Calculation of the Torque on a Permanent Magnet Rotating in a Conducting Tube

The aim of the present paper is to investigate the behavior of a permanent magnet rotating inside a conducting tube of finite length. Especially, the linearity of the dependence of the torque acting on the magnet due to the eddy currents induced in the tube on the number of revolutions per minute is of interest. The movement of the conductor relative to the magnet is taken into account by a Minkowsky transformation. The resulting non symmetrical equations system is solved by a biconjugate gradient method. The calculations have been verified by comparison with a time stepping method and with measurements