Modeling, Testing, and Validation of an Eddy Current Damper for Structural Vibration Control

Abstract

Eddy current damping has been widely applied in mechanical engineering; however, its adaptation for civil engineering applications remains rather limited due to its low density of energy dissipation. This study presents the development of a new type of eddy current damper and theoretical and experimental characterization of its damping properties. In addition to rectangular permanent magnets and conductive plate, both primary back iron and secondary back iron are considered in the proposed eddy current damper, which represents an improved design over previous configurations. The analytical method based on the charge model of permanent magnets is extended to simulate the extra damping effect of the primary back iron and secondary back iron, and the magnet field and damping properties of the dampers are evaluated analytically. The use of a back iron in the proposed damper is shown to increase the damping coefficients by a factor of up to 5. The analytical results are compared with those obtained with the finite-element analysis in terms of accuracy in magnetic field distributions, eddy current distributions, and damping coefficients. The linear assumption, which implies the damping force is linearly proportional to velocity in the analytical model, is also examined for different motional velocities and relative permeability of the permanent magnet. It is shown that the linear damping assumption in the analytical model is only valid for a limited range of low velocity, and this velocity range can be increased by reducing the thickness or conductivity of the conductive plate. In addition, a modification is needed for the analytical model if the relative permeability of the permanent magnet significantly deviates from the assumed value of 1.. Finally, the accuracy of the analytical model and the finite-element model is verified by experiment of a prototype damper mounted in a laboratory steel frame.