Eddy current damper for the Labshare remote laboratory Shake Table rig

The design and performance of an eddy current damper for the Labshare remotely operated "Shake Table" multi-storey building vibration rig is described. The damper comprises stationary E-cores on either side of a copper plate attached to each storey. An approximate formula for the damper retarding force F is derived, of the form F = -kuI² for plate velocity u and E-core current I, and a criterion for its validity is established in terms of the magnetic Reynolds number. A close fit to measurements of the force using a load cell is obtained for k = 0.401 N/(ms^-1 A²). This was about 12% lower than the force determined by three-dimensional (3D) finite element analysis (FEA) using ANSYS 12.1, but the error can be attributed to manufacturing imperfections. Students can use the force formula in their investigation of closed-loop control of the Shake Table vibration. More generally, a formula for the force constant k can be used for the approximate design of any similar E-core damper.