裂缝性地层黏弹性地震多波波动方程

裂缝检测是目前国内外石油勘探界研究的一个热点问题，如何确定裂缝方位等参数是石油公司面临的难题，而解决该难题就要确定裂缝方位等参数与地震波场传播之间的定量关系.但是目前所采用的裂缝性地层介质模型不能完全定量地反映裂缝的方位特征和衰减特征.针对该问题，建立了具有任意裂缝方位的裂缝性地层介质模型；并构造了时间增量的方法，将非线性的卷积积分采用近似的方法实现，建立了以位移场表示的具有任意方位角的黏弹性方位各向异性介质的波动方程.该波动方程定量地给出了黏弹性波场特征与裂缝走向的关系，描述了黏弹性地震波在这种介质中的 关键词： 裂缝 各向异性 黏弹性 波动方程     

各向异性黏弹性介质伪谱法波场模拟

当地震信号通过复杂地球介质时，地层除了表现为各向异性，还表现为内在的黏弹性特征 因此，为准确描述地震波在地球介质中的传播特征，理想的地球介质模型应该能够模拟岩石 的各向异性特征和衰减特征.给出了各向异性黏弹性介质模型的波动方程，推导了伪谱法波场正演模拟的递推公式，并利用伪谱法实现了地震波波场数值模拟.表明了该介质模型中地 震波场特征与各向异性主轴方位和介质的黏滞性参数之间的关系. 关键词： 黏弹性 各向异性 伪谱法     

线性黏弹性各向异性介质速度频散和衰减特征研究

地层岩石既非各向同性的,也非完全弹性的,正确地描述波在地层中的传播需要搞清楚岩石的各向异性和黏弹性特征.针对裂缝性地层的裂缝发育方位问题,建立具有任意方位角的方位各向异性黏弹性本构关系.使用均匀平面简谐波分析方法研究其频散关系,得到Christoffel方程,进而获得均匀平面波的复速度、相速度、衰减系数和品质因子的表达式.通过黏弹性方位各向异性页岩和砂岩进行模拟,研究了波场在地层中的传播特征,如相速度、衰减系数和品质因子等随频率、方位和入射角的变化关系 关键词： 黏弹性 各向异性 相速度 衰减系数 品质因子     

激光激发黏弹表面波有限元数值模拟

研究黏弹性材料中激光激发的Rayleigh波的传播特征. 考虑到黏弹性材料的黏性特征,在频域内建立黏弹性材料中激光激发Rayleigh波的有限元数值模型. 在验证有限元频域数值模型正确性的基础上,模拟脉冲激光作用在黏弹性材料上激发出Rayleigh波,进而讨论激光激发的黏弹Rayleigh波的传播特征,并比较黏弹性材料与弹性材料中激光激发的Rayleigh波差异,同时分析了材料的黏性劲度参量变化对Rayleigh波特征的影响. 关键词： 表面波 激光超声 有限元方法 黏弹性     

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     

各向异性粘弹性孔隙介质地震波场伪谱法正演模拟

地球介质各向异性、粘弹性以及孔隙特征是地震资料描述油气储层时应综合考虑的. 建立了各向异性粘弹性孔隙介质模型，导出了各向异性粘弹性孔隙介质的弹性波波动方程，采用伪谱法正演模拟了各向异性粘弹性孔隙介质地震波，进行了其波场特征分析. 该研究有益于加深对地震波在实际地球介质中传播规律的认识.     

各向异性渗流条件下弹性波的传播特征

研究了弹性波在非均匀裂纹孔隙介质中的传播特性,建立了各向异性喷射流模型.当弹性波通过裂纹孔隙介质时,由于波的扰动及裂纹和孔隙几何结构的不一致,导致在裂纹内部及裂纹与周边孔隙之间同时存在着流体压力梯度.此时的弹性波波动响应中包含着裂纹内连通性特征和背景孔隙渗透率信息.流体的动态流动过程使得介质的等效弹性参数为复数(非完全弹性),并且具有频率依赖性.当弹性波为低频和高频极限时,介质为完全弹性;当处于中间频段时,波有衰减和频率依赖.裂纹孔隙介质的各向异性连通性(渗透率)对应着各向异性特征频率(当渗流长度等于非均匀尺度时的弹性波频率),波的传播受到裂纹内连通性的影响.在一定频段内,随着裂纹厚度的增加,将出现第二峰值,峰值大小同时受到裂纹厚度和半径的影响.     

谱有限元模拟正交各向异性黏弹性材料中导波传播特性

研究了导波在正交各向异性黏弹性复合板中传播的色散特性、波结构及功率流密度。基于二维平面运动方程,采用谱有限元方法得到了导波色散的特征方程。分析了正交各向异性黏弹性板中各向异性和黏性对能量速度和波结构的影响,以及基底对导波功率流密度的影响。数值研究结果表明:导波沿纤维方向传播的能量速度大,材料的黏性对速度影响较小,但会减小波结构的幅度;在高频时,基底的存在使两个基本模态的功率流密度分别集中到波导的上下表面,形成弱色散、高衰减及无色散、零衰减的表面波。数值模拟结果为导波用于复合材料定量无损检测和性能评价提供理论依据。      

广义传播矩阵法分析分层各向异性材料对电磁波的反射与透射

在实验室坐标系下由Maxwell旋度方程出发构造了横向场的状态矢量和耦合矩阵,讨论了各 向异性介质中的特征波.通过引入横向场的传播矩阵,进而得到分层各向异性介质的反射系数和透射系数的解析表达式.该式可以适用于一般情况,包括分层单轴各向异性材料和回旋介质,以及半空间各向异性介质的反射和透射问题. 关键词： 广义传播矩阵 各向异性介质 反射与透射     

光轴平行于界面的单轴手征介质中的负折射研究

研究了光轴平行于界面时单轴各向异性手征介质中实现负折射的条件, 并详细分析了该介质中两个本征波在不同电磁参数和手征参数下折射角随入射角的变化规律. 结果表明, 利用单轴各向异性手征介质实现负折射, 条件更加宽松, 甚至在弱的手征参数下也可能实现负折射, 且在不同的介电常数、手征参数和入射角下, 该手征介质中两个本征波的相折射角存在很大的差异, 在特殊条件下, 某一个或两个本征波不能在介质内传播.     

Numerical solutionsfor acoustic Rayleigh wave problems in anisotropic and layered media

A finite difference iterative formulation which has already been applied successfully to acoustic surface wave scattering problems in homogeneous and layered isotropic as well as non-linear media, is extended to cover Rayleigh type mode propagation in anisotropic materials. The transmission, reflection and conversion into bulk modes of Rayleigh waves are studied as a function of relative step height. The waves are incident normally at upward and downward step discontinuities formed by the sudden termination of an uniform aluminium layer on a semi-infinite fused quartz substrate. In terms of the severity of Rayleigh wave scattering, the layered upward step has the most drastic effects, followed by the layered downward and the homogeneous downward steps respectively. Rayleigh wave scattering at a break in a layered waveguide is discussed.     

Vortex solitons with inhomogeneous polarization in nonlocal self-focusing nonlinear media

Both azimuthally and radially polarized vortex solitons are investigated to be able to exist in highly nonlocal nonlinear media. We get exactly analytical solutions of azimuthally polarized vortex solitons with only polarization singularities and radially polarized vortex solitons with both phase singularities and polarization singularities. Both azimuthally and radially polarized vortex solitons can exist in nonlocal self-focusing nonlinear media with proper modulation of the beam power and the degree of nonlocality. Contrary to those of radially polarized counterparts in local Kerr media, the topological charge can be any integer. When the topological charge m ≠ 0, both phase singularities and polarization singularities work. When m = 0, the polarization singularities work. Azimuthally polarized vortex solitons with polarization singularities corresponds to the linearly polarized vortex solitons with single charge. Our results show that polarization singularities work the same way as phase singularities in some sense.     

Horizontal array beamforming in an azimuthally anisotropic internal wave field

A numerical study of beamforming on a horizontal array is performed in a shallow water waveguide where a summer thermocline is perturbed by a time evolving realization of an internal wave field. The components of the internal wave field consist of a horizontally (azimuthally) isotropic, spatially homogeneous contribution, and a horizontally anisotropic, spatially inhomogeneous component. These terms represent a diffuse ("background") internal wave field and a localized solitary wave packet, respectively. Conventional beamforming is performed as a function of time while the internal wave field evolves throughout a computational volume containing the source-receiver paths. Source-receiver orientation with respect to the azimuthally anisotropic component has a significant effect on the beamformed output. When the source-receiver configuration is oriented approximately parallel to the solitary wave crests, beam wander, fading, beam splitting and coherence length degradation occurs in a time-dependent manner as the solitary wave packet passes through the environment. Both horizontal refraction of energy and a time-dependent modal source excitation distribution are responsible for these beamforming effects. In cases where source-receiver orientation is not approximately parallel to the wave crests, these effects are substantially reduced or eliminated, indicating that an azimuthally selective perturbation of the acoustic field can be attributed to the wave packet. Modal decomposition of the acoustic field and single mode starting fields are used to infer that, for the source-receiver orientation along the wave crests and troughs, acoustic propagation is predominantly adiabatic. A modal phase speed analysis explains several features associated with the beamformed power.     

Study on laser-generated Lamb waves propagation in viscoelastic and anisotropic plate

The propagation characteristics of laser-generated Lamb waves in thin composite plates are theoretically studied. Taking the anisotropic and viscoelastic properties of the composite material into account, the finite element models for simulating laser-generated Lamb waves in the composite material are established in the frequency domain. Numerical results are calculated in purely elastic and viscoelastic transversely isotropic plates, respectively. The effects of the anisotropic and viscoelastic properties on the propagation of Lamb waves are analyzed in detail. The numerical results exhibit that the features of the laser-generated Lamb wave, including attenuation, velocity, frequency, and the dispersive nature, have a close relationship with the anisotropic and viscoelastic properties of the material.