Planar Swirl-shaped Acoustic Black Hole Absorbers for Multi-directional Vibration Suppression

A planar swirl-shaped Acoustic Black Hole (ABH) absorber is proposed and investigated in this paper. In addition to the well-known bending wave retarding phenomena, the speed of torsional waves in the curved ABH with a rectangular cross section is also shown to decrease with the thickness thinning. Alongside the enhanced bending-twisting coupling brought about by the planar and curvilinear configuration, the curved ABH absorber exhibits reduced orientation-dependent properties to cope with multi-directional rotational moment excitations, and meanwhile generates enriched dynamics and enhanced energy trapping and dissipation. As a result, the absorber enables broadband multi-directional vibration suppression when added on a primary thin structure. Experimental studies demonstrate that deploying multiple distributed ABH absorbers can entail effective, robust and broadband vibration reduction for an arbitrarily selected polygon plate. Analyses also confirm the dual vibration reduction mechanisms in terms of structural interaction and damping enhancement, both being fully played out through the proposed curvilinear ABH design.