基于行波分离和角度域衰减的地震波叠前逆时成像条件

为提高陡倾角复杂构造区地震波逆时成像质量,提出一种逆时偏移成像条件.以二维模型为例,采用波印廷矢量实现方向行波的波场分离和地层反射角度的计算,将炮点和检波点的上行波场和下行波场、左行波场和右行波场两两作互相关计算,去除形成逆时偏移噪声的分量,同时将反射角度的余弦函数作为权函数引入互相关逆时成像条件中,进一步实现角度域逆时噪声的衰减.研究表明,炮点和检波点相反传播方向波场的互相关计算是形成偏移噪声的主要原因,相同传播方向的行波波场两两作互相关成像并组合叠加,可以在有效压制偏移噪声的同时,保持对陡倾角和水平界面的成像能力,再在角度域实现逆时噪声衰减,进一步提高逆时成像质量,实际地震资料验证了方法的有效性.所提的逆时成像条件可为复杂构造区高精度逆时成像提供重要的方法指导.     

波动方程角度域偏移成像

在共炮集数据的波动方程深度偏移成像中,利用常规的波场传播算子进行检波点波场和震源波场的向下传播,在各个深度层借助波场的窗口Fourier框架展开,得到局部角度域的检波点波场和震源波场,然后应用偏移成像原理,提出了共炮集数据的波动方程角度域偏移成像方法.通过角度域偏移成像,可以得到地下成像点处的角度域成像矩阵以及共地层倾角偏移成像剖面和共反射角偏移成像剖面.也可为基于偏移成像的后续处理方法技术,如振幅随角度变化分析处理、角度域共成像道集提取和角度域速度分析,提供基础资料.以陡倾角模型和国际标准的Marmousi模型为数值试验例子,验证了波动方程角度域偏移成像方法的正确性和有效性.     

基于波前传播时间插值的三维声线追踪算法

研究了先正向计算波前传播时间,再根据波前传播时间反向确定声线路径的三维非均匀介质声线追踪算法。在正向步骤,根据程函方程,使用基于水平集的GMM(Group Marching Method)波前扩展算法,从声源开始,逐步计算离散介质网格节点上的波前传播时间。在反向步骤,利用正向步骤计算出的网格节点上的波前传播时间,从接收点开始,向声源方向逐单元追踪声线路径。在每个长方体单元内,首先把任意点上的波前传播时间用该单元网格节点上的已知波前传播时间的线性插值函数来表示,再根据Fermat原理,提出了确定三维声线路径的方法。实验结果表明,本文方法提高了三维声线追踪的精度和计算速度。     

具微结构地壳中非线性地震波的演化

非线性地震波在地壳中传播及演化规律的研究具有重要实际意义.利用有限差分方法, 对非线性地震纵波和横波在具微结构地壳中的演化过程进行了详细的数值模拟.结果表明,非线性地震纵波和横波在具微结构地壳中可以逐渐演化成一个孤立波或两个孤立波或孤立波列或消失.地震波的初始幅度、频散系数和体力因子对演化过程和结果都有重要影响.研究结果揭示了非线性地震波在一种微结构地壳中的演化规律,这有助于在理论上解释一些特殊地震波现象.     

人工沿场不均匀体对短波垂直探测影响的理论分析

从人工沿场不均匀体的产生机制出发,分析其对无线电波的散射特性,基于射线追踪技术,建立了短波垂直探测波经人工沿场不均匀体散射的传播模型,理论分析了不同纬度人工沿场不均匀体对垂直探测波传播路径的影响.结果表明:人工沿场不均匀体所导致的垂直探测电离图人工扩展描迹随地理纬度升高和地磁倾角增大而变短,解释了高纬度地区电离层加热不能有效观测人工扩展描迹的缘由.最后对中低纬度地区存在人工沿场不均匀体时可能产生的人工扩展描迹现象进行了预测评估,并分析了其重要应用方向.     

双相各向异性随机介质伪谱法地震波场特征分析

各向异性、双相孔隙以及非均匀性是描述油气储层时应综合考虑的. 结合随机介质理论和双相介质模型建立了双相各向异性随机介质模型,采用伪谱法模拟了双相各向异性随机介质地震波场,结果表明：双相各向异性随机介质地震波场存在散射波、旅行时扰动等复杂的波场特征,这些特征强烈依赖于随机介质模型参数. 在大非均匀空间尺度下,非均匀幅度主要影响波的旅行时扰动;在小非均匀空间尺度下,非均匀幅度主要影响波的散射. 该研究使人们有可能在统计意义下反演油气储层的非均匀特征,有益于加深对地震波在油气储层中传播规律的认识. 关键词： 双相各向异性 随机介质 伪谱法 地震波     

基于射线理论的各向异性煤层地震响应

以VTI型煤层为研究对象,从介质中的地震波的射线方向、走时计算等多个方面展开讨论,分析VTI型煤层的试射法射线追踪技术,充分利用VC++的面向对象类框架泛型编程的特点和Fortran数值计算方面的优势,通过混合编程实现VTI型煤层中的地震波试射法射线追踪;通过各向同性煤层和VTI型煤层的射线追踪试算对比,论证对VTI型煤层进行各向异性射线追踪的必要性,同时验证本文VTI型煤层射线追踪方法的正确性.最后,通过计算时间成本比较,表明该方法计算速度较快,能满足地震正演模拟的要求.该方法适用于各向异性煤层的多波射线追踪.     

楔形弹性海底声矢量场分布规律研究

提出了基于弹性抛物方程的声矢量场计算方法,计算了楔形弹性海底的海洋环境中甚低频声矢量场和弹性海底地震波场分布,研究了声源深度和声源频率对声场分布的影响,仿真结果表明声波在具有弹性楔形海底的海洋环境中传播时存在能量泄漏现象,利用简正波理论解释了能量泄漏位置可由水深—波长比确定。     

舰船地震波远程定位方法研究

随着舰船噪声抑制技术的提高,利用水声远程定位舰船目标变得越来越困难.而舰船地震波能量主要集中在固体和液体的分界表面,在海底衰减缓慢,可以远程传播.利用舰船地震波实现对目标的远程定位可以弥补水声远程定位的不足.本文分析了舰船地震波的传输耦合机理,研究了基于九元海底地震计环形阵列的梯度下降算法和单纯形算法对目标的定位.仿真计算证明,梯度下降算法和单纯形算法可以减小定位误差,单纯形算法具有更高的定位精度和稳定性.     

局部固体填充的水中复杂目标声散射计算与实验

利用二维有限元方法研究水中局部填充的带球冠柱体目标声散射特性,所采用的数值方法可高效地实现精细化、宽带、复杂轴对称模型散射声场计算.根据数值结果解释壳体、填充物以及入射方位对目标散射远场的影响,确定复杂目标散射研究中所必须考虑的重要物理和几何构成.完成水中悬浮目标自由场声散射实验,收发合置条件下将目标旋转360?接收并测量不同传播路径回波到达时刻得到距离-角度伪彩色图像.以表面环绕波和"回廊波"产生理论为基础,解释内真空和局部填充模型正横入射时目标散射信号中几何回波和各种弹性波成分产生的机理.由于固体填充与弹性壳的耦合作用,频率-角度谱的正横方向两侧呈现外八字"碗"形共振曲线.通过对比,理论计算和实验得到的散射函数关键频谱峰值特性符合较好.     

Theorie der Ausbreitung von Röntgen-Wellenfeldstrahlen im schwach deformierten Kristallgitter

A theory is presented for calculating the paths and the absorption of wavefield rays within a weakly deformed crystal lattice. The method of Penning and Polder⁶, suitable only for Laue-case wavefields, is extended to the most general wavefields compatible with the fundamental equations of the dynamical theory of X-ray diffraction. In the theory given here, when calculating the adaption of the wavefield to the deformation along the path of the ray, the wavefield is no longer assumed to stay on a particular branch of the dispersion surface but to form withleast spatial inhomogeneity. Formulas are developed which permit numerical calculation of the propagation of arbitrary types of wavefield rays in a given field of deformation. Any deformation may be split into pure curvature (FF) of, pure gradient of lattice parameter (NN) perpendicular to, and pure fanning out (FN) of the reflecting planes. Typical features of the effect of FF, NN, and FN are discussed for each type of deformation separately.     

TM plane wave scattering and diffraction from a randomly rough half-plane: (part II) An evaluation of the diffraction kernel

In a previous paper (part I), it has been shown that a random wavefield from a randomly rough half-plane for a TM plane wave incidence is written in terms of a Wiener-Hermite expansion with three types of Fourier integrals. This paper studies a concrete representation of the random wavefield by an approximate evaluation of such Fourier integrals, and statistical properties of scattering and diffraction. For a Gaussian roughness spectrum, intensities of the coherent wavefield and the first-order incoherent wavefield are calculated and shown in figures. It is then found that the coherent scattering intensity decreases in the illumination side, but is almost invariant in the shadow side. The incoherent scattering intensity spreads widely in the illumination side, and have ripples at near the grazing angle. Moreover, a major peak at near the antispecular direction, and associated ripples appear in the shadow side. The incoherent scattering intensity increases rapidly at near the random half-plane. These new phenomena for the incoherent scattering are caused by couplings between TM guided waves supported by a slightly random surface and edge diffracted waves excited by a plane wave incidence or by free guided waves on a flat plane without any roughness.     

裂缝诱导TTI双孔隙介质波场传播特征

本文在考虑油藏内流体影响的基础上, 进一步讨论了裂缝诱导各向异性的极化角和方位角的影响, 对裂缝诱导TTI (tilted transverse isotropy)双孔隙介质模型进行了研究. 在裂缝诱导HTI (horizontal transverse isotropy)双孔隙介质理论的基础上, 用Bond变换推导了裂缝诱导TTI双孔隙介质的柔度系数矩阵和耗散系数矩阵, 从而建立了介质的一阶速度应力方程. 采用交错网格高阶有限差分法及PML边界条件, 对xoz平面内的2.5维矢量波动方程进行了数值模拟. 结果表明,裂缝的极化角和方位角的存在都会导致横波分裂, 而在双层裂缝诱导TTI双孔隙介质模型的分界面上,又会产生转换波的分裂和横波的再分裂现象, 这就增加了波场的复杂性, 从而为进一步研究实际地球介质的地震波场传播特征奠定了基础. 关键词： 裂缝诱导TTI 双孔隙 裂缝极化角 裂缝方位角     

湍流大气中斜程传输光场的相位特性

运用功率谱反演法对斜程传输大气湍流扰动相位屏进行了数值模拟。通过建立激光束初始畸变相位模型,从波前峰谷值和波前功率谱密度函数两个方面,对激光束通过大气湍流后的相位特性进行了研究,重点分析了湍流传输距离和天顶角对激光束波前相位分布的影响。研究结果表明：激光束在湍流大气斜程传输后,其波前相位会发生明显畸变,且空间高频相位较低频相位所占比例明显增加;通过湍流后的波前相位与传输距离及天顶角密切相关,传输距离越长,天顶角越大,相位畸变程度越大,高频相位所占比例越多。     

湍流大气中斜程传输光场的相位特性

运用功率谱反演法对斜程传输大气湍流扰动相位屏进行了数值模拟。通过建立激光束初始畸变相位模型,从波前峰谷值和波前功率谱密度函数两个方面,对激光束通过大气湍流后的相位特性进行了研究,重点分析了湍流传输距离和天顶角对激光束波前相位分布的影响。研究结果表明:激光束在湍流大气斜程传输后,其波前相位会发生明显畸变,且空间高频相位较低频相位所占比例明显增加;通过湍流后的波前相位与传输距离及天顶角密切相关,传输距离越长,天顶角越大,相位畸变程度越大,高频相位所占比例越多。     

紫外光非视距多次散射信道模型研究

利用蒙特卡罗方法对紫外光非视距传输过程进行了模拟,讨论了传输过程中固体角的确定,仿真分析了系统的角度设置对传输损耗的影响.结果表明,增大收发仰角可以降低系统的传输损耗,并且小角度集中发射与大视场角接收可以降低系统的传输损耗.     

Extended application of the complex source-point theory

In this paper, the complex source-point theory used for a symmetric concave spherical resonator is extended to an asymmetric concave spherical resonator. Thus, the formulae for the field distribution of the asymmetric spherical resonator can be easily deduced from the formulae for the field distribution of the symmetric resonator, thereby the application range of the complex source-point theory is enlarged and a convenient method is provided for the field analysis of an arbitrary spherical resonator.     

Laser ultrasonic propagation imaging method in the frequency domain based on wavelet transformation

A wavelet-transformed ultrasonic propagation imaging method capable of ultrasonic propagation imaging in the frequency domain was developed and applied as a new structural damage or flaw visualization algorithm. Since the wavelet-transformed ultrasonic propagation imaging method has strong frequency selectivity, it can visualize the propagation of ultrasonic waves of a specific frequency (for example, to isolate ultrasonic mode of interest and a damage-related ultrasonic wave). The strong frequency selectivity of the wavelet-transformed ultrasonic propagation imaging method was demonstrated, isolating only the zeroth-order asymmetrical mode of the fundamental Lamb wave modes in an anisotropic carbon fiber-reinforced plastic plate with a thickness of 5 mm. The wavelet-transformed ultrasonic propagation imaging method can also convert a complex time domain multiple wavefield into a simple frequency domain single wavefield. This feature enables easy interpretation of the results, and facilitates the precise evaluation of the location and size of structural damage or flaws. We demonstrated this capability by detecting a disbond in a sandwich structure made of Al-alloy skins and a foam core. A disbond with a diameter of 20 mm, which is representative of a common manufacturing flaw, was successfully detected, localized, and evaluated. Since a method to determine the allowable maximum pulse repetition frequency depending on target materials and structures was found by investigating the residual wave caused from the previous laser impinging, our laser ultrasonic system can scan rapidly the target with an optimal pulse repetition rate. In addition, the proposed wavelet-transformed ultrasonic propagation imaging method can visualize damage or flaw without the need for reference data from the intact state of the structure. Hence, we propose the wavelet-transformed ultrasonic propagation imaging approach for automatic inspection of in-service engineering structures, or in-process quality inspection in manufacturing.     

Correlation characteristics of waves in lossy media with smooth fluctuations of the refractive index with oblique incidence on boundary

The features of coherence function (and angular spectrum) and also the fluctuation of amplitude and phase of wavefield in a random strongly absorptive medium are investigated in the case of arbitrary angle of incidence at the surface.

In this paper it is elucidated that with oblique incidence a dissipation in the random medium can accelerate the accumulation of wave fluctuations and its incoherence. This effect strongly depends on the rate of decrease of the 'wings' of the scattering indicatrix. An analytical theory (Rytov's approximation and modified method of parabolic equation) has been modelled by Monte Carlo simulation of wave propagation, and also by numerical solution of the model transfer equation. It is revealed that the width of an angle spectrum can nonmonotonically change with the immersion to the absorptive medium.     

Propagation of supercontinuum laser sources in a slant path through the atmosphere

Taking the atmospheric refraction, extinction and turbulence into account, the propagation characteristic of supercontinuum laser sources in a slant path through the turbulent atmosphere is investigated. The effect of spectral width, initial spot size and zenith angle in a slant path on the beam width and propagation efficiency are studied in details. Numerical examples reveal that the beam width and propagation efficiency are different values while the spectral width varies. With the zenith angle in a slant atmospheric path increasing, the beam width of supercontinuum laser sources will increase and propagation efficiency will decrease. The initial spot size has an optimal value when spectral width and zenith angle are fixed.