用于开口声辐射控制的虚拟声屏障实现 方法及机理研究*

建筑物通常留有开口以便人员物料的进出及室内的自然通风采光,但这些开口也是噪声传播的途径。传统被动噪声控制方法需要将开口封闭,且对低频噪声的控制效果不好,故引入有源噪声控制技术降低室内声源通过开口的声辐射。基于惠更斯原理,均布开口的次级源和误差传声器构成的平面型虚拟声屏障可以实现对开口声辐射的有效控制,数值仿真和实验已证明其有效性。将次级源安装在开口边界更有利于保留开口的功能且方便实际安装,但这样的单层边界虚拟声屏障降噪效果存在上限,仅能在低频段实现全局控制。和单层边界次级源相比,双层边界次级源可显著提高降噪量和有效降噪频率上限。该文回顾了开口声辐射有源控制的相关工作,并讨论了未来可能的研究方向。     

波叠加法在结构辐射声功率计算中的应用

描述了用波叠加法来计算任意形状辐射体的辐射声功率的方法。该方法在给定辐射体表面的振动速度后就可求解辐射源的强度,进而求解辐射体表面声功率。文中以脉动球源的辐射问题为列,讨论了波叠加法在应用过程中对单元、节点数目以及单元形状的敏感性。通过将该方法计算结果与解析结果进行对比表明,运用此方法在保证较高精度的前提下能明显减少计算所需的单元节点数,从而节省时间提高计算效率。     

流体加载下加肋板结构的声辐射特性研究

本文采用有限元和边界元方法对加肋板结构的声辐射进行了计算分析,研究分析了加肋板结构的板厚、板面积、板边长比、肋骨惯性矩和间距、边界条件以及板材和流体介质等对结构辐射声功率的影响,得到了一些有意义的结论,从而为揭示加板结构声辐射规律,降低结构的声辐射提供了一定的依据。     

板厚对无障薄板声辐射特性影响的分析

分析无障薄板的声辐射特性时通常忽略板厚对格林函数的影响而采用双层势计算.本文考虑板厚引起的声辐射阻抗,采用混合势计算结构表面声压与振速,并分析板厚对声辐射参数的影响。根据交界相容性条件,采用边界积分方程分别表示平板上下表面的声压和振速,并合并同类项.进一步将结构的动力方程代入混合势形式的振速方程中,离散声压差值和板的位移为振动模态叠加的形式,获得二重积分形式的声辐射阻抗,从而求解振动模态系数,确定声辐射特性参数.以水下简支矩形板为例计算对比了声辐射参数,并讨论了其对板厚的敏感性。结果表明:板厚引起的声辐射阻抗对声辐射参数的大小影响较小,但随着频率的增加致使共振频率发生较大偏移;在相同阶数的共振频率范围内,板厚度越大,采用双层势计算的误差越大。     

Gauss声束对离轴椭圆柱的声辐射力矩

利用部分波展开法求解得到了Gauss声束入射下刚性和非刚性椭圆柱的声散射系数,推导了一般情况下的声辐射力矩表达式.在此基础上,通过一系列数值仿真详细分析了离轴距离、入射角度和束腰半径对声辐射力矩的影响.结果表明:正向与负向声辐射力矩均可以在一定条件下存在;低频情况下刚性椭圆柱比非刚性椭圆柱更容易产生较强的声辐射力矩;特定频率的入射声场可以激发出非刚性椭圆柱不同阶的共振散射模式,因而非刚性椭圆柱的声辐射力矩峰值与频率的关系更密切;增加束腰半径有利于扩大散射截面,进而增加椭圆柱的声辐射力矩.该研究结果预期可以为利用声辐射力矩实现粒子的可控旋转和流体黏度的反演提供一定的理论指导.     

声辐射阻测量系统设计及测量精度影响因素分析*

在噪声控制领域,声辐射阻是一个重要的声学变量,在产品的设计阶段,可以通过改变结构表面形状来改变结构的声辐射阻抗,从而达到降噪的目的。本文基于集中参数模型,设计了测量设备,搭建了实验测量系统,并通过对无限大障板上圆形活塞声源的声辐射阻的测量对影响实验测量结果的因素进行了研究,之后对消音器入口处辐射阻进行了测量。测量结果表明:该实验测量系统具有操作简单,测量方便快捷,测量结果精度高等特点,可用于确定结构表面声辐射阻矩阵。     

烟火药和压缩氮气声源水下声辐射特征对比研究

为研究烟火药水下燃烧声辐射机理,采用烟火药和压缩氮气喷射声源对比的方法,利用水声测试系统,通过实验研究不同体积流量下两种声源装置的声辐射规律。结果表明,烟火药水下燃烧声源与压缩氮气声源的声辐射特征相似,辐射频率主要集中在0～1000 Hz内,峰值频率均位于100 Hz附近,总声压级、峰值声压级均随着气体流量增加而增强。当气体流量从60 ml/s增加到84 ml/s时,烟火药峰值声压级由155 d B增加到163 d B,0～1000 Hz内总声压级由159 d B增加到165 d B;当喷气流量从70 ml/s增加到141 ml/s时,压缩氮气源峰值声压级由136 d B增加到139 d B,0～1000 Hz内总声压级由144 d B增加到147 d B。当气体流量相近时,烟火药相比压缩氮气声压级相差显著,其声压级均高于同频率下压缩氮气源,两者的峰值声压级分别为157 d B、139 d B,0～1000 Hz内总声压级分别为160 d B、147 d B。     

弯管对末端带弹性障板充液管路辐射声能量的影响

基于声固耦合有限元方法建立了末端带弹性障板的充液管路数值模型,重点分析了不同激励下弯管对管口辐射声能量的影响。结果表明:弯管引入的高阶周向模式耦合使结构振动和流体声传播都发生明显改变,以致系统辐射声能量及主要能量贡献源也发生转移,并随激励方式和频率而不同。对本文管路模型,平面波激励下弯管系统在低频的结构辐射声能量明显增加,在高频段呈流体声与结构声交替主导的特点。径向力激励下直管系统的总声能量几乎全部来自于弹性障板辐射结构声,而弯管的声固耦合使得管口流体声功率显著增加。在轴向力激励下弯管耦合使系统总辐射声功率显著下降的同时管出口的流体声功率反而增加。     

炉内管阵列中声源辐射特性数值研究

炉内换热器结构类似于声子晶体,基于声子晶体理论,采用数值计算与软件模拟得到管阵列中声源不同方向的声传播特性,并将两种方法所得结果进行对比分析,研究声源在管阵列中不同位置处的辐射特性.结果表明：声指向性特性与声源通过管排数量,声源频率是否处在声波禁带有关.     

新型气流声源发声特性及其对气溶胶的团聚 实验研究*

为提高气溶胶颗粒物的声波团聚效果,创新性地设计了一种具有气声分离特性的气流声源。新声源使乏气从侧面开口排出,避免了对团聚效果的影响。通过实验研究了侧面开口尺寸对号角出口处气流量与声压级的影响,发现侧面开口尺寸对乏气排出及声压级有较大影响,当侧面开口尺寸约为6.5 mm时排气效果较好,此时在0.3 MPa驱动压力下声压级可达159.6 dB,同时乏气已基本全部从侧面开口排出。利用该声源对超细液滴气溶胶进行团聚实验,结果显示,声源驱动压力越大,声压级越大,气溶胶受声场作用力越强,颗粒间碰撞几率增大,团聚速率越快;初始气溶胶浓度越高,前期团聚效果越好,透光率增长速度越大,而后期团聚效果则趋近一致。     

Accelerated steered response power method for sound source localization using orthogonal linear array

In microphone arrays application, it is a difficult task to accurately and fast localize sound source in a noisy, reverberant environment. In order to solve this problem, many approaches have been presented. Among them, the steered response power-phase transform weighted (SRP–PHAT) source localization algorithm has been proved robust. However, SRP–PHAT requires high computation cost for searching a large location space. To overcome this shortcoming, an improved SRP–PHAT will be presented that reduces a two-dimension searching space into a couple of one-dimension ones by using an orthogonal linear array. In this method, the parameters of direction of arrival (DOA) are separated. The main computation can be carried out independently in two one-dimension spaces, thus the computational load will be greatly cut down. Simulations show that there is no loss in accuracy in the proposed method.     

Improved steered response power method for sound source localization based on principal eigenvector

Sound source localization is essential in many microphone arrays application, ranging from teleconferencing systems to artificial perception in a reverberant noisy environment. The steered response power (SRP) using the phase transform (SRP-PHAT) source localization algorithm has been proved robust, however, the performance of the SRP-PHAT algorithm degrades in highly reverberant noisy environment. Though the SRP-based maximum likelihood localizers are more robust than SRP-PHAT, they have the drawback of requiring noise variance to be estimated in a silent room. This paper presents an improved SRP-PHAT algorithm based on principal eigenvector. Sound source location is estimated from the principal eigenvector computed from the frequency-domain correlation matrix. Using both simulated and real data, we show that the proposed algorithm achieves higher source localization accuracy compared to the SRP-PHAT algorithm.     

Computation of acoustic radiation from vibrating structures in motion

The noises from a vibrating structure in motion are often encountered in engineering practice, for example, tire noise and pass-by noise of moving vehicles. Consequently, research on the radiation characteristics of moving acoustic source is of significance. In this paper, a new computational method based on the wave superposition approach is developed for the acoustic field from a vibrating structure in motion. It inherits the advantages of the wave superposition approach in the acoustic computation, and in which a method of moving simple sources is used to eliminate the influence of the Doppler effect. By the proposed method, the acoustic radiation from the moving vibrating structure can be calculated easily with the same implementation process as the conventional wave superposition approach performed in the stationary acoustic field. Finally, the validity and feasibility of the proposed method are verified by the numerical results.     

电火花声源的某些特性

文中给出了电火花声源的压力波形及其频谱图，着重讨论了储能与压力波峰值P1m,和半峰值之间P1m/2的时间t1之间的关系，以及刚性圆筒内放电时边界对P1m和t1的影响。     

Analysis of errors when using the similar source method to estimate sound fields

The similar source method (SSM) uses an imaginary source distribution to estimate radiated and scattered sound fields. The error analyses in the present study are for possible numerical errors by SSM, solutions of the problem of singularity and non-unique solution by SSM and the effects of possible errors in measurements on the estimation of the sound field by SSM.     

Orthogonal contributor number for the measurement of sound power

Orthogonal contributors to a global error represent a very efficient design method in terms of both sensing and control of noise radiation. In practice the price of a sensing system will be determined by the number of errors it must resolve. Therefore predicting the most efficient way of measuring radiation power is an important problem. Recently work has compared sensing the number of vibration modes to the number of orthogonal contributors to radiated power. The required number of vibration modes was based on the proximity of the structural mode resonance frequency and the excitation frequency. While ultimately this technique will result in a valid estimate of radiated power, it is shown here that the number of structural modes can be minimized by first considering orthogonal radiators based on structural mode amplitudes. Two disturbance cases are considered: a point force and an even disturbance coupling to each structural mode. Also, under these conditions the practicality of estimating the number of orthogonal radiators when it is assumed that each contributor is equal in amplitude is examined. Finally in an attempt to optimism the number of signals to be sensed, a variable error margin for the estimate of power, based on the ratio of the sound power at each frequency to the maximum peak in the considered frequency range is proposed and analyzed.     

弯曲振动阶梯圆盘辐射阻抗的计算方法

辐射阻抗是描述声学振动系统声转换效率的一个重要物理量.具有强功率的阶梯圆盘辐射器在流体介质,尤其是在空气中有着重要的应用.但对阶梯圆盘的辐射阻抗而言,运用传统理论计算时,由于辐射面不在同一几何面,积分上下限很难选取而无法计算.本文从辐射声功率角度,基于叠加原理,提出了利用叠加法计算阶梯盘的辐射阻抗.作为算例,文中计算了带有一个阶梯的阶梯盘的辐射阻抗. 关键词： 阶梯圆盘 辐射功率 辐射阻抗 叠加原理     

海洋波导中目标声辐射场的计算方法

针对海洋波导中目标声辐射场的计算问题,提出了一种基于波叠加法并在近、远场采用不同水声传播模型的建模方法,可以将近、远场作为一个统一的系统进行高效地分析。该方法通过给定的已知表面振动速度的结构计算出目标内部虚拟点声源的源强,再配合在相应的水声环境中点声源传播模型的Green函数计算出结构外的声辐射场。以Green函数为纽带,在求源强和计算近场声辐射场时采用镜像虚源法,而在计算远场声辐射场时采用简正波法。通过该方法得到的有限水深波导中声速剖面为正梯度、负梯度、负跃层的3种情况下的脉动球、刚体摆动球的声辐射场计算结果与COMSOL的有限元计算结果进行对比,结果表明了该方法在提高计算效率的同时保证了计算精度。