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Electrorheological (ER) fluids exhibit damping and stiffness properties which can be modulated by several orders of magnitude when subjected to strong electric fields. In the case of quasi-steady flow an increase in yield stress (from 0 to 3 kPa) is characteristically observed when the field is applied. Newtonian stresses are relatively unaffected by the electric field. A potential application of ER materials is the damping and isolation of dynamically excited structures. In order to capitalize on the unique properties of ER materials in this application it is desirable that the material be configured in a device in such a way that when the device undergoes characteristic motions, the device forces can be modulated to a significant degree (a factor of 10 or more). Because the range of adjustable forces is closely linked to the ratio of finite field-controllable, and flow-independent yield stresses to uncontrollable, and flow-dependent viscous stresses, it is desirable for controllable ER dampers to operate at low flow rates. In addition to the range of available forces, ER dampers should also perform well in other regards. They should have a short characteristic time, low stored electrical energy, and forces high enough to be effective for the intended application. Because of their low yield stresses, ER materials must flow over large surfaces to generate high forces and maintain a large degree of adaptability. In a cylindrical configuration, this can be accomplished by forming multiple flow paths with a series of concentric annular ducts. These ducts can be connected in parallel to maximize the range of adjustable forces or in series to maximize the absolute force levels. A synergistic result is obtained when groups of ducts are interconnected in parallel and in series within a single device. This paper presents the details of a realization of a new design paradigm for dampers which incorporates these issues. The ER damper features multiple concentric electrodes which are electrically in parallel, but may be hydraulically inter-connected through multiple paths. The number of possible interconnections of N concentric ducts is 2(N-1). Each configuration has distinctly different properties. The design of three ER dampers that span a range of performance criteria is presented in this paper. An analysis of these device configurations is completed in closed form by virtue of a linear approximation to the non-Newtonian ER Poiseuille flow equation. These analyses show that high-force ER devices which require low energy, and respond quickly, are feasible.
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