Phenomenological Model of a Magnetorheological Damper

Semi-active control devices have received significant attention in recent years because they offer the adaptability of active control devices without requiring the associated large power sources. Magnetorheological (MR) dampers are semi-active control devices that use MR fluids to produce controllable dampers. They potentially offer highly reliable operation and can be viewed as fail-safe in that they become passive dampers should the control hardware malfunction. To develop control algorithms that take maximum advantage of the unique features of the MR damper, models must be developed that can adequately characterize the damper’s intrinsic nonlinear behavior. Following a review of several idealized mechanical models for controllable fluid dampers, a new model is proposed that can effectively portray the behavior of a typical magnetorheological damper. Comparison with experimental results for a prototype damper indicates that the model is accurate over a wide range of operating conditions and is adequate for control design and analysis. Introduction Passive and active control systems represent the two ends of the spectrum in the use of supplemental damping strategies for response reduction in civil engineering structures subjected to strong earthquakes and severe winds (see, for example, Soong 1990; Soong, et al., 1991; Housner and Masri 1990, 1993; Housner, et al., 1994). On the other hand, semi-active control systems combine the best features of both approaches, offering the reliability of passive devices, yet maintaining the versatility and adaptability of fully active systems. According to presently accepted definitions, a semi-active control device is one that has properties that can be adjusted in real time but cannot input energy into the system being controlled. Such devices typically have very low power requirements, which is particularly critical during seismic events when the main power source to the structure may fail. Moreover, because many active control systems for civil engineering applications operate primarily to modify structural damping, preliminary studies indicate that semi-active control strategies can potentially achieve the majority of the performance of fully active systems. Various semi-active devices have been proposed which utilize forces generated by surface friction or viscous fluids to dissipate vibratory energy in a structural system. Examples of such devices that have been considered for civil engineering applications include variable orifice dampers (e.g., Shinozuka, et al. 1992; Kawashima, et al. 1992; Mizuno, et al. 1992; Constanti1. Professor, Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556, Member ASCE. 2. Doctoral Candidate and Graduate Research Assistant, Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, IN 46556, Student Member ASCE. 3. Freimann Professor, Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556, Member ASCE. 4. Engineering Fellow, Lord Corporation, Mechanical Products Division, Thomas Lord Research Center, 405 Gregson Drive, Cary, NC 27511-7900. To appear in the ASCE Journal of Engineering Mechanics