ER DEVICES FOR CONTROL OF SEISMICALLY EXCITED STRUCTURES

ABSTRACT This study illustrates the behavior of a closed-loop vibration control system making use of electrorheological electrorheological ( er ) devices. ER fluids exhibit damping and stiffness properties which can be modulated by orders of magnitude when subjected to strong electric fields (kV/mm). An increase in yield stress (from 0 to 3 kPa) is characteristically observed when the field is applied. A Lyapunov-based controller results in control decisions which are independent of the structural model, and are therefore insensitive to modeling errors. Structures operated according to the control rule maintain an anti-resonant condition. 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 yield stresses to uncontrollable 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 have a short characteristic time, low stored electrical energy, and forces high enough to be effective for the intended application. The er damper described herein features multiple concentric electrodes which are electrically in parallel, but may be hydraulically interconnected through multiple paths.