Power emitted by a vertical compensated linear array in a Pekeris waveguide

An expression is derived for the acoustic power emitted by a vertical compensated discrete linear array in a Pekeris waveguide. The sound field is represented by the sum of a discrete spectrum and a continuous one. We consider the dependence of the power emitted by the array on both the number of array elements and the array compensation angle.     

Generation of a single normal wave by a vertical linear array in the water layer

The possibility of the acoustic energy emission into a single normal wave by a vertical linear array in a homogeneous water layer is considered for the case of the array aperture being smaller than the layer thickness.     

Fast estimation of array gain of vertical transmit array in Pekeris waveguide

In order to estimate the sound intensity level of vertical transmit array(VTA) from that of single transducer,a fast estimation method of transmit array gain(TAG) in Pekeris waveguide is studied.At first,the average sound intensity of VTA is calculated on the basis of normal mode theory with the effective depth,and the TAG expressed by the summation of modes is derived.Then by using integral,instead of summation,of modes order,the fast estimation expression of TAG in 3/2 power field is derived a...     

Pekeris波导中垂直发射阵的阵增益快速估计

为了利用单换能器的声强级估计垂直发射阵的声强级,研究了Pekeris波导中快速估计发射阵增益的方法。首先,基于等效深度简正波理论,计算了Pekeris波导中垂直发射阵的平均声强,进而得到用模态阶数求和表示的发射阵增益的表达式。然后对模态阶数用积分代替求和,并对引入的误差进行修,得到3/2次方衰减场区发射阵增益的快速估计表达式;有效声影区声场由于只剩1阶简正模态,可直接简化得到发射阵增益的快速估计表达式,在海底参数未知时可用海深近似代替等效深度来估计有效声影区的发射阵增益。计算机仿真和海上实验得到的阵增益快速估计误差均小于1 dB,验证了快速估计方法的有效性,这一发射阵增益快速估计方法可以为工程应用提供参考。     

Pekeris波导中简正波的复声强及其应用

在Pekeris波导模型下,关注了简正波的矢量场,讨论了简正波水平复声强和垂直复声强的表述,并分析了其特征.单阶简正波在水平方向是行波,相应的水平复声强仅为有功的;在垂直方向为驻波,相应的垂直复声强仅为无功的.而多阶简正波相互干涉,因此总声场的复声强既有有功分量,也有无功分量,其中只有有功分量参与声能的输运,但无功分量是反映声场信息的重要组成部分.通过对垂直(交互)复声强无功分量和水平交互复声强有功分量的数值分析,对于甚低频率的点源声场,发现当声源深度变化时,上述声场分量的正负号呈有规变化,当接收传感器置 关键词： 目标深度分类 复声强 矢量场 Pekeris波导     

Interaction of counterpropagating discrete solitons in a nonlinear one-dimensional waveguide array

We experimentally investigate the interaction of counterpropagating discrete solitons in a one-dimensional waveguide array in photorefractive lithium niobate. While for low input powers only weak interaction and formation of counterpropagating vector solitons are observed, for higher input powers a growing instability results in discrete lateral shifting of the formed discrete solitons. Numerical modeling shows the existence of three different regimes: stable propagation of vector solitons at low power, instability for intermediate power levels leading to discrete shifting of the two discrete solitons, and an irregular temporal dynamic behavior of the two beams for high input power.     

Relating waveguide invariant and bottom reflection phase-shift parameter P in a Pekeris waveguide

The waveguide invariant β is affected by the shallow-water environment. The effect due to bottom sediment on β is investigated in this paper. It is found that the effect of sediment bottom can be concentrated on one parameter P-the bottom reflection phase-shift parameter. For a Pekeris waveguide, under Wentzel-Kramers-Brillouin (WKB) approximation, a very simple analytic relation is given: β ≈ 1 + P/(k(0)H(eff)), where H(eff) is the "effective depth," and H(eff) = H + P/2 k(0). The value of β related to different high-speed sediments (including layered sediment) ranges from 1.0 to 1.5. Some numerical examples including the layered sediment case are conducted to verify this result. Good agreement between the results calculated by KRAKEN and by WKB with parameter P has been found. Hence, the application of parameter P provides a model-free platform to investigate the bottom effect on the waveguide invariant β in shallow-water.     

单线阵CCD相机立靶测量原理

针对现有双CCD交汇立靶在室内使用时存在的光源复杂的问题,提出一种单线阵CCD相机立靶测量原理.采用一台线阵CCD相机,配合两个小功率半导体扇形一字线状激光器和投影板作为光源,将CCD相机的探测光幕面和激光光源的光幕面调整在同一个面内,当弹丸穿越探测光幕面时,档住了两个激光器投射在投影板上的部分光线,并在投影板上留下对...     

Piston acoustic radiator in an impedance screen of a Pekeris waveguide

A model problem of seismic hydroacoustics is studied for a piston radiator inserted in an impedance screen that coincides with the lower boundary of a Pekeris waveguide. The radiation resistance of the piston is numerically calculated as a function of the screen type and parameters of the radiator and the waveguide.     

On the feasibility of normal wave selection in a shallow-water waveguide

Long-range propagation of low-frequency narrowband sound signals in the near-bottom acoustic channel with random inhomogeneities caused by internal waves and a rough bottom is investigated in the framework of numerical and field experiments. The feasibility of selecting the signal components corresponding to different normal waves is analyzed. The problem of selecting such components is considered for signals of long duration exceeding the characteristic time of the stationary state of the channel.     

一种单线阵CCD立靶系统参数的标定方法

单线阵CCD立靶相对其它立靶方法而言具有结构简单、成本低等优势,而系统参数的准确标定是测量精度的保证。针对该立靶测量系统,通过建立标定模型确定了影响测量精度的各系统参数,包括镜头主点,激光器位置,相机的倾角、焦距和原向反射膜高度。将整个系统参数看做一个黑盒模型并进行整体标定,只需考虑黑盒的输入和输出端,根据CCD相机所接收到弹丸双投影点的位置计算弹丸的坐标。实验结果表明在靶面大小1m×1m时,理论计算值与实际放置模拟弹丸之间的偏差小于5mm。     

Measuring principle of vertical target density based on single linear array CCD camera

In consideration of the complexity and the high cost of the dual CCD intersection vertical target when it is used indoor. A novel measuring principle of one linear array CCD camera vertical target is presented. One low-power semiconductor sector-like laser with projection board is used to be the lamp-house of the CCD camera. The detection light screen of the CCD camera and the laser lamp-house are adjusted to same plane. When the projectile through the detection light screen, it blocks the part light of the laser and leaves a shadow of projectile on the board. The shadow and its coordinate are acquired and calculated by the CCD camera and computer, and the projectile coordinate of X and Y can be gotten through image processing and further calculation. The measuring principle and the formulas are given, and the measuring error is analyzed. The result indicates that the coordinate error of X and Y less than 1.5 and 2.2 mm, respectively, when the detection light screens is 1 m × 1 m, The principle presented has the advantages that measurement principle is simple, low cost and easy engineering.     

On the acoustic field in a Pekeris waveguide with attenuation in the bottom half-space

The acoustic field in a Pekeris channel with an attenuating basement is critically examined, based on contour integrations of the wave number integrals for the two domains. In both regions, the field consists of a finite sum of proper (square integrable) normal modes plus a branch line integral around a hyperbolic cut. For low bottom attenuation, only "trapped" modes exist but as the loss increases additional "dissipation" modes contribute to the mode sum. A Newton-Raphson iterative procedure is introduced for finding the complex eigenvalues of the modes and a new expression is derived which shows that the total number of proper (trapped plus dissipation) modes supported by the waveguide increases essentially linearly with rising bottom attenuation. Approximations for the complex shape functions of the modes in the water column and the basement are developed and compared with the exact shape functions determined from the Newton-Raphson procedure. An expression derived for the modal attenuation coefficient scales in proportion to the square of the mode number and inversely with the square of the frequency. Stationary-phase approximations for the branch line integrals for both domains are developed, which serve to illustrate the asymptotic range dependence of the lateral wave but otherwise have little utility.     

The directivity of a radiating line array slightly deflected from vertical in a waveguide

The azimuth directivity of a line array in a waveguide is studied for the case of its deflection from the vertical under the effect of underwater currents. The modal composition and the interference pattern of the field radiated by such an array is considered.     

一种可稳定计算Pekeris波导中声场的波数积分方法

提出一种可稳定计算Pekeris波导中声场的波数积分方法,并在此基础上开发出一个数值模型,可用于提供Pekeris波导中声场的精确、稳定的数值解。在这个方法中,由于与深度有关的波动方程齐次解中所有的上行波与下行波均采用了合理的归一化表示,从而得到的系统方程是无条件稳定的。在简正波方法中,割线积分一般只对近场有显著影响。因此,传统的简正波模型一般都忽略割线积分对声场的贡献。但是,如果某号简正波离割线非常近,则割线积分对非常远距离的声场仍可能有显著影响。在这种情况下,传统的简正波模型由于忽略割线积分的贡献,从而得到的声场结果是不准确的。本文通过数值算例比较本文提出的波数积分模型与传统的简正波模型。数值结果表明,本文提出的模型可以提供精确、稳定的Pekeris波导中声场的数值解,而在某些情况下传统的简正波模型得到的声场结果是不准确的。因此,本文提出的模型可以作为Pekeris波导中声传播问题的标准模型使用。     

Minimal size of the focal spot when focusing a field in a waveguide using a vertical array

The paper considers the problem of using a vertical array to focus a monochromatic field in the vicinity of a given point of an underwater sound channel. The solution to the problem is discussed, which has been obtained with a limitation on the initial grazing angles of the emitted waves. The limitation is introduced to increase the stability of the solution to the influence of random perturbations of the sound velocity field. Then, the radiated field represents a wave beam propagating along a reference ray that connects the center of the array and the focusing point. In the geometric optics approximation, analytic estimates of the smallest possible dimensions of the focal spot are obtained. A simplified version of the formula is obtained for the vertical scale of the spot convenient for rough express estimates and comparison of the focusing properties of waveguides with different sound velocity profiles.     

Uniform transverse-electric fundamental wave in a symmetric linear multilayer optical waveguide

In the context of a symmetric linear multilayer optical waveguide, a special transverse-electric fundamental (TE(0)) wave is analyzed that has identical amplitudes in the guide core. The guided structural parameters, such as the core thickness, the number of wells, and the ratio of the well thickness to the periodic length, must have specific relationships to one another to form this kind of uniform TE(0) wave. These relationships are investigated, and some field profiles of the uniform TE(0) wave are plotted.