大陆架低频声传播建模研究

在过去的几十年中大陆架斜坡海域的低频声传播得到越来越多的重视。针对爆炸声作为声源的一次海上实验测量数据,对大陆架海域的低频远距离声传播进行了建模研究。在实验过程中单水听器布放在水下大约240m处接收爆炸声信号,对两条不同测线的传播损失进行了处理。本文结合海底地声模型并考虑了声速剖面的水平变化,利用抛物方程方法对传播损失进行建模。模拟计算该海域的传播损失同实验测量数据相比具有较好的一致性。     

地声参数及传播损失不确定性估计与建模

地声参数的不确定性对水声传播具有重要的影响。通过贝叶斯理论建立水声环境不确定性推理模型,理论推导了地声参数的似然函数以及地声参数和传播损失的后验概率密度,并采用MCMC(Markov Chain Monte Carlo)进行了仿真计算,给出了地声参数的二维后验联合概率密度和一维边缘概率密度,在此基础上对传播损失的不确定性进行了估计,得到了传播损失80%的可信区间。仿真和实验结果表明,该方法适用于地声参数反演和不确定性估计,并能获取因地声参数不确定性导致的传播损失不确定性估计。     

地球曲率对远距离声传播的影响

对于远程声传播问题,地球曲率的影响不可忽略.为分析地球曲率对远距离声传播的影响,本文提出了一种地球曲率影响下环境参数的修正方法,该修正方法无需改动现有声场计算模型,具有可移植性好、计算简便的特点.典型环境下的仿真结果表明,由于地球曲率的影响,在会聚区传播中,会聚区的位置向声源方向偏移,会聚区移动随着距离变换近似为线性关...     

冬季冲绳海域地形及黑潮对声传播的影响

冲绳海域地形复杂且冬季存在较强的黑潮海洋锋,利用数值实验研究斜坡地形和海洋锋同时存在时由浅海至深海的声传播特性。海洋模式数值预报环境数据表明,分布于冲绳海槽斜坡上方的海洋锋导致该海域上层水体声速存在水平变化,纬度越高,水平变化越大。利用抛物方程声场模型计算声传播损失,通过简正模态分析存在表面声道的环境中声能量分布,利用声线轨迹图解释海底斜坡和海洋锋对声传播的影响。结果表明:声源频率低于表面声道截止频率时,声传播主要受海底地形影响;声源频率高于表面声道截止频率时,位于表面声道内的声源激发的声能量主要在表面声道传播,部分声能量从表面声道泄漏沿斜坡向深海传播,位于表面声道深度以下的声源激发的声能量主要沿斜坡向深海传播,斜坡地形导致表面声道下方至共轭深度这一深度范围呈现为声影区,海洋锋的存在可导致表面声道传播损失变化明显,影响程度与声源深度有关。     

管内声传播非线性效应及反声影响的数值研究

本文提出了包括考虑反声效应的一种数值方法来计算跨声速变截面硬壁管道内无声激波非线性声传播问题。通过许多算例,详细讨论了管道形状,喉部流动马赫数,入口声源强度及反声源强度对非线性声传播影响。算例表明,确实存在最佳反声强度,这时管道出口可得到明显的声衰减效果。     

传播起伏对声信号相关处理的影响

本文所讨论的是,复杂脉冲信号经过相关处理之后,其模糊度函数起伏与输入相关器的传播信号起伏之间的联系。在具体计算中,着重于线性调频脉冲情况,得到模糊度函数（或其峰值）起伏的平方差,等于输入信号振幅起伏率与相位起伏方差之平方和,即
σ本文所讨论的是,复杂脉冲信号经过相关处理之后,其模糊度函数起伏与输入相关器的传播信号起伏之间的联系。在具体计算中,着重于线性调频脉冲情况,得到模糊度函数(或其峰值)起伏的平方差,等于输入信号振幅起伏率与相位起伏方差之平方和,即式中,“权重”A和B与输入信号振幅及相位起伏的时间相关半径、脉冲长度、时延等有关。     

浅海涌浪对表面声道声传播的影响

受海面强风和海-气相互作用影响,表面声道普遍存在于冬季海洋环境中,是一种天然有利于声传播的波导.但是海面波浪使得海表形成粗糙界面,会严重破坏这种优良性能.本文利用南海北部海区的一次冬季声传播实验数据,研究表面声道声传播特性.研究表明,海底底质对表面声道内声传播的影响较弱,当海面风较小时,涌浪造成的影响为主要原因.实验数...     

管壁上缝隙对管内声传播的影响

本文在对管壁上有缝隙时管内声场的理论分析基础上得出为计算管内声波传播的等效线路。当缝隙的尺度远小于波长时缝隙用集总参数的阻抗表示。这阻抗包括缝隙本身的阻抗和局部声场扰动引起的质量抗。文中给出矩形缝隙的具体结果并讨论了声源的作用。     

丛聚的含气泡水对线性声传播的影响

含气泡水内气泡的空间分布会对线性声传播产生影响,导致实验结论与理论预测存在较大偏差.为解决这一问题,将准晶体近似引入到自洽方法中,导出了考虑空间分布时多分散含气泡水的等效声波波数.考虑到含气泡水内,气泡间存在小范围的聚集趋势(简称丛聚现象),在此基础上引入Neyman-Scott点过程描述了含气泡水内气泡的丛聚现象.分析发现,丛聚时,声速、声衰减的峰值将受到抑制,并向低频偏移,且抑制和频偏现象会随丛聚加剧而变强;随频率远离峰值段,丛聚对声传播的影响逐渐减弱.此外,考虑到空间分布的统计信息提取对相关研究的精确与否起到重要作用,引入了一种比例无偏估计,通过该方法获得了仿真环境下丛聚含气泡水模型的相速度及衰减系数,该建模及统计方法也可为相关实验工作提供理论基础.     

风速对声点阵立靶系统建模及算法的影响研究

室外靶场中点阵声学立靶应用时风对报靶精度有较大影响。使用几何方法推导了激波到达时间、矢量风速、弹丸速度和入射角、着靶位置之间的模型方程,然后将激波到达时间显式表述。该显式表达式可简化非线性最小二乘法求解并加速了收敛性,可同时求得弹丸着靶位置以及速度、入射角,可适用于不同的传感器阵列样式。通过仿真给出了风速对报靶精度影响的误差图。     

颗粒样品形变对声波传播影响的实验探究

为了更好地理解颗粒间接触结构的变化对通过颗粒介质中的声波的影响,本文利用单轴压缩实验,通过一系列增加的轴向压力使样品塑性应变不断增大,这在颗粒尺度上对应于颗粒间接触结构的改变.我们测量了此过程中通过颗粒样品的声波变化,结果表明颗粒体系内接触结构的变化对声波波形中的非相干波部分和频率有明显的影响,并且在样品接触结构变化的初始阶段声速是偏离有效介质理论的预测的.     

Outdoor sound propagation under the influence of wind and temperature gradients

The situation investigated is sound propagation from a monopole point source located over an impedance surface. The sound propagation is assumed to be influenced by wind and temperature gradients. A very accurate calculation method for taking into account the effect of wind and temperature gradients on sound propagation outdoors is presented and used for verification of a new approximate calculation model. This comparison shows that the approximate model is accurate. A series of loudspeaker measurements has been carried out over a grass-covered ground for distances up to 80 m. The measurements were carried out for a wind speed fo 2–2·5 m/s measured 10 m above the ground. The measured data agree very well with the calculated results. Furthermore the results from the approximate calculation model agree with results from previous investigations [1,2]. Hence, the main conclusion is that a simple and powerful approximate model for sound propagation under the influence of wind and temperature gradients has been developed. However, the influence of turbulence is not taken into account in this paper, and the wind and temperature gradients are assumed to be constant as functions of height.     

The influence of boundary layer on sound propagation in optical fibers

Physical models of two-layered and three-layered fiber were built. These models were used to calculate acoustic properties of optical fibers. Acoustic properties of fibers with boundary layer and without boundary layer calculated from these model were compared. The propagation of acoustic cylindrical symmetric waves in optical fibers was considered. This problem was treated analytically and numerically in continual approximation. The possibility of simultaneous propagation of two cylindrical symmetric waves in optical fibers with a boundary layer was shown (in a three-layered model). The physical phenomenon of the presence of two waves in the fiber with boundary layer is proposed for study of the boundary layer. Formulas for the calculation of the properties of the boundary layer from the acoustic experiment, verified by numerical calculations, are represented.     

水平变化波导中两种耦合简正波方法的比较与分析

分析比较了处理水平变化波导中声传播问题的两种耦合简正波方法:DGMCM(Direct-Global-Matrix Coupled-Mode Method)和CCMM(Consistent Coupled-Mode Method)。首先,两种方法都提供声场的双向解,具有很高的计算精度。其次,DGMCM和CCMM中本地垂直模式序列均具有较快的收敛速度,但DGMCM比CCMM需要较少的水平分段数。再次,两种方法通过求解不同的耦合简正波系统得到声场解,但求解过程中所需参数的计算量基本相同。另外,DGMCM能够处理某些CCMM不容易解决的问题,如海底形状不平滑,线源在斜坡海底上方,以及多声源问题。在DGMCM方法中给出了双层波导问题的耦合矩阵解析表达式,还推导更新了CCMM模型,使其能够处理二维线源问题。     

水平变化波导中两种耦合简正波方法的比较与分析

分析比较了处理水平变化波导中声传播问题的两种耦合简正波方法:DGMCM(Direct-Global-Matrix Coupled-Mode Method)和CCMM(Consistent Coupled-Mode Method)。首先,两种方法都提供声场的双向解,具有很高的计算精度。其次,DGMCM和CCMM中本地垂直模式序列均具有较快的收敛速度,但DGMCM比CCMM需要较少的水平分段数。再次,两种方法通过求解不同的耦合简正波系统得到声场解,但求解过程中所需参数的计算量基本相同。另外,DGMCM能够处理某些CCMM不容易解决的问题,如海底形状不平滑,线源在斜坡海底上方,以及多声源问题。在DGMCM方法中给出了双层波导问题的耦合矩阵解析表达式,还推导更新了CCMM模型,使其能够处理二维线源问题。     

The influence of internal waves on losses during sound propagation on a shelf

We discuss the results of investigations into the influence of internal waves on sound losses during propagation along stationary lanes on shelves of the Sea of Japan and the Sea of Okhotsk. Measurements were conducted with a Mollusk-07 autonomous vertical acoustic-hydrophysical measuring system and TONE-320 and FM-290–330 autonomous electromagnetic-type emitters generating a tonal acoustic signal and a frequency modulated signal, respectively. It is established that sound losses at 290–330 Hz as a result of internal waves do not exceed 5 dB. At the same time, intensive nonlinear internal wave packets that are relatively rare but characteristic of a shelf can increase losses up to 15 dB.     

深海大深度声传播特性及直达声区水下声源距离估计

深海大深度声传播特性对在深海近海底进行水声目标探测和定位具有重要意义。利用一次南海中南部深海不完全声道中的脉冲声传播实验数据,分析了海底附近大深度声传播损失及脉冲多途传播特性,并根据直达波和海底-海面反射波的时延差与收发距离的关系,提出一种利用深海直达声区脉冲多途到达时间进行水下声源距离估计的方法。结果表明:当接收器深度位于南海深海海底附近而声源深度较浅时,直达声区水平宽度可达30 km,传播损失相对影区来说较小,有利于水下声源探测;直达声区的直达波与海底-海面反射波的到达时延差随着收发距离的增大单调减小,可被用于水下声源距离估计。得到水下声源的距离估计结果与实验GPS测量结果较为一致,距离估计均方误差为0.28 km。     

On the influence of spatial correlations on sound propagation in concentrated solutions of rigid particles

In a previous paper [J. Acoust. Soc. Am. 121, 3386-3387 (2007)], a self-consistent effective medium theory has been used to account for hydrodynamic interactions between neighboring rigid particles, which considerably affect the sound propagation in concentrated solutions. However, spatial correlations were completely left out in this model. They correspond to the fact that the presence of one particle at a given position locally affects the location of the other ones. In the present work, the importance of such correlations is demonstrated within a certain frequency range and particle concentration. For that purpose, spatial correlations are integrated in our two-phase formulation by using a closure scheme similar to the one introduced by Spelt et al. ['Attenuation of sound in concentrated suspensions theory and experiments," J. Fluid Mech. 430, 51-86 (2001)]. Then, the effect is shown through a careful comparison of the results obtained with this model, the ones obtained with different self-consistent approximations and the experiments performed by Hipp et al. ["Acoustical characterization of concentrated suspensions and emulsions. 2. Experimental validation," Langmuir, 18, 391-404 (2002)]. With the present formulation, an excellent agreement is reached for all frequencies (within the limit of the long wavelength regime) and for concentrations up to 30% without any adjustable parameter.