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局部透射边界的精度 总被引：6，自引：0，他引：6
廖振鹏 《地震工程与工程振动》1993,13(3):1-6
离散局部透射边界和旁轴近似的精度分析表明,它们所以缺乏透射大角度入射波的能力乃是源于采用单一的透射方向。本文提出将边界节点附近的入射波表示为一系列预定入射角的平面波的叠加以消除这一缺点。在这一思想上建立的局部透射边界能够在全部入射角范围内减小反射。通过模拟稳态SH波动简要地阐明了上述思想及其在建立高精度、稳定的局部透射边界中的意义。 相似文献
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用非零偏P-P波、P-SV波计算零偏反射纵波和反射横波 总被引：3，自引：2，他引：3
在P波入射时，地下同一点产生的P－P波和P－SV波是入射角、界面两侧纵波阻抗和横波阻抗的函数，并且两者是耦合的，利用两者的耦合关系，可在入射角确定的情况下提取与入射角无关的零偏纵波反射和横波反射。本文对此进行了理论推导，结论是：入射角为零时的纵波与横波反射系数是入射角非零时的P－P波和P－SV波反射系数的线性组合，进而可以用纵横波反射计算泊松比反向间面，把多波叠前反演转化到叠后进行，通过合成弹性参数反射剖面，直接反演弹性参数等，都很有意义。文中给出了有关的公式，并对具体实现方法和有关参数进行了讨论。 相似文献
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本文将Ｎｅｗｍａｒｋ法的时间差分格式的有限元与边界元方程相结合，建立了动力问题的边界元与有限元耦合模型。这种耦合模型在求解时域范围内基础动力响应问题中，可充分发挥有限元求解局域问题和边界元求解无限域问题各自的优点。 相似文献
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根据自动控制理论,本文在时域和频域范围内对直接放大地震仪开环系统的动态特性进行了分析与讨论.给出了评价系统动态性能的时域指标.它们是系统阶跃响应的上升时间t_r,峰值时间t_p,最大超调量σ%,调节时间t_s,以及系统稳定性判据和系统的稳态误差e_ss.根据最小相位原理,给出评价系统稳态特性的频域指标.它们是幅频和相频特性,峰值A_m,峰值频率ω_m,截止频率ω_c,频带宽度ω_b,相角裕度,以及系统在可记录的动态范围内的相移范围.最后还讨论了时域里动态性能与频域里稳态性能之间的本质联系. 相似文献
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利用电磁波在导电媒质界面反射系数的附加相角，导出了电场垂直于入射面的非均匀电磁波在导电介质界面的类全反射横向偏移，并对横向偏移进行了相关计算，绘出了横向偏移随入射角的变化曲线. 结果表明：入射角在相移常数临界角、衰减常数临界角和90°处，横向偏移曲线存在三个间断点. 当入射角等于这三个角时，横向偏移为无穷大，即电磁波将沿界面传播；当入射角在这三个角附近时，横向偏移变得非常大. 相似文献
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廖振鹏 《地震工程与工程振动》1982,(4)
本文论述了一般暂态标量波的透射方法,以紧凑形式给出了直接用节点位移表出的透射公式。本文证明,对于任意入射角,透射方法的误差小于目前通行的粘性边界和旁轴近似情形的误差。本文还指出将透射方法的时间域结果推广到频率域以及将标量波透射边界推广到弹性矢量波的途径。 相似文献
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Summary This paper presents a theory of the transient Bernoulli-Euler beam problem on an elastic foundation which takes into account the effects of axial load and linear damping. An analytical solution of the steady state and the transient components has been obtained due to physically realistic load distributions. With a view to extend its practical applicability, the characteristic features of the solution are explored. Several limiting situations are investigated as special cases. It is shown that the steady state vibration can be achieved as the limit of the solution of the transient problem. 相似文献
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Scattering of elastic waves by an orthotropic sedimentary basin is investigated for antiplane strain model using an indirect boundary integral equation approach. Both steady state and transient response were obtained for semicircular and semielliptical basins with different material properties. The results indicate that the basin geometry and the impedance contrast between the half-space and the basin have similar effects on the surface ground motion amplification as for the isotropic case. However, the material anisotropy may change significantly the fundamental resonant frequencies of the basin, resulting in different surface displacement amplification patterns. In addition, it was observed that the arrival time of the main disturbance on the surface strongly depends on material anisotropy for different angles of incidence. The results demonstrate that material anisotropy may be very important in explaining surface ground motion amplification for sedimentary basins. © 1998 John Wiley & Sons, Ltd. 相似文献
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弹性孔隙介质分界面上的反透射系数特征,在岩性划分、流体识别、储层边界判识等方面有重要的应用.本文研究上层为含两项不混合黏性流体孔隙介质、下层为含单项黏性流体孔隙介质分界面上的反透射理论.首先根据两种孔隙介质分界面上的能量守恒得到边界条件,再将波函数、位移、应力与应变关系代入边界条件,推导出完全连通孔隙情况下,第一类纵波入射到孔隙介质分界面上的反透射系数方程.通过建立砂岩孔隙介质模型,分别分析不同孔隙流体类型、不同含油饱和度及不同入射角情况下,各类波的反透射系数特征.研究表明,第二、三类纵波反透射系数数值比第一类纵波小多个数量级,且两者对入射角的变化不敏感,但对孔隙流体性质、含油饱和度的变化较敏感,而横波反透射系数特征恰好与此相反;第一类纵波反透射系数特征比较复杂,入射角、孔隙流体的性质及含油饱和度的变化都对其产生影响.不同孔隙流体弹性物性的差异、孔隙介质中含油饱和度的变化及不同入射角引起垂向和切向应力分量的变化都会影响各类波的反透射系数特征,分析这些特征可以为研究储层含油气性提供理论基础. 相似文献
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Scattering of elastic waves by two dimensional multilayered dipping sediments of arbitrary shape embedded in an elastic half-sapce is investigated by using a bondary method. The displancement field is evaluated throughout the elastic media for both steady state and transient incident SH waves. The unknown scattered field is expressed in terms of wave functions which satisfy the equation of motion, traction-free boundary condition and appropariate radiation conditions. The transient response is constructed from the steady state solution by using the fast Fourier transform technique. The numerical results presented demonstrate that scattering of waves by subsurface irregularities may cause locally very large amplification of surface ground motion. The motion can be affected greatly by the scattered surface waves in the sediments. The results clearly indicate that the surface ground motion depends upon a number of parameters present in the problem, such as frequency and the angle of incidence of the incoming wave, impedance contrast between the layers and location of the observation point. 相似文献
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对于一个包含许多大震震源的复杂系统来说，当外界对它的供能稳定、且边界条件变化不大时，该系统处于定态。定态系统的演变过程呈线性规律，涨落水平稳定。虽然系统的宏观状态不随时间变化，但系统内部仍可发生宏观过程，并会出现局部的突变。在突变前局域往往出现非线性行为。因此定态系统的每一次涨落与其子系统的突变相对应。由定态系统的上下限可预测未来地震发生的时间和强度，由系统的非线性行为可确定其地点。本文以１９７６年松潘７．２级地震为例对所提思路和方法作了检验．应当指出，当复杂震源系统和其子系统均处于非稳定态时，则确定性预报不能进行。 相似文献
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全局反射误差分析是深入研究探地雷达(GPR)吸收边界条件吸收效率的有力工具.基于常规完全匹配层(PML)的标准交错网格有限差分算法必须满足严格的CFL条件限制,即在单位时间步长内,不容许电磁波传播的距离超过单元网格尺寸.为了提高主区域所有网格节点的计算效率,并有效地吸收传播后期出现的低频隐失波,提出基于非分裂递归卷积完全匹配层(UCPML)的旋转交错网格(RSG)GPR正演算法.该算法采用不同的网格交错策略,并在边界条件中引入了吸收低频隐失波的自由可变因子,使得该算法允许选取较大的时间步长,提高了计算效率,并且实现了对低频隐失波的高效吸收.本文首先给出了RSG差分格式,推导了基于UCPML的RSG差分更新方程,探讨了数值色散的稳定性条件,然后以绕射现象严重的衰减夹层数值模拟为例,分别从波场快照、单道波记录、时间域反射误差(TDRE)、频率域反射误差(FDRE)四个方面分析了UCPML与常规PML的全局反射误差,说明了基于UCPML和RSG的GPR正演算法能更有效地吸收低频隐失波. 相似文献
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It has been established that idealized western boundary currents, which encounter a gap in their supporting boundary, will assume one of two dominant steady states: a loop current state and a gap leaping state, and that transitions between these states display hysteresis. However, a question of whether the idealized geometries considered to date apply to the Gulf of Mexico Loop Current (LC) remained. Here, the nonlinear potential vorticity advection-diffusions equations are solved, for Gulf of Mexico topography, using Newton’s method. We demonstrate that, in application to the LC in the Gulf of Mexico, the original conclusions do hold and additionally describe peculiarities of the more realistic steady states. The existence of our numerically calculated steady LC states in the actual Gulf of Mexico are supported through analysis of historical sea surface height data, and implications of our results for LC modeling and forecasting are discussed.
相似文献18.
The novel doubly asymptotic multi-directional transmitting boundary combines the advantages of the doubly asymptotic and multi-directional formulations. It is rigorous for the low-frequency limit (static case) and the high-frequency limit in the wave-propagation direction perpendicular to the artificial boundary and at all the preselected angles corresponding to various apparent velocities. It is implemented straightforwardly in the finite-element method. The doubly asymptotic multi-directional transmitting boundary is temporally local and spatially either global or local depending on the implementation of the static-stiffness matrix. It leads to much higher accuracy than other transmitting boundaries with the same finite-element mesh. 相似文献
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|v|=v 《地震学报(英文版)》1999,12(4):413-418
IntroductionGenerallyspeaking,theinclusionofanisotropy(exceptdeclaration,anisotropyreferstohomogenousanisotropy)rendersthemathematicalformulationquitecomplicated.Snell'Slawisnotanexceptionandthecalculationofreflectionandtransmissionanglesisnotatrivialtask.ThegraphicalapproachestocalculatingreflectionandtransmissionanglesforanisotropicmediawerepresentedbyAuld(1973)andRokhlin,etal(1986).DaleyandHorn(1977,1979)andSlawinski(1996)deriveSnell'slawintheparticularcasesoftransverselyisotropicandelli… 相似文献
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The analytical study of the reflection and transmission coefficient of the seafloor interface is essential for the characterization of the ocean bottom in marine seismic exploration. Based on the boundary conditions of the seafloor interface, the analytical expression of the reflection and transmission coefficient at the submarine interface is derived in this study by using the steady-state wave solution of the elastic wave in a homogeneous, isotropic medium. With this analytical expression, the characteristics of the reflection and transmission coefficient at the submarine interface are analysed and discussed using critical angles. The results show that the change in the reflection and transmission coefficient with the incidence angle presents a “segmented” characteristic, in which the critical angle is the dividing point. The amplitude value and phase angle of the coefficient at the submarine interface change dramatically at the critical angle, which is related to the P- and S-wave velocities in the seabed layer. Compared with the stiff seabed, the soft seabed has a larger P-wave critical angle and an absence of the converted S-wave critical angle, owing to the low P- and S-wave velocities in the solid seabed layer. By analysing and discussing the special changes that occur in the coefficient values at the critical angle, the reflection and transmission characteristics of the different incident angles are obtained. Synthetic models of both stiff and soft seafloors are provided in this study to verify the analytical results. Finally, we compared our synthetic results with real data from the Gulf of Mexico, which enabled the validation of our conclusions. 相似文献