Magnetic levitation force of composite magnets in a ferrofluid damper

Larger radical levitation force is favorable for enhancing energy dissipation in ferrofluid dampers. Utilization of composite magnet structures is one of the candidate methods to increase this force. The numerical, analytical and experimental methods of obtaining the levitation force exerted on composite magnet structures in ferrofluid dampers are summarized. The levitation forces of six composite structures are examined using these methods. It is shown that this force can be effectively increased by using composite structures compared with that by only one whole magnet. More than four times of increase of levitation force was obtained in our experiments. The analytical and numerical methods overestimate the levitation force, especially the analytical one. In comparison with the analytical results, the numerical results are much closer to the experimental ones, whose maximum deviation is 14.2%. The levitation force increases with the length and number of magnets composed of the composite structures. Other factors affecting the levitation force include pole spacing, permanent magnet moment and the permeability of ferrofluid. It is predicted by the analytical method that there is a positive correlation of the force with them in ferrofluid dampers.