Passive mitigation of low-frequency vibration modes in lightweight structures based on a new generation of acoustic black holes

Abstract

Topology optimization and generative design are methods used to lighten structures
under specific loads. The resulting lightweight components are usually softer in the
directions perpendicular to the applied efforts, such as in the case of cranes. This results
in the possible excitation of structural modes at very low frequencies, which can lead
to premature aging of lightweight structures. In this paper, we present a new design
of acoustic black hole (ABH), able to mitigate vibration modes in a test 3D-printed
lightweight structure, from 20 Hz upwards. The novel ABH weights less than 10 grams
and can be readily screwed on the structure. Its design is based on that of a classic
ABH, with additional winglets and/or rods, to increase the vibrating mass without
significantly changing the stiffness of the ABH. This results in a strongly reduced
ABH cut-on frequency. The winglets and/or rods also result in a greatly increased
contact area between the ABH and the viscoelastic dissipative material, with positive
effects on the ABH damping efficiency. The new ABHs could successfully be used, first
to damp the fundamental vibration mode of aluminum cylinders, and then to reduce
the amplitude of the first three structural modes of the test lightweight structure. The
new ABH manages to damp modes at frequencies several times lower than the ones
found in the literature, which are promising results.