Mechanisms of active control of noise transmission through triple-panel system using single control force on the middle plate

This paper presents an active triple-panel sound insulation structure with an idealized controllable point force acting on the middle plate. A novel analytical approach based on sound energy transmission rule is proposed to achieve the physical mechanism study. The transfer impedance matrix of the incident and middle plate is calculated using numerical approach. And the rule of sound energy transmission through the triple-panel structure is concluded by indirectly analyzing the radiated sound power of the three plates. Finally the physical mechanism of noise insulation is investigated from the point of view of the change in behaviors of energy transmission in controlled and uncontrolled conditions. Results obtained demonstrate that there exist four different energy transmission paths for four panel mode groups. The energy transmission is independent in each path and they are all of band-pass characteristic. The role of the middle plate and two cavities is very similar to the band-pass filter whose pass-band is different for different mode groups. The essence of active noise insulation lies in the fact that the energy transmission in each path is suppressed in its pass-band after control. This greatly improves sound insulation capability of the triple-panel structure and leads to sound propagation being blocked.     

Point and transfer mobility of point-connected ribbed plates

The work reported in this paper addresses the problem of structure-borne sound transmission between vibrating sources and ribbed-plate receiver structures. Vibrating sources, such as pumps, motors, fans, etc., transmit vibro-acoustic power, causing noise complaints by occupants in cars, trains, aircraft, buildings and/or material fatigue and damage. The transmission process is complicated in that sources transmit power through several contacts and by up to six components of excitation at each contact. The structure-borne sound power is a function of source activity, source mobility and receiver mobility, and all three quantities must be known to some degree. For non-homogeneous receiver structures, such as thin-plate cavity constructions or lightweight framed constructions, the sheathing plates are typically fastened to the framing members using bolts, screws or spot-welded joints. Hence the resulting system is a point-connected ribbed plate structure and the receiver mobility is expected to vary significantly with position. Since measured receiver data seldom is available for prediction purposes, a method of estimating the point and transfer mobility of point connected ribbed plates is required. In this paper, an approximate approach, based on substitution forces, is described. The model uses infinite beam and infinite plate behaviour as input quantities. Estimates of point and transfer mobility are compared with measured results using a timber joist floor construction as an example.     

The identification of sound generating mechanisms of tyres

Tyre noise is generated by several mechanisms. With a modern tyre, wall vibration, air pumping and air resonant radiation are all considered to be important. But tyre noise generating mechanisms are still not clear due to the complication of tyre vibration behaviour. Vibrations of the tyre shell are the combination of several different wave types which appear at different frequencies. In a low frequency range, where the tyre behaves like an elastically supported beam, the circular ring model is used to analyze the dispersion relations. Above 300 Hz, which is the transition point from one-dimensional to two-dimensional waveguide properties of the passenger car tyre, a cylindrical shell model is used to analyze flexural waves propagation. Two important features on the wave propagation, wave-guide behaviour and the curvature effect of the tyre wall are analyzed. In consideration of noise radiation from tyre waves, most of the tyre waves observed in this study are inefficient sound radiators since their wavenumbers are larger than the acoustic wave number. As a result, It is observed that one of the most important features in sound radiation of a tyre shell is acoustically excited wave motion of the tyre wall.     

点噪声源在近程声场中传播损失的仿真研究

在分层介质条件下，用本征声线法仿真计算了点声源这距离噪声场的传播损失曲线，仿真结果表明，其传播损失不仅依赖于声速分布，海区深度，海底反射特性等环境条件，也依赖于声源及接收水听器的深度，声传播损失显著不同于球面波衰减规律，其传播损失率差别可达８ｄＢ，这表明在测量舰船目标的辐射噪声声源级时必要的声场校正测量是必须的。     

空气中声源的水下匹配场定位

通过水下布放的垂直线列阵采集空中声源在水下激发的测量声场,采用声场波数积分模型(OASES模型)对空中声源激发的水下声场建模,计算出拷贝声场,将二者进行匹配处理从而对空中声源目标定位。首先通过数值仿真验证了匹配场处理技术对空中声源的测距能力,并通过引入宽带匹配场处理器平滑掉距离上的周期性旁瓣。最后分析南海某海域的空气声试验数据,采用常规匹配场方法对700 m以内的32组空中声源目标进行定位,测距结果与GPS计算的收发间实际距离相比,大多数情况下是一致的,在较远距离由于信噪比降低,测量结果容易出现偏差。      

可靠声路径传播特性及目标定位方法研究现状

作为深海中重要的声传播途径之一,可靠声路径声道下的环境噪声级较低,声速剖面变化和海底界面作用对其影响较小。此外,当接收水听器位于该声道下近海底水域时,可实现对近海面中近距离目标的无盲区监测。因此,可靠声路径必将成为一种重要的深海探测与定位途径。该文从可靠声路径的声传播特性着手,综合概述了可靠声路径声传播特性和相应目标定位技术方面的国内外研究现状,旨在回顾当前各项技术成果并展望基于可靠声路径的目标定位技术今后的发展趋势。     

内部体积源作用下的圆柱壳内外声场特性

圆柱壳内各型体积源辐射噪声特性研究是声场建模和声场预报的前提.为了研究具有指向性的大尺度体积源特性对水下航行器结构内外声场的影响,本文结合薄壳理论、等效源和柱腔Green函数构造了体积源激励下的壳体振动耦合方程,研究了体积源表面声散射作用和指向性强弱对圆柱壳内外声场的影响.数值计算结果表明,体积源构造的准确性与其等效源位置有关,等效源配置在体积源几何中心与其结构表面之间0.4—0.6时,可以提高声场计算结果的准确性;大尺度体积源表面的声散射作用会导致壳体内部声场结构发生改变,内声场声腔共振峰发生偏移,并且在部分频段引起较强的声透射现象;此外,体积源指向性变化对壳体内外声场强弱影响较小,其显著作用表现在改变了外辐射声场的远场指向性.该研究结果对噪声预报和控制有一定的参考价值.     

Using streamlines to visualize acoustic energy flow across boundaries

For spherical waves that radiate from a point source in a homogeneous fluid and propagate across a plane boundary into a dissimilar homogeneous fluid, the acoustic field may differ significantly from the geometric acoustic approximation if either the source or receiver is near the interface (in acoustic wavelengths) or if the stationary phase path is near the critical angle. In such cases, the entire acoustic field must be considered, including inhomogeneous waves associated with diffraction (i.e., those components that vanish with increasing frequency). The energy flow from a continuous-wave monopole point source across the boundary is visualized by tracing acoustic streamlines: those curves whose tangent at every point is parallel to the local acoustic intensity vector, averaged over a wave cycle. It is seen that the acoustic energy flow is not always in line with the "Snell's law" or stationary phase path. Also, plots of acoustic energy streamlines do not display unusual behavior in the vicinity of the critical angle. Finally, it is shown that there exists a law of refraction of acoustic energy streamlines at boundaries with density discontinuities analogous to Snell's law of refraction of ray paths across sound speed discontinuities. Examples include water-to-seabed transmission and water-to-air transmission.     

Circulation pumps as structure-borne sound sources: emission to semi-infinite pipe systems

Circulation pumps are an important source of noise from domestic central heating systems. Pumps can generate airborne, liquid-borne and structure-borne sound and although standards exist for airborne and liquid-borne sources, none do for structure-borne sources. This is primarily because the structure-borne acoustic power delivered by the pump not only depends on the pump but also on the connected receiving system, which can be a complicated combination of pipes, valves and radiators. Also pumps deliver liquid-borne and structure-borne acoustic power simultaneously and their relative contributions to the sound radiated from the pipe system is not obviously obtainable. The approach proposed is to estimate the emission from the pump into semi-infinite pipes of material and cross-section typical of heating systems. Then to estimate the ‘mixing’ effect of bends, joints and other pipe discontinuities, due to wave mode conversion, as described in a companion paper. In the present paper, it is demonstrated that the structure-borne power can be calculated from the measured free velocity and mobility of the pump for each component of vibration and from receiver mobilities of idealized pipe systems. The structure-borne power is compared with the liquid-borne power measured directly by intensimetry.     

Transmission of low-frequency sound through the water-to-air interface

L.M. Brekhovskikh revealed and studied the important role played by inhomogeneous waves emitted by a point source when they pass through an interface with a medium in which the velocity of sound is lower, for example, from water to air. This paper studies the energy characteristics of sound emitted into air by an underwater point source. The energy transfer due to inhomogeneous waves is shown to cause the phenomenon of anomalous transparency of the interface for low-frequency sound. The anomalous transparency manifests itself in that the energy flux through the interface increases with decreasing frequency of sound and, at sufficiently low frequencies, almost all of the acoustic energy produced by the underwater source is emitted into air. Conversely, at high frequencies, when the contribution of the inhomogeneous waves becomes negligible, the water-to-air interface is similar to a perfectly reflecting surface and almost all of the acoustic energy produced by the source is emitted into water. The anomalous transparency phenomenon changes the conventional opinion on the possibility of acoustic coupling between points in water and air and on the role played by physical processes evolving in the water column in generating atmospheric acoustic noise.     

Analysis of acoustic communication by ants

An analysis is presented of acoustic communication by ants, based on near-field theory and on data obtained from the black imported fire ant Solenopsis richteri and other sources. Generally ant stridulatory sounds are barely audible, but they occur continuously in ant colonies. Because ants appear unresponsive to airborne sound, myrmecologists have concluded that stridulatory signals are transmitted through the substrate. However, transmission through the substrate is unlikely, for reasons given in the paper. Apparently ants communicate mainly through the air, and the acoustic receptors are hairlike sensilla on the antennae that respond to particle sound velocity. This may seem inconsistent with the fact that ants are unresponsive to airborne sound (on a scale of meters), but the inconsistency can be resolved if acoustic communication occurs within the near field, on a scale of about 100 mm. In the near field, the particle sound velocity is significantly enhanced and has a steep gradient. These features can be used to exclude extraneous sound, and to determine the direction and distance of a near-field source. Additionally, we observed that the tracheal air sacs of S. richteri can expand within the gaster, possibly amplifying the radiation of stridulatory sound.     

An experimental procedure to obtain sound power level of tyre/road noise under Coast-By conditions

The rolling noise from tyre–pavement interaction represents the greatest sound contribution from a vehicle when cruising at a high speed. To evaluate the sound levels from this source, existing standardized methods that establish different measurement procedures in both the immediate tyre surroundings, for example the Close-Proximity method, as well as at greater distances, as the Coast-By method. A fundamental parameter that can quantify the sound generation of a source is its sound power level. The standardized methods establish procedures to measure the sound pressure level but not the power level of a tyre as a noise source. For this reason, this paper presents a novel methodology based on sound pressure measurements to obtain the sound power level that a vehicle emits in Coast-By conditions, where noise is generated at tyre/road interaction. The paper describes the testing procedure used to obtain the sound power level, and it is accompanied by a mathematical simulation that studies the feasibility of the proposal. Finally, the proposed methodology is further validated through a field study.     

匹配垂直质点振速的浅海地声参数反演

海底声学参数对海洋波导中的声场特性研究和相关应用具有重要意义。针对一次夏季黄海声传播实验,分析了浅海负跃层环境下垂直质点振速的传播特性和简正波结构,说明当声源和接收器均位于负跃层下时,除海底附近外的大部分深度上垂直质点振速能量较高,且与声压相比,号数高的简正波对垂直质点振速的贡献更大,利用垂直质点振速进行匹配场反演能获得更高的海底参数敏感性。分析了海底吸收系数对垂直质点振速匹配场反演的影响,结果表明只有当进行匹配场反演时设置的海底吸收系数接近真实值时,才能获得准确的海底声速、密度和海深反演结果。利用实验中矢量水听器获取的垂直质点振速信号进行匹配场反演,将海底吸收系数在变化范围内取不同值对海底声速、密度和平均海深进行全局搜索,根据代价函数值最大确定了海底声速、密度及平均海深的反演结果,并利用不同距离上的声压传播损失反演出不同频率下的海底吸收系数。根据反演得到的海底声学参数计算声压传播损失,与实验中声压水听器测量结果符合较好。     

Interferometric method for estimating the velocity of a noise sound source and the distance to it in shallow water using a vector-scalar receiver

An experiment on estimating the velocity of a noise source and the distance to it using a single vector-scalar receiver has been performed on shallow-water Pacific shelf. Expressions for the components of the vector-scalar receiver field are derived. The source parameters are reconstructed using the interferometric method. The noise immunity of the method is analyzed for different acoustic field components and their combinations. The sensitivity of the method with respect to changes in the bottom parameters is considered.     

基于平面声源的三层有源隔声结构物理机制研究

次级源为平面声源的三层有源隔声结构,深入理解有源隔声的物理机理有助于挖掘降噪潜力及实现系统优化设计。首先对三层有源隔声结构建模并求解系统的振动响应。然后,对控制前三层结构中声能量的传输规律进行深入分析。最后,在辐射板声功率最小条件下,通过分析控制前后声能量传输特性的变化阐述了隔声的物理机理。结果表明,声能量在三层结构中传输形成四个等效的传输通道,中间板与两腔的作用类似带通滤波器,不同的传输通道具有相似的带通特性。有源隔声机理在于,通过控制抑制了通带内的能量传输,显著提高了三层结构整体的隔声性能,从而有效阻止了声波的向后传播。      

Propagation of acoustic waves in a fluid-filled pipe with periodic elastic Helmholtz resonators

Helmholtz resonators are widely used to reduce noise in a fluid-filled pipe system. It is a challenge to obtain lowfrequency and broadband attenuation with a small sized cavity. In this paper, the propagation of acoustic waves in a fluid-filled pipe system with periodic elastic Helmholtz resonators is studied theoretically. The resonance frequency and sound transmission loss of one unit are analyzed to validate the correctness of simplified acoustic impedance. The band structure of infinite periodic cells and sound transmission loss of finite periodic cells are calculated by the transfer matrix method and finite element software. The effects of several parameters on band gap and sound transmission loss are probed.Further, the negative bulk modulus of periodic cells with elastic Helmholtz resonators is analyzed. Numerical results show that the acoustic propagation properties in the periodic pipe, such as low frequency, broadband sound transmission, can be improved.     

基于联合波叠加法的浅海信道下圆柱壳声辐射研究

针对浅海信道下弹性结构声辐射预报尚无高效可靠的研究方法,提出了一种浅海信道下弹性结构声辐射快速预报的联合波叠加法.该方法结合了浅海信道传输函数、多物理场耦合数值计算法和波叠加法理论,运用该方法可对浅海信道下弹性结构辐射声场进行快速预报.经数值法和解析解法验证后,从信道下辐射源、环境影响和辐射声场测量的角度研究分析了浅海信道下弹性圆柱壳的声辐射特性,阐释了进行浅海信道下结构声辐射研究的必要性.研究结果表明,仅在低频浅海信道下弹性结构可近似等效为点源,信道上下边界对声场产生显著的耦合影响,高频段的空间声场指向性分布尤为明显,垂直线列阵进行信道下结构辐射声功率测量时,测量结果受到信道环境边界和潜深的影响较大.     

An indirect hybrid sound transmission loss controller

The control of sound transmission through panels is an important noise control problem in the aerospace, aeronautical, and automotive industries. The trend towards using lightweight composite materials that have lower sound insulation performance is a negative factor regarding low frequency transmission loss. Double-panel partitions with the gap filled with sound absorption materials are often employed to improve the sound insulation performance with reduced added weight penalty. However, in the low frequency range, the strong coupling between the panels through the air cavity and mechanical paths may greatly reduce the sound transmission performance, making it even lower than the performance of a single panel in some frequency ranges. In this work, an experimental investigation of a new kind of hybrid (active/passive) acoustic actuator is presented. The idea consists of replacing the acoustic absorption material by a hybrid actuator aiming at improving the transmission loss at low frequencies without altering the passive attenuation. A prototype of the system is tested in a plane wave acoustic tube setup. Different kinds of SISO feedforward control implementations were used to attenuate the sound power transmitted through the hybrid active–passive panel using an error microphone or a particle velocity sensor placed downstream with respect to the sample panel. Measurement results of the transmission loss with active and hybrid attenuation are presented and discussed.     

Sound transmission of cavity walls due to structure borne transmission via point and line connections

The author has published equations for predicting the air borne sound transmission of double leaf cavity walls due to the structure borne sound transmission across the air cavity via (possibly resilient) line connections, but has never published the full derivation of these equations. The author also derived equations for the case when the connections are rigid point connections but has never used them or published them or their derivations. This paper will present the full derivation of the author's theory of the air borne sound transmission of double leaf cavity walls due to the structure borne sound transmission across the air cavity via point or line connections which are modeled as four pole networks. The theoretical results will be compared with experimental results on wooden stud cavity walls from the National Research Council of Canada because the screw spacing is given for these results. This enables connections via studs and screws to be modeled as point connections and avoids the need to make any assumptions about the compliance of the equivalent point or line connections.