耦合微扰简正波方法与孤立子内波

水平变化环境下声场简正波解的计算精度和效率取决于本地简正波的计算方法。提出一种完备的一阶微扰理论方法,并引入迭代算法,获得了本地简正波水平波数和本征函数的精确表达式。数值结果表明,改进后的微扰简正波方法得到的简正波水平波数和本征函数精度比前人方法更高,与KRAKENC计算结果吻合较好,而计算速度比KRAKENC快100倍。同时将微扰简正波方法与耦合简正波理论结合,应用到海水声速水平变化剧烈的孤立子内波群环境。数值结果表明,该方法计算得到的传播损失与COUPLE07在单次散射近似下的计算结果吻合较好,计算速度比COUPLE07快25倍,并将该方法在声场计算中的适用频率提高到了3 kHz。     

孤立子内波引起的高号简正波到达时间起伏

在新泽西附近海域进行的浅海实验(SW'06)观测到了大量的孤立子内波。利用SW'06海洋环境资料分析了有无孤立子内波存在时的脉冲声到达时间起伏。发现当孤立子内波出现时,1号简正波到达时间较为稳定,而一些高号简正波到达时间比第1号简正波提前,且随着温跃层深度变化而起伏。经射线理论分析表明:由于孤立子内波出现,导致温跃层深度下降,进而引起满足一定掠射角条件的高号简正波将主要在温跃层上传播。这类高号简正波到达时间对孤立子内波活动敏感,有可能被用来监测浅海中的孤立子内波。     

浅海波导中简正波干涉特征频率增强

针对浅海波导中水平线列阵接收的低频宽带低信噪比信号,提出了一种利用多拍信号相干累加来提高干涉简正波特征频谱信噪比的方法。这种方法主要针对未知距离和声源形式的运动声源,对不同时刻(或接收距离)处阵列输出信号进行warping变换,根据干涉简正波的特征频率不变性,通过搜索距离与径向速度的比值来对齐未知距离下warping变换后的谱峰频率,进而通过相干累加来增强信号干涉简正波的特征频率。仿真和海上实验数据分析均验证了方法的性能。     

南中国海海域存在孤立子内波条件下的声场统计特性

利用南中国海浅海海域低频声传播起伏实验中获取的水文数据,结合二维平流模型重构出声传播路径上的动态声速场,使用蒙特卡洛方法研究了有无孤立子内波经过时声传播路径上的声传播损失统计特性,并与实验结果进行了对比分析。仿真和实验结果表明:当孤立子内波经过声传播路径时,声传播损失起伏剧烈;与"下发上收"相比,"下发下收"情况下传播损失的概率分布更加分散。     

浅海中孤立子内波引起的声能量起伏

当孤立子内波的波阵面与声传播路径所成角度较大时,简正波耦合是导致声信号起伏的主要因素。研究了浅海中孤立子内波引起的声能量起伏规律,给出声场起伏的耦合简正波表达式,并使用抛物方程模型进行仿真。数值分析表明,接收点声强随时间变化呈准周期性。在频谱图中能够得到声强起伏的主导频率,主导频率与孤立子内波沿声传播路径的移动速度成正比,与无扰动波导中简正波在距离上的干涉周期(对应于射线理论中临界声线的跨度)成反比,与孤立子内波的形状无关。此外,对声强频谱的垂直结构进行了分析,该结构与对声场起伏起主要作用简正波的本征函数相关。     

短垂直阵简正波匹配的声源定位

声源被动定位的匹配简正波处理是实现远距离水下目标检测的一种重要手段。本文提出的简正波分解快速迭代方法是一种有效的算法,不仅收敛速度快,而且迭代得到的简正波幅度矢量进行定位匹配处理后,提高了声源定位精度、抑制了旁瓣、该方法的最大优点是降低了垂直阵长度的要求,有潜在的实用价值。通过我们对Pekeris浅海声道和北冰洋深海声道的数值模拟,证明这种简正波分解新方法是合理和有效的。93年冬季成功地完成短垂直阵声源定位海上实验。     

多线谱加权的匹配简正波处理声源定位

文献[6]介绍了一种适用短垂直阵的简正波分解快速送代方法,它的最大优点和实用之处是使场匹配技术对垂直阵长度的苛刻要求变得宽容。本文模拟计算用小型快艇辐射噪声线谱作为声源,提出了多线谱加权匹配简正波处理(MMP)声源定位方法。计算表明,这种加权计算方法提高了声源定位的距离估计和深度估计的精度,使模糊平面上的主瓣增高变窄,旁瓣受到有效抑制,优于该艇线谱能量最大的100Hz单线谱的声源定位。     

南中国海存在孤立子内波条件下的声场时间相关半径

在动态的海洋环境中,由于数据向量和拷贝场之间的失配,匹配场处理器的性能会发生退化。数据向量的时间相关半径是这种退化的一种量度。通过2001年ASIAEX南海实验中垂直阵上水听器接收到的声场数据求取了400 Hz窄带信号的声场时间相关。从实验数据处理结果观察到,伴随着传播路径上非线性内波的进入,声场的时间相关半径减小。同时利用一个二维的平流冻结海洋模型和传播路径上三个温度链的温度数据对声场进行了数值仿真,分析了不同频率下的声场时间相关半径。结果表明:实验结果与仿真的400 Hz信号的声场时间相关较为一致。可见,在时变的海洋环境下,声信道中存在孤立子内波将会使声场的时间相关半径大大缩短。     

涡旋中的简正波相速度、群速度和干涉距离的变化

采用声道相积分近似表示的频散方程,并把涡旋(或水团)的作用认为是对声道的一种扰动,讨论无扰声道、冷核和热核涡旋扰动对声传播特性的影响.根据频散方程的解,给出涡旋中的简正波相速度、群速度和干涉距离与涡旋强度的关系.当平面声波(入射掠角α)向热核涡旋(核心强度B_M)的中心推进时,只要sin²α<B_M<2(1-cosα),则声道创面将出现\     

生物大分子中的孤立子激发与分形特性

 本文研究了生物大分子如DNA在ATP水解作用或其它刺激作用下所产生的局域性涨落和结构畸变（如碱基对的相对运动等）所诱导的孤立子激发的特性，以及这种激发与生物大分子的生物能（如DNA的复制等）之间的关系和它的分形、分维特性。     

Broadband interference of received pulse for single normal mode and solitary internal wave localization

To analyze the solitary internal wave(SIW) influence on acoustic field interference pattern and thereby monitor SIW, for broadband pulse signal propagating through SIWs, we adopt a parabolic equation model, and simulate the variation of received single normal mode(SNM) pulse sequence with SIW position, and analyze the spatiotemporal interference characteristics and mechanism of the sequence. Based on the coupled mode theory, we derive the relationship between SIW position and interference striat...     

Estimation and validation of characteristic length of internal solitary wave based on normal mode coupling

For a fluid medium with density stratification, the internal wave is easily observed under disturbance of waves, and the acoustic transmission loss and the characteristic parameters of the internal solitary wave are related. The mathematical relationship between the horizontal wavenumber difference of normal modes and the characteristic length of internal wave is established according to the coupling theory of normal modes. Furthermore, a method for estimating the characteristic length of intern...     

Acoustic normal mode fluctuation statistics in the 1995 SWARM internal wave scattering experiment

In order to understand the fluctuations imposed upon low frequency (50 to 500 Hz) acoustic signals due to coastal internal waves, a large multilaboratory, multidisciplinary experiment was performed in the Mid-Atlantic Bight in the summer of 1995. This experiment featured the most complete set of environmental measurements (especially physical oceanography and geology) made to date in support of a coastal acoustics study. This support enabled the correlation of acoustic fluctuations to clearly observed ocean processes, especially those associated with the internal wave field. More specifically, a 16 element WHOI vertical line array (WVLA) was moored in 70 m of water off the New Jersey coast. Tomography sources of 224 Hz and 400 Hz were moored 32 km directly shoreward of this array, such that an acoustic path was constructed that was anti-parallel to the primary, onshore propagation direction for shelf generated internal wave solitons. These nonlinear internal waves, produced in packets as the tide shifts from ebb to flood, produce strong semidiurnal effects on the acoustic signals at our measurement location. Specifically, the internal waves in the acoustic waveguide cause significant coupling of energy between the propagating acoustic modes, resulting in broadband fluctuations in modal intensity, travel-time, and temporal coherence. The strong correlations between the environmental parameters and the internal wave field include an interesting sensitivity of the spread of an acoustic pulse to solitons near the receiver.     

Broadband nearly-zero ultra-flattened dispersion single mode index guiding holey fiber

This paper proposes and demonstrates a novel type of silica index guiding holey fibers (IGHFs) that has two cladding layers at the defective innermost structures. The proposed IGHFs exhibit remarkable chromatic dispersion properties such as nearly-zero and flattened dispersion over a wide spectral range and single mode guidance along with very low confinement loss. The numerical results indicate that 5 air-hole rings of nearly zero ultra-flattened dispersion single mode IGHFs can be designed with desire flattened dispersion of over a 340 nm bandwidth including the entire band of interest with low confinement loss of less than 10⁻⁶ dB/m.     

Broadband dispersion compensation of conventional single mode fibers using microstructure optical fibers

This paper presents a microstructure optical fiber for dispersion compensation in a wide range of wavelengths. The finite-element method with perfectly matched absorbing layers boundary condition is used to investigate the guiding properties. The designed novel dispersion compensating fiber shows that it is possible to obtain a larger negative dispersion coefficient of about −130 to −360 ps/(nm km), better dispersion slope compensation, better compensation ratio, and lower confinement losses less than 10⁻² dB/km in the entire telecommunication (1400–1600 nm) band by using a modest number of design parameters and very simple cladding design.     

组合KdV方程的双扭结孤立波及其稳定性研究

利用扩展的双曲函数法得到了combined KdV-mKdV (cKdV)方程的几类精确解,其中一类为具有扭结—反扭结状结构的双扭结单孤子解.在不同的极限情况下,该解分别退化为cKdV方程的扭结状或钟状孤波解.理论分析表明,cKdV方程既有传播型孤立波解,也有非传播型孤立波解.文中对双扭结型孤立波解的稳定性进行了数值研究,结果表明,cKdV方程既存在稳定的双扭结型孤立波,也存在不稳定的双扭结型孤立波. 关键词： cKdV方程 双扭结单孤子 稳定性     

耦合KdV方程的双峰孤立子及其稳定性

利用扩展双曲函数法求解了耦合KdV方程,得到了6类精确解,其中一类为具有双峰状结构的单孤子解.在不同的极限情况下,该解分别退化为耦合KdV方程的扭结状或钟状孤波解.文中对双峰孤立波的稳定性进行了数值研究,结果表明:耦合KdV方程的双峰孤立波在长波小振幅扰动和小振幅钟型孤立波扰动下,均稳定. 关键词： 耦合KdV方程 双峰孤立子 稳定性     

New type of an acoustic plate mode: quasi-longitudinal normal wave

A new type of an acoustic wave belonging to the family of the normal plate modes is discovered numerically and verified experimentally in ST, x-quartz plates with free surfaces. It exists within restricted bands of the normalized plate thickness H/λ, where H is the thickness, λ is the wavelength, separated by forbidden H/λ-bands attributed to the common plate modes. Polarization of the wave over the whole plate thickness is almost longitudinal. Velocity of the wave is close to or equal to the velocity of the longitudinal bulk wave, propagating in the same direction. The proximity or/and equality of the velocities is a necessary, but not sufficient condition of the existence of the new wave.