc-Wen,optimized BP and NARX neural network forward models of MRE-IB are established,so as to instead of the real bearing to generate output force in numerical simulation.Secondly,the optimized BP and NARX neural network backward models are also established,so as to determine the current in control experiment.Lastly,the accuracy of each model is compared and analyzed,so as to select the optimal combination of forward and backward models,and a joint simulation is conducted to verify the effectiveness of bulited model.(5)To solve the problem of the difficulty in suppression of seismic wave vibration in time-delay systems,a linearquadratic regulator(LQR)controller based on time-delay and state feedback is designed.Firstly,a set of miniature MRE flexible light steel frame system is set up,and numerical model analysis is carried out for the system,in which the motion and state equations are established.Secondly,based on MRE semi-active control conditions,On-Off control,fuzzy control,LQR control and time-delay LQR(TD-LQR)control algorithms are designed for the isolation system.Then,the control simulation system of MRE isolation system is constructed,and the simulation analysis and comparison of control effect of each algorithm are realized.Lastly,the real-time control experiment of MRE isolation system is carried out,and the effectiveness of TD-LQR control algorithm is verified under the excitation of seismic wave. |
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