基于柱坐标系抛物方程和矩量法的电波传播混合算法

针对包含近源障碍物条件下的电波传播问题,提出了一种新颖的电波传播预测混合建模方法:矩量法(MOM)和圆柱坐标系抛物方程法(PEM)混合建模方法(MOM-PEM);MOM用于包含辐射源和近源障碍物的小圆柱区域内的电波传播建模,PEM用于MOM计算空间外的大区域范围内电波传播建模。MOM和PEM的计算过渡区域进行精细化网格剖分处理以避免场强数值传递的不兼容。仿真模拟了三类近源障碍物存在场景下的电波传播问题:有限开窗屏障碍物、立方体障碍物以及包含辐射源的半封闭空间障碍物,并将混合算法计算得到的结果和相同环境下采用全矩量法计算得到的结果进行了数值对比,结果表明混合算法和矩量法在精度上吻合较好。     

Generating ultra wide low-frequency gap for transverse wave isolation via inertial amplification effects

Low-frequency transverse wave propagation plays a significant role in the out-of-plane vibration control. To efficiently attenuate the propagation of transverse waves at low-frequency range, this letter proposed a new type phononic beam by attaching inertial amplification mechanisms on it. The wave propagation of the beam with enhanced effective inertia is analyzed using the transfer matrix method. It is demonstrated that the low-frequency gap within inertial amplification effects can possess much wider bandwidth than using the local resonance method, thus is more suitable for designing applications to suppress transverse wave propagation.     

Wave mode diffusion and propagation in structural wave guide under Varying Temperature

A numerical approach is presented to study the guided wave propagation through periodic specimen with thermal dependence of material properties. There is a great interest in extending the skills of the wave finite element (WFE) method to figure out the variations in the wave propagation properties due to temperature fluctuations. Thermal effects on the dispersion curves thereby on group velocity are discussed. Comparisons between numerical results and analytical developments for various temperatures are given to prove the effectiveness of the proposed approach to predict the sensitivity of guided wave propagation characteristics in presence of temperature variations.     

扩散平板光波导的等效阶跃平板波导方法

本文引入一种研究扩散光波导传播特性及设计计算的新方法——等效阶跃平板波导方法.建立了扩散平板光波导的等效阶跃平板波导模型,进行了一系列的模拟计算,得出了一系列波导传播参量、结构参量与工艺参量之间的关系曲线.这些曲线对于扩散平板光波导的设计计算、工艺参量选择等具有重要指导意义.     

Laser ultrasonic anomalous wave propagation imaging method with adjacent wave subtraction: Application to actual damages in composite wing

Laser ultrasonic wave propagation imaging methods have great potential for integrated structural health management and non-destructive evaluation. However, application of these techniques to complex structures in the field is difficult because they give rise to complicated wave propagation patterns. We developed an anomalous wave propagation imaging method with adjacent wave subtraction using laser ultrasonic scanning to solve this problem. The proposed method is suitable for non-destructive evaluation of complex structures because it highlights the propagation of anomalous waves related to structural discontinuities, and suppresses complex incident waves without the need of pre-stored reference data. In this study, the method was applied to a real composite wing subjected to bending and impact tests. The method enhanced the visibility of the anomalous waves related to damages such as stringer tip debonding, skin-spar debonding, and invisible impact damage. Based on these anomalous waves, variable time window amplitude mapping was performed to show the damage location, size, and shape resemble to the actual damage. Comparisons showed that the methods performed better than the ultrasonic A-scan in terms of damage detection and sizing accuracy. The presence of structural elements such as spars, stringers, ribs, and surface-mounted PZT elements did not adversely affect the inspection. The proposed wing test setup with a built-in ultrasonic propagation imaging system for automatic NDE could be easily expanded throughout a hanger for maintenance inspection.     

气动光学效应湍流脉动模型系数修正

以光学窗口的气动光学效应研究为背景,研究影响光学传输预测的流场湍流脉动量预测.选取平板、压缩拐角、凹腔流动模型,采用大涡模拟（LES）方法研究超声速湍流脉动工程预测模型的系数修正.结果表明：LES方法能够获得无激波干扰、强激波干扰及底部大分离条件下,湍流密度脉动的定量分布,并据此给出脉动工程模型的系数修正,结果已经应用于型号飞行器的光学窗口气动光学效应预测.     

The dynamic analysis of a cracked Timoshenko beam by the spectral element method

The aim of this paper is to introduce a new finite spectral element of a cracked Timoshenko beam for modal and elastic wave propagation analysis. The proposed approach deals with the spectral element method. This method is suitable for analyzing wave propagation problems as well as for calculating modal parameters of the structure. In the paper, the results of the change in modal parameters due to crack appearance are presented. The influence of the crack parameters, especially of the changing location of the crack, on the wave propagation is examined. Responses obtained at different points of the beam are presented. Proper analysis of these responses allows one to indicate the crack location in a very precise way. This fact is very promising for the future work in the damage detection field.     

利用光谱技术研究硝基甲烷快速反应波传播

本文利用研制的光谱技术，在爆炸激波管中成功地研究了硝基甲烷和氧混合物快速反应波传播的微观特性。光谱测量结果说明：ＯＨ基和Ｈ_２Ｏ、ＮＨ_３的辐射没有发生明显改变，ＣＨ_３Ｏ、ＣＨ、ＮＯ_２、ＣＯ_２、ＮＯ、ＨＣＮ的辐射随反应波传播距离的增加而增长；但是ＣＯ和ＣＨ_２Ｏ的辐射呈倒“Ｕ”型曲线。本文的研究为我国开展含能材料快速反应微观机理的研究探索到一个方法，这种方法投资不大，而且行之有效。     

地震波传播路径追踪的波动方程方法

在地震勘探的地震波传播研究中,波场传播路径追踪是一项重要研究内容,通常采用射线理论追踪地震波传播路径.提出一种波动方程波场传播路径追踪方法,首先利用窗口Fourier框架展开技术对源点和目标点的波场进行角度分解,并计算它们的方向照明,然后利用角度相干技术获取源点和目标点间的波场传播路径.该方法可以有效考虑地下非均匀介质对地震波场传播的聚焦与散焦作用.     

Solving the time-dependent Schrödinger equation by combining smooth exterior complex scaling and Arnoldi propagator

Abstract We develop a highly efficient scheme for numerically solving the three-dimensional time-dependent Schr?dinger equation of the single-active-electron atom in the field of laser pulses by combining smooth exterior complex scaling(SECS)absorbing method and Arnoldi propagation method.Such combination has not been reported in the literature.The proposed scheme is particularly useful in the applications involving long-time wave propagation.The SECS is a wonderful absorber,but its application results in a non-Hermitian Hamiltonian,invalidating propagators utilizing the Hermitian symmetry of the Hamiltonian.We demonstrate that the routine Arnoldi propagator can be modified to treat the non-Hermitian Hamiltonian.The efficiency of the proposed scheme is checked by tracking the time-dependent electron wave packet in the case of both weak extreme ultraviolet(XUV)and strong infrared(IR)laser pulses.Both perfect absorption and stable propagation are observed.     

Characterizing the properties of ultrasonics propagating on the surface of materials with defect by Laser-ultrasonics method

A laser ultrasonics method is used to characterize the propagation properties of surface wave traveling on the surface of materials with sub-surface defect in 2D.Linear and nonlinear propagation properties of ultrasonics caused by the defects have been detected in experiment. A theoretical model is proposed and used to study the linear and nonlinear properties of ultrasonics caused by the defect.The numerical results indicate that the nonlinear ultrasonic wave will be excited when a finite amplitude ultrasonics propagates on the surface of materials with sub-surface defect.The theoretical analysis confirms that the nonlinear wave is caused by the "clapping"of the interface of defect instead of the mode conversions of ultrasonics.     

Singular perturbation method for short waves in random media

The problem of wave propagation in a randomly inhomogeneous medium is considered on the basis of the parabolic equation approximation. The method of asymptotic expansions construction in powers of the radius of correlation of the random media for the moments of the wave field are proposed.     

Single frequency sound propagation in flat waveguides with locally reactive impedance boundaries

A coherent image source method is presented for evaluating single frequency sound propagation from a point source in a flat waveguide with two infinite and parallel locally reactive boundaries. The method starts from formulating reflections of the spherical sound radiation into integrals of plane wave expansion, and the analytical evaluation of the integrals is simplified by introducing a physically plausible assumption that wave front shapes remain the same before and after each reflection on a reflective boundary. The proposed model can determine coherently the sound fields at arbitrary receiver locations in a flat waveguide, even when one boundary is highly sound absorptive. Being compared with the classical wave theory and the existing coherent ray-based methods, it is shown that the proposed method provides considerable accuracy and advantages to predict sound propagation in flat waveguides with a sound absorptive ceiling and a reflective floor over a broad frequency range, particularly at large distances from the source where the existing methods are problematic.     

基于纳米天线的多通道高强度定向表面等离子体波激发

设计了一种带有纳米天线的金属微腔结构, 以实现高强度表面等离子的定向激发. 在利用双狭缝结构实现表面等离子体波定向激发的基础上, 分别结合共振增强和干涉相长原理, 在传统结构的入射端面上添加纳米天线结构, 并增加狭缝通道数, 实现了定向激发的表面等离子体波的能量增强. 基于纳米天线的多通道高强度定向表面等离子体波激发装置结构简单, 系统紧凑, 并能够有效提高定向传播的表面等离子体波的能量密度和传播距离, 其对微纳光学传输和高密度光学集成领域等方面的研究具有重要意义.     

二元复合波片延迟相位方位效应探讨

在多级波片方位效应的基础上，探讨了复合波片的方位效应问题。通过对多级波片的设计与测量，论证了入射光方位是影响波片延迟量的关键因素。     

Large-eddy simulation of MILD combustion using partially stirred reactor approach

Subgrid-scale (SGS) parameterization and method for calculating filtered reaction rate are critical components of an accurate large-eddy simulation (LES) of turbulent flames. In this study, we integrate gradient-type structural SGS models with a partially stirred reactor approach by using detailed chemical kinetics to simulate a turbulent methane/hydrogen jet flame under moderate or intense low-oxygen dilution (MILD) conditions. The study examines two oxygen dilution levels. The framework is assessed through a systematic and comprehensive comparison of temperature, and mass fractions of major and minor species with experimental data and other reference simulation results. Overall, the statistics of the combustion field show excellent agreement with measurements at different axial locations, and a significant improvement compared to some previous simulations. It suggests that the proposed nonlinear LES framework is able to accurately model MILD combustion with reasonable computational cost.     

Analysis of plasma sheath propagation attenuation based on ray tracing

Based on the complex Snell's law of lossy media, a ray tracing method is proposed to study the propagation attenuation characteristics of electromagnetic (EM) waves in plasma sheaths. The plasma sheath is modelled as layered media. This method considers the complex ray characteristics of inhomogeneous plane EM waves, tracks the propagation rays of EM waves in each layer of media, and calculates the propagation attenuation of EM waves in each layer of media according to the propagation direction of the complex rays. The attenuation during numerical cumulative propagation is the total attenuation of EM waves through the plasma sheath. By comparing the results with that obtained from the WKB method, the accuracy of the ray tracing algorithm is proved. The results of the propagation attenuation of a blunt cone model are calculated by the proposed method, and the effects of different parameters on the EM wave propagation attenuation in the plasma sheath are analysed at different heights, velocities, incident angles, and incident positions. Studying the propagation characteristics of EM waves in the plasma sheath is of importance in application for radar target tracking, blackout communication, and other issues.     

双横波声速法检测单向受压混凝土构件永存应力*

该文力求寻找一种高效准确检测混凝土构件永存应力的方法。基于声弹性理论提出了一种双横波声速法检测单向受压混凝土构件永存应力的方法,该方法通过测试受力构件第一波速和第二波速,以第一波速和第二波速的平方差为基础构建综合声学参数来检测单向受压混凝土构件永存应力。所述第一波速为声波传播方向与应力方向垂直、质点振动方向与应力方向平行的横波波速,第二波速为声波传播方向及质点振动方向均与应力方向垂直的横波波速。实验结果显示,该声学参数用于检测混凝土单向受压构件永存应力的效果与使用单一声速参数相比,对应力的敏感性有所提高,受混凝土黏滞性及材质离散性的影响更小,并且测试结果基本不受温度和湿度变化影响。     

多尺度有限差分法模拟复杂介质波传问题

利用有限差分和紧支集正交小波变换对波动方程的时间、空间进行联合近似求解,提出一种适合于一般边界非均匀耗散介质中波传问题数值模拟的快速自适应混合算法——多尺度有限差分(multiresolution finite difference缩写为MRFD)方法.将波传问题的求解转换到小波域中进行,利用小波基的自适应性与消失矩特性,使偏微分算子矩阵稀疏化,有效改善了计算量等.地球物理勘探中的数值实例显示了算法具有良好效率 关键词： MRFD 小波变换 多尺度 波传问题