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摘要: 声学黑洞(acoustic black hole, ABH) 效应是利用薄壁结构几何参数或者材料特性参数的梯度变化, 使波在结构中的传播速度逐渐减小, 理想情况下波速减小至零从而不发生反射的现象.实现声学黑洞效应的主要方法是将薄板结构的厚度按照一定规律裁剪, 利用声学黑洞可以将结构中传播的波动能量聚集在特定的位置.声学黑洞对波的聚集具有宽频高效、实现方法简单灵活等特点, 在薄壁结构的减振降噪、能量回收等应用中具有明显的优势.本文介绍声学黑洞效应的基本原理、相关力学问题的研究进展和有待进一步探究的问题, 包括声学黑洞结构的建模与分析方法、实验研究方法及进展、声学黑洞结构中波的传播与操控, 以及声学黑洞在工程应用中的相关问题.Abstract: Acoustic black hole (ABH) efiect utilizes the gradient variance of the structural conflguration or material properties to diminish wave velocity in the structure. The wave velocity decreases to zero in an ideal scenario, resulting in zero reflection. The mainstream method to realize ABH efiect is to tailor the structure thickness properly, such that energy is captured in a certain area. Great advantages and potential in applications for flexural wave manipulation in thin-walled structure result from its high e-ciency, broadband characteristics and flexible implementation. We introduce basic principles of ABH efiect, recent progress of related mechanical problems, and problems to be further explored. We describe the modeling and analysis method of ABH structure, the method and progress of experimental studies, manipulation and propagation of waves in ABH structures, and related issues in engineering applications of ABH structures.
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图 9 反射系数R1与激励频率之间的关系(实线:厚度700 μm的阻尼层; 点虚线:厚度10 μm的阻尼层; 虚线:黑洞区域不贴阻尼层; 点线:无声学黑洞的均匀梁结构粘贴厚度700 μm的阻尼层) (Georgiev et al. 2011)
图 11 厚度变化的阻尼材料对系统阻尼损失因子的影响, 厚度均匀的阻尼材料对应厚度为hd=0.005 cm, 阻尼材料分布的位置为xd=1~2 cm (Tang et al. 2016)
图 17 特定频率下的位移响应. (a) f=0.22 kHz, (b) f=1.85 kHz, (c) f=3.74 kHz, (d) f=0.49 kHz, (e) f=1.20 kHz, (f) f=2.20 kHz, (g) f=0.98 kHz, (h) f=1.90 kHz, (i) f=3.10 kHz (O'Boy & Krylov 2011)
图 18 带黑洞的圆板和不带黑洞环板在同一点处的机械导纳w˙ (Rm, θ=0, ω)/p (Rf) 的比较(O'Boy & Krylov 2011)
图 19 (a) 辐射声功率在频域上的幅值, (b) 对应的结构表面加速度(其中黑色实线表示均匀板, 红色虚线为25个周期排布声学黑洞的板结构) (声学黑洞由于截断会在中心形成小孔) (Conlon et al. 2015b)
图 20 (a) 模态损失因子, (b) 周期排布25个声学黑洞时板结构辐射声功率的幅频特性(其中黑色实线表示声学黑洞中心圆孔较大的情况, 红色虚线表示声学黑洞中心圆孔(ABH-SH) 较小的情况) (Conlon et al. 2015)
图 21 (a) 数值仿真模型: (a1) 声学黑洞结构, (a2) 声学黑洞与阻尼材料(ABH-Damp) 结合, (a3) 声学黑洞与阻尼材料和动力吸振器(ABH-DVA) 结合; (b) 数值仿真结果(Jia et al. 2015)
图 26 实验测量所得椭圆形板的点导纳对比图, 实线表示含声学黑洞并粘贴阻尼材料, 虚线表示不含声学黑洞但在同一位置粘贴同样面积的阻尼材料, 点划线表示不含声学黑洞但在整个试件上粘贴阻尼材料(Georgiev et al. 2011)
图 27 结构的机械导纳. (a) 不含声学黑洞的结构, (b) 含有声学黑洞的结构(O'Boy & Krylov 2011)
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