Effective mass and energy loss factor in granular dampers

FERREYRA, MARÍA VICTORIA; PUGNALONI, LUIS ARIEL; JOB, STÉPHANE; BALDINI, MAURO

Puerto Varas

Workshop; Southern Workshop on Granular Materials 2018; 2018

A granular damper is a passive device used to attenuate mechanical vibrations. Such a system is an enclosure containing particles which is usually connected to a vibrating structure. The energy is dissipated thanks to inelastic collisions and friction between the grains and between grains and the inner walls of the container.We simulate the behavior of a granular damper filled with spheres using Discrete Element Method. Our device is attached to an oscillating rigid plate via a spring and a dashpot, through which a harmonic vertical motion is applied. We characterize its mechanical response, as a function of frequency and amplitude, in terms of an effective mass and a loss angle. The latter are estimated from the magnitude and the phase of the driving force to acceleration ratio.At moderate amplitudes, when the particles do not collide with the ceiling of the container, we find that the effective mass of the device and the loss factor both scale with the driving acceleration as observed in recent experiments. In addition, under conditions for which the particles collide the ceiling of the enclosure, a new phenomenology is observed. In particular, the effective mass of the damper presents a non-monotonic dependence on the vibration acceleration. Interestingly, the effective mass can reach negative values, but also magnitudes larger than the total mass of the system.