Modelling of nonlinear magnetic damping in vibrating coupled structures

Vibrations of a three degrees of freedom mechanical structure are attenuated using a magnetic damper, obtained by coupling a conductive structure with a magnetic field generated by permanent magnets. The magnetic dissipations are experimentally investigated focusing on their nonlinearity with respect to frequency and amplitude of oscillations. The system exhibits two types of nonlinearities: one proper of the mechanical system and one of due to the magnetic coupling. The availability of an electromagnetic-motional model allows for the separation of these two effects. A frequency domain model to describe the magneto-mechanical interaction under harmonic excitation is developed by means of a partial element equivalent circuit of the conductive parts. The restitution magnetic force model is then introduced in the numerical model of the system. Results obtained by simulations are validated versus experimental measurements on the three degrees of freedom structure.