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。     

一种微穿孔板消声器

本文根据马大猷教授提出的“微穿孔板吸声体精确理论”，在对微穿孔板消声器结构参数与吸声特性之间的相互影响进行了分析的基础上，设计了微穿孔板消声器并将其应用在新舟60飞机APU(辅助动力装置)降噪的实际工程中，并通过编写的噪音数据采集分析程序，对降噪效果进行了测试和分析，验证出微穿孔板消声器对消除飞机的APU的排气噪声具有良好的消声效果，平均降噪7．16dB。     

面向微穿孔板吸声结构和吸声特性混合设计的软件平台

微穿孔板吸声结构是由微穿孔板与板后空腔组成的共振吸声结构,被认为是继多孔吸声材料之后发展起来的最有吸引力的吸声结构,其吸声特性与结构参数孔径d、板厚t、孔距b及空腔深度D有关,如何按需设计一个有效的微穿孔板吸声结构已成为目前研究的热点。本文从微穿孔板吸声结构和吸声特性混合设计的角度出发,使用面向对象的编程语言C++开发了微穿孔板吸声结构设计平台。与以往设计方法不同,本文开发的软件平台综合考虑了结构参数和吸声特性参数两方面的限制,根据实际应用要求平衡微穿孔板吸声结构的最大吸声系数与吸声带宽之间的制约关系,并以饱满的吸声曲线为目标,提供满足混合设计要求的优化结构参数。     

微穿孔板和微缝板吸声体研究进展

介绍了我国在新型吸声体微穿孔板和微缝板的特点、首创、理论分析、加工制作、多方面的应用情况，以及其在国外的影响。也讨论了这些吸声体的部分发展方向。     

穿纤维微穿孔板吸声系数的有限元仿真

为拓宽微穿孔板的吸声频带,该文用有限元算法建立了典型微穿孔板和穿入不同数量金属纤维的微穿孔板模型,研究了两种微穿孔板的吸声系数、声阻抗和微孔内法向质点速度的空间分布,并进行了试验验证。有限元仿真和试验数据表明:穿入金属纤维可以拓宽微穿孔板的吸声频带,吸声系数也随纤维根数的增加而下降;吸声系数仿真结果与试验结果趋势一致,仿真模型可以有效模拟穿入纤维前后微穿孔板的吸声特性;穿入金属纤维导致黏滞效应引起的低质点速度区域增大,声阻增加,引起吸声系数的降低,而声抗变化不大。研究发现,有限元仿真方法适用于结构相对复杂的微穿孔结构的声学建模,能直观地体现微孔复杂结构的影响,值得继续深入研究和工程应用。     

微穿孔板和小孔喷注——马大猷教授对声学的特殊贡献

微穿孔板吸声体是马大猷教授提出的一项特殊的设计技术,自上世纪80年代以来被广泛地应用在音质处理和噪声控制中。微穿孔板吸声体是一种无纤维的宽带吸声材料,它不仅能够应用在传统的建筑声学和噪声控制等领域中,更有意义的是它适用于高温、高速气流、高洁净、需要透明采光等一些极端条件下。当微穿孔板后面有一定的空腔时,它可以在低频的几个频程内具有很高的吸声系数。
在喷注噪声控制理论方面,马教授根据小孔喷注噪声与其压力和直径的关系,根据人的听觉生理和心理特性,提出了在气流或者蒸汽出口的颈部处设计合适的小孔结构,可以大大减少气流噪声对人的干扰作用可听声频段内的声辐射,降噪量一般来说可以达到20~60 dBA的降噪量。这就是小孔喷注理论。
本文回顾了马大猷教授在他学术生涯第二个春天里结出的这两颗硕果——微穿孔板和小孔喷注,关于微穿孔板在声场和声源噪声控制中的声学特性理论,主要回顾和讨论了微穿孔板结构的研究进展及其在噪声控制中的实际应用,以及小孔喷注噪声的主要能量转移到超声波频段内的物理概念,这一概念对现代喷注噪声控制的发展依然具有重要意义。     

无纤维吸声材料研究进展

简要地介绍了吸声材料的基本特点，阐述无纤维性吸声材料（特别是微穿孔板吸声结构）取代传统的纤维性吸声材料的可能性及其重要意义，较详细地介绍了近年来德国以及我国科研人员在纤维吸声材料研究上取所得的进展。     

关于微穿孔板吸声体频带宽度极限的讨论

依据马大猷教授的微穿孔板吸声体准确理论,利用计算机辅助设计对于该结构频带宽度极限情况从理论上进行了讨论,把极限频宽和最大吸声系数的制约关系量化,并得到此情况下应用于低频或高频环境孔径的选用范围,以及此情况下板厚和穿孔率与传统观念不同的特点。以上分析结果以及所提供的结构参数为宽频带微穿孔板的具体设计提供有价值的参考。     

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。     

切向流对微穿孔共振吸声结构声学性能的影响

切向流对微穿孔共振吸声结构声学性能的影响可以分成三类:(1)对小孔辐射声抗的影响;(2)对结构斜入射吸声性能的影响;(3)对消声通道消声性能的影响。根据声学基本理论,详细讨论这些影响,得到对应的理论分析公式。定性而言,若声波的传播方向与气流的运动方向一致,小孔外侧的辐射声抗、空腔声阻抗函数coth (ξ)的宗量ξ赋值和消声通道的消声系数都会减小;同时呈现多普勒效应,使得结构的吸声系数共振峰频率向低频移动。理论分析得到相应实验研究的支持。     

微穿孔平板式空间吸声体的理论分析

对微穿孔平板式空间吸声体的吸声特性进行了理论预计,其中运用了半厚度模型分析和四端网络计算方法。计算结果与混响室实测数据符合较好。文中根据预测结果,分析了影响微穿孔平板式空间吸声体吸声性能的诸项主要因素,可为设计应用提供指南。     

Acoustic properties of micro-perforated panel absorber having arbitrary cross-sectional perforations

Micro-perforated panel absorber is used in many noise control applications as a next-generation absorbing material. Perforation shapes of micro-perforated panel studied are usually circular in the past. However, in practice, the perforations are often non-circular or irregular shape due to manufacturing techniques. Sound absorption coefficient and absorption bandwidth of the micro-perforated panel absorber may be further improved, when the perforations in shape are changed. In view of the existing exact solutions of sound propagation in tubes, the simple formulas of specific acoustic impedances of the tubes for triangle and square cross-sectional perforations are derived. Mass reactance end correction of the micro-perforated panel is obtained based on the sound radiation of a shaped piston. The specific acoustic impedance ratio of the micro-perforated panel absorber is calculated and analyzed, which can predict its sound absorption bandwidth. Finally, for closed perforations, the influences of the perforations in shape (including triangle, circle, square and irregular circle) on sound absorption of the MPP absorber are discussed in collaboration with FE simulations.     

微穿孔板抑制不稳定燃烧的声学数值仿真

为了研究微穿孔板吸声结构对不稳定燃烧的抑制作用,采用高精度的计算气动声学(Computational Aeroacoustics,CAA)方法开展时域下的数值仿真。首先对带有压力时滞模型的三维声学扰动方程进行求解,给出发动机不稳定燃烧的频率信息。然后通过解析模型分析微穿孔板吸声结构的阻抗特性,并由多自由度宽频阻抗模型模拟微穿孔板对该不稳定频率的抑制作用。仿真捕捉到的不稳定燃烧频率与地面试车测得的频率相一致。表明采用的计算气动声学方法及相应模型可以准确地捕捉不稳定燃烧的频率信息,并分析微穿孔板对不稳定燃烧的抑制作用,对于工程上快速预测不稳定燃烧具有一定意义。     

Vibroacoustic properties of thin micro-perforated panel absorbers

This paper presents theoretical and experimental results on the influence of panel vibrations on the sound absorption properties of thin micro-perforated panel absorbers (MPPA). Measurements show that the absorption performance of thin MPPAs generates extra absorption peaks or dips that cannot be understood assuming a rigid MPPA. A theoretical model is established that accounts for structural-acoustic interaction between the micro-perforated panel and the backing cavity, assuming uniform conservative boundary conditions for the panel and separable coordinates for the cavity cross-section. This model is verified experimentally against impedance tube measurements and laser vibrometric scans of the cavity-backed panel response. It is shown analytically and experimentally that the air-frame relative velocity is a key factor that alters the input acoustic impedance of thin MPPAs. Coupled mode analysis reveals that the two first resonances of an elastic MPPA are either panel-cavity, hole-cavity, or panel-controlled resonances, depending on whether the effective air mass of the perforations is greater or lower than the first panel modal mass. A critical value of the perforation ratio is found through which the MPPA resonances experience a frequency "jump" and that determines two absorption mechanisms operating out of the transitional region.     

Enhancing micro-perforated panel attenuation by partitioning the adjoining cavity

The sound attenuation performance of micro-perforated panels (MPP) with adjoining air cavity is investigated for a plenum. The sound field inside of a plenum is compared for two cases. In the first case, the plenum is treated with an MPP and adjoining air cavity without any partitioning. For the second case, the adjoining air cavity is partitioned into a number of sub-cavities. The resulting sound pressure fields indicate that partitioning the adjoining air cavity increases the overall sound attenuation due to the MPP by approximately 4 dB. The explanation for this phenomenon was investigated by measuring the sound pressure level on planes in front of the MPP. Additionally, boundary element analyses were conducted to simulate the effect of the MPP and adjoining cavity with and without partitioning on the sound field in the plenum. It was demonstrated that a MPP can be modeled as a transfer impedance and that partitioning the adjoining cavity enhances attenuation to acoustic modes that propagate transverse to the MPP.     

多层微穿孔板结构声学性能计算方法对比分析

计算多层微穿孔板结构声学特性方法传统主要用声电类比法,目前出现阻抗转移法和传递矩阵法,对比分析这三种计算方法,同时进行相应的实验验证。结果表明:阻抗转移法和传递矩阵法实质上是相同的,这两种方法计算结果与实验结果吻合良好。声电类比法在空腔较大时计算结果偏离实验值,原因是声电类比法采用集总参数分析,计算多层结构时,空腔单元只考虑声顺,忽略声质量,导致误差。阻抗转移法和传递矩阵法不存在这一误差,计算准确。     

Design of a single layer micro-perforated sound absorber by finite element analysis

Micro-perforated sound absorbers with sub-millimeter size holes can provide high absorption coefficients. This paper presents results of work on the development of an effective single layer micro-perforated sound absorber from the commercial composite material Parabeam^® with micro diameter holes drilled on one side. Parabeam^® is used as a structural material made from a fabric woven out of a E-glass yarn and consists of two decklayers bonded together by vertical piles in a sandwich structure with piles (thick fibers) woven into the decklayers. The paper includes, the analytical model developed for prediction of absorption coefficients, finite element solution using commercial software MSC.ACTRAN and experimental results obtained from impedance tube measurements. A simple optimization is performed based on the developed models to obtain an efficient absorber configuration. It has been anticipated that several different and interesting applications can be deduced by combining structural and sound absorption properties of this new micro-perforated absorber.     

Empirical model of the acoustic impedance of a circular orifice in grazing mean flow

Although there are many analytical and empirical models for orifice impedance, the predicted acoustical performance when adopting any one of them sometimes shows a large discrepancy with the measured result in some cases. In order to obtain a new practical and precise empirical impedance model under grazing flow conditions, the acoustic impedance of circular orifices has been measured with a variation of the involved parameters under very carefully tested and controlled measurement conditions. The parameters involved in determining the acoustic impedance of an orifice are comprised of the orifice diameter, orifice thickness, perforation ratio, mean flow velocity, and frequency. The range of involved parameters is chosen to cover the practical data span of perforates in typical exhaust systems of internal combustion engines. The empirical impedance model is obtained by using nonlinear regression analysis of the various results of the parametric tests. The proposed empirical model of orifice impedance, with a very high correlation coefficient, is applied to the prediction of the transmission loss of concentric resonators, which have geometric configurations typical of acoustically short and long through-flow resonators. By comparing the measured and predicted results, in which the predictions are made by employing many previous orifice impedance models as well as the present model, it is confirmed that the proposed orifice impedance model yields the most accurate prediction among all other existing impedance models.