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

Time dependent motion induced eddy current forces can be quite difficu lt to compute. The movement of null flux coils between magnets is appr oached using a coupled boundary element - circuit approach to compute the forces on the structure. The technique involves treating the magne ts as a separate circuit whose current is dictated by the product of t he magnet thickness and the working coercivity, The mutual inductance between the windows of the moving null flux coil and the stationary eq uivalent magnet coil hold the key for predicting Lilt, guidance, and d rag forces on the coil The rate of change of these inductances with re spect to position determines the forces and currents. A steady state a pproximation to these forces is derived in addition to a numerical sim ulation when the steady state assumption is invalid. The results compa re favorably to laboratory results from a 4' diameter experimental tes t wheel.