Ma Li, Cheng Li
Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People's Republic of China.
J Acoust Soc Am. 2019 Jan;145(1):164. doi: 10.1121/1.5081680.
The acoustic black hole (ABH) phenomenon has shown promise for noise and vibration control applications. In this paper, a two-dimensional (2-D) Daubechies wavelet (DW) model is established for the sound radiation prediction of plates embedded with a circular ABH indentation. ABH plates are shown to exhibit a reduced sound radiation efficiency as compared with their flat counterpart. Below the critical frequency, this is caused by the weakening of the structural stiffness due to the ABH indentation. Above the critical frequency, a subsonic region inside the ABH cell may appear, containing acoustically slow structural waves. This region, confined within a transonic boundary, is due to the ABH-specific phase velocity reduction of the bending waves. Drawing energy away from the supersonic region of the plate, this subsonic region warrants a reduced sound radiation to the far field. Numerical results on the investigated configuration show an increase in the sound radiation efficiency due to the added stiffness effect of damping layers. Sound radiation efficiency alongside the transonic boundary changes is scrutinized and quantified. Visualization of the supersonic acoustic intensity and radiation allows identifying the effective sound radiation regions of ABH plates and their relationship with the transonic boundaries at different frequencies.
声学黑洞（ABH）现象在噪声与振动控制应用方面已展现出前景。本文针对嵌入圆形ABH凹槽的板建立了二维（2 - D）Daubechies小波（DW）模型，用于预测其声辐射。与平板相比，ABH板的声辐射效率降低。在临界频率以下，这是由于ABH凹槽导致结构刚度减弱所致。在临界频率以上，ABH单元内部可能会出现一个亚声速区域，其中包含声学慢结构波。该区域局限于跨声速边界内，是由于ABH特定的弯曲波相速度降低造成的。该亚声速区域从板的超声速区域吸取能量，使得向远场的声辐射减少。所研究构型的数值结果表明，由于阻尼层的附加刚度效应，声辐射效率有所增加。对跨声速边界变化时的声辐射效率进行了详细审查和量化。通过对超声声声强和辐射的可视化，可以确定ABH板的有效声辐射区域及其与不同频率下跨声速边界的关系。
