声波在水-多孔介质海底界面上的反射与透射

声波在海底界面的反射和透射是海底散射、海底混响、海底目标探测的重要问题。利用Biot多孔介质声传播理论对声波在水-多孔海底界面上的反射和透射进行了分析,具体给出反射声波的反射系数,3种透射声波的透射系数以及声能透射系数随入射波入射角和频率(10~40 kHz)的变化关系,分析了各种透射波对透射声能的贡献。多孔海底介质参数分别采用Stoll和Chotiros给出的2组参数进行理论计算。     

Analytical Study on Transmission and Reflection of Non-Linear Shallow Water Waves

The analytical study is made by using the method of matched asymptotic expansions on the transmission and reflection of solitary waves and cnoidal waves on two-dimensional floating bodies. The solutions give explicitly the variation pattern of the transmitted waves and the characteristics of the reflected waves, including the wave profile, amplitude, phase shift and evolution. The effects of the gap between the body and the sea bottom on the transmission and reflection of those waves are also discussed.     

运动物体生成内波的一类非线性谱方程组

本文给出了由运动物体所生成内波的基本方程组和对应的谱方程组。该方程组的线性部分是一具有体积源 (其下简称为体源 )的 Sturm- Liouville本征值问题 ,而它的非线性部分是由体源与线性波场相互作用的谱表示。在这类强迫方程的源项中包含了 10类内波谱 ,这些谱最终均可利用内波的振幅谱表示。本文给出了线性波场波要素的谱表示和运动物体生成内波的非线性谱方程可解性的讨论。为了检验所得到的谱方程组 ,文中又进行了该谱方程组线性部分的数值计算。     

Instability of Two Interacting Quasi-Monochromatic Waves in Shallow Water

The nonlinear interactions of waves with a double-peaked power spectrum have been studied in shallow water.The starting point is the prototypical equation for nonlinear unidirectional waves in shallow water,i.e.the Korteweg de Vries equation.By means of a multiple-scale technique two defocusing coupled Nonlinear Schrdinger equations are derived.It is found analytically that plane wave solutions of such a system are unstable for small perturbations,showing that the existence of a new energy exchange mechanism which can influence the behavior of ocean waves in shallow water.     

浅海双跃层脉冲声传播

利用在东海测量的双跃层声速剖面和修改的单跃层声速剖面,数值模拟了2种跃层条件下不同收发深度声脉冲传播的波形。模拟结果表明,当声源或接收器位于上混合层时,信号波形在2种条件下都出现梳状多途结构。当声源和接收器都位于下混合层时,信号波形在2种条件下均相似。当声源位于中间均匀层时,信号波形在除上混合层以外的4层都有显著差异。用简正波的深度-简正波号域的幅度和相应的群速度解释了双跃层和单跃层声速剖面条件下信号波形特点以及异同的原因。     

Nonlinear Effect of Wave Propagation in Shallow Water

—In this paper,a nonlinear model is presented to describe wave transformation in shallow wat-er with the zero-vorticity equation of wave-number vector and energy conservation equation.Thenonlinear effect due to an empirical dispersion relation(by Hedges)is compared with that of Dalrymple＇sdispersion relation.The model is tested against the laboratory measurements for the case of a submergedelliptical shoal on a slope beach,where both refraction and diffraction are significant.The computation re-sults,compared with those obtained through linear dispersion relation.show that the nonlinear effect ofwave transformation in shallow water is important.And the empirical dispersion relation is suitable for re-searching the nonlinearity of wave in shallow water.     

MIMO Underwater Acoustic Communication in Shallow Water with Ice Cover

Although multiple-input multiple-output(MIMO) underwater acoustic(UWA) communication has been intensively investigated in the past years, existing works mainly focus on open-water environment. There is no work reporting MIMO acoustic communication in under-ice environment. This paper presents results from a recent MIMO acoustic communication experiment which was conducted in Bohai Gulf during winter. In this experiment, high frequency MIMO signals centered at 10 kHz were transmitted from a two-element source array to a four-element vertical receiving array at 1 km range. According to the received signal of different array elements, MIMO acoustic communication in under-ice environment suffers less effect from co-channel interference compared with that in open-water environment. In this paper, time reversal followed by a single channel decision feedback equalizer is used to process the experimental data. It is demonstrated that this simple receiver is capable of realizing robust performance using fewer hydrophones(i.e. 2) without the explicit use of complex co-channel interference cancelation algorithms, such as parallel interference cancelation or serial interference cancelation.     

Effects of Topography and Current on Horizontal Irrotational Waves in Shallow Water

Based on the Boussinesq assumption,derived are couple equations of free surface elevationand horizontal velocities for horizontal irrotational flow,and analytical expressions of the correspondingpressure and vertical velocity.After the free surface elevation and horizontal velocity at a certain depth areobtained by numerical method,the pressure and vertical velocity distributions can be obtained by simplecalculation.The dispersion at different depths is the same at the O(ε)approximation.The waveamplitude will decrease with increasing time due to viscosity,but it will increase due to the matching ofviscosity and the bed slope.thus,flow is unstable.Numerical or analytical results show that the waveamplitude.velocity and length will increase as the current increases along the wave direction.but theamplitude will increase.and the wave velocity and length will decrease as the water depth decreases.     

Nonlinear Wave Force on Pier Group in Shallow Water

Based on the 1st order cnoidal wave theory, the wave diffraction around the pier group inshallow water is studied in this paper. The formulas for calculating the nonlinear wave forces are also presented here. In order to verify the theoretical results, model tests are conducted in the wave flume in The State Key Laboratory of Coastal and Offshore Engineering located in Dalian University of Technology. The range of the wave parameters in the experiments is characteristic wave period T g/d~(1/2) = 8.08- 22.86, characteristic wave height H/ d= 0.1 ~ 0.45. The results obtained from the experiments agree with the theoretical results quite well. It is shown that, in shallow water the nonlinear wave forces acting on a pier group are greater than those calculated by linear wave theory, the value of increment in wave force increases with the increases of the nonlinearity of the wave. In the wave range studied in this paper, the nonlinear wave force can reach over 4 times the force calculatecd by linear wave theory. Thus, it is suggested that, when Tg / d~(1/2)> 8, the wave force on the piers in the pier group in shallow water should be calculated by using the cnoidal wave theory.     

Influence of Nonlinear Interaction on the Evolution of Waves in a Shallow Basin

Izvestiya, Atmospheric and Oceanic Physics - The influence of nonlinear interaction of oppositely directed nonlinear waves in a shallow basin is studied theoretically and numerically within the...     

Theoretical and Experimental Study on the Acoustic Wave Energy After the Nonlinear Interaction of Acoustic Waves in Aqueous Media

Based on the Burgers equation and Manley?Rowe equation, the derivation about nonlinear interaction of the acoustic waves has been done in this paper. After nonlinear interaction among the low-frequency weak waves and the pump wave, the analytical solutions of acoustic waves’ amplitude in the field are deduced. The relationship between normalized energy of high-frequency and the change of acoustic energy before and after the nonlinear interaction of the acoustic waves is analyzed. The experimental results about the changes of the acoustic energy are presented. The study shows that new frequencies are generated and the energies of the low-frequency are modulated in a long term by the pump waves, which leads the energies of the low-frequency acoustic waves to change in the pulse trend in the process of the nonlinear interaction of the acoustic waves. The increase and decrease of the energies of the low-frequency are observed under certain typical conditions, which lays a foundation for practical engineering applications.     

水槽中浅水非线性长波传播的 Boussinesq 数值模拟

浅水非线性长波传播变形中会产生波-波相互作用,为较好地模拟这种现象,在非交错网格下建立了近似在阶完全非线性的高阶 Boussinesq 数值模型.数值模型中采用了混合 4 阶 Adams- Bashforth -Moulton 格式和内部造波技术.数值计算了非线性长波在波浪水槽中的传播变形,计算结果与相关实验数据吻合较好,验证了该数值模型实用性.     

浅海环境水声传播数据实测与仿真分析

搭建了一套水下录音记录系统,在复杂浅海环境进行了水声数据采集实验;对于水声采集数据进行了距离、频率谱分析,利用MIT开发的声学计算程序OASES针对声场进行了仿真分析。通过模拟结果和实测结果的比较,优化调整仿真程序的环境参数,分析发现影响声场分布的主要因素为沉积层压缩波声速与声源深度。通过这种方式,优化了仿真软件的环境参数,初步建立了比较准确的浅海水声环境仿真模型,取得了预期实验效果。     

The Influence of Emitter and Receiver Motion on Acoustic Coherence in Shallow Water

This paper is aimed at studying the source and receiver motion effects on the energy and correlation characteristics of the acoustic field in shallow water. The statistical analysis is based on the radiation transport equation for the mutual coherence function (MCF) of the multimodal Doppler-shifted field. A general computer program has been elaborated to implement this theory for rough surface scattering by fully developed wind seas. Calculations of the expected total average acoustic intensity and two-point coherence function are presented.      

南黄海非线性内波的数值模拟研究(2)——内潮的非线性演变

在本工作的先行部分的基础上,本文中考虑第一模态半日内潮波分别从A站位(34°4′N,125°6′E)和B站位(36°34′N,123°51′E)向西、西南和西北方向的反射和非线性演变过程,使用的数学物理模型为适用于连续层化海洋并且考虑背景正压落潮流与涨潮流不同作用的一般化的KdV模型(简称之为GKdV模型)。模拟结果表明,南黄海的内孤立波集中分布于南黄海的南部,而在其北部极少出现内孤立波的主要原因是在南黄海的南部存在较强的背景斜压环流和很强的背景正压潮流,而且在涨潮时段(相对于朝鲜半岛的西海岸而言)背景斜压环流和背景正压潮流的方向基本相同,而在南黄海的北部这2种背景流都很弱。另外,由于出现高达0.75 m/s的正压潮流,自A站位向西北方向传播的半日内潮波处于不稳定状态。     

The Nonlinear Wave Force on a Circular Cylinder in Shallow Water

Based on the 1st order cnoidal wave theory, the nonlinear wave diffraction around a circular cylinder in shallow water is studied in this paper. The equation of the wave surface around the cylinder is formulated and by using this formula the wave surface elevation on the cylinder surface can be obtained. In this paper, the formula for calculating the cnoidal wave force on a circular cylinder is also derived. For the wave conditions which are often encountered in practical engineering designs, the ratios of the nonlinear wave forces to the linear wave forces are calculated, and the results are plotted in this paper for design purposes. In order to verify the theoretical results, model tests are conducted. After comparing the test results with the theoretical ones, it is concluded that, in shallow water, for the case of T g / d~(1/2) > 8-10 and H / d > 0.3, the cnoidal wave theory should be used to calculate the wave action on a cylindrical pier.     

Asymmetry of Jet Streams Formed under Nonlinear Geostrophic Adjustment in Shallow Water

Oceanology - The process of geostrophic adjustment in a rotating layer of shallow water is considered. For initial distributions of the fluid depth in the form of a step and a localized rectangle,...     

2005黄海声学实验-声传播起伏

2005年夏末、秋初在黄海南部进行一次多家联合海洋声学实验研究,主要目的是研究浅海内波(线形、非线性)及其海洋温度峰面对远距离声传播的起伏效应及其声学方法监测海洋新方法研究。文章综述这几年实验数据处理的一些结果。     

Transformation of the Indonesian Throughflow Water by Vertical Mixing and Its Relation to Tidally Generated Internal Waves

Numerical experiments with two-dimensional nonhydrostatic model have been performed to investigate tidally generated internal waves at the Dewakang sill at the southern Makassar Strait where two large-amplitude “bumps” of relatively shallow water exist. We investigate the effect of these features on vertical mixing, with emphasis on the transformation of the Indonesian throughflow (ITF) water properties. The result shows that large-amplitude internal waves are generated at both bumps by the predominant M₂ tidal flow, even though the condition of the critical Froude number and the critical slope are not satisfied. The internal waves induce such vigorous vertical mixing in the sill region that the vertical diffusivity attains a maximum value of 6 × 10⁻³ m²s⁻¹ and the salinity maximum and minimum core layers characterizing the ITF thermocline water are considerably weakened. Close examination reveals that bottom-intensified currents produced mainly by the joint effect of barotropic M₂ flow and internal tides generated in the concave region surrounding both bumps can excite unsteady lee waves (Nakamura et al., 2000) on the inside slopes of the bumps, which tend to be trapped at the generation region and grow into large-amplitude waves. Such generation of unsteady lee waves does not occur in case of one bump alone. Trapping and amplification of the waves in the sill region induce large vertical displacements (∼60 m) of water parcels during one tidal period, leading to strong vertical mixing there. Since the K₁ tidal currents are relatively weak, large-amplitude internal waves causing intense vertical mixing are not generated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Numerical Simulation of Nonlinear Three Dimensional Waves in Water of Arbitrary Varying Topography

—The numerical simulation is based on the authors＇high-order models with a dissipative termfor nonlinear and dispersive wave in water of varying depth.Corresponding finite-difference equations andgeneral conditions for open and fixed natural boundaries with an arbitrary reflection coefficient and phaseshift are also given in this paper.The systematical tests of numerical simulation show that the theoreticalmodels,the finite-difference algorithms and the boundary conditions can give good calculation results forthe wave propagating in shallow and deep water with an arbitrary slope varying from gentle to steep.