Abstract
Acoustic Black Holes (ABHs) are structural features that are typically realised by introducing a tapering thickness profile into a structure that results in local regions of wave-speed reduction and a corresponding enhancement in the structural damping. In the ideal theoretical case, where the ABH tapers to zero thickness, the wave-speed reaches zero and the wave entering the ABH can be perfectly absorbed. In practical realisations, however, the thickness of the ABH taper and thus the wave-speed remain finite. In this case, to obtain high levels of structural damping, the ABH is typically combined with a passive damping material, such as a viscoelastic layer. This paper investigates the potential performance enhancements that can be achieved by replacing the complementary passive damping material with an active vibration control (AVC) system in a beam-based ABH, thus creating an active ABH (AABH). The proposed smart structure thus consists of a piezo-electric patch actuator, which is integrated into the ABH taper in place of the passive damping, and a wave-based, feedforward AVC strategy, which aims to minimise the broadband flexural wave reflection coefficient. To evaluate the relative performance of the proposed AABH, an identical AVC strategy is also applied to a beam with a constant thickness termination. It is demonstrated through experimental implementation, that the AABH is able to achieve equivalent broadband performance to the constant thickness beam-based AVC system, but with a lower computational requirement and a lower control effort, thus offering significant practical benefits.
Highlights
This paper has proposed and presented an investigation into the Active Acoustic Black Hole (AABH), which combines the Acoustic Black Holes (ABHs) effect with active control technology in order to enhance the achievable levels of vibration control via a smart structure
An Active ABH (AABH) beam termination has been described, in which a single piezoelectric patch actuator is applied to the tapered ABH termination and driven to minimise the flexural wave reflected from the beam termination
The presented comparison has demonstrated that the plant model required by the feedforward wave-based active control strategy can be implemented with less filter coefficients for the AABH than for the constant thickness active beam termination
Summary
The ‘Acoustic Black Hole’ (ABH) effect is a mechanism for attenuating flexural vibrations in structures, such as beams [1, 2, 3, 4, 5, 6, 7, 8, 9] or plates [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20] and inherently provides a lightweight vibration control solution. The ABH effect is achieved by introducing a smooth impedance change into a structure and this introduces a local reduction in the flexural wave speed This has typically been realised using a power law taper [1], which governs the thickness of the beam within the ABH section and can be described as h(x) = ε ltaper − x ltaper μ. Due to the lightweight nature of ABHs and the high levels of vibration control that they can achieve, there have been many studies into their design and optimisation, which have been reviewed in [23] It has been shown through both simulation and experimental studies that ABHs can be tuned by changing the geometrical properties of the taper, such as the tip height, taper gradient and taper length [19, 24, 25, 26, 27, 28, 29].
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