Numerical analysis of the vibroacoustic properties of plates with embedded grids of acoustic black holes

Abstract

The concept of an Acoustic Black Hole (ABH) has been developed and exploited as an approach for passively attenuating structural vibration. The basic principle of the ABH relies on proper tailoring of the structure geometrical properties in order to produce a gradual reduction of the flexural wave speed, theoretically approaching zero. For practical systems the idealized "zero" wave speed condition cannot be achieved so the structural areas of low wave speed are treated with surface damping layers to allow the ABH to approach the idealized dissipation level. In this work, an investigation was conducted to assess the effects that distributions of ABHs embedded in plate-like structures have on both vibration and structure radiated sound, focusing on characterizing and improving low frequency performance. Finite Element and Boundary Element models were used to assess the vibration response and radiated sound power performance of several plate configurations, comparing baseline uniform plates with embedded periodic ABH designs. The computed modal loss factors showed the importance of the ABH unit cell low order modes in the overall vibration reduction effectiveness of the embedded ABH plates at low frequencies where the free plate bending wavelengths are longer than the scale of the ABH.

Improvement of the acoustic black hole effect by using energy transfer due to geometric nonlinearity

“…Experimental evidences of the eect are numerous [10,11,12]. While it is very ecient at high frequencies, several works point out the ineciency of the ABH technique in the low frequency regime [9,13], which may be a drawback in its potential applications.…”

Enhanced Acoustic Black Hole effect in beams with a modified thickness profile and extended platform

“…ABH effect attracts increasing attention as a promising passive vibration control method because vibration energy can be channeled and only a very small amount of damping materials is required at the energy focalization region to achieve efficient damping to flexural waves [4][5][6][7][8][9]. It also shows appealing potential in sound radiation control [10,11] and energy harvesting [12,13] due to the high energy concentration within a confined area. Krylov et al [3] showed that the inevitable truncation (the residual thickness at the wedge tip) resulting from the manufacturing difficulty would significantly compromise the ideal ABH effect by generating wave reflections.…”

Multi-objective optimization of acoustic black hole vibration absorbers

“…The optimization results also show that ABH vibration reduction can be achieved at frequencies lower than expected by the wavelength smaller than the taper length limit (k b < x L ) defined by Conlon et al 4 For the aluminum taper length of 20 cm, this occurs at 243 Hz. However, these results are achieved only when NWV is significantly violated (see objective 2 of Fig.…”

“…[1][2][3][4] By introducing a power-law taper in a beam, the wavespeed will approach zero as the beam thickness decreases and a wave will never reflect back into the beam once it enters the taper. Higher-power tapers have been shown to have a lower total reflection coefficient and therefore better performance.…”