运动型汽车排气系统消声器的研究

为了获得运动型排气噪声,本文研究了汽车排气系统消声器结构对运动声学品质的影响。通过改变消声器的内部结构,建立与之对应的GT-Power模型,利用一维流体动力学原理对排气系统的声学性能进行模拟和仿真,并运用声学测试平台测试节气门全开加速时的尾管噪声。验证了去除排气系统的中排消声器并在后排消声器内加入消声棉的结构,可明显提高噪声的运动性,另外,消音棉的利用可以有效降低高频噪声,消声器进气管处的穿孔结构可以有效消除中低频噪声。     

阻抗复合消声器声学性能有限元预测方法及分析

为计算和分析具有复杂结构的阻抗复合式消声器的宽频消声性能,建立了一种高效声学有限元方法,给出了不同边界条件下的边界积分处理细节,得到有限元全局系数矩阵表达式,设计出计算程序框架以实现这些算法,其求解规模和计算速度与商业软件相比有优势。为计算阻抗复合式消声器的传递损失,通过阻抗管测量和数据拟合得到了吸声材料声学特性的经验公式。计算和测量了两通穿孔阻抗复合式消声器的传递损失,二者良好的吻合验证了声学有限元方法和计算程序的正确性。研究表明,插管长度影响消声器在中高频段的消声特性,右侧隔板上穿孔会消除共振峰,中高频消声性能随着出口管穿孔率的增加而提升。      

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。     

管道有源消声器

有源消声器对于管道中低频噪声的抑制比较有效。本文介绍的由单指向性传声器、延时器、单指向性扬声器构成的有源消声器,对于单频声,在100—315Hz频率范围可降低35—55dB;对于1/3倍频程噪声,可降低14—24dB;对于宽频带噪声,在一个倍频程内可降低8—20dB。     

不同声强宽带噪声激励下结构参数对穿孔板消声器吸声特性影响的实验研究

高声压级激励下,由于非线性效应的存在,穿孔板消声器的吸声特性将发生改变,而改变量的大小与穿孔板的结构参数(穿孔率,孔径,板厚)密切相关。本文设计搭建了实验平台来研究结构参数的变化对穿孔板消声器的吸声特性的影响。根据实验结果发现:随着声压级的升高,由于穿孔板结构的非线性加剧,其声阻抗将发生变化,导致穿孔板消声器的吸收峰值降低,但吸收频带却拓宽了;在穿孔率一定的情况下,孔径越小的穿孔板消声器更适合低声压级环境工作;在孔径一定的情况下,穿孔率越低的穿孔板消声器也更适合低声压级环境工作。     

均匀流直通穿孔消声器的声学特性分析

将数值模态匹配法(NMM)扩展应用于计算有均匀流存在时直通穿孔管抗性和阻性消声器的声学特性,编写了相应的计算程序。对于圆形同轴穿孔管抗性和阻性消声器,应用数值模态匹配法计算得到的传递损失结果与实验测量结果吻合良好,从而验证了计算方法和计算程序的正确性。进而应用数值模态匹配法研究了运流效应和穿孔阻抗以及穿孔管偏移对穿孔管抗性和阻性消声器传递损失的影响。研究结果表明,马赫数越高,穿孔管抗性消声器在中高频的消声量越高,阻性消声器在整体频段内的消声性能越差;低马赫数时运流效应对穿孔管抗性消声器的影响可以忽略,马赫数较高时运流效应和穿孔阻抗的影响比较明显;对于穿孔管阻性消声器,穿孔阻抗对消声器声学特性的影响比运流效应的影响小,但是与真实值的差别不可忽略;穿孔管偏移对消声器声学特性的影响与频率和消声器结构均相关。      

间歇性排气噪声源的特性及消声器结构的研究

排气噪声可分为稳定排气噪声，周期性排气噪声和间歇性排气噪声，通过对锻压机离合器与制动器的排气噪声源的特性研究，指出间歇性气噪声是由管道噪声，阀门噪声和喷口噪声所组成，首次指出了间歇性排气噪声存在单极子噪声及爆炸声。通过理论计算及试验建立了一种有效的滤波了噪消声器结构。     

穿孔管消声器声学长度修正的理论公式

推导出穿孔管消声器声学长度修正以及共振频率的理论公式。证明了在均匀分布情况下,多小孔向膨胀腔声辐射与单个小孔向膨胀腔声辐射的声学长度修正系数是一致的。对于小孔向主管道的声辐射,根据理论公式研究了穿孔率、周向均布数以及亥姆赫兹数对声学长度修正的影响,有限元计算得出在直径比小于0.4的情况下声学长度修正系数理论公式与仿真计算结果吻合良好。并利用理论公式的性质以及仿真结果获得了实用的拟合公式,提升了穿孔管消声器在高频时共振频率的计算精度。      

均匀流直通穿孔消声器的声学特性分析

将数值模态匹配法(NMM)扩展应用于计算有均匀流存在时直通穿孔管抗性和阻性消声器的声学特性,编写了相应的计算程序。对于圆形同轴穿孔管抗性和阻性消声器,应用数值模态匹配法计算得到的传递损失结果与实验测量结果吻合良好,从而验证了计算方法和计算程序的正确性。进而应用数值模态匹配法研究了运流效应和穿孔阻抗以及穿孔管偏移对穿孔管抗性和阻性消声器传递损失的影响。研究结果表明,马赫数越高,穿孔管抗性消声器在中高频的消声量越高,阻性消声器在整体频段内的消声性能越差;低马赫数时运流效应对穿孔管抗性消声器的影响可以忽略,马赫数较高时运流效应和穿孔阻抗的影响比较明显;对于穿孔管阻性消声器,穿孔阻抗对消声器声学特性的影响比运流效应的影响小,但是与真实值的差别不可忽略;穿孔管偏移对消声器声学特性的影响与频率和消声器结构均相关。     

直通穿孔管消声器声学特性预测的数值模态匹配法

将数值模态匹配法应用于计算横截面为任意形状的直通穿孔管抗性消声器的声学特性。应用二维有限元法计算横截面的本征值和本征向量,应用模态匹配技术求解模态幅值系数,进而得到所需的声学量。对于圆形和椭圆形直通穿孔管消声器的传递损失,数值模态匹配法计算结果与三维有限元计算结果和相应的实验测量结果吻合良好,表明数值模态匹配法能够精确计算直通穿孔管消声器的声学特性。计算结果表明,穿孔管的偏移影响消声器在中高频段的消声特性,同轴结构消声器的消声性能好于非同轴结构。      

The research on semi-active muffler device of controlling the exhaust pipe’s low-frequency noise

In order to control low frequency noise in exhaust pipe, this paper puts forward a new concept of H-Q tube based semi-active muffler device. The semi-active muffler device and bench testing system have been designed and operated. Finite element simulation study on semi-active muffler and experimental study on semi-active muffler and passive muffler have been carried on. The effect of simulation and experiment are consistent. The semi-active muffler device acts well in low frequency band, especially between 50 Hz and 150 Hz. The average level of noise reduction is around 35 dB, which is much better than passive muffler. Between 150 Hz and 350 Hz, semi-active muffler has a better performance than passive muffler; above 350 Hz, it has worse performance compared with the passive muffler.     

水介质管路弹性背腔微穿孔消声器的传递损失特性

为抑制水介质管路系统低频噪声,兼顾结构的紧凑性,提出弹性背腔微穿孔管路消声结构,弹性管壁为橡胶帘线复合材料,并推导了传递损失的数值解法.首先,基于Biot-Allard多孔弹性理论,将弹性微穿孔板等效为弹性多孔材料;然后,利用双尺度法建立帘布的周期性代表单元,求得其刚度矩阵;接着,基于分层理论,建立弹性管壁的多层复合材...     

Sound attenuation of a periodic array of micro-perforated tube mufflers

The wave propagation in a periodic array of micro-perforated tube mufflers is investigated theoretically, numerically and experimentally. Because of the high acoustic resistance and low mass reactance due to the sub-millimeter perforation, the micro-perforated muffler can provide considerable sound attenuation of duct noise. Multiple mufflers are often used to enhance attenuation performance. When mufflers are distributed periodically in a duct, the periodic structure produces special dispersion characteristics in the overall sound transmission loss. The Bloch wave theory and the transfer matrix method are used to study the wave propagation in periodic micro-perforated tube mufflers and the dispersion characteristics of periodic micro-perforated mufflers are examined. The results predicted by the theory are compared with finite element method simulation and experimental results. The results indicate that the periodic structure can influence the performance of micro-perforated mufflers. With different periodic distances, the combination of the periodic structure and the micro-perforated tube muffler can contribute to the control of lower frequency noise with a broader frequency range or improvement of the peak transmission loss around the resonant frequency.     

Transmission loss of a flexible micro-perforated muffler with a flexible back cavity for water-filled pipelines

To reduce low-frequency noise of the water-filled pipeline system,a compact flexible micro-perforated muffler with a flexible back cavity(FMPMFBC) is proposed.The flexible pipe wall is made of a rubber-cord composite material.A numerical solution for the transmission loss is derived.Firstly,the flexible micro-perforated panel(FMPP) is equivalent to a flexible porous material based on Biot-Allard porous-elastic theory.Then,a periodic structural unit of the aramid fabric cloth is established with the two-scale method,and the equivalent stiffness matrix is obtained.Besides,a multi-layer composite model for the flexible pipe wall is constructed according to the lamination theory.Coupling with the internal sound field,the transmission loss of the FMPMFBC is calculated.On a water-filled impedance tube,the transmission loss curves of the FMPMFBC prototypes are measured with the two source-location method,and compared with those of a flexible micro-perforated muffler with a rigid back cavity(FMPMRBC)and an expansion muffler.Theoretical results are experimentally verified.The FMPMFBC is a hybrid muffler combining reflection with dissipation,capable of attenuating broadband lowfrequency noise.The transmission loss of prototype B2 in the frequency bands of [40 300] Hz and [40 1200] Hz is 36 dB and 30 dB,respectively,while the transmission loss of the same-sized expansion muffler in the corresponding frequency bands is 7 dB and 11 dB,respectively.     

Numerical studies on venting system with multi-chamber perforated mufflers by GA optimization

Research on new techniques of perforated silencers has been well addressed and developed; however, the research work in shape optimization for a volume-constrained silence requested upon the demands of operation and maintenance inside a constrained machine room is rare. Therefore, the main purpose of this paper is to not only analyze the sound transmission loss of a multi-chamber perforated muffler but also to optimize the best design shape under space-constrained condition.In this paper, both the generalized decoupling technique and plane wave theory are used. The four-pole system matrix in evaluating the acoustic performance of sound transmission loss (STL) is also deduced in conjunction with a genetic algorithm (GA). To demonstrate the precision of the tuning ability in a muffler, various targeted pure tones are proposed in numerical cases. Results reveal that the maximal acoustical performance precisely occurred in the desired frequency. Furthermore, a noise reduction with respect to full-band exhausted noise emitted from a diesel engine is also introduced and assessed. To achieve a better optimization in GA, several test parameter values were used. Before a GA operation can be carried out, the accuracy of the mathematical models have to be checked by experimental data.The optimal result in eliminating full-band noise reveals that the overall noise reduction of a multi-chamber muffler can achieve 68 dB under space-constraint conditions. Consequently, the approach used for the optimal design of the STL proposed in this study is indeed easy, economical and quite effective.     

GA optimization on multi-segments muffler under space constraints

Whilst the space volume of muffler in noise control system is often constrained for maintenance in practical engineering work, the maximization on muffler’s performance becomes important and essential. In this paper, a novel approach genetic algorithms (GAs) based on the principles of natural biological evolution will be used to tackle this optimization of muffler design [M. Mitchell, An Introduction to Genetic Algorithms, The MIT Press, Cambridge, MA, 1996]. Here, the shape optimization of multi-segments muffler coupled with the GA searching technique is presented. The techniques of binary genetic algorithms (BGA) together with the commercial MATLAB package [G. Lindfield, J. Penny, Numerical Method Using Matlab, second ed., Prentice Hall, Englewood Cliffs, NJ, 2000] are applied in GA searching. In addition, a numerical case of pure tone elimination with 2-5 segments on muffler is introduced and fully discussed. To achieve the best optimization in GA, several GA parameters are on trial in various values. Results show that the GA operators, including crossover mutation and elitism, are essential in accuracy. Consequently, results verify that the optimal sound transmission loss at the designed frequency of 500 Hz is exactly maximized. The GA optimization on multi-segments muffler proposed in this study surely provides a quick and correct approach.     

二次余数扩散结构复合穿孔板扩散吸声研究

声学结构研究一直以来都是学术领域的研究热点。扩散吸声结构(Diffsorber)由于兼具扩散和吸声性能而具有很好的研究意义。本研究将具有良好扩散性能的二次余数扩散(Quedratic:residue diffusers,QRD)结构和具有良好共振吸声性能的穿孔板结构进行组合,依据标准AES-4id-2001对二次余数扩散结构及其与厚度为1 mm,穿孔率分别为3%,5%,8%的穿孔板复合后结构的扩散性能进行了实验研究,得到了相应的反射声能极坐标图和扩散系数。结果表明,复合结构在100 Hz至800 Hz的频率范围内仍具有良好的扩散性能;复合结构反射声能在穿孔板共振频率范围内有明显的下降(平均超过2 dB)。本研究可为扩散吸声结构的设计与研制提供依据。      

轻卡进气管的结构优化及其声学性能

为有效降低轻卡进气管的噪声,首先通过原始进气管的噪声实验,测试得出噪声的主要贡献频率,结合管道的布置情况,进行了消声器(谐振腔)的设计,进而完成对进气管的优化设计;通过专业声学分析软件LMS Virtual.lab对优化前后的进气管进行声学性能的模拟研究,得出了谐振腔对声场的具体影响;通过噪声实验,分析出加装谐振腔的进气管相比于原始进气管的降噪效果。研究结果表明：在所研究的进气管噪声的主要贡献频率下(即125 Hz、180 Hz、465 Hz、640 Hz),加装谐振腔后,传递损失均能得到有效增加;在怠速工况和加速工况下,优化后的进气管噪声值均能满足限定值。因此,通过添加谐振腔来优化进气管可以达到了较好的降噪效果。该研究可为汽车进气管降噪元件的优化设计提供一定的指导。     

Diffusion and sound absorption properties of the quadratic residue diffuser structure with perforated panel

Acoustic structure study always is the academic research interest. Diffusion ab?sorbing structure(DiflFsorber) has good research value because it has both diflFusion property and sound absorption property. Quadratic residue diffusers(QRD) structure which had good diffusion property was combined with the perforated panel which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-panels which had1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams of different structure were analyzed to derive the diffusion coefficients. Results showed that the composite structure still had good diffusion performance in the frequency range from100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated panel resonance frequency range where there was about 2 dB reduction averagely.The study result can provide the reference for the design and development of diifsorber.