JOURNAL zyxwvutsrqp OF zyxwvutsrqp SlRoCnrrW COmOL, Vot. zyxwvu 4 N. 2 DECEMBER zyxw 1997 A Scale Study of Electro-rheological Fluid Dampers 5 F. Gordaninejad and R. Bindu Department of Mechanical Engineering University of Nevada Reno, Nevada 89557 zyxwvut - USA Abstract. The go.al of this study is to develop a scale analysis for predicting the behavior of cylindrical electro-rheological fluid (ERF) dampers. Theoretical and experimental scale studies are conducted to investigate the effects of the length of dampers and applied electric field strength on the damping and stiffness coefficients of ERF shock absorbers. It is demonstrated that by employing the results obtained from smaller size prototypes, the damping coefficient of larger size dampers can be estimated with reasonable accuracy. Key words: Electro-rheological fluid, dampers, semi-active, scale analysis 1 Introduction Many mechanical systems and civil structures undergo unwanted vibration. For example, bridges are constantly under predictable vibration (e.g., wind excita- tions and traffic loads) and sometimes unpredictable strong motions such as severe storms and earthquakes. Large civil structures should have the ability of dissipating considerable amount of energy under earthquakes and strong storms. Passive, semi- active, active and hybrid devices can potentially be used to suppress predictable as well as unpredictable structural vibration. Although passive energy-absorption devices, such as base isolations, friction and viscoelastic dampers, and bracing sys- tems offer some capability to suppress the vibration of structures, they may not be able to control the motion under severe and unpredictable dynamic loads. Semi-Active vibration control devices are receiving significant attention because they can offer combined advantages of passive and active systems. Examples of such devices include variable orifice dampers (Shinozuka, et al, 1992, Kawashima, et al, 1992, Mizuno, et al, 1992, Constantinou, et al, 1993, Sack et al, 1994, Pat- ten et al, 1994, Kurata et al, 1994), variable stiffness devices (Kobori et al, 1993, Inaudi, and Kelly, 1994), friction controllable isolators and braces (Akbay and Aktan, 1990, 1991, Dowdell and Cherry, 1994, CherryJ994, Feng and Shinozuka, 1990). Of special interest, are those shock absorbers that are controllable. A class of active controllable devices utilizes fluids, such as electrorhoelogical fluid (EFU?), has been established. There has been numerous investigations on ERF dampers in recent years, for example: (Ehrgott and Masri, 1992, 1994, Gavin et al, 1994a, 1994b, Gavin, 1994, Gordaninejad et al, 1993, 1994a, 1994b, 1997, Makris et al, 1995, 1996, Stanway et al, 1985, 1987). The readers are refereed to, for example, (Stanway, et a], 1996), if they are interested in an extensive state-of-art review of the literature on ER fluids and devices.