控制颈部开口横截面积的可变共振型消声装置

以前,大多数消声器都是被动式的。而最近对主动式消声器的研究日益多起来了。主动式消声法可分两种方式:一种是采用扬声器等做附加声源,产生与应消去噪声的声压波形反相位的声压波形,使两者相互抵消的方式。这种方式,从理论上说,在相当宽的低频带范围具有消声能力。但是,实际上存在着附加声源的耐久性及其所产生低频波等有关问题。另一种是根据声噪声的频率特性调整消声器的形状方式。本文就是研究这种方式加上控制技术的可变共振腔消声法。这是根据周期性噪声的周期变化,改变共振型消声器的共振腔容积,使共振频率跟踪噪声的主要频率,让共振型消声器的消声能力最大限度地发挥出来。这     

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。     

微机在有源消声中的应用

本文讨论将微机技术引入单源有源消声器。微机控制其可变参数,使消声系统能对噪声源进行自动跟踪。其参数在一定范围内随着消声情况的变化而变化,始终保持最佳的消声效果。对线状谱噪声可将其剩余噪声控制在本底噪声或比本底噪声稍高一点的范围内(～3dB)。跟踪速度较快,最佳消声状态的稳定性也较好。     

消声器测试设备的特性

消声器对飞机噪声、厂矿排气动力噪声和现代城市交通运输噪声的控制都非常重要。对于消声元件的理论已有系统的工作。我们设计的消声器测试设备     

汽车排气消声器的正向设计研究*

本文以实现汽车排气消声器的正向设计为目的,提出消声器的开发思路:首先采用从分析设计目标到确定总体方案,再到具体设计的路线,结合Virtual.Lab Acoustics、GT-Power和Fluent等数值分析软件与发动机台架试验。然后以主消声器的设计为主,副消声器的设计为辅;以声学性能为主,流场及其他性能为辅。再通过对消声频率的分析,逐级设计消声结构并进行组合、验证和改进,并在与企业提供的消声器方案进行对比后初步判断设计方案的可行性。最后通过实验验证了消声器设计方案的综合性能达到设计目标,表明了本文提出的消声器正向开发思路的合理性,在汽车排气消声器的设计开发上具有实用价值。     

基于低频吸声超构材料的复合消声器研究*

针对管道内低频噪声难以抑制的问题，本文基于亥姆霍兹共振腔（HR）阵列吸声板和穿孔管消声器组合，设计了一种复合式宽带消声器。首先利用有限元法仿真分析传统穿孔管消声器，发现中低频消声能力较差，通过嵌入HR阵列吸声板吸收中低频噪声。采用仿真与实验的方式研究吸声板的声学性能：在400-1000 Hz频段内的平均吸声系数达到了0.88。然后对复合式消声器进行数值模拟及3D打印阻抗管实验测试对比：复合式消声器在400-1718Hz频率范围内的平均传递损失为18.15 dB ，最终实现了管道内全频带噪声有效控制。     

轴对称抗性消声器的有限元分析

扩张室消声器结构简单,因此在噪声控制工程中得到广泛的应用。近年来异形插管消声器更得到重视。但是用经典的一维平面波理论来估计它的消声特性或指导设计都很困难。本文采用有限元方法,求出它的声场分布和消声特性,为设计此类消声器提供了理论基础和新方法。文中以简单扩张室消声器为例,证实有限元方法计算值与经典的一维平面波理论值在低频范围内能很好的符合。在较高频率的范围,一维理论方法要受到限制,而有限元方法仍然适用,并能估计出消声器中的二维效应。对于异形插管消声器,则只能用有限元方法求其消声特性。本文着重介绍具有轴对称和自然边界条件波动方程的有限元方法。     

噪声与振动控制系列产品简介(5)

隔声房(罩)、风冷机组通风消声罩隔声房（罩）在工业与民用领域得到了广泛的应用。它采用特制模块板结构,按用户要求选配隔声门。消声器、消声百叶、隔声窗等模块式结构,兼顾隔声、吸声、通风,对于特殊要求,加装隔振系统减低噪声和振动的影响。模块式风冷机组通风消声罩在保证通风量的同时有效地降低机组噪声,并可提供数十种机组的消声数据。优点：１特制连接槽性能可靠,保证整体声学性能;２．灵活组合,适应不同情况;３现场安装快捷,费用低;４日常操作、检修方便,维护性好;５拆卸方便,易于扩大、改装,不影响其声学性能。可视…     

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。     

微穿孔板消声器及其在高速气流下的消声性能

《物理》杂志1974年第4期 报导了降低噪声的新手段——微穿孔板吸声结构.本文介绍新型消声器——微穿孔板消声器及其在高速气流下的消声性能.一、消声器和微穿孔板消声器随着近代工业和科学技术的发展,空气动力机械得到越来越广泛的应用,它已经成为国民经济和国防事业中不可缺少的设备.但任何空气动力过程都伴随着噪声的发生.这种由于气体的非稳定过程,或者说由于气体的扰动而产生的噪声,叫做空气动力性噪声.如航空发动机喷气噪声、内燃机和燃汽轮机噪声、压缩气体和大流量蒸汽排汽放空噪声、大型鼓风机和压缩机噪声……等等,皆属空气动力性…     

一种防尘、耐高温消声器的研究

一种新型的消声器能应用在高温,含尘的条件下,消声器设计采用了四分之一波长吸声,其内部消声构造与防尘,耐高温有机结合起来,实现了防尘和消声的较佳效果。     

Attenuation of a resonant dissipative silencer in a rigid duct

Sound attenuation characteristics of a resonant-type dissipative silencer consisting of a reactive chamber with a porous facing have been considered. Such a silencer provides a high degree of attenuation within a narrow frequency range. Predicted attenuation values are compared with experiment for plane waves propagating in a rigid duct containing the dissipative silencer. The sound field is described by one-dimensional acoustical expressions taking into account the effect of boundary conditions and the presence of the silencer. The theoretical model incorporates the acoustical properties of porous materials and inertance of the sound field in the duct adjacent to the silencer. Good agreement was achieved between theoretical predictions and actual measurements. Results presented indicate the dependence of the attenuation spectrum upon flow resistivity and thickness of the porous material.     

Development of composite plate for compact silencer design

A compact flow-through plate silencer is constructed for low frequency noise control using new reinforced composite plates. The concept comes from the previous theoretical study [L. Huang, Journal of the Acoustical Society of America 119 (2006) 2628–2638] which concerns a clamped supported plate enclosed by rigid cavities. When the grazing incident sound wave comes and induces the plate into the vibration, it will radiate sound and reflect sound. Such sound reflection causes a desirable noise reduction from low to medium frequency with wide broadband. The structural property of the very light plate with high bending stiffness is very crucial element in such plate silencer. In this study, an approach to fabricate new reinforced composite panel with light weight and high flexibility to increase the bending stiffness is developed in order to realize the function of this plate silencer practically. The plate silencer can be constructed in more compact size compared with the previous two-plate silencer with two rectangular cavities and the performance with the stopband of the range from 229 to 618 Hz, in which the transmission loss is higher than 10 dB over the whole frequency band without flow or with flow at the speed of 15 m/s, can be achieved. The experimental data also proves that the non-uniform clamped plates with thinner ends perform very well. To implement the use of such silencer practically in controlling noise at different dominant frequency ranges, a design chart has been established for searching the optimal bending stiffness and corresponding stopband at different geometries.     

A direct mixed-body boundary element method for packed silencers

Bulk-reacting sound absorbing materials are often used in packed silencers to reduce broadband noise. A bulk-reacting material is characterized by a complex mean density and a complex speed of sound. These two material properties can be measured by the two-cavity method or calculated by empirical formulas. Modeling the entire silencer domain with a bulk-reacting lining will involve two different acoustic media, air and the bulk-reacting material. Traditionally, the interior silencer domain is divided into different zones and a multi-domain boundary element method (BEM) may be applied to solve the problem. However, defining different zones and matching the elements along each interface is tedious, especially when the zones are intricately connected. In this paper, a direct mixed-body boundary element method is used to model a packed silencer without subdividing it into different zones. This is achieved by summing up all the integral equations in different zones and then adding the hypersingular integral equations at interfaces. Several test cases, including a packed expansion chamber with and without an absorbing center bullet, and a parallel baffle silencer, are studied. Numerical results for the prediction of transmission loss (TL) are compared to experimental data.     

阵列式阻性消声器传递损失计算模型*

针对气流通道彼此独立且截面尺寸较小的直管式阻性消声器,Belov基于声波导管理论推导了其消声量计算公式,该公式不适用于气流通道彼此连通且截面尺寸较大的阵列式阻性消声器。为此,本研究提出了一种阵列式消声器消声量计算方法。将阵列式消声器划分为周期性排列的消声单元,每个消声单元包含1个吸声柱。分别参照扩张式消声器和直管阻性消声器计算消声单元的抗性部分（进、出口气流通道截面突变处）和阻性部分消声量的理论值TL1和TL2。在此基础上,采用有限元法仿真得到消声器消声量仿真值TLs,基于阻性部分消声量仿真值和理论值的比值(TLs-TL1)/TL2,拟合确定各倍频带阻性消声量修正函数Nf,即修正后的消声量理论值计算模型为TLt''=TL1+TL2·Nf。作为算例,建立了多孔吸声材料流阻率为11425 Pa·s/m2时适用于不同结构尺寸的阵列式消声器消声量计算模型。实测结果验证表明,各倍频带修正后的消声量理论值与实测值绝对误差均小于3 dB。当吸声材料的流阻率与算例中取值相差较大时,消声量计算模型需参照本研究所述方法另行建立。     

Active membrane-based silencer and its acoustic characteristics

A membrane-based silencer using dielectric elastomer absorbers (DEAs) was developed and explored in the present study. Dielectric elastomer, a soft smart material, was used to fabricate this actuator. It has the characteristic of lightweight, high elastic energy density and large deformation under external direct current (DC) or alternating current (AC) voltages. The typical acoustic performances of this membrane-based silencer were experimentally identified using a transmission loss (TL) duct acoustic measurement system. It was found that the resonance peaks of this membrane-based silencer could be controlled by applying different external voltages, a maximum resonance frequency shift of 59.5 Hz for the resonance peaks was achieved which indicated that this membrane-based silencer could be adjusted to absorb the target noise without any addition mechanical part. Furthermore, the resonance shift and multiple resonances mechanisms using DEAs were proposed and discussed which was aiming to achieve multi-peaks noise reduction. The present results also provide insight into the appropriateness of the absorber for possible use as an acoustic treatment to replace the traditional acoustic treatment in the noise reduction technology.     

Influence of boundary restraint on sound attenuation performance of a duct-membrane silencer

Low frequency noise in duct is a challenge for the traditional passive noise control techniques. Recently, a so-called duct-membrane silencer has attracted much research attention due to its simple configuration and potential application, however, the current studies are merely limited to the cases in which just the classical boundary conditions are considered. Actually, as an important factor affecting the modal characteristics of the membrane, and the existing studies are not enough to fully understand the vibro-acoustic characteristics of such silencer with complicated boundary conditions. Motivated by this, in this paper, the structural–acoustic coupling model of duct-membrane system is established by a modified Fourier series method in combination with Rayleigh–Ritz procedure, in which the transverse elastic boundary restraints are taken into account. Energy principle is formulated for the vibro-acoustic coupling of such duct-membrane silencer to obtain the system matrix equation. Numerical results are then presented to validate the proposed model, and the influence of boundary restraining stiffness on sound attenuation performance is also studied. To the best of authors’ knowledge, this work represents the first time that the elastic boundary restraints have been considered for such duct-membrane silencing system.     

Study on plate silencer with general boundary conditions

A plate silencer consists of an expansion chamber with two side-branch rigid cavities covered by plates. Previous studies showed that, in a duct, the introduction of simply supported or clamped plates into an air conveying system could achieve broadband quieting from low to medium frequencies. In this study, analytical formulation is extended to the plate silencer with general boundary conditions. A set of static beam functions, which are a combination of sine series and third-order polynomial, is employed as the trial functions of the plate vibration velocity. Green?s function and Kirchhoff–Helmholtz integral are used to solve the sound radiation in the duct and the cavity, and then the vibration velocity of the plate is obtained. Having obtained the vibration velocity, the pressure perturbations induced by the plate oscillation and the transmission loss are found. Optimization is carried out in order to obtain the widest stopband. The transmission loss calculated by the analytical method agrees closely with the result of the finite element method simulation. Further studies with regard to the plate under several different classical boundary conditions based on the validated model show that a clamped-free plate silencer has the worst stopband. Attempts to release the boundary restriction of the plate are also made to study its effect on sound reflection. Results show that a softer end for a clamped–clamped plate silencer helps increase the optimal bandwidth, while the same treatment for simply supported plate silencer will result in performance degradation.     

Evaluation of the acoustic and non-acoustic properties of sound absorbing materials using a three-microphone impedance tube

This paper presents a straightforward application of an indirect method based on a three-microphone impedance tube setup to determine the non-acoustic properties of a sound absorbing porous material. First, a three-microphone impedance tube technique is used to measure some acoustic properties of the material (i.e., sound absorption coefficient, sound transmission loss, effective density and effective bulk modulus) regarded here as an equivalent fluid. Second, an indirect characterization allows one to extract its non-acoustic properties (i.e., static airflow resistivity, tortuosity, viscous and thermal characteristic lengths) from the measured effective properties and the material open porosity. The procedure is applied to four different sound absorbing materials and results of the characterization are compared with existing direct and inverse methods. Predictions of the acoustic behavior using an equivalent fluid model and the found non-acoustic properties are in good agreement with impedance tube measurements.     

Multiple drumlike silencer for low frequency duct noise reflection

Low frequency duct noise is difficult to tackle by passive means within a certain space limitation. Drumlike silencer offers broadband sound reflection in the low-frequency region, e.g. 0.1–0.3 times the first cut-on frequency of the central duct. Optimization was carried out for the logarithmic bandwidth in which the transmission loss (TL) is greater than a pre-determined criterion value. The prediction was validated in laboratory but it was anticipated that the required high level of tension is difficult to implement in practice. It is found that the optimal tension is approximately proportional to the 3rd power of membrane length, so a partitioned membrane is expected to reduce the required tension. In order to optimize the partitioned drumlike silencer, a new cost function of total transmission loss, or insertion loss, with a frequency weighting in favour of a certain wide band of low frequencies is introduced. The new cost function removes the undesirable discontinuous behaviour occurring in the previous optimization process. It is also found that the partitioned silencer can drastically improve the weighted total TL and the tension required is indeed much reduced. The main performance improvement derives from around the lower frequency limit of interest.