管壁上缝隙对管内声传播的影响

本文在对管壁上有缝隙时管内声场的理论分析基础上得出为计算管内声波传播的等效线路。当缝隙的尺度远小于波长时缝隙用集总参数的阻抗表示。这阻抗包括缝隙本身的阻抗和局部声场扰动引起的质量抗。文中给出矩形缝隙的具体结果并讨论了声源的作用。     

Effect of a sloping bottom on sound propagation

Acoustical Physics - The paper presents the results of field measurements of acoustic fields generated in autumn hydrological conditions of the Sea of Japan shelf by a TON-320Hz autonomous signal...     

Study on propagation properties of a radially polarized partially coherent dark hollow beam through a high numerical aperture lens

In recent years the partially coherent beams have attracted very much due to novel properties and its applications. In this paper the tight focusing properties of radially polarized partially coherent dark hollow beam (DHB) through a high numerical aperture lens are investigated numerically based on vectorial Debye theory in detail. The result shows that the optical intensity distribution in the focal region directly fluctuates due to small change in coherence length and high numerical aperture angle of the focused radially polarized partially coherent DHB.     

通过有光阑近轴ABCD光学系统激光束的近似解析传输公式

用傅立叶级数展开法研究光束通过有光阑限制的近轴ABCD光学系统的传输特性,导出了光阑透射率函数不同时的传输公式。硬边光阑的情况可作为其它光阑的特例得到,其它光阑也可视作硬边光阑来处理。数值计算表明了该方法快速的优点,并得到与用Collins公式直接积分一致结果。     

Recurrence propagation equation of Hermite-Gaussian beams through a paraxial optical ABCD system with hard-edge aperture

Based on the generalized Huygens-Fresnel diffraction integral, a recurrence propagation equation of Hermite-Gaussian (H-G) beams through a paraxial optical ABCD system with hard-edge aperture is derived, which permits us to obtain the analytical propagation expression for H-G beams of any order. The advantages of our analytical results are analyzed, and the application is illustrated with numerical examples.     

Tune调制对HIRFL-CSRm动力学孔径影响的模拟研究

通过引进包含tune调制的传输矩阵,模拟计算了由四极铁电源纹波所引起的tune调制对HIRFL-CSRm动力学孔径的影响。模拟计算中,对HIRFL-CSRm实际(lattice)跟踪1.0×106圈。从结果可以看出,动力学孔径随调制振幅的增大迅速减小,大体呈线性变化;动力学孔径随调制tune值的变化在研究范围内也有变化,变化的范围在0.049~0.089 m之间。     

Tune调制对HIRFL-CSRm动力学孔径影响的模拟研究

 通过引进包含tune调制的传输矩阵,模拟计算了由四极铁电源纹波所引起的tune调制对HIRFL-CSRm动力学孔径的影响。模拟计算中,对HIRFL-CSRm实际(lattice)跟踪1.0×10⁶圈。从结果可以看出,动力学孔径随调制振幅的增大迅速减小,大体呈线性变化;动力学孔径随调制tune值的变化在研究范围内也有变化,变化的范围在0.049~0.089 m之间。     

Simultaneous measurement of sound velocity and wall thickness of a tube.

A method for simultaneously measuring the sound propagation velocity and the thickness of each wall on the opposite sides of a tube is presented. The method uses a pair of ultrasound transducers to produce two reflected pulses from the outer and inner surfaces of the tube wall on the each side, and two transmitted pulses, one with and one without the tube sample between the two transducers. Using the time-domain analysis, sound velocity and wall thickness of the tube are determined from the time delays between the three pairs of ultrasound pulses, whereas using the frequency-domain analysis, phase velocity, group velocity, and wall thickness of the tube are determined from the phase differences between the three pairs of ultrasound pulses. Results of measurements on five tube samples are reported.     

The aperture effect on the propagation of partially polarized Gaussian Schell-model beams

Based on the beam coherence-polarization (BCP) matrix approach and propagation law of partially coherent beams, the propagation of partially polarized Gaussian Schell-model (PGSM) beams through an aperture is studied. Numerical calculation results are given to illustrate the propagation-induced polarization changes and irradiance distribution of PGSM beams for the apertured case.     

上下行传输孔径接收光强起伏特性分析

为了研究地星上行和星地下行激光链路孔径内接收光强信号的典型特征,基于大气湍流理论和位相屏方法,计算了短波和中波红外激光在特定大气相干长度条件下,孔径内接收激光功率与总功率的比值及起伏情况。根据统计结果讨论了上下行大气通道传播特性的差异,结果表明相同外界条件下,直径50 cm孔径内接收的下行激光信号强度大于上行激光信号强度1个数量级以上,其信号的起伏程度也低于上行激光;中等湍流下,下行激光孔径接收光强的概率分布函数服从对数正态分布,最大概率接收功率比与无湍流条件下的功率比值一致,分别为0.42%(1.315 m)和 0.26%(3.8 m)。     

大气声传播通道的声源当量估计方法

提出了一种基于大气声传播通道的爆炸声源能量估计方法,通过将计算大气声学的传播能量分布结果与大气中传播的声压幅度衰减模型相结合,使用平流层通道与热层通道传播损失能量比例作为修正量,提高了对爆炸声源能量的估计精度。在多次地面爆炸实验得到的数据中,使用观测距离800 km以上且同时存在平流层通道与热层通道的次声接收信号,对比了平流层顶风速修正的能量估计方法与该文提出的基于大气声传播通道的能量估计方法。实验结果验证了相对于传统风速修正的能量估计方法,该方法可显著降低估计误差。     

Effect of Mesoscale eddies on underwater sound propagation

The effects of sound speed variables induced by an anticyclonic eddy and a field of three cyclonic eddies on long-range sound propagation are investigated respectively. A deep-sea analytical eddy model [Henrick RF, Siegmann WL, Jacobson MJ. General analysis of ocean eddy effects for sound transmission applications. J Acoust Soc Am 1977;62:860-870] is used to determined sound speed distributions produced by warm-core ring in the southwest of South China Sea. Furthermore, the above analytical eddy model is generalize to include the azimuth angle variation and is used to determined sound speed distributions produced by Gulf Stream rings with different strengths. The theoretical temperature fluctuations induced by the warm eddy and a eddy field including three cyclonic eddies agree qualitatively with the in situ investigation data. The transmission loss of acoustic energy through the cross section of the warm-core ring center and three cyclonic eddy centers is simulated using 2-D parabolic-equation (PE) numerical modeling. It is found that the acoustic field has a significant change with variation of the location of SOFAR axis in the presence of the warm eddy and three cyclonic eddies comparing with the scenario of no eddies. When the source is located in the outside of the warm-core eddy and three cyclonic eddies respectively, and the receiver is located in outside of the eddy, the transmission loss as a function of range is investigated at different receive depth. It is shown that the changes of transmission loss caused by the warm-core eddy and three cyclonic eddies are as much as 20 dB than that of no-eddy situation. In the case of three cyclonic eddies, the largest discrepancy of transmission loss is about 40 dB near the range of 45 km for a 25-Hz source being located at a depth of 1500 m.     

一类与椭圆和矩形相关的孔径的夫琅禾费衍射研究

依据一类与椭圆和矩形相关的几何形状孔径的数学模型及其傅里叶变换，得出了其夫琅禾费衍射光场分布的一维积分表达式及其衍射图样，应用特征说明；在椭圆和矩形的特例情况下，其夫琅禾费衍射解析解与其他献相一致；通过分析衍射图样的特征，指出了边的形状和角的存在与否对衍射图样有着巨大的影响。     

Analytical propagation expression of elliptical Gaussian beams through nonsymmetric systems with an elliptical aperture

A tensor form for describing approximately the elliptical aperture function is defined that can be expanded into a finite sum of complex Gaussian functions. An analytical propagation formula of elliptical Gaussian beams through nonsymmetric and paraxial optical systems with an elliptical aperture is obtained by using tensor method. A simple numerical example is given to illustrate for its applications.     

海洋内波对水下声场的影响

海洋内波是海水内部的波动之一,它与海洋表面的海浪运动有着非常不同的物理特征。海洋内波会引起海水温度剖面发生剧烈的波动,这种波动具有很强的方向性和时变性,对水下声传播影响巨大,并展现出一些很奇特的声波导效应(包括二维波导效应和三维波导效应),给水下目标的探测与定位以及水声通信等带来严重影响。海洋内波对声场的影响研究涉及到海洋动力学和水声学两个学科领域,文章重点介绍海洋内波对声场影响研究领域的相关进展,并对内波环境下典型声波导现象进行了讨论,最后对该领域未来的发展进行了总结和展望。     

伪部分相干高斯-谢尔模型光束在湍流大气中传播的闪烁孔径平滑效应

采用光传播的数值模拟方法, 对伪部分相干高斯-谢尔模型光束大气传播过程进行数值模拟, 统计分析不同接收口径内的光强起伏特性,计算闪烁的孔径平滑因子, 讨论了表征伪部分相干光的调制相位屏的相对变化频率对闪烁指数的影响, 并将其与充分发展的部分相干高斯-谢尔模型光束及完全相干光的闪烁指数对比. 结果表明: 降低光源相干性可大幅度降低闪烁指数, 但同时其闪烁指数的孔径平滑效应减弱, 在相同接收孔径下, 伪部分相干光闪烁指数的孔径平滑效果要比完全相干光差; 增大调制相位屏的相对变化频率可在一定程度上降低闪烁指数, 随着其相对频率的增大, 伪部分相干光的闪烁指数与部分相干光的结果趋于一致. 关键词： 伪部分相干高斯-谢尔模型光束 湍流大气 孔径平滑闪烁指数 数值模拟     

高斯光束照射下与矩孔相关的孔径衍射

依据基尔霍夫衍射理论,利用幂级数展开的方法,推导出傍轴条件下高斯光束的矩孔及单缝衍射的近似计算公式,并通过数值计算、数值模拟等方法对衍射场的基本特性进行了讨论。     

Effects of a wall on the self-ignition patterns and flame propagation of high-pressure hydrogen release through a tube

High-pressure hydrogen gas is gaining more attention as the next-generation energy carrier, but its safe handling and storage remains an important issue. The possibility of self-ignition near an obstacle is a realistic concern in practical applications such as a hydrogen car, but only a few studies related to this issue have been conducted. In this paper, experimental investigations were carried out to understand the effects of a wall on ignition patterns by high-speed imaging. This study was conducted using extension tubes of different lengths at burst pressures up to 30 MPa. The wall height, distance of the wall from the tube exit and the burst pressure were considered as the main wall parameters affecting self-ignition. The results showed that the existence of a wall could not change the type of ignition patterns (i.e., the wall does not initiate or extinguish a flame) regardless of the wall height and burst pressure, but only when the tube was too short to generate a strong flame inside the tube. When the tube was long enough to induce a strong flame in the tube, however, the wall promoted flame stabilization, e.g., the flame stabilization time outside the tube was shortened by locating the wall near the tube. But its effect disappeared when the distance of the wall from the tube exceeded 10D.     

光学薄膜诱导偏振像差对大数值孔径光学系统聚焦特性的影响

大数值孔径光学系统表面光线的入射角较大, 会导致薄膜的偏振分离, 诱发偏振像差, 影响光学系统的聚焦特性. 本文利用矢量光衍射理论, 建立了光学薄膜各参量与光学系统聚焦光场的模型. 利用该模型分析了线偏振光入射时, 光学薄膜对光学系统聚焦光斑的扰动. 在此基础上, 探讨了应用了不同约束条件下得到的光学薄膜对最终聚焦光场的影响, 确定了减小薄膜扰动光学系统光斑的设计方法, 即额外添加透射率差和位相差的约束条件, 并且适当增加位相差约束的权重. 利用该方法优化设计的薄膜, 相比于普通减反膜而言, 对系统聚焦光场中心强度的提升可达约12.5%.     

Nonparaxial diffraction of vectorial plane waves at a small aperture

By using the vectorial Rayleigh diffraction integrals, a nonparaxial propagation equation of vectorial plane waves diffracted at a small rectangular aperture is derived analytically and some special cases are discussed. Numerical calculation results are given to illustrate the applicability and validity of our theoretical formulae. It is shown that for the apertured case the ratio of the aperture width and wavelength affects the beam nonparaxiality. The nonparaxial approach presented in this paper has to be used for diffracted plane waves if the aperture width is comparable with or less than the wavelength.