Dynamic vibration absorbers (DVAs) have been designed with variable spring and damping elements to enable realtime
or non-real-time adaptation to vibration conditions. Mass, the third element of a DVA, is more difficult to adjust.
The subject paper describes an experimental study of a small electromagnet immersed in magnetorheological (MR)
fluid and vibrated at a single frequency by an electrodynamic shaker as force and acceleration data are acquired.
When the magnet is energized, MR fluid clings to it, potentially allowing for design of a DVA with variable mass and
even damping, as the shape of the electromagnet-MR fluid mass changes. It is found that the effective mass of the
system depends on the vibration conditions, with less mass adhering at higher frequencies and displacements, but
significant increases in mass are possible at lower frequencies and displacements. The paper outlines the experimental
apparatus used, presents data acquired, and proposes a dependency of the effective mass on frequency and displacement.
A Bouc-Wen element has been employed by a number of researchers to model magnetorheological (MR) linear dampers with success. In this work, a modified commercial MR brake was modeled using a Bouc-Wen element and experimental data gathered on the torque response of the brake to oscillation. An optimization was undertaken using torque and displacement time-series data to determine the parameters of the brake model, and comparisons were made between experimental and predicted torque response.
Two control techniques are explored analytically for a dynamic vibration absorber with a magnetorheological fluid damper replacing the absorber dashpot. The approaches include skyhook control and an approximation to a linear quadratic optimal control. The approximate-optimal control, which attempts to match the magnetorheological damper force to an optimal control force based on a linear absorber, is shown to improve the dymanic absorber performance over a substantial range of excitation frequencies and force levels, while the skyhook approach is less successful. Detuning the absorber natural frequency below the optimal detuning for a linear absorber improves performance in the approximate- optimal case.