收发分置声纳浅海近程混响信号建模研究

研究了收发分置声纳浅海近程混响的建模与仿真,模型主要基于单元散射理论,依据散射系数相关半径来划分海面、海底散射单元,通过模拟海面、海底混响形成的物理过程建立单接收与多接收模型。模型中考虑声纳设备参数(指向性、收发位置、发射信号)及环境因素(海面运动、海底粗糙程度)对混响建模的影响。设计程序实现浅海近程单接收与多接收混响信号模型并仿真计算出混响时间序列,提供GUI(Graphical User Interface)用户图形界面支持。对建模仿真的混响信号进行统计分析,验证了论文建立的浅海混响信号模型的正确性。     

海底声散射特性研究进展

海底是水下声场的重要边界,其声散射特性对水下声场空间结构及分布规律具有至关重要的影响。对目前国际上海底声散射特性研究方面的进展进行了系统的分析和总结,从海底声散射测量技术、海底声散射特性及机理、海底声散射预测模型3个方面进行了论述,并提出了未来研究的方向、研究重点与难点。该工作对于充分了解和认识海底声散射研究的目前现状和未来发展趋势具有很好的借鉴和指导意义。     

浅海声传播和混响的选频衰减

在强负跃层浅海的爆炸声实验中,发现当声源和接收器都位于跃层之上时,平均混响强度和某一航向的声传播损失在频率1000-2000Hz之间出现强烈的异常衰减现象,而且很有意思的是发射和接收均无指向性的平均混响强度的异常衰减与该航向声传播损失的异常衰减具有中心频率相同、带宽一致、附加衰减值相近的窄带共振或选频衰减特权.显然,这一异常衰减现象无法用各向异性的机理(内波、海面或海底的有规律起伏等)来解释.根据本文实验所得的传播损失和混响强度的深度结构以及一些间接的证据,我们认为这一选频附加衰减是由分散活动干跃居上部的有鳔鱼(极可能是鱼)所引起的.     

浅海爆炸声传播损失及简正波分离实验研究

文章简要介绍了浅海声传播损失的研究背景和基本理论方法。通过1/3倍频程滤波对浅海爆炸宽带信号的不同频段在浅海的传播损失情况进行了分析,描述了浅海环境对声传播损失的影响;同时在不知道先验信息的条件下,利用垂直阵声压数据成功地进行了简正波分离,并与理想条件下Kraken简正波模型计算出的结果进行了比较分析。     

浅海角度-时间灵敏度核特性研究

灵敏度核是声学观测量扰动与声速扰动之间的关系量,为探究浅海声波导中声场的扰动位置对声波到达时间、到达角度等声学观测量的影响程度,用格林函数一阶玻恩近似结合双波束形成的阵处理方法,推导得到角度-时间灵敏度核。对选取的本征声线进行研究,相关结果表明角度-时间灵敏度核包含了更多的空间属性,弥补了传统灵敏度核在声场扰动位置判断上的不足,为灵敏度核在海洋观测中实验站点布设优化及海洋环境参数反演等方面的应用提供了有力支撑。     

浅海内波及声场起伏数值研究

为探讨声学方法监测(反演)海洋内波的可行性,分析ASIAEX2001亚洲海海洋声学实验定点温度链实验数据,结果表明：实验期间存在M2内潮波、周期10～30min非线性内波现象,并观测到双温跃层同相传播“双非线性内波”。分别对垂直和平行于内波传播方向传播声场进行了数值计算分析。垂直于内波传播方向的声传播计算结果表明：简正波波数时间演化函数的频谱与内波引起的声速剖面变化频谱基本一致;简正波系数(模值)时间演化函数的频谱与内波引起的声源位置处的声速演化函数的频谱基本一致;高阶简正波波数差随时间的变化要比低阶简正波波数差小约1个量级。平行于内波传播方向的声传播计算结果表明：内潮波主要导致相邻简正波间耦合;非线性内波包能够导致跨号甚至垮多号简正波间耦合。讨论了2种海洋内波声学监测方法。     

一种分层海底反向散射模型

In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment layer with finite thickness. On the basis of calculating acoustic field in the water, the sediment layer, and the basement, four kinds of scattering mechanisms are taken into account, including roughness scattering from the water-sediment interface, volume scattering from the sediment layer, roughness scattering from the sediment-basement interface,and volume scattering from the basement. Then a backscattering model for a stratified seafloor applying to low frequency(0.1–10 kHz) is established. The simulation results show that the roughness scattering from the sediment-basement interface and the volume scattering from the basement are more prominent at relative low frequency(below 1.0 kHz). While with the increase of the frequency, the contribution of them to total bottom scattering gradually becomes weak. And the results ultimately approach to the predictions of the high-frequency(10–100 kHz) bottom scattering model. When the sound speed and attenuation of the shear wave in the basement gradually decrease, the prediction of the model tends to that of the full fluid model, which validates the backscattering model for the stratified seafloor in another aspect.     

浅海污染扩散的高精度数值模型

本文将ADI差分方法与紧凑格式相结合,对平流扩散方程进行数值处理,建立了浅海污染扩散的高精度数值模型.本模型将数值精度提高到四阶,从而有效地避免了数值弥散问题.由于采用隐显交替方向法,数值格式稳定且保持了差分方程组的三对角性质,计算过程简便.在理想条件下的数值试验结果与解析解的比较,说明了本文所建立的模型的精确性.利用北黄海倾废区域碱渣倾倒现场试验资料对本模型进行了实际验证.通过在渤海M₂分潮流场条件下的数值试验,揭示了污染云团在浅海中输移扩散的物理过程.     

浅海污染扩散的高精度数值模型

本文将ADI差分方法与紧凑格式相结合,对平流扩散方程进行数值处理,建立了浅海污染扩散的高精度数值模型。本模型将数值精度提高到四阶,从而有效地避免了数值弥散问题。由于采用隐显交替方向法,数值格式稳定且保持了差分方程组的三对角性质,计算过程简便。 在理想条件下的数值试验结果与解析解的比较,说明了本文所建立的模型的精确性。利用北黄海倾废区域碱渣倾倒现场试验资料对本模型进行了实际验证。通过在渤海M_2分潮流场条件下的数值试验,揭示了污染云团在浅海中输移扩散的物理过程。     

多波束测深海底混响仿真研究

海底混响是海洋混响的重要组成部分,采用模拟仿真进行验证分析,是仿真技术的一项重要应用。采用单元散射模型,研究在单发射阵元下,分布在同一直线上多个接收阵元接收的海底回波,忽略声波传播的相位起伏,只考虑振幅起伏,将传播损失、声吸收系数、海底反射损失、海底沉积层密度等参数带入海底混响仿真数学模型,仿真海底混响,使其更加接近海底的实际情况。     

双基地海底散射模型仿真与试验研究

无论对于双基地海底混响仿真,还是混响预报,散射强度都是一个十分重要的物理量.针对小斜度模型和K扰动模型,根据试验结果,结合对比理论仿真计算,证明双基地散射强度模型计算的可行性,研究结果对双基地混响特性研究具有重要意义.     

浅海波导中刚性球声散射特性研究

目标特性研究对军事及海洋开发具有重要意义。作者用Ingenito的简正波方法对浅海波导中刚性球的散射进行了理论研究。在理论推导中直接利用波导中简正波解,同时去掉文F．Izngenito等研究中的远场假设,使理论结果更具一般性。文中对浅海波导中刚性球的散射进行了数值计算,并进行了分析。结果表明,浅海波导中目标散射场特性与自由场中明显不同,海底、海面的存在使散射场在深度方向产生干涉,从而影响散射场的空间分布,海底声速及衰减系数对散射场空间分布有重要影响。     

Environmental Effects of Waveguide Uncertainty on Coherent Aspects of Propagation, Scattering, and Reverberation

The robustness of the coherence of waveguide propagation to environmental uncertainty becomes an important consideration for systems that seek to exploit coherence for gain. Examples include matched field processing for passive localization and time reversal mirrors (TRMs) for active systems. Here, efficient normal mode representations of midfrequency time-domain propagation using the narrowband and adiabatic approximations are used to explore the deterioration of coherent active system predictability and performance in the presence sound-speed perturbations in the water column. Results show that for TRMs the reverberation level at the focal range is increased, and the scattering from an illuminated object is reduced for ensembles over oceanographic uncertainty. Results are obtained analytically as formal averages and are believed to represent a lower limit on the deterioration of TRM performance in the presence of environmental uncertainty for shallow-water waveguides.     

Investigation on Touching Sea Bottom by a FPSO in Bohai Oilfield with Shallow Water

As one of the key safety problems, the motion performance and touching sea bottom of a FPSO are paid much attention by the ocean oil companies when the FPSO is exposed to survival storms in the shallow-water working areas. In this paper, timedomain numerical simulations are carried out on a 160 kDWT FPSO with a Yoke mooring system moored in the BZ25-1 oilfield with a water depth of 16.7m. The results are compared with those of the corresponding model tests. Good agreement shows that the time-domain simulations can be used to predict the performance of the FPSO in shallow-water reasonably. It is found that the touch of seabed by a fully loaded FPSO occurred few times under survival storm conditions. Therefore, the FPSO should be less loaded than that in the fully loaded condition under the survival storms.     

Wave Numerical Model for Shallow Water

The history of forecasting wind waves by wave energy conservation equation is briefly des-cribed.Several currently used wave numerical models for shallow water based on different wave theoriesare discussed.Wave energy conservation models for the simulation of shallow water waves are introduced,with emphasis placed on the SWAN model,which takes use of the most advanced wave research achieve-ments and has been applied to several theoretical and field conditions.The characteristics and applicabilityof the model,the finite difference numerical scheme of the action balance equation and its source termscomputing methods are described in detail.The model has been verified with the propagation refractionnumerical experiments for waves propagating in following and opposing currents;finally.the model is ap-plied to the Haian Gulf area to simulate the wave height and wave period field there,and the results arecompared with observed data.     

A Model of Wave Spectrum in Shallow Water

By using the shallow water wave data continuously recorded in the Bohai Sea, Huanghai Sea, East China sea and South China Sea. a model of wave spectrum in shallow water is developed with three parameters—average wave height, average period and relative depth—on the basis of the principle of the spectrum pattern simularity and the method of parameterization. The magnitude of frequency index in the high frequency     

浅水潮波模式变分同化共轭码技术研究

以浅水潮波模式为例，详细讨论了共轭码技术的使用方法以及代码检验，并建立了海洋浅水模式的共轭模式。利用浅水潮波模式及其共轭模式进行了流速和水位的初始场优化试验。试验结果表明，初始场优化对于潮波系统数值模拟具有重要的作用，同时也说明利用共轭码技术可以有效地设计共轭模式，进行各种同化试验研究，显示了共轭码技术的诸多优点。     

Forward Scattering Observation With Partially Coherent Spatial Processing of Vertical Array Signals in Shallow Water

In this paper, we address the problem of detecting an inhomogeneity in shallow water by observing changes in the acoustic field as the inhomogeneity passes between an acoustic source and vertical line array of receivers. A signal processing scheme is developed to detect the perturbed field in the presence of the much stronger primary source signal, and to estimate such parameters as the time when the inhomogeneity crosses the source-receiver path, its velocity, and its size. The effectiveness of incoherent, coherent, and partially coherent spatial processing of the array signals is evaluated using models and data obtained from experiments in a lake. The effect of different bottom types is also considered, and it is shown that partially coherent processing can have a significant advantage depending on the bottom type. Estimates of the minimum input signal-to-noise ratios (SNRs) for which the diffracted signal can be observed are presented.     

Model Tests Research on A Float-Over Barge in Shallow Water Under the Undocking Conditions

In this study, the Jinzhou 9-3 CEPD float-over installation project was investigated. During the undocking condition, the water depth of the motion path of the working barge gradually changed from 10.31 m to 9.41 m. The undocking clearance of the HYSY 228 is smaller than 1 m; therefore, the barge shows highly nonlinear hydrodynamic characteristics, and it is difficult to be accurately simulated by numerical analysis. Thus, it is necessary to obtain the hydrodynamic characteristics and laws of the float-over barge at different water depths by using tank model test, to provide some reference and guidance for float-over operations in shallow water.