基于声学黑洞效应的直升机驾驶舱宽带降噪

声学黑洞（ABH）效应是利用结构阻抗的变化，使结构中传播的波相速度和群速度发生变化，在结构局部区域实现波的聚集，进而通过少量阻尼将能量耗损。该方法具有高效、轻质、宽频等优点，为结构振动噪声控制提供了新的思路，具有较强的潜能和应用前景。本文针对直升机驾驶舱复杂的噪声问题，根据噪声源和传递路径，提出基于ABH效应的内嵌式和附加式2种减振降噪设计方案。利用有限元软件建立了结构声振耦合模型，分析了直升机驾驶舱模型的声振特性，解释了ABH效应有助于降低舱室噪声的机理，并搭建了实验平台，开展了效果测试和性能评估。结果表明，内嵌式ABH结构可以有效降低舱内的中高频噪声，而低频控制能力略显不足。附加式ABH结构可以弥补这一局限性，拓宽有效频带。结合内嵌式和附加式ABH 2种控制方案，相比传统结构在总质量不增加甚至略有降低的前提下，舱室平均噪声水平在1/3倍频程内降低3~10 dB。该研究成果有助于推进ABH新技术在未来直升机工程减振降噪中的应用。

Broadband noise reduction inside helicopter cockpit with acoustic black hole effect

Acoustic Black Hole (ABH) effect allows alteration of the phase velocity and group velocity of wave propagation in a structure by changing the impedance to concentrate the waves in local areas of the structure and dissipate energy with a little damping. With the advantages of high efficiency, light weight, and wide frequency, the ABH provides a new perspective for structural vibration and noise control, exhibiting strong potential and application prospects. To reduce the broadband noise inside helicopter cockpits, this paper presents two kinds of structural design schemes based on the ABH effect after considering noise sources and transmission paths. The coupling model of the helicopter cockpit is established using the finite element software. The vibro-acoustic characteristics are then analyzed, and the mechanism of the ABH induced cabin noise reduction is explained. The effect test and performance evaluation are carried out on the established experimental platform. Results show that the embedded ABH structure can effectively reduce the medium-high frequency noise inside the cockpit, while its insufficient performance on low frequency noise is compensated by the additional ABH structure, therefore widening the effective frequency band. The average noise level can be reduced by 3-10 dB in the one-third octave band after employing both the embedded ABH and the additional one. Moreover, the total mass is slightly decreased compared with the traditional structure. This research contributes to the application of ABH new technology to vibration and noise reduction of helicopter engineering in the future.