基于近场声压传感的结构声辐射有源控制

为了解决有源声学结构中误差信息的传感问题,提出利用近场声压估算结构声辐功率的方法。首先推导了基于近场声压的声辐射功率计算公式,然后针对单频和宽带辐射噪声,提出了不同的有源控制目标函数,推粤了相应的计算有源控制效果的公式,并借助计算机仿真研究了影响有源控制效果的各种因素。最后探讨了实际条件下实现有源控制误差信息传感的各种方法。结果表明:有限阶声压辐射模态和近场均方声压都可以作为自适应声学结构的目标函数。     

结构振动模态和声辐射模态之间的对应关系及其应用

声辐射模态和结构振动模态之间的内在关系一直缺乏有效的证明。该文证明并揭示了结构振动模态和声辐射模态之间的对应关系,而且对该关系的有效性和实用性进行了验证。首先从声辐射模态和振动模态的概念出发,利用结构振速的模态叠加特性,建立了两种模态之间的联系方程式；在此基础上根据各种模态形状的对称或反对称性推导出两种模态之间的对应关系；然后对其进行了数值仿真验证。研究表明：对于简支矩形平板而言,在低频范围内,奇-奇振动模态对应的主导声辐射模态是第1阶；偶-奇模态对应第2阶；奇-偶模态对应第3阶；偶-偶模态对应第4阶。最后将这种对应关系应用于结构声辐射有源控制中,通过对主导声辐射模态进行抵消,取得了很好的控制效果。     

分布式位移传感下的有源声学结构误差传感策略

有源声学结构是近年来提出的一种控制结构低频声辐射的有效方案,它是智能结构在噪声控制领域中的具体应用,而实现该结构的关键问题之一是近场误差传感。本文提出将分布式位移传感材料PVDF敷设于有源声学结构初、次级板表面,用有限个PVDF、对测量辐射声功率实现有源声学结构的近场误差传感。论文首先建立了有源声学结构理论模型,然后基于声辐射模态概念和PVDF传感模型,推导了PVDF形状系数理论公式,最后用一系列的计算机仿真实例给出了初、次级板PVDF形状及有源控制效果,证明所提出的方案是有效的。     

利用声辐射模态重构任意目标的散射声场

水下目标散射声场的重构可以作为水下目标散射特性的研究基础。本文主要利用声辐射模态对水下目标进行散射声场重构研究。首先,在借助声传递矩阵给出的任意结构声辐射模态的流体域求解方法基础上,通过理论证明了目标的散射声压与声辐射模态具有函数关系。其次,借助声场分布模态的概念,同时考虑到声场分布模态病态及声压测量易受噪声污染,提出基于声辐射模态的正则化散射声场重构算法。仿真结果表明,波数越低,重构所需声辐射模态阶数越少,在较高波数时仅需总模态数的大约20%即可对声场进行重构。与基于边界元的声场重构算法相比,计算量减小了至少80%,且克服了赫姆霍兹积分方程最小二乘法仅对球壳结构的重构效果较好而不适用于长条形结构重构的缺陷。     

结构声辐射的振动模态分析和声辐射模态分析研究

基于辐射声功率的二次型表达式,采用有限元法、Rayleigh积分和边界元法对结构声辐射进行了振动模态分析和声辐射模态分析研究。振动模态间的耦合对辐射声功率影响的研究表明: 结构各阶振动模态自身对结构辐射声功率的贡献是增大结构的辐射声功率,而振动模态间的耦合可能会增大结构辐射声功率,也可能会减小结构辐射声功率,或对辐射声功率没有影响。而且,当振动模态间的耦合作用对辐射声功率的影响不大时,采用振动模态控制可取得较好的减振降噪双重控制效果。将混合的Helmholtz积分方程方法用广义逆引入到三维复杂结构声辐射分析的声辐射模态公式中,解决了特征频率下解不唯一问题。还研究了正方形封闭空间结构声辐射模态的辐射效率和形状,并对结构声辐射的振动模态控制和声辐射模态控制进行了讨论。     

基于平面声源实施结构声辐射有源控制的理论研究

研究了利用分布式平面声源对结构声辐射进行有源控制的问题。首先建立了系统的数学模型,然后推导了有源控制条件下次级声源的强度和声功率降低的计算公式。在实际应用中,次级声源参数(面积大小、安放位置、个数等)对控制效果有重要影响,本文基于有源控制的物理机理和数值仿真研究这些问题。结果表明:一般情况下,次级声源板的振动模态分布与初级结构振动模态分布不相同,因此,在低频范围内,需要至少4个分布式次级声源,方能有效地控制初级结构声辐射。     

基于声压-振速测量的平面近场声全息实验研究

常规的近场声全息均是采用全息面声压或质点振速作为输入量求解,由于采用单一输入量无法分离来自全息面背向声波的干扰,因此要求所有声源均位于全息面的同一侧,即测量声场为自由声场,这种要求大大限制了近场声全息的实际应用.基于声压-速度测量的近场声全息以全息面上声压和质点振速同时作为输入量,通过建立和求解两侧声源在全息面上的声压和质点振速耦合关系,可以实现全息面两侧声波的分离,从而解决上述问题.文中在前期对声场分离技术研究的基础上,基于欧拉公式和有限差分近似,推导了新的基于声压-速度测量的平面近场声全息理论公式.随后通过实验检验了该方法在有背景源干扰情况下实现声场分离和重建的有效性.     

适用于循环平稳声场的基于波叠加法的近场声全息技术

在原有的平面循环平稳近场声全息基础上，提出一种基于波叠加法的循环平稳近场声全息技术，可以对具有复杂表面的声源进行全息重建，重建的声源表面声压谱相关密度函数能反映出调制信号的信息.声源表面声压谱相关密度函数全息图形象地反映了调制信号在表面的强弱分布情况，可由此确定调制信号源的产生位置.仿真分析和实验验证表明，基于波叠加法的循环平稳近场声全息技术可以更准确地反映循环平稳声场的调制特性.该方法继承了波叠加法的优点，无需计算边界奇异积分，计算效率高、精度好.     

板结构的声辐射模态分析及其高分辨率法向振动速度重建

提出了一种基于声辐射模态的速度基向量构建方法,该速度基向量不受网格划分的影响,可用于高分辨率的板结构法向振动速度重建。首先对板表面稀疏网格的声辐射模态进行计算,再以声辐射模态和模态系数构建板法向振动速度分布的基向量,然后由声场测量声压求解基向量系数,最后由该系数和加密网格的速度基向量重建高分辨率的板法向振动速度分布。以简支板声源进行仿真计算,当测量声压信噪比为30 dB时,低频的法向振动速度重建误差最低可达3.7%;以固支板声源在消声室中进行实验验证,131.5 Hz振动频率下的重建误差低于7%。该方法实现了只需要少量声压测量点即可精确重建板声源更高分辨率的法向振动速度分布。      

双层板腔结构声传输及其有源控制研究

利用子系统模态综合方法,结合阻抗-导纳矩阵法,建立了双层板腔结构向自由空间声传输及其在入射板PZT控制、辐射板PZT控制,和腔中次级声源作动等多种控制策略下,系统物理模型的统一的分析模型,导出了系统模态响应及最优次级源强度的统一的阻抗-导纳矩阵表达式。该模型表达式各部分物理意义清晰、明确,便于进行系统耦合理论、有源控制及其机理的分析和数值研究。然后,在此基础上对双层板腔结构声传输有源控制进行了全面深入的数值计算和分析研究,重点探讨了控制方法策略及系统参数对有源控制效果的影响及其对应的控制机理。结果表明:入射板PZT作动辐射声功率最小控制策略是通过入射板、声腔和辐射板三个子系统的模态抑制或重组达到消声的目的,涉及多种复杂控制机理,对入射板、辐射板和声腔模态均有效,但对入射板模态更有效;在低频段声腔(0,0,0)模态在系统耦合响应中起主导作用,因此利用腔中次级声源作动能获得较理想的控制效果,是一种较好的控制策略;由于声腔模态与结构模态间复杂的耦合关系,使得某些频率处腔中声势能一定程度上的降低并不一定导致系统声传输损失的增加,因此,腔中声势能最小控制策略不一定能够获得理想的声传输控制效果。      

线阵波束形成声强缩放方法估算声源的辐射声功率

为了解决波束形成声源识别过程中声源辐射声功率定量计算的问题,给出了阵型简洁、便于组合的线阵声强缩放模型。通过推导线阵的声强缩放系数,建立起线阵波束输出结果与声源辐射声功率之间的换算关系。无论是线阵还是平面阵的声强缩放方法,对于偏离阵列中心位置较远处的声源进行辐射声功率估算时都存在较为明显的误差。通过理论推导和仿真模拟计算,研究了同一单极子点声源在不同位置处的声功率估算偏差随频率、幅度的变化规律,发现该估算偏差只与声源偏离位置有关,而与声源自身的强度信息无关的结论,据此给出了相应的声功率估算修正方法。半消声室实验结果和声压法测量结果对比表明:修正后的线阵声强缩放方法用于中高频声源的辐射声功率计算时,单频声源的估算误差不超过1.0 dB,宽带声源的估算误差不超过1.8 dB。      

双声源位置和强度识别的三维声强方法

目前在远场识别声源空间位置和强度缺乏行之有效的方法。针对此问题,提出采用四传声器进行三维声强测量,从而构建出声强、声源坐标和声功率的非车线性方程组,求解方程得出声源空间坐标和强度的方法。以3个三维声强探头对两个同频率单极子声源的识别为例,分别利用数值仿真和半消声室内的实验进行方法验证,并对声源的识别空间分辨率做了测试,得出角度识别最大误差为3.83°,为真实值的8.5%,距离识别最大误差0.1 m,为真实距离的10%。结果表明采用该方法空间坐标和声功率识别均具有很高的准确度,双声源的空间位置分辨力也优于远场声全息方法。      

Active sound scatterers based on the JMC method

The principle of formulating the JMC method to produce secondary sources that function as active scatterers on a hypothetical scattering surface is established, to be applied, e.g., in concert halls. The examination is based on the modified JMC method, to ensure that the logic does not lead to the need of changing the primary sources. The actively reflecting plane serves as an example of the JMC formulation for the active scatterer. The solution is extended to a general planar JMC element with well-defined reflection and transmission properties. The solution works on the local control principle: each reflecting subarea needs information of the primary field only at that subarea. The solution can also apply approximately to piecemeal planar surfaces and to smooth convex surfaces. Further, general active boundary condition elements are defined. Based on the element definitions, simple reflecting source, the pressure- and velocity-reflecting boundaries, and the impedance boundary are introduced. Boundary condition elements do not work on the local control principle: in a general case secondary sources on each subarea need information of the primary field at each subarea. True boundary condition elements are also defined based on their net sound power radiation.     

次级源近场和管壁弹性对充液管路有源消声性能的影响EI北大核心CSCD

建立了含次级源结构的充液直管有源消声系统数值模型,重点分析了声激励下次级源近场和管壁弹性对有源消声性能的影响。结果表明:次级源近场为非均匀声场,误差点位于该区域时部分频点控制效果较差甚至放大,而处于声场均匀区域时可使降噪量提高10 dB以上,增加误差点数量可使绝大多数频点的降噪量提高5 dB以上;管壁弹性使次级源与管壁间的耦合较强,非对称分布的次级源容易激起管壁振动,导致降噪谷值的出现,采用对称分布的次级源可显著提升控制效果;增加次级源数量能够提高系统的有源无源复合控制效果,但使得管内声场变得复杂,多次级源模型的有源消声效果随频率升高而有所降低。     

Broadband sound generation by confined turbulent jets

Sound generation by confined stationary jets is of interest to the study of voice and speech production, among other applications. The generation of sound by low Mach number, confined, stationary circular jets was investigated. Experiments were performed using a quiet flow supply, muffler-terminated rigid uniform tubes, and acrylic orifice plates. A spectral decomposition method based on a linear source-filter model was used to decompose radiated nondimensional sound pressure spectra measured for various gas mixtures and mean flow velocities into the product of (1) a source spectral distribution function; (2) a function accounting for near field effects and radiation efficiency; and (3) an acoustic frequency response function. The acoustic frequency response function agreed, as expected, with the transfer function between the radiated acoustic pressure at one fixed location and the strength of an equivalent velocity source located at the orifice. The radiation efficiency function indicated a radiation efficiency of the order (kD)2 over the planar wave frequency range and (kD)4 at higher frequencies, where k is the wavenumber and D is the tube cross sectional dimension. This is consistent with theoretical predictions for the planar wave radiation efficiency of quadrupole sources in uniform rigid anechoic tubes. The effects of the Reynolds number, Re, on the source spectral distribution function were found to be insignificant over the range 20002.5. The influence of a reflective open tube termination on the source function spectral distribution was found to be insignificant, confirming the absence of a feedback mechanism.     

The active minimization of harmonic enclosed sound fields,part II: A computer simulation

This paper is Part II in a series of three papers on the active minimization of harmonic enclosed sound fields. In Part I it was shown that in order to achieve appreciable reductions in the total time averaged acoustic potential energy, E_p, in an enclosed sound field of high modal density then the primary and secondary sources must be separated by less than one half wavelength, even when a relatively large number of secondary sources are used. In this report the same theoretical basis is used to investigate the application of active control to sound fields of low modal density. By the use of a computer model of a shallow rectangular enclosure it is demonstrated that whilst the reductions in E_p which can be achieved are still critically dependent on the source locations, the criteria governing the levels of reduction are somewhat different. In particular it is shown that for a lightly damped sound field of low modal density substantial reductions in E_p can be achieved by using a single secondary source placed greater than half a wavelength from the primary source, provided that the source is placed at a maximum of the primary sound field. The problems of applying this idealized form of active noise control are then discussed, and a more practical method is presented. This involves the sampling of the sound field at a number of discrete sensor locations, and then minimizing the sum of the squared pressures at these locations. Again by use of the computer model of a shallow rectangular enclosure, the effects of the number of sensors and of the locations of these sensors are investigated. It is demonstrated that when a single mode dominates the response near optimal reductions in E_p can be achieved by minimizing the pressure at a single sensor, provided the sensor is at a maximum of the primary sound field. When two or three modes dominate the response it is found that if only a limited number of sensors are available then minimizing the sum of the squared pressures in the corners of the enclosure gives the best reductions in E_p. The reasons for this behaviour are discussed.     

A hybrid modal analysis for enclosed sound fields

A hybrid modal expansion that combines the free field Green's function and a modal expansion will be presented in this paper based on a review and an extension of the existing modal analysis theories for the sound field in enclosures. The enclosed sound field will be separated into the direct field and reverberant field, which have been treated together in the traditional modal analysis. Studies on a point source in rectangular enclosures show that the hybrid modal expansion converges notably faster than the traditional modal expansions, especially in the region near the source, and introduces much smaller errors with a limited number of modes. The hybrid modal expansion can be easily applied to complex sound sources if the free field responses of the sources are known. Damped boundaries are also considered in this paper, and a set of modified modal functions is introduced, which is shown to be suitable for many damped boundary conditions.     

阵列式双水听器平面扫描声强分布测量和声功率计算实验研究

根据双水听器法测量声强的基本原理，本文提出了基阵在湖中的布放及测量声强分布的实施步骤。通过对试验数据的处理与分析，给出了声强分布的三维力和等值曲线图，并利用扫描平面上的声强分布。计算出声源辐射的声功率。实验表明，本文提出的用列阵式双水听器声强测量系统，作平面扫描测量声强分布的方案是合理的；利用所测得的双平面近场声强分布来计算源的辐射也是可行的。     

线阵声强缩放方法在水下声源辐射功率估算中的应用_

为了解决水下声源辐射声功率难以计算的问题,利用线阵声强缩放方法在波束形成声源识别的基础上,根据波束输出结果与声源辐射声功率之间的换算关系来获得相应的声功率.为了提高线阵声强缩放方法的水下声功率估算精度,给出了一定动态范围限制的主瓣区域积分方法,并通过仿真验证了该方法的有效性.在消声水池中开展了水下声功率估算的实验研究....     

单层传声器阵列重建相干声场的近场声全息方法研究

针对传声器阵列两侧存在相干声源的非自由声场重建问题,提出基于球面谐波函数扩展近场声全息理论的相干声场重建方法。该方法在已知测量面两侧声源几何位置时,使用单层传声器阵列获取测量面处的声压分布,通过最小二乘法获得与目标声源和干扰噪声源响应对应的最优球波函数扩展项数和最优系数向量,结合测点位置的空间坐标进行声波分解,并分别重建出各声源在测量面上的声压分布。为了验证方法的有效性,分别给出了相干噪声源为球形声源和非球形声源的仿真验证,并在全消声室内对双扬声器产生的相干声场的重建进行了实验验证。结果表明:该方法对球形声源和非球形声源干扰下的声场重建都具有较好的效果,球形声源干扰下的重建精度更高。