CALCULATION OF MOTION-INDUCED EDDY-CURRENT FORCES IN NULL FLUX COILS

Time dependent motion induced eddy current forces can be quite difficult to compute. The movement of null flux coils between magnets is approached using a coupled boundary element - circuit approach to compute the forces on the structure. The technique involves treating the magnets as a separate circuit whose current is dictated by the product of the magnet thickness and the working coercivity, The mutual inductance between the windows of the moving null flux coil and the stationary equivalent magnet coil hold the key for predicting Lilt, guidance, and drag forces on the coil The rate of change of these inductances with respect to position determines the forces and currents. A steady state approximation to these forces is derived in addition to a numerical simulation when the steady state assumption is invalid. The results compare favorably to laboratory results from a 4' diameter experimental test wheel.