浅海平均混响强度的简正波理论

本文用简正波方法导出了浅海远程混响强度的一般表式,该式对较广泛的一类声速剖面、海底反射与散射系数皆适用。由于考虑了复本征值对简正波入射场的影响,所得结果比以往的混响场简正波理论有较大的改进。所得出的平均混响强度的表式物理意义清楚,形式简单,便于进行数值计算与解析讨论。作为例子,文中分析了负跃层浅海中平均混响强度的衰减规律。计算表明,当声源与接收器皆位于跃变层之上时,远程混响强度与r~-5成正比。     

浅海平均混响强度的数值模拟

海中混响是回声探测的严重干扰。利用本文给出的混响模型可较快地计算分层海洋中平均混响强度的衰减规律及深度结构。 对于近程混响,由于海水非均匀性的影响较小,使用均匀层的射线方法计算。对于远程混响,使用简正波方法计算,它保持了平滑平均后的深度结构。在中等距离上两者能很好地衔接起来,由于考虑了复本征值对简正波入射场的影响,提高了计算精度,通过比较不同散射模型对混响强度计算的影响,提出以分离型二元散射模型作为混响数值模拟的基础,使能由界面反向散射系数估算二元后向散射系数,并大大简化混响强度的数值计算。     

水平缓变声道中的WKBZ绝热简正波理论

本文利用具有海面相移修正的本征函数的ＷＫＢＺ近似，并同时考虑波导简正波和海底反射简正波的贡献，提出了适合于水平缓变水下声道的ＷＫＢＺ绝热简正波理论。数值结果表明，会聚区声场主要由波导简正波决定，而影区声场主要由海底反射简正波决定。在菲律宾海中，频率范围在１０９ＨＺ至８６０ＨＺ，距离至２５０ｋｍ范围时，用ＷＫＢＺ绝热简正波理论计算的结果与实验数据符合得很好。     

浅海异地混响理论与实验比较

在亚洲海国际声学实验(ASIAEX2001)中记录了本地混响和异地混响的实验数据。对数据进行处理时,发现异地混响数据和本地混响数据有较大差异:本地混响衰减和混响垂直相关小于异地混响衰减和垂直相关。为了解释这一现象,根据浅海混响的射线简正波理论,结合三维海底散射模型,给出了浅海异地混响衰减和混响垂直相关的一般表达式。讨论了与本地混响衰减和混响垂直相关的关系,并与实验数据进行了比较。理论计算和实验数据表明:在经过时延(从声源到接收器的传播时间)后,较远距离的异地混响衰减与混响垂直相关可以由本地混响衰减和垂直相关近似表示。     

水下声道中脉冲传播的WKBZ简正波方法

本文将ＷＫＢＺ简正波方法应用于水下声道中的脉冲能量和波形传播。文中分别给出在两种不同水下声道中的数值结果，并与精确简正波数值解进行了比较。数值模拟结果表明，ＷＫＢＺ简正波方法能精确地计算水下声道中脉冲声信号的波形，计算速度比传统的简正波方法提高近两个数量级。     

浅海混响的垂直相干性

浅海混响垂直相干特性是海洋混响研究中一个重要的课题。在射线简正波混响理论的基础上,给出了浅海混响垂直相关的一般表达式,并推导出了在均匀层浅海中混响垂直相关的简化解析表达式。同时,通过对数值计算及实验结果的讨论,研究了浅海混响垂直相关与混响时间、频率、声源深度、接收器深度、海底衰减特性及海底散射系数等参数的变化关系。研究表明,在海底散射满足可分离性的条件下,浅海海底混响的垂直相关与声源位置无关,随着混响时间和海底衰减的增加、或随频率、接收器间隔和海深的减小,混响的垂直相关增大。     

水平不变海洋声道中的WKBZ简正波方法

本文利用本征函数的ＷＫＢＺ近似和海面相移修正发展了一种新的计算海洋声场的数值方法，该方法具有形式简明、易于计算、精度满足实用要求的优点．本文给出了ＷＫＢＺ方法应用于北太平洋声道中声传播的一些数值结果，这些结果表明该方法是一种计算分层海洋声道会聚区声场的快速而精确的数值方法．     

浅海混响建模的声束跟踪理论

研究建立了基于声束跟踪理论的浅海混响强度计算方法和混响时间序列仿真方法。给出了混响强度计算的简要理论推导,并进行了模型计算值与实验值的比较。建立了一种混响时间序列仿真模型,给出了其实现框架和方法。结合实验数据与文献研究结果,进行了混响序列相关特性的检验与分析。结果表明:建立的混响强度计算模型能很好地进行浅海混响强度的预报,混响序列仿真模型能仿真具有不同包络分布的混响序列,且其相关特性符合实验与文献研究结果。      

浅海混响的垂直相关和海底反射损失与散射强度的反演

根据浅海混响射线简正波理论和可分离的海底散射模型,导出了混响垂直相关的表达式,理论研究和实验结果表明垂直相关与接收深度有关,与声源深度无关。提出一种利用混响强度衰减曲线与混响垂直相关曲线联合反演海底反射损失和海底散射强度的方法。数值模拟反演及对实验数据的反演表明:所提出的反演方法具有实验简便、反演速度比较快及反演的结果比较稳定等特点。     

（Ba_（1－x）K_x）BiO_3芯态能级随组份的变化

本文用第一原理的ＬＤＦ－ＬＭＴＯ－ＡＳＡ方法，以超元胞Ｂａ４Ｂｉ４Ｏ（１２），（Ｂａ３Ｋ）Ｂｉ４Ｏ（１２），（ＢａＫ）Ｂｉ２Ｏ６，（ＢａＫ３）Ｂｉ４Ｏ（１２），Ｋ２Ｂｉ２Ｏ６五种“样本”计算由于Ｂｉ（＋３）和Ｂｉ（＋５）二种价态以及Ｋ掺杂引起各芯态能级化学位移的变化．“样本”的电子结构与实验相符，即Ｂａ４Ｂｉ４Ｏ（１２）是Ｅｇ＝２．０ｅＶ的半导体，（Ｂａ３Ｋ）Ｂｉ４Ｏ１２是Ｅｇ＝１．６ｅＶ其价带顶有少量空穴的半导体．其余“样本”是金属．芯态的ＬＤＦ本征值经原子模型△ＳＣＦ修正更接近实验值．用正态分布表达各芯态能级除化学位移外各种“环境因子”的影响，结合任意组份五种“样本”的伯努利分布，计算芯态电子能谱随ｘ的变化．结果表明，所有芯态的自旋一轨道分裂与实验完全相符，Ｂｉ（＋３）和Ｂｉ（＋５）二种价态引起各芯态化学位移的变化均小于０．２ｅＶ，Ｋ掺杂使各芯态结合能略有增加，其中Ｂｉ（４ｆ），Ｂａ（５ｄ）约１．３～１．５ｅＶ，其他芯态约０．４ｅＶ，以上计算结果与实验基本一致．     

Numerical simulations and experiment ofreverberation loss in shallow water

I.IntroductionUndcrwatersoundrevcrberationhasrccentlybecomeatopicofgreatinterestlI-3l.Sincethcrcverberationincludescombincdeffcctsofsoundpropagahonandscattering,andthesoundpropagationinshallowwaterismuchmorecomplicatedthanthatinthedeepsea,itisnecessarytOstudycarefullybothintheoryandexperimcnt.Fortheshortrangereverberationinshal1owwatcrtheray-basedmodelisavai1ab1e,whilefOr1ongrangethewave-basedmodelmustbeusedbecauscofcomp1icatcdmu1tipaths,refractioneffcctsandfrequencydependence.Thenorma1-mode…     

Normal-mode theory of average reverberation intensity in shallow water

In this paper, the general expressions of long-range reverberation intensity in shallow water have been developed on the basis of the normal mode theory. Because the effects of the complex eigenvalues on the mode incident field have been considered, the results are more accurate than those in previous former normal mode theories of reverberation. In addition, for the sake of simplifying the calculations and making the results convenient to compare with experiments, the reverberation intensity has been smoothed by space averaging. The expressions obtained have obvious physical meaning and concise form so that they can be used for numerical calculation and analytical discussion. These expressions are suitable for wider types of velocity profile, bottom-reflection and scattering coefficients. As an example, the average reverberation intensity in shallow water with a thermocline is evaluated. The result shows that when both the source and receiver are located above the thermocline, the long-range reverberation intensity is proportional to r⁻⁵. This result is in agreement with the experimental data.     

The WKBZ mode approach to sound propagation in range-independent ocean channels

I.IntroductionThenorma1-modeapproachcangiveanexactso1utiontotheacousticfie1dinastratifiedmedium,soitisoftenusedtocomparewithotherapproximatemethodssuchasraytheory,parabo1icequationl'](PE)methodandGaussianbeam[21approach,andtakenasacriteriontochecktheaccuracyofapproximatemeth0dsl3J.Themodeapproachmayalsobeextendedtorange-dcpendente..i,onmentsl4.5l.Thoughtherearemanynumerica1propagationcodesbasedonthemodeapproachI'],theconventionalmodeapproachisawkwardtoapplyt0'higherfrequencya-ndbroadbandprop…     

低频混响信号中的简正波衰减系数提取方法

提出一种从低频混响信号中提取简正波衰减系数的方法。利用简正波过滤技术对垂直阵混响信号进行分析,获得单阶简正波混响声场。假设海底反向散射矩阵可分离,从单阶简正波平均混响强度中提取出有效海底反向散射矩阵元素,最后利用不同距离上的有效海底反向散射矩阵元素计算出简正波的衰减系数。利用该方法从混响信号中提取出的简正波衰减系数预报的声传播损失和相同海域实测声传播损失一致。该简正波衰减系数提取方法有效避免了海底散射衰减和简正波传播衰减耦合的问题,同时对海底参数反演和水声环境的快速评估也具有重要的意义。      

The combined effects of reverberation and nonstationary noise on sentence intelligibility

Listening conditions in everyday life typically include a combination of reverberation and nonstationary background noise. It is well known that sentence intelligibility is adversely affected by these factors. To assess their combined effects, an approach is introduced which combines two methods of predicting speech intelligibility, the extended speech intelligibility index (ESII) and the speech transmission index. First, the effects of reverberation on nonstationary noise (i.e., reduction of masker modulations) and on speech modulations are evaluated separately. Subsequently, the ESII is applied to predict the speech reception threshold (SRT) in the masker with reduced modulations. To validate this approach, SRTs were measured for ten normal-hearing listeners, in various combinations of nonstationary noise and artificially created reverberation. After taking the characteristics of the speech corpus into account, results show that the approach accurately predicts SRTs in nonstationary noise and reverberation for normal-hearing listeners. Furthermore, it is shown that, when reverberation is present, the benefit from masker fluctuations may be substantially reduced.     

The WKBZ mode approach to pulsed propagation in ocean channels

In the paper, the WKBZ normal mode approach has been applied to the propagation of the pulsed energy and waveform in ocean channels. The numerical results in two different channels are given. Comparison between the WKBZ and conventional normal mode codes shows that the WKBZ mode approach is a fast and accurate method and the running time by the WKBZ approach is reduced by about two orders of magnitude.     

双模环型激光增益噪声模型的非线性效应

讨论了一个双模环型激光增益噪声模型，其中考虑了完全饱和效应且乘法噪声由增益系数涨落引起。在共振及两模具有相同泵参数时，获得了光强联合定态分布的精确解析表达式。通过与现有的双模激光摸型（其中乘法噪声由损失系数涨落引起）的比较，发现乘法噪声系数的非线性效应减弱了乘法噪声给激光光强统计性质带来的反常特性，并且这种减弱随着乘法噪声增强或损失系数减小而愈加明显。     

基于BDRM理论的深海声场快速预报研究

深海存在深海声道和双轴声道两种典型环境，WKBZ简正波方法已实现了深海声道中声场的快速准确预报，而对于双轴海洋声道则存在一定的误差。本文在WKBZ本征函数的基础上，推导出了参考界面相位修正的一致表达式，并将浅海声传播的波束位移射线简正波（BDRM）理论应用于计算双轴海洋声道中的声场，进行了数值模拟并与传统简正波方法进行比较，结果表明应用BDRM理论计算的传播损失具有很高的精度和速度。     

The average absorption coefficient for enclosed spaces with non uniformly distributed absorption

This study concerns the determination of an equivalent acoustic absorption model of the flat heterogeneous walls present in industrial rooms. Numerous measurements of the reverberation time in reverberant room were carried out for several facings with different distributed spatial absorption. Experimental results were compared to classical reverberation time models. The measurements showed that the change in average acoustic absorption depends on the relative distance between the sound source and the absorbent panels, as it is this which creates heterogeneity. Therefore, taking into consideration, in the theoretical models of average acoustic absorption studied, the solid angles representing the equivalent area of the panels as viewed by the source, improved the accuracy of the calculated reverberation time compared to the measurements. This equivalent acoustic absorption model, based on Sabine's absorption coefficient and employing the solid angle ratio, was used to calculate the reverberation time of several industrial rooms. The results obtained are better than those obtained with the standard formula.