Electrorheological dampers for structural vibration suppression.

Abstract

The ability to regulate forces by several orders of magnitude, in a matter of milliseconds, and with very little required input energy, is attractive for various actuation and control applications. This dissertation addresses the use of electrorheological (scER) materials in damping devices for structural vibration suppression. The physics of scER materials and devices which use them are reviewed. Electrorheological materials exhibit remarkable changes in properties (stiffness, damping, and yield properties) when subjected to strong electric fields (kV/mm). Suspensions of polarizeable particles in insulating dielectric oils, exhibit scER effects. At strain levels less than 0.5, the electric field enhances the stiffness and viscous damping of the scER material. In fully developed flow, an electric field dependent yield stress conveniently models the energy dissipation mechanisms. Primitive scER materials suffer from small yield stresses, high current densities and irreversible particulate sedimentation. Recently developed anhydrous scER gels mitigate these problems, but are shear-thinning at low shear rates. The pre-yield region of scER materials is very difficult to model. A simple analogy of a fluid with a variable yield stress permits an analysis based on the flow geometry. Using this analogy, the Navier-Stokes equations are solved for steady and transient scER flows. Closed form solutions, and simplified approximations to these solutions, are presented. The approximate solutions are useful in designing scER devices. Analytic modeling and small scale experiments are used to evaluate the design equations. The experimental results support the damper design procedures. The adjustable range of forces in dash-pot devices increases exponentially with the ratio of the gap width to plunger width. As the device design moves toward a larger dynamic range, (i.e. the viscous stresses decrease), the inertial response time increases, and pre-yield behavior becomes important. To model the complexities of the behavior of actual scER dampers, a multi-variate curve-fit of experimental data is applied. This method is successful in capturing the behavior of scER materials in complex geometries. This polynomial model can be used for simulations, and for feedback linearization.