一种基于模态域波束形成的水平阵被动目标深度估计

水面水下目标分辨与识别一直是被动声呐探测领域的难题.利用一种水平阵模态域波束形成算法获得己知方位目标声源的各阶模态强度,将其与不同深度的各阶参考模态强度进行匹配,最终实现了对声源的深度估计.仿真结果表明,该算法可以在信噪比为-10 dB的情况下,用300Hz带宽的信号样本,实现对声源深度的有效估计.系统分析了不同参数和不同波导条件对该方法目标深度估计性能的影响.其中,阵元数越多,模态样本数越多,计算频段越宽,方位估计精度越高,有效阵长越长,深度估计的性能越好.阵元间距和波导深度的变化不会影响该方法的深度估计性能,并且该方法的深度估计性能在声速剖面、海底参数等波导条件存在扰动时具有鲁棒性.     

水平阵信号压缩感知用于简正波分离

针对水平阵信号简正波分离过程中常规波束形成分辨率低以及warping模态滤波不适用于复杂声信号的问题,提出水平阵信号压缩感知用于简正波分离的方法。利用压缩感知在方位估计中的高分辨特性,通过估计水平阵接收信号在频率方位角上的二维分布,分离得到各阶简正波的方位谱,并逆Fourier变换得到时域波形。仿真孔径1 km、阵元间隔10 m水平阵接收20~200 Hz伪随机声信号和脉冲声信号,所提方法分离出的各阶简正波与理论波形的相关系数在0.97~1.0。对2011年北黄海声学实验中的海底28元水平阵接收的气枪信号,在合成至1 km孔径后使用压缩感知方法分离简正波,其与warping模态滤波分离得的前5阶简正波相关系数在0.82~0.93。仿真与实验都说明了水平阵信号压缩感知简正波分离方法的有效性。      

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests)

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.     

三维浅海环境下孤立子内波对低频声能流的传播影响

针对三维浅海环境下孤立子内波对低频声信号传播特性的影响问题,基于Oxyz坐标系下的三维浅海低频声场有限元计算方法,以声能流为研究对象,仿真分析了内波存在对低频声信号传播特性的影响规律。研究结果表明:受内波影响,在xOz平面,声能流垂直分量的传播偏转角度呈现周期性的起伏规律;随着声源深度的增加,内波对声能流偏转角度的影响深度也随之增加。对xOy平面,当声源位于温跃层以上时,随着接收深度的增加,各深度平面上声能流水平分量的偏转角越大;随着声源深度的增加,内波对各深度平面上声能流的影响逐渐减弱。      

用分数阶微分实现时频重叠多模式兰姆波的模式分离

为了分离时频重叠多模式超声兰姆波,提出了一种用分数阶微分理论实现多模式兰姆波模式分离的方法。以时频重叠的S1和A1模式混合信号为例,用赛利斯分布作为幅值谱的模型,首先对信号做频散补偿,由补偿后信号幅值谱分数阶微分推导了幅值谱特征参数的计算式并根据信号模型重建幅值谱,然后结合兰姆波的频散特性推导出对应的相位谱,并通过幅值谱和相位谱重构各模式的信号,实现模式分离。对1 mm钢板中仿真时频重叠的S₁和A₁模式信号分离结果显示分离出信号的幅值和带宽相对误差小于6%,中心频率相对误差小于0.25%。实验结果也证实了方法的可行性。因此当混合信号幅值谱不完全交叠时,本方法可以实现多模式兰姆波信号的分离,有助于多模式兰姆波频散信号的分析和识别。      

空气中快速运动声源水下声场的波数积分模型

本文采用二维波数积分，对空气中高速运动声源激发的水下声场进行建模。针对二维波数积分计算声场时域解计算量大的问题，提出一种快速计算方法。用本文提出的方法，对深海和浅海情况下，空气中高速运动单频点声源激发的水下声场进行了计算和仿真。计算结果表明：在深海，水下接收信号的幅度和瞬时频率随时间发生变化；接收器深度、接收器与声源运动轨迹的最小距离对接收信号的变化快慢有较大影响，而声源高度的影响较小；在浅海中，接收信号呈现快速的幅度起伏，明显的多普勒频移和大的频率展宽效应。与简正波方法相比，本文方法主要适用于近场计算，而简正波方法适用于远场。另外，当声源频率较高时，二维波数积分方法的计算量将迅速增大。     

A multifrequency scintillation method for ocean flow measurement.

The transverse flow of inhomogeneous fluid produces fluctuation of the acoustic signal passing through it. The coherence of frequency-spaced signal fluctuation is related to the advection of the inhomogeneous medium through the sound path, thus providing a basis for the current velocity measurement. This method can be considered to be the "frequency-domain" version of the conventional scintillation approach to the current velocity registration based on the measurement of the signal correlation transmitted from the source to the two separated in space receivers (space-domain scintillation) [S. Clifford and D. Farmer, J. Acoust. Soc. Am. 74, 1826-1832 (1983)]. The sensitivity of the method depends on the features of the ocean fine structure, which is determined mainly by the internal waves and turbulence. To estimate the sensitivity of the multifrequency method of transverse current probing, the coherence function of two signals propagating through a frozen and moving internal wave field and through the turbulence is considered. The application of the multifrequency signal allows estimation of the fine-structure parameters as well as the current velocity.     

The Spectrum of Squeezing in Degenerate Four-Wave Mixing

We analyze a simple model for degenerate four wave mixing, introduced by Savage and Walls. In the resonant case, the system exhibits a phase instability when the pump intensity is increased well beyond the threshold for generation of the signal mode. Still in the resonant configuration, we calculate the amplitude and phase squeezing spectra both for the signal and the pump mode. In the signal (pump) mode, the squeezing becomes especially large when the signal (pump) mode is much more damped than the pump (signal) mode. The signal field can exhibit both phase and amplitude squeezing, in distinct domains of the parameter space. On the other hand, the pump field can show squeezing only in the amplitude quadrature component. In general, the model exhibits sizable squeezing over very extended regions of the parameter space.     

基于声传播算子的声源定位实验模拟方法研究

声传播算子是一种高效的时域声场计算方法,它能够很方便地计算出给定系统参数下任意时刻任意位置的声场变化情况,本文采用这种方法计算所得的二维房间声场信息进行传声器阵列的声源定位仿真实验。计算结果表明,用该方法获取的阵列数据能有效地应用于阵列信号处理算法中,准确地估计出初始高斯脉冲声源的方向。声传播算子声场计算方法能为传声器阵列声源定位的实验提供方便,使得传声器阵列声源定位算法在不同混响时间的鲁棒性实验研究变得更加简捷。     

小波分析方法在合肥光源逐束团测量系统中的应用

介绍了小波分析方法在逐束团束流位置测量系统中的应用。小波分析方法在高频处频率窗口较宽,具有较高的时间分辨力,使用小波分析可分离并提取信号的振荡成分及基线漂移成分,各成分在时间轴上的位置与原信号相同,原有的线性关系保持不变,在处理非平稳信号时不会造成信号明显劣化,如幅度失真和相位偏差。基于小波分解和重构的时间序列多分辨力滤波处理非平稳信号时不会造成信号明显劣化,保证了追踪束团振荡强度、相位、频率和振荡模式随时间变化的结果更真实可信。在合肥光源中,小波分析方法成功用于横向振荡振幅包络的提取及增长率、阻尼率的计算,也可用于提取横向振荡振幅包络及计算增长率和阻尼率,为机器研究、束流诊断和逐束团反馈系统调试提供了准确的依据。     

Focusing of acoustic fields in a randomly inhomogeneous waveguide by using the time reversal method

We perform theoretical analysis of the method of field focusing in a randomly inhomogeneous waveguide using reradiation of the received signal with time reversal. The simplest case where point sources and receivers are used for emission and reception is considered. As an example, the waveguide is chosen which simulates an underwater sound channel with refractive-index fluctuations caused by random internal waves. In underwater acoustics, the considered method of field focusing is usually applied at relatively short distances that are shorter than or about 10 km. This work deals with much longer paths, along which sound waves propagate under conditions of well-developed ray and wave chaos. Main attention is given to studying the width of the focal spot and the field amplitude at its center. It is shown that the amplitude distribution in the vertical section of the focal spot and the peak amplitude value at its center can be estimated analytically using the stochastic ray theory.     

板状结构Lamb波频散补偿与聚焦接收成像检测

对板状结构中Lamb波的频散和多模现象进行了理论分析,采用有限元仿真方法获取了Lamb波与缺陷作用后的回波信号,对信号进行聚焦接收处理,即在一定距离范围内利用导波频散特性对各个模式信号进行频散补偿,提取补偿后信号的幅值,结果表明当所得信号幅值最大时,所对应的补偿距离等于缺陷与换能器之间的实际距离.利用这一结论,提出了以...     

Application of surface and normal ultrasonic waves for measuring the parameters of technical fluids: I. Shear viscosity measurements

The effect of the viscosity of a fluid on the propagation of the zero mode of a horizontally polarized normal wave in a thin (compared to the wavelength) waveguide immersed in the fluid is studied. It is shown that, to a first approximation in the ratio of the shear impedance of the fluid to the shear impedance of the waveguide, the wave amplitude decays exponentially as a function of the distance at a damping coefficient proportional to the square root of the shear viscosity of the fluid. The decrease in the wave amplitude induced by the shear viscosity of the fluid is numerically estimated, and the results obtained point to the possibility of developing a method for its measurement at a high accuracy. This method was developed and tested on a waveguide in the form of an aluminum ribbon 0.3 mm thick and 14 cm long at a frequency of 2 MHz. The decrease in the signal amplitude when the waveguide is immersed in distilled water (tabulated shear viscosity is 1.05 × 10^?3 Pa s) is found to be 0.42 dB as compared to the amplitude in the unloaded waveguide, which can be considered as the sensitivity of the experimental setup. A method for calibrating the sensor is described. The shear viscosities of solutions of saccharose in distilled water are measured, and the experimental results agree well with the theoretical estimates.     

A quality of parametric wave phase conjugation of ultrasound

The criterion, known from optics, of wave phase conjugation quality is accommodated for acoustical experiment. An incident focused sound beam at 5 MHz is propagated towards a supercritical magnetoelastic conjugator through an introduced random phase layer, and the conjugate beam propagates backwards through the layer to the source. 1D and 2D distributions of wave field are measured for the conjugate beam of finite amplitude using a membrane hydrophone. The maximum sound intensity of 640 W/cm2 and acoustic power of 4 W are registered in the focal maximum of the conjugate wave. The quality of WPC is calculated from the ratio between the power in the central maximum and the total power of the conjugate beam. The method is applied to compare two operation modes of a supercritical parametric conjugator. It is shown that in the linear mode the conjugator provides higher quality than in the nonlinear (0.54 compared to 0.24).     

基于时间反转理论的聚焦Lamb波结构损伤成像

从理论和实验上研究了时间反转法在频散和多模式的Lamb波结构健康检测方面的应用.当Lamb波在包含有损伤的板类结构中传播时,损伤的存在表现为一个被动波源.采用分布式传感器网络,基于传递函数的观点,通过推导由损伤这个被动波源产生的时间反转波场幅值的表达式,证实了当观察点位于损伤位置时,时间反转波场的幅值最大.为验证时间反转方法的聚焦效应,提出了一种适合于分布的激励/接收传感器网络的成像方法,该方法可以对损伤定位并近似确定损伤尺寸.结合有限元的实验结果显示了Lamb波检测信号的能量可在损伤处聚焦,表明时间反转     

浅海孤子内波对水平纵向相关性的影响*

基于理论和模型仿真对孤子内波存在下的水平纵向相关系数的变化进行了研究。理论上推导出浅海孤子内波存在情况下的声场水平纵向相关系数随时间的变化规律,并且运用二维抛物方程模型（Ram）验证理论推导结果。结果表明,孤子内波会导致水声纵向相关系数的变化,并且水平纵向相关系数的变化是由于简正波的干涉所导致。我们给出特定环境下的水平纵向相关系数随时间变化的结果,当环境中第一、二号简正波占主导地位时,水平纵向相关系数会呈现出周期变化的结果。     

用于浅海有源声呐目标深度估计的匹配相位处理EI北大核心CSCD

针对浅海波导中有源声呐目标深度估计问题,提出了通过单个声源发射低频宽带信号,垂直双接收水听器接收目标回波,利用宽带目标回波比值的相位特征进行匹配相位处理的方法,不仅消除了目标散射特性对有源声呐目标深度估计的影响,而且仅需计算单程的信道传递函数,运算量小,有利于实时处理的实现需求。首先通过理论推导,定义了一个隐含目标深度、且与目标散射特性无关的声场特征——单程传播向量宽带干涉结构,在Pekeris波导条件下仿真分析了简正波阶数与单程传播向量宽带干涉结构的幅度和相位的关系,发现选取较多的简正波阶数贡献的单程传播向量宽带干涉结构进行匹配相位处理可以提高目标深度估计的性能。进一步仿真分析表明,在发射信号选取一定的时间长度和带宽的条件下,利用全部阶简正波且信噪比大于-10 dB时,方法的深度估计误差在5 m之内。最后分析了信号时间长度和处理带宽对有源声呐目标深度估计性能的影响,以及海底声速、海深和声速剖面失配时方法的鲁棒性。     

Localizing impulse sources in an open space by time reversal with very few transducers

Localizing impulse point sources is a problem of major practical importance for numerous applications in security or equipment monitoring. It is difficult to solve when posed in a strongly congested propagation medium. This paper concerns the case where, in an open space, obstructing bodies are of a sufficient size and number to impede reception of certain direct paths from the source to the receivers. They produce reflected or diffracted paths. A low number of point receivers is used, 2-5, depending on the case. This fits practical constraints one meets in the field. The localization principle being time reversal, the aim is therefore to model the time reversed signal propagation from the receivers. From a direct signal obtained from measurements or computer simulations, the reversed propagation computation is made in the frequency domain or in the time domain. Despite the low number of receivers, which we would expect not to give good refocusing of the reversed wave, we are able in each case to localize the source with a conveniently chosen criterion, based on the time shortness of the signal. The advantage of this technique is its simplicity and speed: in a time formulation, a unique computation allows the localization. This result opens the way to economical measurement techniques for localizing impulse sources in congested or disturbed media, as long as a propagation model allowing integration of refraction, diffraction and reflection effects is available.     

基于频散补偿和分数阶微分的多模式兰姆波分离

由于兰姆波的多模和频散特性,实际检测时在同一激发频率下存在多种模式的混合信号,而各模式信号有不同的频散特性,使得在时频混叠的情况下兰姆波的检测变得十分复杂.本文在频散补偿的基础上,通过时延函数建模,依靠不同模式频散趋势的差异性,将时频混叠信号的分离问题转化为部分模式混叠信号的分离问题.基于分数阶微分的理论,用信号幅值谱分数阶微分极大值和对应频率分别与微分阶次拟合多项式实现特征参数的提取并依靠特征参数重建幅值谱.结合相位谱重构时域信号以实现部分混叠信号中频散补偿后的模式的分离.最后恢复频散获得分离后的兰姆波信号.仿真和实验结果表明,本文方法不仅可以实现时频混叠多模式兰姆波信号的分离,更能保证分离精度,有助于复杂多模式频散信号的分离与处理的进一步研究.