Design and analysis of Acoustic Black Holes for dynamic stress

Abstract

Acoustic Black Holes (ABHs) are lightweight, high-performance structures for the attenuation of vibration. However, the ABH effect is known to cause a large amount of energy to be directed at a thin structural section, resulting in very high amplitude vibration of the ABH tip. This raises concerns about the level of dynamic stress within ABH tapers, which could limit the practical applications for which they are suitable. This thesis, therefore, presents an exploration into the possibility of reducing the dynamic stress within an ABH taper using both passive and active strategies.

Initially, an assessment of the dynamic stress and vibration attenuation of a conventional ABH profile is presented using numerical simulations, including an exploration of the effect that varying several geometric parameters has on the performance of the structure. Following this, a parametrically defined modified ABH profile is proposed that implements an increased structural thickness in areas of high stress in a conventional ABH. The parameters defining the profile are optimised, aiming to reduce ABH taper stress while maintaining the vibration attenuation performance of the conventional profile. In order to validate these findings, experimental measurements of both the reflection coefficient and the dynamic bending stress are taken.

Following the assessment of the performance of the modified ABH profile, the possibility of reducing the ABH taper stress using active control strategies is considered. Initially, the ABH taper stress is assessed for a feedforward wave-based active control strategy that has previously been shown to achieve good vibration attenuation performance. Following this, an active control strategy that aims to reduce the ABH taper stress is implemented, and its effect on the vibration attenuation performance of the ABH structure is assessed. Finally, the possibility of a combined control strategy that includes both the reflection coefficient and the ABH taper stress in the cost function is considered.

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Identifiers

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

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