点噪声源在近程声场中传播损失的仿真研究

在分层介质条件下，用本征声线法仿真计算了点声源这距离噪声场的传播损失曲线，仿真结果表明，其传播损失不仅依赖于声速分布，海区深度，海底反射特性等环境条件，也依赖于声源及接收水听器的深度，声传播损失显著不同于球面波衰减规律，其传播损失率差别可达８ｄＢ，这表明在测量舰船目标的辐射噪声声源级时必要的声场校正测量是必须的。     

一种考虑声线弯曲的温度场重建算法

声波在非均匀温度场中传播时会由于声波的折射而产生声线弯曲现象。为提高非均匀温度场声学CT (Computer Tomography)重建精度,提出一种考虑声线弯曲的重建算法。首先用最小二乘法获得一个不考虑声线弯曲的重建温度场,然后用打靶-插值法确定本征声线出射角,用三角形前向展开法追踪声线,获得此温度场中声波发射/接收器间的本征声线,建立本征声线上声波传播时间与温度分布间的关系,进而实现考虑声线弯曲的最小二乘法温度场重建。单峰、双峰温度场仿真重建结果表明:所采用的本征声线追踪法计算简单运行速度快;考虑声线弯曲后,可明显提高温度场重建精度。因此所提重建算法能更好地适应实际温度场重建需求。      

基于波前传播时间插值的三维声线追踪算法

研究了先正向计算波前传播时间,再根据波前传播时间反向确定声线路径的三维非均匀介质声线追踪算法.在正向步骤,根据程函方程,使用基于水平集的GMM(Group Marching Method)波前扩展算法,从声源开始,逐步计算离散介质网格节点上的波前传播时间.在反向步骤,利用正向步骤计算出的网格节点上的波前传播时间,从接收点开始,向声源方向逐单元追踪声线路径.在每个长方体单元内,首先把任意点上的波前传播时间用该单元网格节点上的已知波前传播时间的线性插值函数来表示,再根据Fermat原理,提出了确定三维声线路径的方法.实验结果表明,本文方法提高了三维声线追踪的精度和计算速度.     

深海海底声反射区多途时延差分析与近海面声源定位

深海海底反射声工作方式下的声场主要由4条一次海底反射声线路径构成。根据4条声线路径到达接收点的时间不同,可以得到6个不同的声线到达时延差值,当声源位于近海面时, 6条声线路径的时延差曲线随接收深度近似呈线性变化。本文基于虚源理论推导了海底声反射区的多途到达时延结构,给出了6条声线路径的时延差曲线随接收深度变化的近似表达式,通过分析时延差曲线与声源水平距离和深度之间的关系,提出了一种利用多途时延差估计深海海底声反射区近海面声源距离与深度的方法,仿真实验与影响因素分析验证了该原理的正确性。南海实验结果表明,当收发距离在10～33 km时,距离估计结果和深度估计结果都同实际声源距离和深度吻合较好,估计误差不超过15%,验证了该方法的有效性。     

扰动声线声压敏感核用于浅水前向散射小目标定位

针对收发合置声呐在浅水信道中对小目标的定位能力受强混响制约的问题,开展了利用目标前向散射的声屏障实验研究,通过计算扰动声线的声压敏感核实现了在自然环境中、非等声速条件下的小目标定位。扰动声线的声压敏感核反映的是因目标进入探测区域而扰动到的声线所包含的目标位置信息.首先,从众多本征声线中确定可以用于目标定位的扰动声线;然后,利用扰动声线的声压敏感核的空间特性实现定位。将该定位算法用于湖试数据,实现了利用20~28 kHz的线性调频信号对直径0.4 m目标球的定位。并且通过比较不同参数假设下的计算结果,发现该定位算法对于目标材质和尺寸的失配均具有较好的鲁棒性.      

陆架斜坡海域上坡波导环境中声能量急剧下降现象及其定量分析

深度较浅的声源其辐射声波在陆架斜坡海域上坡传播时,在斜坡顶端会出现声能量急剧下降现象.利用射线声学模型分析了造成这一现象的原因,并根据抛物方程声场模型计算的深海和浅海平均传播损失定义了"声能量急剧下降距离",定量分析了声源位置对该现象的影响.结果表明:声源深度对"声能量急剧下降距离"影响较大,而声源与斜坡底端水平距离对其影响较小;当声源深度变大时,部分掠射角较小的声线最终能够达到斜坡顶端,致使"声能量急剧下降距离"增大,继续增加声源深度,将导致上坡声能量急剧下降现象消失.利用抛物方程声场模型对陆架斜坡海域上坡声传播进行数值仿真,结合"声能量急剧下降距离"的定义,计算并比较了声源位置不同时该距离的变化,数值计算结果验证了理论分析.     

一种基于单水听器宽带信号自相关函数的水下目标定位稳健方法

在浅海波导中, 未知声源的本征声线相对到达时延估计是非常困难的. 声源位置在邻域内变化和声速剖面扰动对本征声线相对达到时延的影响是类似的. 基于这种思想, 提出了基于单水听器宽带信号自相关函数的水下目标定位稳健方法. 通过设计邻域位置约束, 构造加权函数, 将宽带信号自相关函数包含的交叉干扰峰值转化为能够改善目标定位性能的有用信息. 该方法不仅不需要估计本征声线的相对到达时延, 而且对搜索网格失配和环境参数失配具有相当的宽容性. 利用典型浅海环境下的仿真数据和海上实验数据(Shallow Water 2006 experiments)对所提出方法的有效性进行了验证.     

基于声线跟踪法对闭空间声场预测的接收球半径计算

接收球半径是采用声线跟踪法进行声场预测的一个重要参数。以前所用到的接收球半径一般是通过经验估计得到的,缺乏详细的理论分析。本文从声波传播机理角度分析了根据声线密度来确定接收球半径的原因,并推导了矩形闭空间中声线密度和接收球半径的计算方法。声线密度可以通过原始声线数目,声场空间体积与形状,边界吸声系数来确定。在一给定闭空间里,声线密度可看作是均匀分布的,所以接收球半径与空间位置无关,可看作是一个常数。但对不同的声场空间来说,由于空间体积、形状和吸声系数的变化,声线密度是不同的,因此接收球半径也会不同。声线密度越大,接收球半径越小;声线密度越小,接收球半径越大。实验表明,所提出的接收球模型能用来较准确地预测闭空间里的声压级和混响时间等声学参数。     

深海海底反射区声场的相干结构及其有源声呐估距

有源声呐在探测深海海底反射区的目标时,由于声线大掠射角弯曲且声速沿声线传播路径不断变化,造成了常规估距方法产生较大的误差。有效声速法是减小常规估距方法误差的有效途径,但由于需要预先计算空间每一位置点的"声线时延有效声速"对,复杂度高,实时性差。针对有效声速法的实时性问题,本文基于深海海底反射区声场的相干结构,提出一种改进的有效声速估距方法.首先指出深海声场能量沿声源出射角强弱相间变化及其引起的海底反射区离散声呐可探测区现象,并利用深海近水面声源的声线干涉效应解释了该现象的物理机理,建立了声呐可探测区与高能量声线的量化关系。在此基础上,计算声呐可探测区边界位置的"声线时延-有效声速"对,并线性拟合出可探测区所有位置点对应的值。经仿真验证,该方法与传统的有效声速法均可实现对常规估距方法估距误差的有效校正。虽然该方法估距精度较传统的有效声速法略有增大,但计算复杂度和计算时间显著减小,实时性好,具有良好的工程应用前景。      

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。     

Ray tracing/correlation approach to estimation of surface-based duct parameters from radar clutter

This paper describes a technique to estimate surface-based duct parameters by using a simple ray tracing/correlation method. The approach is novel in that it incorporates the Spearman rank-order correlation scheme between the observed surface clutter and the surface ray density for a given propagation path. The simulation results and the real data results both demonstrate the ability of this method to estimate surface-based duct parameters. Compared with the results obtained by a modified genetic algorithm combined with the parabolic wave equation, the results retrieved from the ray tracing/correlation scheme show a minor reduction in accuracy but a great improvement on computation time. Therefore the ray tracing/correlation method might be used as a precursor to more sophisticated and slower techniques, such as genetic algorithm and particle filters, by narrowing the parameter search space and providing a comprehensive and more efficient estimation algorithm.     

Generic-II routing and wavelength assignment algorithm for a wavelength-routed WDM network

In this paper, we have developed a Generic routing and wavelength assignment algorithm (Generic RWA-II) which is used for the calculation of blocking probability of network. A simple mathematical model has also been proposed for the optimization and minimization of blocking probability. The implementation of the proposed model and algorithm has less complexity and the computation used in this model is quite efficient. This paper suggests an optimum path and assigns wavelength to that path, as a solution to routing and wavelength assignment problem to have least blocking probability. This model can be implemented on different network topologies. Further, the model is also used to evaluate the blocking performance of a 6-node simple network topology and hence used to improve its performance on the basis of blocking probability.     

Routing and wavelength assignment in wavelength-routed all-optical WDM networks

In this paper, low-complexity mathematical model has been developed which is used for the calculation of the blocking probability of network and this model does not require any simulation statistics. The implementation of the model proposed has less complexity and the computation used in this model is quite efficient. The routing algorithm has also been proposed in this paper depending upon the proposed model, which is very efficient in calculation and minimization of the blocking probability. This algorithm suggests an optimum path as a solution to routing problem. The wavelength assignment technique has also been suggested in this paper to minimize the blocking probability. The proposed model and algorithms can be implemented on different network topologies. Furthermore, the model, routing algorithm and wavelength assignment technique is also used to evaluate the blocking performance of NSFNet and EUPAN Network topology and hence used to improve its performance on the basis of the blocking probability.     

Generic routing and wavelength assignment algorithm for a wavelength-routed WDM network

In this paper, we have developed a simple mathematical model which is used for the calculation of blocking probability of network. A generic routing and wavelength assignment algorithm has also been proposed for the optimization and minimization of blocking probability. The implementation of the proposed model has less complexity and the computation used in this model is quite efficient. This paper suggests an optimum path and assigns wavelength to that path, as a solution to routing and wavelength assignment problem to have least blocking probability. This model can be implemented on different network topologies. Further, the model is also used to evaluate the blocking performance of a 6-node simple network topology and hence used to improve its performance on the basis of blocking probability.     

Interfacial shape and contact-angle measurement of transparent samples with confocal interference microscopy

A model has been developed that predicts the effective optical path through a thick, refractive specimen on a reflective substrate, as measured with a scanning confocal interference microscope equipped with a high-numerical-aperture objective. Assuming that the effective pinhole of the confocal microscope has an infinitesimal diameter, only one ray in the illumination bundle (the magic ray) contributes to the differential optical path length (OPL). A pinhole with finite diameter, however, allows rays within a small angular cone centered on the magic ray to contribute to the OPL. The model was incorporated into an iterative algorithm that allows the measured phase to be corrected for refractive errors by use of an a priori estimate of the sample profile. The algorithm was validated with a reflected-light microscope equipped with a phase-shifting laser-feedback interferometer to measure the interface shape and the 68 degrees contact angle of a silicone-oil drop on a coated silicon wafer.     

The information transmission in community networks

The community structure has been empirically found in many real networks. This paper proposes an efficient Double Shortest Path routing strategy trying to avoid the modules of traffic congestion, which means that we adopt the shortest routing strategy both in the inter-modules and in the intra-module. Simulations show that this routing algorithm is superior to the traditional shortest path routing protocol with appropriate selection of the tunable parameters. In addition, this algorithm can also be improved by integrating it with several alternative routing strategies.     

Confocal depth‐resolved fluorescence micro‐X‐ray absorption spectroscopy for the study of cultural heritage materials: a new mobile endstation at the Beijing Synchrotron Radiation Facility

A confocal fluorescence endstation for depth‐resolved micro‐X‐ray absorption spectroscopy is described. A polycapillary half‐lens defines the incident beam path and a second polycapillary half‐lens at 90° defines the probe sample volume. An automatic alignment program based on an evolutionary algorithm is employed to make the alignment procedure efficient. This depth‐resolved system was examined on a general X‐ray absorption spectroscopy (XAS) beamline at the Beijing Synchrotron Radiation Facility. Sacrificial red glaze (AD 1368–1644) china was studied to show the capability of the instrument. As a mobile endstation to be applied on multiple beamlines, the confocal system can improve the function and flexibility of general XAS beamlines, and extend their capabilities to a wider user community.     

奥氏体不锈钢焊缝中的声学仿真模型与全聚焦成像检测

声波在奥氏体不锈钢焊缝中传播时声束弯曲,为超声成像带来了困难。基于Ogilvy焊缝模型,建立了奥氏体不锈钢焊缝非均匀各向异性声场仿真模型,采用Dijkstra路径搜索算法对各向异性条件下的声传播路径和声传播时间进行了数值模拟和分析。在此基础上,采用Verasonics超声相控阵成像系统,进行了奥氏体不锈钢焊缝的全聚焦成像实验,采集全矩阵回波数据,并结合理论模型计算的声传播路径和相应的传播时间,进行了成像结果修正。结果表明,与均匀介质模型的全聚焦成像结果相比,基于该文模型的焊缝全聚焦成像检测结果具有更高的缺陷定位精度和分辨率,验证了该方法的可行性,为奥氏体不锈钢焊缝成像检测提供了新的思路。     

Three-dimensional shape measurement for an underwater object based on two-dimensional grating pattern projection

In this paper, a practical method using phase tracking and ray tracing algorithms is proposed for measuring the three-dimensional (3D) shape of an underwater object. A 2D projected sinusoidal fringe goes through the water and illuminates the tested object. Firstly, the phase tracking algorithm is employed to identify homologous points in phase distributions of the deformed fringe captured by the camera and these of the fringe pattern projected by the projector. The projector is regarded as a special camera as regards the stereovision principle. In the calibrated system, both ray directions of the homologous points can be easily figured out. Secondly, the ray tracing algorithm is used to trace the propagation path of each ray and to calculate the 3D coordinates of each point on the tested object's surface. Finally, the whole shape of the tested object can be reconstructed.     

基于遗传算法的输电线路无人机巡检路径规划

针对无人机有效、安全巡检输电线路的路径问题,提出了一种基于遗传算法的输电线路无人机巡检路径规划方法,采用极坐标编码方式对无人机巡检路径构造染色体。结合实际情况中的无人机巡检各种约束问题,设计了适合于无人机巡检路径规划的遗传算子。实验结果证明算法能综合考虑各种因素,提高了全局寻优能力,是解决实际输电线路无人机巡检路径规划问题的较好办法。