覆黏弹层加肋双层板的声反射

为评估覆盖层的吸声性能,研究黏弹层在无限大周期加肋双层板背衬下的声反射。首先通过弯曲波与Lamb波的比较,揭示了板近似理论不适用于黏弹性板的原因。为此采用(黏)弹性理论处理(黏)弹性板,而肋板的处理则采用板近似理论,并用Hull提出的方法解决肋板和平板的耦合问题,得到反射声场的解。与板近似理论计算加肋双层板声反射的结果进行比较验证了本文方法的正确性,对反射系数进行计算分析了背衬对声反射的影响,定义平均反射系数比较了不同覆盖层的性能。结果表明,频率较低时覆盖层无法有效抑制背衬的影响,板间流体层与双层板的耦合作用引起共振散射,肋板与双层板的耦合作用降低声反射。      

高声压级时多孔金属板的吸声特性研究

针对高声压级下有限厚度多孔金属板在线性阻抗背衬条件下(背衬表面声压与声质点速度为线性关系)的吸声问题,提出了一个描述不同声压级下材料层法向吸声性能的一维模型,并给出求解材料层内部声质点速度的线化与差分方法,以预测多孔金属板在高声压级下的非线性吸声特性。在阻抗管中对两块多孔金属板进行了声学测试,得到了材料层法向表面阻抗和吸声系数随入射声压级变化的实验结果。研究表明:实验与理论预测符合良好,验证了模型与数值方法的正确性。本文所提原理和方法,可用于一般硬质多孔材料。      

含圆柱形空腔吸声覆盖层的二维理论

发展了一种基于线性粘弹性Kelvin-Voigt模型的二维解析理论,分析声波垂直入射情况下含有周期分布圆柱形空腔的吸声覆盖层的反声和吸声特性。将覆盖层单元近似为粘弹性圆柱管,导出轴对称波的特征方程。再利用前后界面的边界条件得到这些轴对称波的共振频率和覆盖层的反射系数公式。根据理论模型计算了刚性背衬下某种材料吸声覆盖层的低频吸声性能。计算结果表明:(1)材料损耗因子越大吸声系数越大,但吸声峰值频率基本上不变,(2)覆盖层越厚吸声峰值频率越低, (3)穿孔率越小吸声峰频率越高,吸声系数峰值越大。     

薄纤维层对穿孔板的声学影响研究

为了提高附着薄纤维层穿孔板的声学预测精度,通过实验及理论分析方法研究薄纤维层对穿孔板的声学影响。采用声学阻抗管系统测试穿孔饰面板及背腔的吸声系数。测试结果显示,薄纤维层对吸声层的吸声性能具有明显的提高作用。以穿孔板声阻抗模型为基础构建附着薄纤维层的穿孔饰面板等效声阻抗模型,以附加修正参数等效薄纤维层的声学影响。依据吸声系数测试结果计算薄纤维层的等效声学修正参数,结果显示薄纤维层造成的附加阻性修正比较显著。     

黏弹性吸声材料复弹性模量优化研究

针对黏弹性材料吸声效率问题,利用分层介质声传播理论和数值算法优化了不同物理条件下材料的复弹性模量。采用参数等效的方法分析了含气泡黏弹性材料的声学特性,并给出了此种材料优化后的弹性模量曲线。根据物理模型计算了一定边界条件下材料复弹性模量等吸声系数曲线,得到了几种背衬条件下黏弹性材料吸声系数大于0.8的弹性模量和损耗因子范围。研究表明调节黏弹性材料的复弹性模量可以有效提高材料的吸声性能,吸声系数大于0.8时其弹性模量和损耗因子范围在不同背衬条件下差异较大,发现一定厚度的钢背衬会降低调控复弹性模量的难度,对含气泡黏弹性材料的计算也可得到类似结果。      

经典局域共振型水声超材料的吸隔声性能研究*

基于水声超材料吸声机理和多层平行介质平面波理论,建立局域共振型水声超材料结构,通过COMSOL进行建模计算,研究该结构的吸声性能机理,此外为了验证钢背衬的隔声性能,在该水声超材料结构基础上添加一层0.005m厚的钢背衬进行仿真对比。研究结果表明,在频段为200Hz-4000Hz时,水声超材料声学性能较好,吸声性能整体较优,且添加钢背衬的水声超材料隔声性能较优,甚至在某频率点达到15dB的隔声差值;此外通过位移场图进一步揭示水声超材料的吸声机理,发现水声超材料结构的位移场和钢背衬都对吸声性能会产生影响,钢背衬通过影响共振吸收来影响吸声性能,而位移场则通过位移幅度大小影响吸声性能。     

多重散射方法研究轴对称空腔覆盖层的声学特性

发展了一种多重散射方法研究声学覆盖层的半数值半解析模型,分析了影响轴对称空腔结构声学性能的主要能量耗散机制。在球坐标条件下推导出轴对称空腔结构的位移和应力场基函数,通过对空腔表面基函数的数值积分,得到散射波和入射波之间的传输矩阵方程,结合分层介质声传播理论计算了周期性空腔结构覆盖层的反射、透射和吸声性能。研究结果表明;空腔共振是低频能量耗散的主要形式,边界条件对材料空腔结构的谐振特性影响很大,利用双空腔耦合共振可以拓宽材料的低频吸声频带;背衬对材料的高频吸声影响较小,材料的高频能量损耗取决于空腔的散射和波型转换特性。      

基于等效参数反演的敷设声学覆盖层的水下圆柱壳体声散射研究

应用了一种等效方法计算敷设声学覆盖层无限长圆柱壳体水下声散射特性.等效方法的核心是忽略复杂声学覆盖层内部的声学结构,将其作为具有等效材料参数的均匀阻尼层进行建模,该均匀阻尼层具有和原覆盖层相同的复反射系数.进而,应用COMSOL Multiphysics软件建立敷设均匀阻尼层圆柱壳体的有限元模型并求解其声散射特性.等效方法的关键是等效材料参数的获取.采用充水阻抗管实验和有限元数值实验两种方法获取声学覆盖层贴敷在与壳体具有相同厚度、相同材料背衬条件下的复反射系数,在此基础上,基于遗传算法反演材料的等效参数.研究表明,等效参数具有频变特性,且尽管等效杨氏模量和等效泊松比在频率范围内存在较大波动,但是等效前后复反射系数仍保持一致.为了验证等效方法求解壳体声散射特性的准确性,同时建立了敷设声学覆盖层壳体的完整有限元模型,将覆盖层内部声学结构进行精细建模,并求其声散射特性.结果表明,两种方法求得的形态函数符合得较好,在整个频率范围内平均误差大约为1 d B.     

黏弹性材料的动态力学特性及其对覆盖层吸声性能的影响

本文利用标准化动态力学测量手段获得了某种高分子聚合物的动态杨氏模量,并根据时温等效原理对动态杨氏模量与声学测量在频段上的差异加以分析和转换,得到了500—7500 Hz频率范围内该黏弹性材料杨氏模量随频率变化的特性.基于所测得动态杨氏模量,采用有限元方法分析了均匀黏弹材料的吸声性能,并将仿真结果与样品声管实验数据进行对比,验证了测试所得参数的准确性.进一步仿真分析了含有局域共振结构的声学覆盖层吸声性能,并讨论了黏弹性材料的动态特性对其吸声性能的影响,提出了改进水声覆盖层低频宽带吸声特性的建议.     

含三聚氰胺多孔材料分层复合介质吸声特性*

三聚氰胺泡沫材料是一种具有高开孔率的多孔材料,具备优良的吸音、防火隔热及环保性能,可以作为吸声材料与弹性板、空腔介质形成复合结构,在建筑、航空、交通工具等工程领域有广泛的应用。该文基于Biot理论和分层介质在交界面处的不同边界条件,建立非均匀复合介质背衬刚性壁面结构的理论声学模型,详细分析了多孔材料布局对复合结构吸声特性的影响。该文理论模型计算的结果与阻抗实验得到的垂直入射吸声系数基本一致,验证了理论模型的正确性。结果表明:在多孔材料前面增加空气层可以改善高频吸声特性;在多孔材料后面增加空气层可以改善复合结构低频吸声特性。通过合理配置多孔材料,可以在应用需求频段上达到满意的吸声效果。     

Analysis of absorption performances of anechoic layers with steel plate backing

Rubber layers with air-filled cavities or local resonance scatters can be used as anechoic coatings. A lot of researches have focused on the absorption mechanism of the anechoic coatings. As the anechoic coatings are bonded to the hull of submarine, the vibration of the hull should not be neglected when the analysis of the absorption characters is carried out. Therefore, it is more reasonable to treat the anechoic coating and the backing as a whole when the acoustic performance is analyzed. Considering the effects of the steel plate backing, the sound absorption performances on different models of anechoic coatings are investigated in this paper. The Finite Element Method is used to illustrate the vibrational behaviors of the anechoic coatings under the steel backings by which the displacement contours is obtained for analysis. The theoretical results show that an absorption peak is induced by the resonance of the steel slab and rubber layer. At the frequency of this absorption peak, the steel plate and the coating vibrates longitudinally like a mass-spring system in which the steel slab serves for mass and the coating layer is the spring. To illuminate the effects of the steel slab backing on the acoustic absorption, the thicknesses of the steel slab and the anechoic layer are discussed. Finally, an experiment is performed and the results show a good agreement with the theoretical analysis.     

含空腔的功能梯度声学覆盖层水下吸声特性

针对传统的声学覆盖层吸声频带窄的问题,基于功能梯度材料的特点提出了一种含空腔结构的水下功能梯度声学覆盖层结构,引入梯度有限元法建立了功能梯度型声学覆盖层的水下声学计算模型,研究了功能梯度声学覆盖层结构的水下吸声特性。与传统的功能梯度结构声学建模方法相比,在保证计算精度和计算效率的基础上,文中所建立的功能梯度结构声学计算模型可适用于更复杂的功能梯度声学结构声学性能评估。研究结果表明,功能梯度声学覆盖层能够有效改善中高频段的吸声性能,获得较好的宽频吸声效果。此外,空腔形状采用锥型空腔结构或者组合型空腔结构可以有效地拓宽功能梯度声学覆盖层的吸声频带。      

Acoustic anechoic layers with singly periodic array of scatterers: Computational methods,absorption mechanisms,and optimal design

The acoustic properties of anechoic layers with a singly periodic array of cylindrical scatterers are investigated. A method combined plane wave expansion and finite element analysis is extended for out-of-plane incidence. The reflection characteristics of the anechoic layers with cavities and locally resonant scatterers are discussed. The backing is a steel plate followed by an air half space. Under this approximate zero transmission backing condition, the reflection reduction is induced by the absorption enhancement. The absorption mechanism is explained by the scattering/absorption cross section of the isolated scatterer. Three types of resonant modes which can induce efficient absorption are revealed. Due to the fact that the frequencies of the resonant modes are related to the size of the scatterers, anechoic layers with scatterers of mixed size can broaden the absorption band. A genetic optimization algorithm is adopted to design the anechoic layer with scatterers of mixed size at a desired frequency band from 2 kHz to l0 kHz for normal incidence, and the influence of the incident angle is also discussed.     

Tri-component phononic crystals for underwater anechoic coatings

Localized resonance in phononic crystal, composed of three-dimensional arrays of composite units, has been discovered recently. The composite unit is a high-density sphere coated by soft silicon rubber. In this Letter, the absorptive properties induced by the localized resonance are systemically investigated. The mode conversions during the Mie scattering of a single coated lead sphere in unbounded epoxy are analyzed by referring the elements of the scattering matrix. Then the anechoic properties of a slab containing a plane of such composite scatterers are investigated with the multiple-scattering method by accounting the effects of the multiple scattering and the viscous dissipation. The results show that the longitudinal to transverse mode conversion nearby the locally resonant region is an effective way to enhance the anechoic performance of the finite slab of phononic crystal. Then, the influences of the viscoelasticity of the silicon rubber and the coating thickness on the acoustic properties of the finite slab are investigated for anechoic optimization. Finally, we synthetically consider the destructive scattering in the finite slab of phononic crystal and the backing, and design an anechoic slab composed of bi-layer coated spheres. The results show that the most of the incident energy is absorbed at the desired frequency band.     

Absorption of a rigid frame porous layer with periodic circular inclusions backed by a periodic grating

The acoustic properties of a periodic rigid frame porous layer with multiple irregularities in the rigid backing and embedded rigid circular inclusions are investigated theoretically and numerically. The theoretical representation of the sound field in the structure is obtained using a combination of multipole method that accounts for the periodic inclusions and multi-modal method that accounts for the multiple irregularities of the rigid backing. The theoretical model is validated against a finite element method. The predictions show that the acoustic response of this structure exhibits quasi-total, high absorption peaks at low frequencies which are below the frequency of the quarter-wavelength resonance typical for a flat homogeneous porous layer backed by a rigid plate. This result is explained by excitation of additional modes in the porous layer and by a complex interaction between various acoustic modes. These modes relate to the resonances associated with the presence of a profiled rigid backing and rigid inclusions in the porous layer.     

Backing effects on the underwater acoustic absorption of a viscoelastic slab with locally resonant scatterers

Backing effects on the underwater acoustic absorption of a viscoelastic polymer slab embedded with locally resonant scatterers are reported. The polymer slab is embedded with two layers of locally resonant scatterers, i.e. Al spheres coated by soft silicon rubber. Theoretical absorption coefficients of the polymer slab under different backings using a layer multiple scattering method show good agreement with the experimental results, which supports unambiguously the experimental observation. Then relations between the resonance modes and the low-frequency absorption peaks of the composite slab are clarified to address the absorption mechanisms. It shows that the mass of the steel backing affects evidently the low-frequency absorption, the absorption peak shifts to lower frequency range while increasing the backing mass.     

含有周期球腔的黏弹性覆盖层消声性能分析

利用散射矩阵法分析了单个球状空腔在黏弹性橡胶中的Mie散射特性以及振动模式.以此为基础，利用多重散射法分析了不同背衬条件下，含有单层周期球状空腔的橡胶覆盖层(厚度为8mm)的消声性能.结果表明，单个球腔的径向共振对覆盖层的低频消声性能有重要贡献，覆盖薄层在共振区具有良好的消声性能.最后，设计了双层消声覆盖层(厚度为20mm)，有效拓展了消声带宽. 关键词： Mie散射 多重散射法 消声材料 声子晶体     

吸声材料对水下小平台上矢量传感器声学特性的影响研究

本文围绕粘贴黏弹性吸声材料方法对水下小平台上安装矢量传感器的指向性和测向的影响展开理论分析和实验研究.首先建立了吸声材料和平台结构组成的复合层结构的数学模型,对声波经过复合层结构的声学特性进行了分析,在此基础上利用有限元耦合边界元法对粘贴吸声材料前后的水下小平台上的矢量传感器的声学特性进行研究.通过理论计算和数值分析研究了吸声材料对矢量传感器的各通道的指向性的影响,并计算了覆盖吸声材料前后矢量传感器的测向精度.水池实验验证了分析结果的正确性.