匹配垂直质点振速的浅海地声参数反演

海底声学参数对海洋波导中的声场特性研究和相关应用具有重要意义。针对一次夏季黄海声传播实验,分析了浅海负跃层环境下垂直质点振速的传播特性和简正波结构,说明当声源和接收器均位于负跃层下时,除海底附近外的大部分深度上垂直质点振速能量较高,且与声压相比,号数高的简正波对垂直质点振速的贡献更大,利用垂直质点振速进行匹配场反演能获得更高的海底参数敏感性。分析了海底吸收系数对垂直质点振速匹配场反演的影响,结果表明只有当进行匹配场反演时设置的海底吸收系数接近真实值时,才能获得准确的海底声速、密度和海深反演结果。利用实验中矢量水听器获取的垂直质点振速信号进行匹配场反演,将海底吸收系数在变化范围内取不同值对海底声速、密度和平均海深进行全局搜索,根据代价函数值最大确定了海底声速、密度及平均海深的反演结果,并利用不同距离上的声压传播损失反演出不同频率下的海底吸收系数。根据反演得到的海底声学参数计算声压传播损失,与实验中声压水听器测量结果符合较好。     

大深度接收时深海直达波区的复声强及声线到达角估计

基于射线模型给出了质点水平振速、垂直振速及复声强的表达式.结合深海直达波区的声线到达结构,分析了大深度接收时深海直达波区复声强的特点,理论分析与仿真结果表明,利用声场中不同组声线的复声强可以估计声线到达接收点的掠射角.根据在2014年进行的一次深海实验中布放在3146 m深处的矢量水听器获取的实验信号,利用直达波和海面反射波的复声强估计了直达声线与海面反射声线到达接收矢量水听器处的掠射角,结果表明,估计的声线到达角与理论计算结果基本一致.     

基于矢量水听器的声压和质点振速的空间相关系数

矢量水听器同步测量声场空间一点处的声压和质点振速的三个正交分量,由此得到的幅度和相位信息有利于改善声呐的检测和估计性能。对三维球形各向同性噪声场中声压和质点振速的时空相关性本文进行了研究,推导了矢量水听器的噪声协方差矩阵的理论表达式;给出了矢量水听器水平线阵和垂直线阵的协方差矩阵;研究单个矢量水听器的噪声协方差矩阵,并给出了浅海近岸水域的试验结果;利用上述理论结果推导了矢量水听器阵列的声能流阵增益。     

基于频带分解和距离加权的单矢量水听器浅海被动测距方法研究

本文针对浅海环境下中低频宽带脉冲声源被动测距问题, 提出了一种声压和水平振速联合处理的被动测距方法. 在浅海波导中, 声压和质点振速的自相关函数卷绕(warping)谱具有稳定的频率特征. 声压和水平振速的自相关卷绕谱具有相同的准线谱特征, 垂直振速自相关卷绕谱具有宽谱叠加线谱的特征, 与声压自相关卷绕谱相比, 其尖峰个数比更多, 且尖峰宽度更宽. 利用引导源, 本文提出了基于频带分解和距离加权的声压和水平振速联合被动测距方法. 利用该方法对2008年冬季青岛海域综合实验中单矢量水听器接收的气枪信号进行处理, 结果表明, 该方法能够实现气枪声源的有效测距. 与传统单声压水听器被动测距方法相比, 该方法可以有效减小代价函数的主瓣宽度、提高测距精度.     

基于矢量水听器的深海直达波区域声传播特性及其应用

对于深海近水面声源产生的声场, 处于较大深度处的接收器在一定水平距离范围内能接收到直达波. 2014年在某深海海域进行的水声考察实验中, 应用深度为140 m的拖曳声源发射实验信号, 布放在水下3146 m深处的矢量水听器成功地接收到了直达波信号. 本文应用射线理论, 分析了深海直达波区域声场的传播特性, 得出了水平振速与垂直振速的传播损失与声线到达接收点处的掠射角以及收发水平距离之间的关系. 在以上分析的基础上, 提出了一种利用水平振速与垂直振速的能量差估计声源距离的方法, 并结合2014年实验数据对实验中两条航线上8 km范围内的目标声源进行了测距, 测距结果与目标的GPS数据符合得较好.     

基于声压振速联合信息处理的声矢量阵相干信号子空间方法

为解决水下宽带源的远程测向问题,提出了一种基于声压P与振速V的互谱矩阵的声矢量阵相干信号子空间方法。与现有的将声矢量传感器的振速信息仅仅作为独立阵元来处理的声矢量阵测向方法不同,新方法完全基于声压与振速联合信息处理,充分利用了声矢量阵中P-V互谱的抗噪能力,能将相干信号子空间方法的宽带高分辨能力及去相干能力与声矢量阵的抗噪能力有机地结合起来,实现对宽带源的远程、高分辨方位估计。理论分析给出了基于P-V互谱矩阵的宽带聚焦原理和特征分解原理,以及信源数检测准则。基于湖试数据的仿真实验结果显示,采用3元声矢量阵,在信噪比为-10dB和观测时间为20s时,新方法方位估计的均方根误差约为5°,明显强于现有方法。     

压差式矢量水听器方位估计中的干扰抵消

矢量水听器由于能获取声场中标量（声压）和矢量（振速）信息，因此单个的矢量水听器就可实现目标方位估计。单个矢量水听器是利用信号的声压和质点振速之间相关性进行信号方位估计，但是当存在干扰，并且干扰和信号之间相关时，如果对运用能量流进行方位估计的方法不加改进，则会出现很大的误差，甚至出现错误的估计。本文提出一种存在已知噪声干扰情况下的干扰抵消方法，并针对该方法进行了仿真试验，最后运用湖试数据进行了验证。结果表明，该方法能有效地减弱相千千柑对信号的影响，实现对信号的方位估计。     

同振球型矢量水听器声波接收理论研究

对同振球型矢量水听器声压和质点振速的声波接收理论进行了研究。以同振球型振速水听器测量原理为基础,推导了自由运动刚性球体和弹性球体的声波接收响应数学表达式,分析了振速水听器几何尺寸、平均密度与其频响特性曲线之间的关系;另外,根据球面接收器的声波接收理论,推导了矢量水听器声压接收响应数学表达式,通过理论分析和数值计算,研究了振速水听器表面上的声压分布规律以及声压水听器的声波接收压力系数与其接收面的大小、质点振速水听器的半径、布放的位置和半径等参数之间的关系;从理论上建立了矢量水听器声波接收理论模型和分析方法,为矢量水听器的设计和研制提供了理论依据。      

基于声压振速联合处理的声矢量阵信源数检测与方位估计

为解决水下远程测向问题,首先论述了基于声压与振速互协方差矩阵的声矢量阵特征子空间方法,然后利用空时虚拟抽头处理,提出了一种基于特征向量的信源数检测与子空间划分准则.理论分析表明,与现有的将声矢量传感器的振速信息作为独立阵元来处理的声矢量阵测向方法不同,新的信源数检测与方位估计方法完全基于声压与振速联合信息处理,能将子空间方法的高分辨能力与声矢量阵的抗噪能力有机结合起来,可实现对远程目标的高分辨检测与定向.基于湖试数据的仿真实验证明了所述方法的有效性.     

利用矢量海洋环境噪声提取声场格林函数

考虑到矢量水听器在垂直方向上具有8字形指向性,能够有效抑制远方非平稳噪声源的干扰,提出了一种矢量环境噪声相关函数(NCF)提取声场时域格林函数(TDGF)的方法。基于简正波理论建立了声压和垂直振速垂直相关性模型。在此基础上,给出了声压和垂直振速相关函数提取声场纵向格林函数的过程.数值仿真对比和实验数据分析表明,相对于声压提取方法,垂直振速提取方法能够有效消除直达波前出现的亮纹与亮区干扰。此外,对于同等时间长度噪声序列,声压提取方法只提取到直达波路径,而垂直振速提取方法还提取到了我们更为关心的海底反射路径。利用直达波与海底反射波到达时延差估计的海深与实测海深吻合较好。      

Acoustic particle velocity horns

The paper considers receiving acoustic horns designed for particle velocity amplification and suitable for use in vector sensing applications. Unlike conventional horns, designed for acoustic pressure amplification, acoustic velocity horns (AVHs) deliver significant velocity amplification even when the overall size of the horn is much less than an acoustic wavelength. An AVH requires an open-ended configuration, as compared to pressure horns which are terminated at the throat. The appropriate formulation, based on Webster's one-dimensional horn equation, is derived and analyzed for single conical and exponential horns as well as for double-horn configurations. Predicted horn amplification factors (ratio of mouth-to-throat radii) were verified using numerical modeling. It is shown that three independent geometrical parameters principally control a horn's performance: length l, throat radius R(1), and flare rate. Below a predicted resonance region, velocity amplification is practically independent of frequency. Acoustic velocity horns are naturally directional, providing maximum velocity amplification along the boresight.     

Horns as particle velocity amplifiers

Preliminary measurements and numerical predictions reveal that simple, and relatively small, horns generate remarkable amplification of acoustic particle velocity. For example, below 2 kHz, a 2.5 cm conical horn has a uniform velocity amplification ratio (throat-to-mouth) factor of approximately 3, or, in terms of a decibel level, 9.5 dB. It is shown that the velocity amplification factor depends on the horn's mouth-to-throat ratio as well as, though to a lesser degree, the horn's flare rate. A double horn configuration provides limited additional gain, approximately an increase of up to 25%.     

A particle timing laser velocity meter

A fluid velocity meter is described; this operates by measuring the time taken for individual dust particles carried in the flow to travel between two points in space. A laser is used to produce two light beams parallel to one another and approximately normal to the flow direction. These beams are focused to two point or line foci in the region of interest: these foci are separated by a distance of the order of 1 mm in the flow direction. A particle crossing both foci in succession gives two scattered light pulses, and the time interval between these is measured by an oscilloscope or digital chronometer. The particles are natural dust particles occurring in the laboratory air or tap water. As in Doppler and fringe anemometers, the advantage of the laser is its spatial coherence: it enables extreme intensity to be obtained in small, well-defined regions. The instrument might be described as a fringe anemometer in which all the light is concentrated into the two end fringes, the others being eliminated.     

Computing particle velocity and intensity in diffracting systems

In a previous paper the authors have shown how it is possible to compute the acoustic pressure due to an axi-symmetric radiator with different boundary conditions. The technique involves the conversion of a double integral to a single integral by means of a geometric transform, and may be applied with the Green's function appropriate to each boundary condition.The present work shows how the form of the single integrals makes it possible to derive and compute both the particle velocity and the wave intensity. It has become apparent that the particle velocity must be described as an elliptic vector. A new concept, the ‘diffraction front’, has been defined as a surface in which there is no net energy transfer, and this has been applied to the evaluation of the magnitude and direction of energy flow. Plots have been made of flow lines and diffraction fronts, and also three-dimensional representations of energy intensity have been made for those acoustic fields in which pressure has already been evaluated.     

Simultaneous measurement of moving particle size and velocity

An optical method that makes it possible to measure the size and velocity of particles in flows and mixtures independently and simultaneously is considered. Measurements are taken by analyzing a moving diffraction pattern using a multielement photodetector and a special signal processing algorithm. The shape of photocurrent pulses arising when the particle crosses a light beam is determined. Examples of applying this method to particles with internal optical inhomogeneities are given in comparison with other methods, such as the method of low-angle scattering.     

Noninvariant one-way velocity of light and particle collisions

Recently published space-time transformations between inertial systems (different from the Lorentz transformations) are reviewed. Energy and momentum are defined consistently with these new transformation laws. Formally they equal the usual relativistic expressions only in the privileged frame, but numerically they do so in all inertial frames. All the precise experimental data concerning thresholds for inelastic processes, particle masses, and so on, can thus be explained also within this new theoretical framework.     

Influence of particle packing structure on sound velocity

The anisotropy in the particle systems of different packing structures affects the sound velocity. The acoustic propagation process in four kinds of packing structures(denoted as S45, H60, S90, and D) of two-dimensional granular system is simulated by the discrete element method. The velocity v_(tof) obtained by the time of flight method and the velocity vc obtained from the stiffness tensor of the system are compared. Different sound velocities reflect various packing structures and force distributions within the system. The compression wave velocities of H60 and S90 are nearly the same, and transmit faster than that of D packing structure, while the sound velocity of S45 is the smallest. The shear wave velocities of S45 and H60 are nearly the same, and transmit faster than that of D packing structure. The compression wave velocity is sensitive to the volume fraction of the structure, however, the shear wave velocity is more sensitive to the geometrical structure itself. As the normal stress p is larger than 1 MPa, v_(tof) and vc are almost equal, and the stiffness tensors of various structures explain the difference of sound velocities. When the normal stress is less than 1 MPa, with the coordination number unchanged, the law v_(tof) ∝ p~(1/4) still exists. This demonstrates that apart from different power laws between force and deformation as well as the change of the coordination number under different stresses, there are other complicated causes of v_(tof)∝ p~(1/4), and an explanation of the deviation from v_(tof) ∝ p~(1/6) is given from the perspective of dissipation.     

用于空气声测量的质点振速传感器

矢量传声器的核心组成器件是质点振速传感器,该传感器具有与频率无关的‘8'字指向性。本文在分析空气声质点振速传感器工作原理基础上,采用数值分析方法系统研究了质点振速传感器中敏感头桥式结构尺寸、热扩散和材料比热容等参数对频率响应的影响,着重分析了质点振速传感器最优灵敏度和低通滤波器效应。根据优化设计结果,采用MEMS工艺技术加工出敏感头桥式结构,并测试了0℃条件下Pt的电阻值R和热阻温度系数θ,以及传感器的频响曲线和‘8'指向性。实验结果表明:空气声质点振速传感器具有良好的声学性能。     

用于空气声测量的质点振速传感器

矢量传声器的核心组成器件是质点振速传感器,该传感器具有与频率无关的‘8'字指向性。本文在分析空气声质点振速传感器工作原理基础上,采用数值分析方法系统研究了质点振速传感器中敏感头桥式结构尺寸、热扩散和材料比热容等参数对频率响应的影响,着重分析了质点振速传感器最优灵敏度和低通滤波器效应。根据优化设计结果,采用MEMS工艺技术加工出敏感头桥式结构,并测试了0℃条件下Pt的电阻值R和热阻温度系数θ,以及传感器的频响曲线和‘8'指向性。实验结果表明:空气声质点振速传感器具有良好的声学性能。      

Delay and Doppler spreads in underwater acoustic particle velocity channels

Signal processing and communication in acoustic particle velocity channels using vector sensors are of interest in the underwater medium. Due to the presence of multiple propagation paths, a mobile receiver collects the signal with different delays and Doppler shifts. This introduces certain delay and Doppler spreads in particle velocity channels. In this paper, these channel spreads are characterized using the zero-crossing rates of channel responses in frequency and time domain. Useful expressions for delay and Doppler spreads are derived in terms of the key channel parameters mean angle of arrival and angle spread. These results are needed for design and performance prediction of systems that utilize underwater acoustic particle velocity and pressure channels.