Design and dynamic characterization of a large-scale eddy current damper with enhanced performance for vibration control

Eddy current dampers (ECD) are promising devices for vibration control of dynamic systems, but their application in civil structures is very limited due to a low damping density. This study describes the development and dynamic characterization of a large-scale rotary ECD with enhanced performance for structural applications. The rotary ECD consists of a conductive rotor, a stator with permanent magnets, and a set of ball screw which converts the linear motions across the damper into rotations of rotor. The torque at different rotating speeds is evaluated by using a 2-D analytical method considering the reaction magnetic field caused by eddy currents. Laboratory experiments are conducted to validate the numerical results obtained for a simple eddy current torque generator and a large-scale ECD. It is shown that the analytical model agrees with nonlinear finite-element simulations, but is higher than the test results. The large-scale rotary ECD achieves a high damping density up to 24.9 MN·s/m4 at a low speed. Moreover, the damping force of rotary ECD is highly nonlinear and self-limiting as a function of rotating speeds; it first increases with speeds and after reaching a maximum at a critical speed it decreases for higher speeds. Numerical simulation on seismic control of a SDOF system and a 5-DOF system showed that the rotary ECD performs as well as the fluid viscous dampers having the same secant damping coefficients. Finally, effects of changing design parameters on force-speed curve are studied in details.