水下非均匀复合层结构吸声的理论研究

本文对水下非均匀阻尼板与多层介质组成的吸附结构进行了研究，基于非均匀波导理论，导出非均匀性阻尼层的传递矩阵及多层结构表同反声，吸声系数，对任意非均匀层，提出分层近似求传递的方法，数值计算研究了结果反声，吸声性能及其随各参数的变化。     

水下多层均匀材料的声特性

本文研究水和空气中由不同厚度的两层弹性板及消声橡胶共同组成的分层介质在斜入射时的声特性,并采用数值方法求解多层结构声场的线性方程组。得到反射,透射系数,当板的厚度远小于波长时,采用弹性薄壳振动模型和弹性波模型进行计算,它们的结果基本相同,但是薄壳振动模型更便于计算和理论分析;对系统反射系数和透射系数的计算结果表明,系统增加消声橡胶层后,极大地改变后射系数和透射系数的频率响应;频率升高,反射系数减小     

水下复合层吸声结构中反向声能与振动能量传输的研究

本文对文献「１，２」所讨论了水下复合层吸声结构中能量的反向传输进行了研究。利用多层结构的文献矩阵求逆，导出声能和振动能的反向传输关系，给出传递损失。数值计算分析了结构的各层参数变化对能量传递损失的影响。     

水下复合层吸声结构中反向声能与振动能量传输的研究

本文对文献[1，2]所讨论的水下复合层吸声结构中能量的反向传输送行了研究．利用多层结构的传递矩阵求逆．导出声能和振动能的反向传输关系，给出传递损失．数值计算分析了结构的各层参数变化对能量传递损失的影响．     

高分子颗粒孔隙结构材料的吸声特性研究

在噪声控制与治理工程中，许多场合了消除由物体表面产生的反射声波，往往需要在物体表面敷设具有吸声性能的材料或结构，以吸收入射声波的声能，本文对一种新型的以高分子材料为基底的颗粒型微孔结构进行了吸声特性研究，首先对颗粒微孔结构的吸声机理进行分析，认为由于受材料自身化学性质与结构特征所决定，这种颗粒微孔结构除了具一般多孔吸声材料的空气粘滞阻力作用吸声外，还存在颗粒材料的内部的弹性弛豫效应吸声，因而吸怕系     

水下弹性微穿孔吸声结构吸声系数研究

利用模态叠加法建立了水介质微穿孔板的数学模型,基于声电类比法得到其等效电路模型。研究了弹性微穿孔板和弹性背腔对垂直入射吸声系数的影响。与空气介质中的微穿孔板不同,水下微穿孔板因结构阻抗不足,难以取得满意的吸声效果,为此提出了增强型微穿孔吸声结构,并在水介质阻抗管内对理论结果予以验证。结果表明,随着增强型弹性微穿孔板弯曲刚度的增大,其在[20,2000]Hz范围内的平均吸声系数得到提高,逐步趋近于刚性微穿孔板的结果,弹性背板使微穿孔吸声结构的吸声峰向低频移动,低频吸声效果得到提高。     

波纹穿孔板吸声特性研究

研究了平面波垂直入射和掠入射两种情况下波纹穿孔板对声波的耗散作用, 结果表明在这两种情况下波纹穿孔板的声学特性都有别于平板穿孔板。在垂直入射条件下, 通过“等效穿孔率”可以在中、低频率范围内使波纹穿孔板和平板穿孔板的吸声特性“重合”。波纹穿孔板在高频范围会出现异于平板穿孔板的双尖峰现象, 进一步研究发现这是由波纹板形状导致的背腔深度的连续变化所引起的。在掠入射条件下, 波纹穿孔板与平板穿孔板无法通过“等效穿孔率”替代。波纹穿孔板的板高和板长对其声学性能都有明显影响, 当波纹穿孔板夹角(板高与1/4板长对应的正切角)相同时, 在板长小于75 mm范围内波纹穿孔板有相似的声学性能。

     

微穿孔板吸声结构水下应用研究

马大猷教授提出的微穿孔板吸声结构在空气噪声降低和隔离方面得到了广泛的应用,但未见水下应用的相关研究和报道。本文将空气中微穿孔板理论应用到水中,得到了水下微穿孔板吸声结构的吸声公式。通过理论分析,得出了微穿孔板结构直接应用于水中无法获得宽频吸收的结论。提出了通过匹配液将微穿孔板间接应用到水下的设想。设计了单层板和双层板吸声结构,并对它们的吸声特性进行了理论分析与仿真。结果表明,本文设计的微穿孔板吸声结构在水中能够获得优于空气中的宽频带吸声效果。实验测量了自制的微穿孔板吸声结构,吸声系数的测量值与理论曲线基本吻合,从而验证了理论分析的正确性。     

计及孔间相互作用的微穿孔板吸声特性研究

计算微穿孔板吸声系数时,假设孔间的相互作用可以忽略。计算具有不同直径微孔的穿孔板吸声系数并提高其计算精度,孔间的相互作用不能再忽略。在马大猷、Melling(梅尔林)等前人研究的基础上,根据声波辐射和传播原理,分析微孔之间的相互作用,通过修正微孔的实际等效长度,得到计及孔间相互作用微孔板吸声系数模型,并进行理论计算和实验测试。研究结果表明:影响微穿孔板吸声系数除结构参数外,还应考虑孔间的相互作用;计及微孔板各孔间相互作用,能提高共振频率、吸声系数理论值的计算精度,计算值逼近实验测试结果。     

0-3型压电复合材料覆盖层水下 吸声性能的理论研究

目前压电分流阻尼技术在振动和噪声领域的应用得到了广泛的关注. 本文尝试将压电分流阻尼技术应用于水下吸声领域, 以提高覆盖层的吸声性能. 将压电覆盖层厚度模态的机电方程和声波传播的传递矩阵相结合, 建立一维电声模型. 该模型可以用于分析多层压电和非压电水下吸声覆盖层的吸声性能. 采用该模型分析了0-3型压电复合材料覆盖层的水下吸声性能. 压电复合材料的参数是采用Furukawa的模型计算的. 研究结果表明, 采用合适的分流电阻, 负电容分流电路可以在较宽的频率范围显著提高覆盖层的吸声性能. 其原理可以从阻抗匹配的角度解释, 负电容分流电路可以调整压电覆盖层的表面声阻抗, 使之与水的特性声阻抗相匹配.     

Experimental studies of sound absorption by church pews

The influence of pews on the acoustical characteristics of churches may be significant because they occupy large areas in rooms lacking absorbing surfaces. However, the information about this particular category of seating is sparse and, sometimes, contradictory. Different types of pews, differing in materials and construction, were analysed in a reverberant chamber by means of Bradley’s method, measuring the absorption coefficients of blocks with different perimeter-to-area ratios. A substantial dependence on the latter parameter was found, allowing prediction of absorption coefficients as a function of actual block dimensions. The presence of upholstered kneelers showed improved absorption properties which were also replicated on other pew types by adding strips of polyester fibre. On-site measurements in three churches were used to validate the method by means of direct application of Sabine’s formula and by means of virtual acoustic modelling. The first only provided satisfactory results in rooms complying with Sabine’s assumptions, while the second also gave good results in the other church with markedly non-uniform absorption. Finally, the application to computer models of absorption coefficients measured in the chamber was discussed.     

Analytic ray curve tracing for outdoor sound propagation

Outdoor sound propagation, which propagates sound through inhomogeneous, moving media with complex obstacles, presents challenging scenarios for computational simulation. In this paper, we present a ray-tracing method that uses analytic ray curves as tracing primitives in order to improve the efficiency of outdoor sound propagation in fully general settings. This ray-curve tracer inherits the efficiency and flexibility of rectilinear ray tracers in handling boundary surfaces, and it overcomes the performance limitations imposed by approximating the curved propagation paths in inhomogeneous media with rectilinear rays. Adaptive media traversal, as well as acceleration structures for surfaces intersections, lead to further savings in computation. Our method’s speedup over existing ray models, at least an order of magnitude for simple 2D scenarios and up to two orders of magnitude for 3D complex scenes, is demonstrated on outdoor benchmark scenes.     

Investigation of industrial tea-leaf-fibre waste material for its sound absorption properties

The sound absorption of an industrial waste, developed during the processing of tea leaves has been investigated. Three different layers of tea-leaf-fibre waste materials with and without backing provided by a single layer of woven textile cloth were tested for their sound absorption properties. The experimental data indicate that a 1 cm thick tea-leaf-fibre waste material with backing, provides sound absorption which is almost equivalent to that provided by six layers of woven textile cloth. Twenty millimeters thick layers of rigidly backed tea-leaf-fibres and non-woven fibre materials exhibit almost equivalent sound absorption in the frequency range between 500 and 3200 Hz.     

Measurement of sound absorption by underwater acoustic material using pulse-separation method

An alternative pulse-separation method is presented for measuring the sound absorption at normal incidence of an underwater acoustic material in a water-filled impedance tube. A damped sine pulse was generated in the water-filled impedance tube with a regular waveform and a short duration time of approximately 1 ms. During the generation of the pulse, the inverse filter principle was used to compensate for the transducer response. In addition, the effects of the characteristics of the tube termination can be eliminated during the generation of the pulse to obtain a single plane pulse wave in the impedance tube, which is a necessary condition for this technique. Measurements of the sound absorption coefficient of the rubber material and the reflection coefficient from a water/air interface were used to verify the pulse-separation method.     

伪随机扩散体的吸声性能及其应用

本文介绍伪随机扩散体吸声性能的应用，提出减少扩散体结构厚度的实用设计，并应用于剧场观众厅以减少混响时间．