Active acoustic black holes for controlling vibration

Abstract

An Acoustic Black Hole (ABH) is a lightweight and compact damping solution, which can be realised as a lightly damped structural taper. Although ABHs are effective at attenuating vibration, their performance at lower frequencies is strongly dependent on the local modes of the taper. Limiting the size of an ABH therefore physically limits its cut-on frequency and accurate tuning is required to address low frequency problems. To improve the performance of ABHs at lower frequencies, this thesis proposes and investigates the integration of active control technologies into the ABH taper. Initially, a parametric study has been carried out which highlights how a beam based ABH termination can be geometrically tuned to maximise both narrow and broadband performance. Particularly, it is shown that the tip height and power law can be selected to minimise broadband reflection. With guidance from this study, an ABH termination has been designed and a piezoelectric patch has been attached to the taper. It has been shown through the implementation of a wave-based feedforward active control strategy that the Active ABH (AABH) outperforms a traditional constant thickness active termination and requires less electrical and computational power. However, it has also been shown that when the reflection coefficient is controlled, the local vibration in the AABH is significantly enhanced. To provide further insight into this connection, a remote damping control strategy has been considered and it has been shown that there is a control trade off between maximising performance and minimising the vibration of the taper. The AABH concept has then been extended to a plate with five embedded AABHs. It has been shown that the AABHs reduce the electrical power required to implement active control and provide a higher level of damping over a significantly wider bandwidth than achievable via a constant thickness plate with active elements.
In summary, this thesis presents the first exploration of integrating active control technologies into both one-dimensional and two-dimensional ABHs and demonstrates the significant benefits of combining passive and active control technologies. Future work will likely extend the novel AABH to more complex structures and consider not only their effect on structural vibration, but also on the structural radiation.

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Identifiers

ORCID for Kristian Hook: orcid.org/0000-0002-5011-0414

ORCID for Jordan Cheer: orcid.org/0000-0002-0552-5506

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