Modeling and control of smart structures embedded with magnetorheological devices

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Engineering structures are the essence of supporting the development of society. However, quite often do they suffer from hostile dynamic loadings or external disturbances that may affect structural health or function. Modeling and control techniques can be applied to resiliently preserve structural health and function with a low energy cost, which is the main theme of the thesis. Smart structures embedded with semi-active control devices offer a promising solution to the problem, such as the magnetorheological (MR) damper (MRD), pin joint (MRP), and elastomer base isolator (MRE). This study first aims at exploring the solutions to the present problem in system modeling and controller design of MR based systems to effectively damp out unwanted vibrations as well as control the embodied energy level. Multi-variable hysteresis models for these structural members are developed, capable of effectively working in a wide scale of loading amplitude and frequency. The modeling objective is to illustrate the intrinsic nonlinearity with traceable relationships between model parameters and control signals in order to realize the field-controlled method for MR structure systems. Experimental data are obtained from a long-stroke MRD, a recent prototype of MRP and an MRE under different loading conditions for model identification and performance assessment. To achieve robustness, a second-order sliding mode controller is designed and applied to the MRE to provide a real-time feedback control of structures. The performance of the proposed technique is evaluated in the simulation of a seismically excited three-storey benchmark building model. To exploit the frequency domain advantage, this study also focuses on the cyclic dissipation of vibration-induced energy in the smart devices under a controlled magnetic field to analyze the energy relationships of the smart devices in the structures. A frequency-shaped second-order sliding mode controller (FS2SMC) is designed along with a low-pass filter to implement the desired dynamic sliding surface. The proposed controller can shape the frequency characteristics of the equivalent dynamics for the MR structure against induced vibrations, and hence, dissipate the mechanical energy flow within the devices to prevent structural damage. The energy spectra of a 10-floor building subject to four benchmark earthquakes are analyzed in terms of kinetic, damping, strain, and input energies to illustrate the capability of an energy-efficient embedded structure. The merits of FS2SMC in engineering structures can also be verified in a half-car model for reducing the roll angle while adjusting the spectrum to prevent natural modes of the structure under external excitations.
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