Reconstruction and prediction of coherent acoustic field with the combined wave superposition approach

The routine wave superposition approach cannot be used in reconstruction and prediction of a coherent acoustic field, because it is impossible to separate the pressures generated by individual sources. According to the superposition theory of the coherent acoustic field , a novel method based on the combined wave superposition approach is developed to reconstruct and predict the coherent acoustic field by building the combined pressure matching matrixes between the hologram surfaces and the sources. The method can reconstruct the acoustic information on surfaces of the individual sources, and it is possible to predict the acoustic field radiated from every source and the total coherent acoustic field can also be calculated spontaneously. The experimental and numerical simulation results show that this method can effectively solve the holographic reconstruction and prediction of the coherent acoustic field and it can also be used as a coherent acoustic field separation technique. The study on this novel method extends the application scope of the acoustic holography technique.     

Investigation on acoustic holography reconstruction of scattering field of target

1 IlltroductionStudy on scattering sound field of underwater target is one of important subject in underwater acoustics. Owing to research of detection and identification technique and anti-detectiontechnique, it must know not only the scattering strength but also other characteristics of thewhole scattering field of the target.The whole scattering field can not be gotten by general measurement .techniques. Since theimpulse method is used to measuxe the scattering sound field, it's impossible …     

Patch nearfield acoustic holography combined with sound field separation technique applied to a non-free field

The conventional nearfield acoustic holography(NAH) is usually based on the assumption of free-field conditions, and it also requires that the measurement aperture should be larger than the actual source. This paper is to focus on the problem that neither of the above-mentioned requirements can be met, and to examine the feasibility of reconstructing the sound field radiated by partial source, based on double-layer pressure measurements made in a non-free field by using patch NAH combined with sound field separation technique. And also, the sensitivity of the reconstructed result to the measurement error is analyzed in detail. Two experiments involving two speakers in an exterior space and one speaker inside a car cabin are presented. The experimental results demonstrate that the patch NAH based on single-layer pressure measurement cannot obtain a satisfied result due to the influences of disturbing sources and reflections, while the patch NAH based on double-layer pressure measurements can successfully remove these influences and reconstruct the patch sound field effectively.     

Sound field separation technique with double holographic planes and its applications in acoustic holography

Sound field separation technique with double holographic planes is proposed, which overcomes the limitation on applications of near-field acoustic holography (NAH) and broadband acoustic holography from intensity measurement (BAHIM). The limitation is that sound field on one side of holographic plane must be free, that is to say, all the sound sources must be confined to the other side; but it is not easy to achieve for industrial measurements. The technique builds the sound field separation formula in wave number domain according to the wave field extrapolation theorem, and the sound pressure caused by sources on one side of holographic plane can be obtained as expected by taking two-dimensional Fourier transform of the formula. The derivation of the principle verifies the technique theoretically. The numerical simulations demonstrate its feasibility and effectiveness.     

A Bayesian method of seabed structure and geoacoustic parameters inversion using ship radiated noise

Aiming at the problem of inversion shallow seabed layered structure and geoacoustic parameter inversion with ship radiated noise as the reference sound source,a shallow sea multi-layered seabed geoacoustic parameter inversion method based on Bayesian theory is studied.In the inversion,the line spectrum component of the ship radiated noise is the research object,and then the nonlinear Bayesian inversion method is used to invert the seabed structure,the wave speed in the layer,the wave speed atten...     

Video visualization for moving sound sources based on binoculars stereo and acoustic holography

The video visualization methods for moving sound sources are very important. The spatial positions in the sound filed measurement of moving sources arc measured by an automated method based on the binoculars stereo technique,the spatial coordinates of the surface of the moving sound source are determined automatically.The sound field of the surface of the moving source is reconstructed with a microphone array using the acoustic holography method for moving sound sources.The spatial mapping between the sound field and the video images is constructed,and also the time sequence of the sound field and the images is founded. Then,the reconstructed sound field and the real-world images are merged,and the visualized sound field video of the moving source is generated automatically.A sound field measurement system based on this method is developed,the measurement results of the moving sound source with this system indicate that the sound field video visualization is realized effectively with the proposed method,the sound sources and their changing process can be seen directly from the generated video,the identification and localization for the moving sound sources can be easier with this method.     

Influence of a high-speed dielectric spherical particle''''s movement on its scattering characteristics

The scattered field and differential scattered section (DSS) of a moving spherical particle with a high speed are investigated numerically.The coordinate and vector transformations are used to establish a theoretical basis for studying the laser scattering of a moving particle.The DSS of a moving spherical particle is explained by the electric and magnetic field from Mie scattering theory.Assuming the laser wavelength of 1.06μm,we compute the ratio of the laser DSS of the moving dielectric spherical particle to that of the static dielectric spherical particle,which changes with radii,speeds and scattering angles of the particle.The numerical results show that the laser DSS of the moving spherical particle is tightly connected with its speed and scattering zenith angle.If a spherical particle moves with high speed,the laser DSS due to movement of the particle could not be neglected.If the speed of the dielectric spherical particle is fluctuating,the Doppler effect and the frequency spectrum expansion play important roles.     

Sound scattering from partially water-filled elastic spherical shell with an internal elastic plate

According to the equation of motion in the elastic medium and integral equation of target scattering, the sound scattering from the partially water-filled elastic spherical shells with and without an inner plate is studied using the finite element and boundary element method, and the scattering normalized form functions of the shell filled with different volume of water are computed and the mechanism of resonance scattering is analyzed. The results show that the resonance of the shell with partially water-filled and without the plate is mainly related to the volume of water, and the resonance is produced by inner water and the spherical shell. The resonance characteristics of partially water-filled elastic shell with the plate are similar to that of empty structured elastic spherical shell, and the sound field in inner water is weaker which indicates the main resonance characteristics are decided by spherical shell and the plate. In addition, the scattering characteristics of spherical shell with plate and one side full water-filled are greatly different from the partially water-filled ones.     

Perturbation characteristics of ambient sea noise caused by submerged objects

The perturbation characteristics of ambient sea noise field caused by scattering of submerged objects are discussed theoretically. Based on the sea noise source model with Gaussian-correlation amplitude, and applying the integral expressions for arbitrary source distribution and the spherical wave expression of Green function for a monopole in half-infinite space, the expressions of direct-arrival noise fields, scattering fields and total noise fields of a rigid spherical object under the irradiation of monopole and dipole sources, as well as the covariance among those noise fields at two receiving points are obtained. The numerical results of scattering directional patterns of rigid spherical objects and the visibility are given. It is shown that the total noise field is affected by not only the impedance characteristics of the object, the direction of receiver, but also the correlation between surface sources, and the interference between direct-arrival and scattering fields greatly. The results show that the sound visibility of a rigid spherical object is about 4-5 dB in near range and the scattering directivity characteristics of a rigid spherical object under the irradiation of surface sources are different from those of plane wave incidence.     

Sound scattering from underwater elastic spherical shell covered with multilayered medium approximated acoustic cloak

The anechoic performance and mechanism of underwater elastic spherical shell covered with coating are studied at low frequencies.The acoustic cloak is anisotropic material,which can be designed with homogeneous isotropic materials on the basis of effective medium approximation theory.The analytic expression of scattering acoustic field from the shell covered with multilayered medium is formulated and the scattering form function,resonance mode,acoustic field distribution are computed,the scattering characteristics and mechanism of transmission are analyzed.The results show that the direction of sound transmission inside the multilayered medium is changed,the acoustic field is deflected gradually,and the acoustic energy flux is guided around the target,which reduces the scattering intensity at low frequencies,the acoustic intensity of target＇s surface is very weak.Excepting the first resonance peak in spectrum produced by the zero order partial wave,the other resonance modes of elastic spherical shell are not excitated and the multilayered medium can suppress the resonance of the spherical shell effectively.     

非自由声场中目标声场还原与重建的等效源方法

为消除在非自由声场中重建声场时干扰声源对重建效果的影响,提出一种采用单个测量面上的声压和质点振速作为输入、等效源法作为分离和重建算法的非自由声场中目标声场还原与重建方法。该方法首先利用单面声压-质点振速测量和基于等效源法的声场分离技术将测量的混合声场分离为来自目标声源的向外传播的声场和来自干扰声源的向内传播的声场,然后利用向内传播的声场和目标声源的边界条件计算出干扰声在目标声源表面产生的散射声场,并将其从向外传播的声场中去除,还原出目标声源在自由声场条件下的辐射声场,最后利用还原的声场实现目标声场重建。通过数值仿真和实验检验了该方法的有效性和必要性。仿真和实验的结果表明,该方法可以在非自由声场的测量条件下,有效地去除干扰声的影响,实现目标声场的准确重建。      

An equivalent source method for recovering and reconstructing the target sound field in a non-free field

In a non-free field,the existence of disturbing sources would destroy the free-field condition required by near-field acoustic holography,and confuse the identification of target source due to the scattering effect caused by disturbing sound falling on the target source.To totally remove the influence of disturbing source,a method for recovering and reconstructing the target sound field in a non-free field was proposed based on the equivalent source method and the pressure-velocity measurement.In the proposed method,the sound field separation technique was firstly used to separate the mixed sound field into the outgoing field coming from the target source and the incoming field coming from the disturbing source.Then the scattered component contained in the outgoing field was calculated by using the disturbing sound and the surface impedance of the target source.Finally,the sound field radiated by the target source in a free field was obtained by subtracting the scattered component from the outgoing field and was further used to reconstruct the sound field of the target source.The proposed method was numerically and experimentally testified and the results of both the simulation and the experiment demonstrated the validity of the proposed method.     

单层传声器阵列信号空间重采样的声波分离方法

为了重构非自由声场中目标声源的声场响应,提出单层传声器阵列信号空间重采样的声波分离方法.以球面波函数为基函数,建立由系列球面波函数叠加表达的声场数学模型.基于近场声全息原理,利用单层传声器阵列面上空间重采样形成的两组声压测量信号,求解基函数系数,并重构出传声器阵列两侧声源各自的声场响应,实现声波分离.使用脉动球和振动球共同作用的非自由声场,检验了数学模型以及传声器信号信噪比、传声器阵列形状和面积、声源中心位置、频率等关键参数对声波分离精度的影响,并在全消声室内进行了实验验证.最后,对单层传声器阵列重采样的声波分离方法的实施给出了建议.     

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.     

Extension of planar nearfield acoustic holography for sound source identification in a noisy environment

Planar nearfield acoustic holography (NAH) is extended to identify the sound source in a noisy environment. The extended method requires the knowledge of the pressures on two closely spaced parallel hologram planes and the plane wave reflection coefficient on the target source surface. First, the incoming field coming from the back side of the microphone array and the scattered field due to the incoming wave falling on the target source are correlated through the plane wave reflection coefficient on the target source surface. Then, the mixed field on the hologram plane can be represented by the field that would be radiated by the target source into free space and the incoming field. Finally, the field that would be radiated by the target source into free space can be extracted by using the pressures measured on two hologram planes, which will be further used to accurately identify the sound source via planar NAH. The validity of the proposed method is demonstrated by simulations and experiment, and the influence of the relative strength of the disturbing source to the target source is also investigated.     

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。      

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。     

A hybrid approach to reconstruct transient sound field based on the free-field time reversal method and interpolated time-domain equivalent source method

A hybrid approach is presented in the current work, which reconstructs the transient sound field radiated from the two-dimensional sources with unknown locations and sizes, by combining the free-field time reversal method and the interpolated time-domain equivalent source method (TDESM). In the first step of the proposed method, the time reversal focusing algorithm is performed to estimate the source locations on the source plane. And then, the interpolated TDESM is applied to reconstruct the transient sound field on the reconstruction plane by assuming that the equivalent sources are located near the estimated source locations found in the previous step. The proposed technique, in principle, requires fewer microphones in the measurement since the equivalent sources are only placed in the vicinity of the ‘real’ sound sources. Reconstruction of the transient sound field radiated from the dual-planar-piston model is studied by numerical simulation for feasibility demonstration. A measurement of the sound fields radiated from two baffled loudspeakers is performed in the anechoic chamber, which shows that a better reconstruction result can be achieved by using the proposed hybrid scheme than the original interpolated TDESM with relatively the same number of sampling channels.