基于深海会聚区声强匹配处理的声源定位方法

匹配场处理技术(Matched Field Processing MFP)近年来在声源被动定位、海洋环境声学参数反演等方面得到广泛的应用。根据深海声道中声场的会聚现象,提出了一种基于深海会聚区声强匹配处理(Matched Convergence Intensity Processing,MCIP)的深海声源定位方法。当声源和接收水听器处在会聚区深度范围内时,MCIP方法利用单个水听器即可实现声源距离和声源深度估计。对单个水听器的实测信号进行相位补偿到会聚区距离上,得到实测场声强,与拷贝场会聚区声强进行相关计算并搜索峰值来确定声源位置。数值仿真实验验证了MCIP方法,并分析了环境失配情况下MCIP的估计性能。     

Noise,anti-noise and fluid flow control

This paper celebrates Thomas Young's discovery that wave interference was responsible for much that is known about light and colour. A substantial programme of work has been aimed at controlling the noise of aerodynamic flows. Much of that field can be explained in terms of interference and it is argued in this paper that the theoretical techniques for analysing noise can also be seen to rest on interference effects. Interference can change the character of wave fields to produce, out of well-ordered fields, wave systems quite different from the interfering wave elements. Lighthill's acoustic analogy is described as an example of this effect, an example in which the exact model of turbulence-generated noise is seen to consist of elementary interfering sound waves; waves that are sometimes heard in advance of their sources. The paper goes on to describe an emerging field of technology where sound is suppressed by superimposing on it a destructively interfering secondary sound; one designed and manufactured specifically for interference. That sound is known as anti-sound, or anti-noise when the sound is chaotic enough. Examples are then referred to where the noisy effect to be controlled is actually a disturbance of a linearly unstable system; a disturbance that is destroyed by destructive interference with a deliberately constructed antidote. The practical benefits of this kind of instability control are much greater and can even change the whole character of flows. It is argued that completely unnatural unstable conditions can be held with active controllers generating destructively interfering elements. Examples are given in which gravitational instability of stratified fluids can be prevented. The Kelvin-Helmholtz instability of shear flows can also be avoided by simple controls. Those are speculative examples of what might be possible in future developments of an interference effect, which has made anti-noise a useful technology.     

复杂声场环境下目标声源声场重建误差分析

针对目标声源在复杂声场环境下进行声场重建易受到其它声源干扰的问题,提出存在干扰源声场、散射声场及目标声源声场的混合声场环境下基于单面声场分离技术的目标声源声场分离及重建方法。首先,通过理论分析和公式推导,清除干扰源声场及散射声场的影响;然后,利用传递函数性质对声场分离及重建误差进行分析,并对计算公式中存在的奇异性问题予以消除,得到高分辨率的声场重建图像。数值仿真表明:利用常规的单面声场分离技术很难重建混合声场环境下目标声源的声场,而利用本文研究的声场分离及重建方法能够很好反映目标声源声场的实际情况,提高声场重建的精度。     

E150柴油机缸内压缩温度场的全息干涉测量

介绍了采用激光双曝光全息干涉技术测取柴油机压缩温芳场的基本原理及实验过程。提出了利用绝热压缩缩区的温度作为计算干涉条纹的初始条件,从而为计算全息干涉条纹所对应温度提供了可行的方法。由柴油机压缩过程中缸内的温度场的测量结果可以看出,在柴油机压缩过程中,缸内温度变化幅度在４０Ｋ左右,最大温度梯度是在靠近燃烧室壁面大约０．５ｍｍ的区域内。本文的实验结果,为分析柴油机压缩过程缸内传热过程提供了依据;所使用     

固定干扰抑制的声场匹配方法

利用波导中的声场匹配与自由空间中的阵列处理的相似性,从自由空间的阵列零点方法出发推导～一种适用于波导中垂直阵列声场匹配的抑制固定干扰的方法。通过声场模型预报已知空间位置干扰的声传播特征,形成空间矢量。在保持期望点增益的前提下,约束干扰点邻域增益,得到垂直阵列的零点指向干扰的阵列权向量。     

高架轻轨噪声预报模型及实验对比

城市高架轻轨在缓解交通压力的同时也给其周边的环境带来了噪声问题。因此,其噪声预报开始逐渐受到技术人员的广泛关注。在前人研究的基础上提出一个轨道交通噪声沿水平方向传播的计算模型,把通过的列车看作一有限长线声源,将声场分为声影区和声照区。该模型不仅考虑了直达声的影响,还附加考虑声照区内的地面反射声、声影区内桥面与地面间的混响声以及地面振动引起的二次辐射声的贡献。为了验证理论模型的有效性,对上海市某高架轻轨运行段进行实测,测试与计算结果的趋势保持一致。通过不同模型计算结果与实测值的比较可见：在近场区增加混响声、地面反射声和地面辐射声,修正后的预报结果误差明显减小;在远场区,三种修正的影响随距离的增大而减小,因为声场趋于自由场。因此,所提出的预报模型可以作为高架轻轨声学设计参考。     

气流式雾化火焰声压分布特性试验研究

研究气流式雾化火焰声压分布特性,建立火焰长度与声压分布之间的关系,分析不同火焰长度对火焰噪声辐射特性的影响。结果表明:火焰噪声声压场可根据火焰长度L划分为三个区域:近场区、衰减区和远场区;近场区声压值最大,为气流式雾化火焰噪声的产生区域,燃烧噪声为主要噪声源;衰减区为噪声的最佳采样区域,可测得噪声的总声压值;远场区声压变化幅度很小,可近似等于远场声压;随着火焰长度的增加,火焰噪声的指向性越明显,辐射强度越大。     

基于干涉条纹移动量的非接触振动测量研究

为了实现大振幅、高带宽振动的非接触精密测量,本文提出了一种全新的光学测量系统.两束相干光的远场干涉条纹位置与两束光之间相位差有关,相位差的变化将引起干涉条纹移动.获取主条纹的位置,可以计算两束光之间的相位差,基于此可以还原物体的振动位移量.对振幅为10μm的单频余弦信号以及频率为44.1 kHz的声音信号仿真还原结果表明,本文所提光学系统和还原算法可以还原出亚微米级的振动信号,并能准确还原出音频信息.     

基于深海声影区海底反射损失的地声参数反演方法

海底的声速、密度、衰减系数等地声参数,在声场预报、目标定位中十分重要。因地声参数原位测量和海底采样在深海中实施困难,需要寻找新的方法来获取地声参数。在深海声影区环境下,直达波会随着距离的增加而逐渐消失,一次反射波及多次反射波是对深海声影区声场起重要作用的多途信号。文章首先对声影区多途达到结构进行分析,利用多次比较法得到随掠射角变化的反射损失,并对海底地声参数进行反演,然后将反演的地声参数代入声场模型得到海底反射损失,将其与实验测量结果进行比较,结果吻合较好。并通过对反演过程的散点图和后验概率进行分析,证明了反演结果的可靠性。该方法可用于深海声影区的海底地声参数的反演。     

爆炸声源投放间隔对会聚区声传播损失测量的影响

会聚区声传播损失测量是水声调查的重要内容。爆炸声源投放间隔对会聚区声传播损失结构的刻画具有直接影响。基于Argo资料、与距离有关声学模型(Range-dependent Acoustic Model, RAM)和实验数据,对不同投放间隔下获得的会聚区声传播损失进行了比较。结果表明,在不同声源深度和频率下,0.5 km的投放间隔能够很好地刻画出会聚区声场结构的精细特征;1 km的投放间隔基本满足对会聚区结构精细测量的要求;2 km的投放间隔能够测量到会聚区的大致结构,但可能出现对会聚区峰值结构的漏测或欠精确的会聚区增益。考虑到实际条件难以支持全测线0.5 km的投放间隔,建议对会聚区精细测量时,在可知会聚区范围的海域使用在会聚区0.5 km的投放间隔、在影区1 km的投放间隔;在未知海域使用全测线1 km的投放间隔;对了解会聚区大致结构的调查,使用2 km的投放间隔。     

类高尔夫球表面处理对受电弓气动噪声的影响

针对高速列车弓网噪声,为降低主要由细长圆柱杆件构成的受电弓的气动噪声,建立三维圆柱绕流气动噪声分析模型,基于大涡模拟方法、声类比理论模拟圆柱杆件的流场特征,分析远场气动噪声频谱特性与分布规律,并对圆柱杆件表面作球缺型凹坑处理,分析表面处理方案的降噪效果。数值结果表明,来流与圆柱轴向所在平面法向的气动噪声受升力波动影响,声压级最大;圆柱来流方向前后气动噪声受阻力波动影响,声压级最小。圆柱表面球缺型凹坑处理方式可以有效降低圆柱杆件远场R=5 m处最大声压级,凹坑加密,降噪效果更好,优化模型II-1、II-2和II-3在R=5 m处最大声压级分别降低1.5 d B、1.9 d B和2.4 d B。相关结果可为高速列车噪声控制提供参考。     

均匀活塞阵辐射声场研究

主要研究了均匀活塞阵的近-远场的辐射声场。首先利用点源声波干涉原理建立均匀点源活塞阵的辐射声场理论,进而推导均匀活塞阵的近-远场的辐射声场函数表达式,并采用Matlab软件仿真了近-远场的辐射声场,分析了近-远场的声场变化规律、声轴方向声压的变化规律和旁瓣级的变化规律。通过与实测的80 kHz均匀活塞阵换能器近-远场的辐射声场对比,表明了实测结果与仿真结果基本一致,验证了理论与测量方法的可行性,能够为实际测量工作提供指导。     

强干扰环境下声源可视化重建方法的研究进展

准确识别噪声源是机电产品噪声控制的关键,其中,近场声全息和波束形成是两种常用的声源可视化重建方法,分别适用于近场低频和远场高频声源重建的情况。传统的声全息和波束形成方法基于自由场假设,即适用于目标声源辐射声与干扰噪声之间的信噪比大于10 dB的情况。然而很多机电产品的噪声测试只能在工作现场进行,不满足自由场条件。为此,从声学传播方程和信号处理两个方面出发,回顾了强干扰环境下声源可视化重建方法的研究发展历程,评点了每种方法的特点和适用范围。重点介绍了强干扰环境下的近场声全息方法,包括声场分离法和逆块传递函数法。另外,还介绍了混响环境下的声源重建方法以及基于信号处理的信号噪声分离方法。最后,讨论了强干扰环境下声源重建有待解决的问题及其发展趋势。     

水下稳态涡流场声传播的数值模拟和实验研究

声波穿过涡流场时声传播特性会发生改变,可由此判断涡流场的存在及其特征参数。文章首先推导了二维稳态涡流场的射线微分方程组,实现了声波通过涡流场的声线轨迹模拟。然后开展水池超声传感器实验,采用现代计算流体力学(Computational Fluid Dynamics,CFD)仿真方法获取涡流场参数。最后将通过涡流场声信号的时延结果,与实验测量值进行对比分析。结果表明,对于涡核半径为30 mm,最大切向速度为1.2 m·s^-1的涡流场,数值模拟误差小于10%,验证了基于射线声学的水下稳态涡流场声传播数值模拟的有效性。     

浅海相干声场的单参数海底模型建构

海底反射性质在浅海声传播中起着决定性的影响。利用海底反射损失对掠射角的斜率可作为单个参数F dB来描述海底这一前提,对平面波入射液态半无限空间的情况进行推导,提出一种基于简单近似表示反射相位角关系的算法。将单参数F dB以及反射相变作为计算模型的边界条件输入参数,对浅海相干声场进行计算,将适用范围推广到复杂声速和水平变化情况。通过对三种类型海底进行仿真,比较基本参数海底模型及单参数海底模型计算所得传播损失曲线,验证了所提包含反射相变关系的单参数模型的有效性。     

Numerical modelling of MHD waves in the solar chromosphere

Acoustic waves are generated by the convective motions in the solar convection zone. When propagating upwards into the chromosphere they reach the height where the sound speed equals the Alfvén speed and they undergo mode conversion, refraction and reflection. We use numerical simulations to study these processes in realistic configurations where the wavelength of the waves is similar to the length scales of the magnetic field. Even though this regime is outside the validity of previous analytic studies or studies using ray-tracing theory, we show that some of their basic results remain valid: the critical quantity for mode conversion is the angle between the magnetic field and the k-vector: the attack angle. At angles smaller than 30 degrees much of the acoustic, fast mode from the photosphere is transmitted as an acoustic, slow mode propagating along the field lines. At larger angles, most of the energy is refracted/reflected and returns as a fast mode creating an interference pattern between the upward and downward propagating waves. In three-dimensions, this interference between waves at small angles creates patterns with large horizontal phase speeds, especially close to magnetic field concentrations. When damping from shock dissipation and radiation is taken into account, the waves in the low-mid chromosphere have mostly the character of upward propagating acoustic waves and it is only close to the reflecting layer we get similar amplitudes for the upward propagating and refracted/reflected waves. The oscillatory power is suppressed in magnetic field concentrations and enhanced in ring-formed patterns around them. The complex interference patterns caused by mode-conversion, refraction and reflection, even with simple incident waves and in simple magnetic field geometries, make direct inversion of observables exceedingly difficult. In a dynamic chromosphere it is doubtful if the determination of mean quantities is even meaningful.     

声级计抗电磁场辐射干扰试验研究

介绍了射频电磁场对声级计进行电磁辐射干扰的详细情况以及利用工频磁场测试装置进行声级计抗工频磁场干扰的研究设计     

运用内积相关性结合迭代相减识别两点声源

提出运用内积相关性识别两点声源的新方法,通过在声源面上构造虚拟声源,计算虚拟声源在传声器阵列上的声压,构造虚拟声源的声压向量,将其归一化,与传声器实际测得的声压信号作内积运算,通过优化算法搜索内积模的极值,当内积模达到最大值时,根据内积相关性原理,识别出目标声源的位置。当声源间距离较近时,声源识别精度受到声源间的干扰影响,引入迭代循环算法降低声源相互干扰的影响,以传声器测量面上剩余的声压作为判断循环终止的条件。计算结果表明,利用内积相关性结合迭代循环相减算法能有效识别出两点声源。     

干涉角度显微测量提高光子相关法空气声声压测量精度研究

在光子相关法测量自由场空气声声压中,光束夹角的准确测量影响着测量声压结果。提出了采用显微放大成像方法,利用CCD测量干涉区条纹间距,从而得到更为精确的光束夹角。首先,通过仿真分析高斯光束干涉条纹间距均匀性对光束夹角测量的影响,优化了声场测量的光路结构;然后,使用标准分辨率板对CCD显微成像的放大倍率进行标定并实现了干涉角度测量;最后,构建了光子相关法自由场空气声声压测量的实验系统。实验结果表明,相比于测量光的空间传播距离等传统三角方法获得的光束夹角,该方法得到的光束夹角提高了空气声声压测量的精度。     

Diffraction and Interference of Partially Coherent Light Traversing Two Superposed Sound Fields

The diffraction and interference of a light wave passing through two superposed sound waves have been studied theoretically on the basis of Huygens' principle. As a result of frequency shifts in every deflected light ray caused by the sound waves, the instantaneous intensity resulting from linear superposition of the deflected light rays consists of the d.c. component as well as the a.c. component as a sum of beating signals among those rays, provided that the coherence time of the light is long enough compared with the period of a beating signal under consideration. A general formula for diffraction is derived and two-beam interference is considered as a special case. The resultant formula illustrates that the complex degree of coherence is modulated, after traversing the sound field, with a form of the Bessel function of zeroth-order which varies with Raman-Nath parameters as well as with the separation of two points on the wavefront of the light. This validity will hold so long as the inclination factors for the deflected light rays in Huygens' principle are regarded to be nearly equivalent. The results for progressive and standing sound waves are described as special cases.