弹性波斜入射声子晶体的缺陷模及其转型

推导出弹性波斜入射固-固掺杂结构声子晶体的转移矩阵和透射系数公式.计算固-固掺杂结构声子晶体中弹性波的透射系数.得到当横波斜入射时,透射波中横波的缺陷模随着入射角的增大而减弱,横波向纵波的转型随着入射角的增大而增强.当纵波斜入射时,透射波中纵波的缺陷模随着入射角的增大而减弱,纵波向横波的转型随着入射角的增大而增强.     

多层介质的转移矩阵及其在声子晶体中的应用

引入四维波矢的概念,推导出弹性波斜入射到多层介质系统时的转移矩阵以及透射系数和反射系数。利用这些公式计算了纵波和横波正入射到一维掺杂声子晶体时纵波和横波的透射系数。得出:当纵波正入射时,透射波中纵波在一定频率范围内出现了禁带,并且在禁带的中心频率处出现了缺陷模。当横波正入射时也有相同的结果。     

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.     

偶极声波实现钻前地质探测的方法研究

针对随钻地震技术在声波长距离传播导致的衰减和信号混叠等问题,本文提出采用井下发射和接收声波的方式,利用偶极声波实现前方地质情况探测。结合数值模拟结果,分析了偶极辐射声场和反射声场特征,重点讨论了反射波信号与钻头前方反射面之间的关系。结果表明,偶极横波在低倾角反射面的反射强度较大,尤其是SH波具有振幅强、倾角覆盖范围大的特点,可以用于前方地质情况探测。偶极横波还表现出了较高的方位灵敏度,有助于识别前方反射体的方位。     

纵向带状裂隙形貌的逆时偏移超声成像

传统的工业超声成像方法通常只能确定缺陷的位置与横向尺寸,无法获得缺陷的形貌信息.一些特殊的缺陷,如纵向裂纹,是典型的例子.基于多阵元技术,开展了固体介质缺陷逆时偏移超声成像方法的数值与实验研究.针对铝块平底纵裂纹及内部纵裂纹两种传统方法无法有效成像的缺陷,首先开展了单分量逆时偏移成像方法研究,给出了基于数值仿真的逆时偏移成像结果以及基于多阵元超声成像实验系统实验测试的逆时偏移成像结果.进一步开展了基于多分量位移检测与转换横波分离的逆时偏移成像方法研究,并提出了基于新型多分量激光干涉仪进行检测的思路.数值仿真结果证实了多分量逆时偏移图像重建结果可以克服单分量方式的缺点,得到明显优于单分量检测时的图像.     

双重弹性波波场分离数值模拟及相关理论证明

提出一种等效的双重弹性波波场分离数值模拟方法,用于模拟纯纵波和纯横波分离模式的质点振动速度、位移以及散度场和旋度场,并将该方法应用于全弹性波波动方程数值模拟中.同时,详细推导双重弹性波波场分离波动方程的高阶交错网格有限差分数值计算公式及其稳定性条件、数值频散关系和完全匹配层(PML)吸收边界条件.理论分析和数值计算均表明,该方法可以实现高精度双重弹性波波场分离数值模拟,且纯纵波和纯横波得到完全分离,边界吸收效果较好.与前人工作相比,存储量和计算时间均得到有效改善,数值计算结果进一步验证了该方法的优越性.     

裂缝诱导TTI双孔隙介质的纵波偏移成像研究

将交错网格高阶有限差分纵横波分离的方法与逆时偏移成像方法相结合,给出了基于裂缝诱导TTI双孔隙介质模型的纵波逆时偏移成像算法,并对二维水平层状模型的数据进行偏移成像.结果表明,对于裂缝诱导TTI双孔隙介质模型,常规的基于各向同性背景孔隙岩石速度的偏移方法会导致成像结果出现过偏移现象.为研究裂缝参数对过偏移程度的影响,利用Christoffel方程,对裂缝诱导TTI双孔隙介质模型中的相速度公式进行了推导,并在此基础上,分析了裂缝角度和密度参数对介质纵波相速度及成像位置的影响.结果表明,在二维情况下,裂缝极化角增大会减小成像速度与真实速度之间的误差,从而使得成像结果逐渐接近储层的真实位置;而裂缝密度的增大则使得速度误差增大,导致成像结果与真实模型的偏差越来越大.     

超声反射成像测井的有限元分析*

利用有限元方法研究了有限长换能器激发的超声波在套管井多层介质中的传播规律。数值模拟了换能器长度及套管曲率对反射回波的影响。随着换能器长度增加,反射回波频谱谱陷个数由单一向多个变化;套管共振透射窗的反射波相对能量先逐渐减小后振荡变化,较小长度的换能器对套管与水泥环界面的声阻抗区分能力优于较大长度的换能器。随着套管曲率的增大,套管共振透射窗的反射波由单一模式的厚度振动纵波向其他模式波变化。数值模拟结果对超声脉冲反射声波测井仪器的换能器结构优化设计起到了良好的指导作用。     

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.     

含气孔裂隙地层的声波测井响应特征

本文以径向分层的孔、裂隙地层多极子井孔声场理论为基础,利用孔、裂隙介质弹性波动统一理论,数值模拟了井壁上有侵入时,单极和偶极声源激发的井孔声场随原状地层含气饱和度变化的特征和规律。结果表明：当原状地层裂隙发育时,相较于饱含水,饱含气时纵波幅度衰减严重,横波波至提前,波幅增大,斯通利波幅度变化不明显,低频时弯曲波到时提前,幅度增大;当原状地层裂隙不发育时,单极子、偶极子波形都对流体性质没有明显响应。可见,原状地层中裂隙的存在加剧了含气对纵波、横波的幅度以及到时的影响,而侵入带的存在使得斯通利波和高频弯曲波对原状地层流体性质变化不敏感。数值计算结果为利用声波响应特征识别致密气层提供了参考。     

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     

The role of Biot slow waves in electroseismic wave phenomena

The electromagnetic fields that are generated as a spherical seismic wave (either P or S) traverses an interface separating two porous materials are numerically modeled both with and without the generation of Biot slow waves at the interface. In the case of an incident fast-P wave, the predicted electric-field amplitudes when slow waves are neglected can easily be off by as much as an order of magnitude. In the case of an incident S wave, the error is much smaller (typically on the order of 10% or less) because not much S-wave energy gets converted into slow waves. In neglecting the slow waves, only six plane waves (reflected and transmitted fast-P, S, and EM waves) are available with which to match the eight continuity conditions that hold at each interface. This overdetermined problem is solved by placing weights on the eight continuity conditions so that those conditions that are most important for obtaining the proper response are emphasized. It is demonstrated that when slow waves are neglected, it is best to also neglect the continuity of the Darcy flow and fluid pressure across an interface. The principal conclusion of this work is that to properly model the electromagnetic (EM) fields generated at an interface by an incident seismic wave, the full Biot theory that allows for generation of slow waves must be employed.     

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.     

基于模式分离的兰姆波逆时偏移成像

应用频率域逆时偏移方法实现各向同性和各向异性板中缺陷的兰姆波成像.由于缺陷引起的多模态散射信号会在重建图像中形成伪像,根据基本导波模式振动对称性的差别进行了模式分离预处理.基于多元阵列超声技术,开展了铝板和复合板内缺陷频率域逆时偏移超声成像方法的数值仿真研究.首先,建立有限元模型,采用环形传感器数值采集由缺陷引起的兰姆波散射信号,然后,将采集到的多模式散射信号进行模式分离处理,再将模式分离后的兰姆波散射信号经时间反转后并在相应的接收器处重新激励,在频域中运用格林函数反向传播兰姆波散射信号,获取监测区域的声场信息,与正向传播声场进行互相关,重建缺陷图像.首先对铝板中单缺陷以及复合材料板中相邻的两个相同缺陷进行数值仿真,对比有无模式分离处理的缺陷逆时偏移成像效果,体现出模式分离的重要性.在此基础上,采用逆时偏移方法对复合板材内位置邻近、深度不同的双缺陷进行识别.数值结果表明,模式分离预处理后的缺陷重建图像能够有效去除多模式干扰产生的伪像.文中提出的成像方法对各向同性板和各向异性板内缺陷的检测和成像具有很好的发展潜力,可以准确地探测多个缺陷的形状、尺寸和深度.     

Laser ultrasonic anomalous wave propagation imaging method with adjacent wave subtraction: Algorithm

The anomalous wave propagation imaging (AWPI) method is proposed for the laser ultrasonic propagation imaging system using a Q-switched laser and a laser mirror scanner to highlight the anomalies in complex structures. The AWPI algorithm was developed based on the observation that the waves from two adjacent scanning points are very similar, and that the propagation direction of the incident wave is different from that of the anomalous wave caused by structural anomalies including damage. The structural anomaly is highlighted by suppressing the incident waves and exaggerating the anomalous wave through adjacent waves subtraction after arrival time and amplitude matching. The variable time window amplitude mapping (VTWAM) method was also developed, based on the difference in arrival time between the residual incident wave and anomalous waves. The VTWAM method enhances anomaly visualization and sizing, notably for composite damages, by mapping the amplitudes of the confining wave within the damage. Our results showed that the AWPI increased the signal-to-noise ratio of a back-surface hole damage in a steel plate by 13.76 dB, while in another inspection of a composite wing with two impact damages, the AWPI results enhanced by the VTWAM compared favorably with the results of the immersion ultrasonic C-scan. The AWPI and VTWAM adopt implicit spatial referencing wherein all necessary data can be obtained through a single-time scan, therefore circumvent the disadvantages of conventional temporal baseline referencing.     

反射声波成像测井的有限元模拟

应用有限元法对新兴的反射声波成像测井进行了数值模拟研究，计算了井旁附近存在不同倾角声阻抗不连续界面对声波的反射，使用的井内激励源为幅度加权相控线阵声波辐射器。从计算出的声全波波形上可以清楚地看到沿井壁传播的折射波和来自井旁界面的反射纵波。应用偏移叠加等数据处理技术对数值模拟波形进行了处理，从偏移剖面上反演出的反射界面的尺寸、位置和倾角等几何特性与数值模拟输入参数基本一致。     

快照的时间反转和逆时偏移法对含有固体分层介质中目标的超声检测

快照的时间反转和逆时偏移方法已实现了液-液分层介质中目标的超声检测和定位,现进一步推广到含有固体分层介质情形.由于在含有固体分层介质中,都存在多种的反射波和散射波,因此提出一种筛选方法,首先从中筛选出散射波以及所属波型,再利用快照的时间反转和逆时偏移方法进行处理.实验分别研究了固-液、液-固和固-固分层介质3种情况.利...     

Poroelastic modeling of seismic boundary conditions across a fracture

Permeability of a fracture can affect how the fracture interacts with seismic waves. To examine this effect, a simple mathematical model that describes the poroelastic nature of wave-fracture interaction is useful. In this paper, a set of boundary conditions is presented which relate wave-induced particle velocity (or displacement) and stress including fluid pressure across a compliant, fluid-bearing fracture. These conditions are derived by modeling a fracture as a thin porous layer with increased compliance and finite permeability. Assuming a small layer thickness, the boundary conditions can be derived by integrating the governing equations of poroelastic wave propagation. A finite jump in the stress and velocity across a fracture is expressed as a function of the stress and velocity at the boundaries. Further simplification for a thin fracture yields a set of characteristic parameters that control the seismic response of single fractures with a wide range of mechanical and hydraulic properties. These boundary conditions have potential applications in simplifying numerical models such as finite-difference and finite-element methods to compute seismic wave scattering off nonplanar (e.g., curved and intersecting) fractures.     

Fast continuous terahertz wave imaging system for security

Continuous terahertz wave (CW THz) has been widely used in imaging field. However, the speed of imaging calls for an improvement for security screening since the speed of previous CW imaging systems which scan point to point is too slow to be applied in security field. To increase the imaging speed, we proposed a fast CW-THz imaging system in which a galvanometer is introduced. The galvanometer makes the beams reflected in different angles by vibrating at a certain frequency which can significantly decrease the image acquisition time compared to traditional CW-THz imaging system. Furthermore, the system is compact due to source and detector of small size. Examples of measurements of concealed weapons are presented and discussed. Ideal results of better resolution are obtained.