Simple Control Algorithms for MR Dampers and Smart Passive Control System
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This dissertation proposes simple and efficient control algorithms for seismically excited structures using MR dampers and a smart passive system based on MR dampers. Magnetorheological (MR) dampers are one of the most promising control devices for civil engineering applications to earthquake hazard mitigation, because they have many advantages such as small power requirement, reliability, and low price to manufacture. A number of control algorithms have been adopted for semi active systems including the MR damper. In spite of good features of previous studies, some algorithms have drawbacks such as poor performances or difficulties in designing the weighting matrix of the controller. Thus, the control algorithm is required, which is simple to use and efficient to give comparable or better performance over the previous algorithms. As a simple and efficient control algorithm, a modal control scheme and a maximum energy dissipation algorithm (MEDA) are implemented for the MR damper based control system. Modal control reshapes the motion of a structure by merely controlling a few selected vibration modes. Hence, a modal control scheme is more convenient to design the controller than other control algorithms. Although modal control has been investigated for the several decades, its potential for a semi active control, especially for the MR damper, has not been exploited. Thus, in order to study the effectiveness for the MR damper system, a modal control scheme is implemented to seismically excited ii structures. A Kalman filter is included in a control scheme to estimate modal states from physical measurements by sensors. Three cases of the structural measurement are considered as a feedback to verify the effect of each measurement; displacement, velocity, and acceleration, respectively. Moreover, a low-pass filter is applied to eliminate the spillover problem. In a numerical example, a six-story building model with the MR dampers on the bottom two floors is used to verify the proposed modal control scheme. The El Centro earthquake is used to excite the system, and the reduction in the drifts, accelerations, and relative displacements throughout the structure is examined. The performance of the proposed modal control scheme is compared with that of other control algorithms that were previously suggested. The maximum energy dissipation algorithm represents one control class which employs the Lyapunovâ„¢s direct approach to stability analysis in the design of a feedback controller. However, their potential for civil engineering applications using semi active control, especially with MR dampers, has not yet been fully exploited. This paper investigates the performance and the robustness of the maximum energy dissipation algorithm for civil engineering structures using MR dampers. The numerical examples contain the cable-stayed bridge and the nonlinear building. Various earthquakes are used to excite the systems. Through the series of numerical simulations, the performance is compared with that of other control algorithms that are previously proposed: The reduction in the drifts, accelerations, and relative displacements throughout the structure are examined according to the evaluation criteria. Meanwhile, to reduce the responses of the controlled structure by using MR dampers, a control system including a power supply, controller, and sensors is needed. However, it is not easy to apply the MR damper-based control system to large-scale civil structures, such as cable-stayed bridges and high-rise buildings, because of the difficulties of building up and maintaining the control system. iii Thus, this dissertation proposes a Ëœsmartâ„¢ passive damper system. The smart passive damper system is based on MR dampers. Of course, the MR damper is a semiactive device that needs an external power source to change the damping characteristics of the MR fluids. However, the smart passive damper system based on MR dampers is not using an external power source, but self-powered by an electromagnetic induction (EMI) system that is attached to the MR damper. The EMI system consists of a permanent magnet and a coil. According to the Faradayâ„¢s law of induction, the EMI system changes the kinetic energy of the MR damper to the electric energy and then the electric energy is used to vary the damping characteristics of the MR damper. Therefore, it is easy to build up and maintain the proposed smart damper system that consists of the MR damper and the EMI system, because it does not require any control system such as a power supply, controller, and sensors. To verify the effectiveness of the proposed EMI system, the performances are compared with those of the semi active MR damper.

Advisor : Professor In-Won Lee

Presented By:
Sang-Won Cho
Department of Civil and Environmental Engineering
Korea Advanced Institute of Science and Technology[h]r
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