共查询到20条相似文献，搜索用时 31 毫秒
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Elastic wave propagation in inhomogeneous anisotropic media 总被引：1，自引：0，他引：1
XIU CHENG WEI ) MIN YU DONG ) YUN YAI CHEN ) ) Geoscience Department University of Petroleum Beijing China ) Institute of Geophysics China Seismological Bureau Beijing China 《地震学报(英文版)》1998,11(6):655-667
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Jian-Fei Lu Dong-Sheng Jeng Tsung-Lin Lee 《Soil Dynamics and Earthquake Engineering》2007,27(9):875-891
Recently, considerable efforts have been devoted to evaluation of seismic dynamic response of a circular tunnel. Conventional approaches have considered integral liners embedded in an elastic medium. In this study, we re-examine the problem with piecewise liners embedded in a porous medium. Surrounding saturated porous medium of tunnels is described by Biot's poroelastic theory, while the liner pieces and the connecting joints are treated as curved beams and characterized by curved beam theories. The scattered wave field in the porous medium is obtained by the wave function expansion method. The differential equations governing the vibration of a curved beam is discretized by the General Differential Quadrature (GDQ) method. The domain decomposition method is used to establish the global discrete dynamic equations for the piecewise tunnel. The surrounding soil and the tunnel are coupled together via the stress and the displacement continuation conditions which are implemented by the boundary collocation method. Numerical results demonstrate that the stiffness difference between the liner piece and the connecting joints has a considerable influence on the internal forces of the liner piece. 相似文献
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裂缝诱导的双相具有水平对称轴的横向各向同性(HTI)介质模型是由一组平行排列的垂直裂缝嵌入到统计各向同性的流体饱和多孔隙岩石中而组成的,它综合考虑了裂缝型储层岩石的各向异性和孔隙性.高精度的地震波场数值模拟技术是研究该介质中地震波传播规律的主要方法.本文结合错格伪谱法和时间分裂法,求解描述该介质中地震波传播的一阶速度-应力方程.模拟了单层和双层模型中的地震波场,并对其进行了特征分析.研究结果表明:错格伪谱法能有效消除标准网格伪谱法波场模拟结果中出现的数值伪影现象,与时间分裂法结合能够获得稳定的、高精度的模拟结果;裂缝诱导双相HTI介质中的地震波场兼具裂缝各向异性介质和双相介质中传播的地震波的波场特征. 相似文献
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Wave propagation in soil is dependent on both the stiffness and the material damping of the soil. While some researchers have performed finite element modelling of resonant column tests and wave propagation in soil, most do not describe the methodology in detail and there is little or no verification of the correctness of the model. Viscoelastic model has been used to model wave propagation in soil. However, the determination of the parameters in the viscoelastic model is complicated and the parameters may not be related to the soil properties. This paper presents a simplified viscoelastic model with soil parameters obtainable from advanced geotechnical testing to simulate wave propagation in soil medium taking into account of material damping. The viscoelastic material model was first calibrated by replicating torsional, longitudinal and flexural modes resonant column tests. The relationships between the parameters of the simplified viscoelastic model and their corresponding stiffness and damping properties were investigated. An equation was proposed to correlate the decay constant used in the simplified viscoelastic model and the material damping ratio obtained through the application of the logarithmic decrement method on the modelled resonant column test results. The simplified viscoelastic model was then evaluated by modelling wave propagation in a semi-infinite medium. Results indicated that the viscoelastic model with parameters as proposed in this paper is able to model wave propagation in soils. 相似文献
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In this paper we calculate a synthetic medium surface displacement response that is consistent with real measurement data by applying the least-square principle and a niche genetic algorithm to the parameters inversion problem of the wave equation in a two-phase medium. We propose a niche genetic multi-parameter (including porosity, solid phase density and fluid phase density) joint inversion algorithm based on a two-phase fractured medium in the BISQ model. We take the two-phase fractured medium of the BISQ model in a two-dimensional half space as an example, and carry out the numerical reservoir parameters inversion. Results show that this method is very convenient for solving the parameters inversion problem for the wave equation in a two-phase medium, and has the advantage of strong noise rejection. Relative to conventional genetic algorithms, the niche genetic algorithm based on a sharing function can not only significantly speed up the convergence, but also improve the inversion precision. 相似文献
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采用规则网格有限差分方法对二维平面弹性波动方程进行差分离散,得到相应的弹性波动方程的有限差分方程,再将弹性波动方程的差分格式与吸收边界、自由边界的离散形式结合形成弹性波动方程有限差分方程解决问题的主体,将其应用于含方形凹陷半无限非均匀介质的模型中进行数值模拟,得到此离散化模型中不同时刻不同节点的位移值。针对具体算例,运用上述方法结合科学计算软件MATLAB和结果后处理软件DIFEM ISOLINE PLOTER得到不同时刻的水平方向位移等值线图与接收器测量点处的合成位移记录,讨论非均匀介质、吸收边界、方形凹陷等对波动特性的影响。 相似文献
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The analysis of Stoneley wave propagation in a fracture is essential for the identification and evaluation of fracture parameters from the borehole Stoneley wave. Also, it is important for many geophysics considerations, e.g. for tremor and long-period events observed in volcanoes and geothermal areas. In this paper, we investigate the guided waves propagation in a fluid layer lying between two viscoelastic vertically transversely isotropic media. The viscoelastic mechanism models the attenuation due to the presence of fluid saturation in the rock. A model based on the superposition of three inhomogeneous partial plane waves: one in the fluid and two heterogeneous waves in the solid is developed. The dispersion equation is obtained for this case. A numerical solution is carried out to obtain the guided wave velocity and attenuation coefficient. The results of this investigation show that there is a strong correlation between the velocity dispersion and attenuation of Stoneley wave and the anisotropic parameters of the medium especially in a sandstone (fast) medium. 相似文献
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伪谱法是一种高效、高精度计算非均匀介质地震波传播的数值算法,由于它的微分算子的全局性,一般认为该方法不适于并行计算. 本文介绍了并行计算非均匀介质中地震波传播的重叠区域分解算法,给出了一种基于傅里叶伪谱法的并行算法. 文中给出的算法将介质划分为相互重叠的若干区域,在各个子域上单独求解,利用重叠部分的解的传递,将各个子域连接起来,实现了伪谱法在分布式并行处理机上的计算. 文中给出了一个将二维区域分解的算例,比较了并行算法和整体算法的结果,分析了并行算法的计算精度. 结果表明,并行算法会有效降低计算时间,并且保证计算精度. 该方法在大规模三维非均匀介质的地震波场模拟方面有应用价值. 相似文献
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传统利用灰色关联分析方法对地震波动强度变化进行数学建模分析与仿真时,对地震波动强度变化的数列进行仿真分析时,忽略了地震波动强度的时间属性对结果的影响,导致分析结果准确性较低。本论述提出新的地震波动强度变化数学建模分析与仿真方法,通过地震波动强度序列的经验分布确定门限自回归模型的门限值,依据该门限值、AIC最小准则以及最小残差平方等方法获取地震波动强度序列的门限自回归模型,分析自回归模型的极限环和振荡的属性特点,得到地震波动强度变化的初步数值模拟结果。本论述构建了基于均生函数的地震波动强度序列的数学模型,通过均生函数数学建模方法拟合地震波动强度时间序列,依据时间序列基于双评分准则选取拟合周期,实现地震波动强度的数值仿真。实验结果表明,所提方法对地震波动强度变化模型具有较高的准确性和稳定性。 相似文献
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A first-order one-way wave system has been created based on characteristic analysis of the acoustic wave system and optimization of the dispersion relation. We demonstrate that this system is equivalent to a third-order scalar partial-differential equation which, for a homogeneous medium, reduces to a form similar to the 45° paraxial wave equation. This system describes accurately waves propagating in a 2D heterogeneous medium at angles up to 75°. The one-way wave system representing downgoing waves is used for a modified reverse time migration method. As a wavefield extrapolator in migration, the downgoing wave system propagates the reflection events backwards to their reflectors without scattering at the discontinuities in the velocity model. Hence, images with amplitudes proportional to reflectivity can be obtained from this migration technique. We present examples of the application of the new migration method to synthetic seismic data where P-P reflections P-SV converted waves are present. Absorbing boundaries, useful in the generation of synthetic seismograms, have been constructed by using the one-way wave system. These boundaries absorb effectively waves impinging over a wide range of angles of incidence. 相似文献
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N. T. Afanasiev A. A. Zheonykh M. K. Ivelskaya V. I. Sazhin M. V. Tinin V. E. Unuchkov 《Journal of Atmospheric and Solar》2001,63(18)
This paper is concerned with the oblique propagation of decametric radio waves in the ionosphere with random electron density irregularities. Effective parameters are introduced for calculating the influence of irregularities on the wave field structure. A technique is proposed for determining these parameters from measurements of statistical characteristics of the signal in the vicinity of a regular caustic. The technique uses asymptotic expressions obtained using the interference integral method and perturbation theory, as well as matching them to the numerical solution on the basis of the method of characteristics. A global semi-empirical model that is updated for current ionospheric conditions is used to specify the background medium. The proposed technique has been tested using data from a number of mid-latitude paths. Results obtained in this study testify that the technique deserves a practical implementation. 相似文献
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O. A. Laryunin 《Geomagnetism and Aeronomy》2016,56(5):610-615
The goal of this work is to solve Maxwell equations analytically and numerically in a one-dimensional case under the conditions of a nonstationary medium. Analytical solutions to the Maxwell equations have been obtained in two partial cases of the linear and quadratic time dependence of medium permittivity. Since the number of models for which the wave equation can be solved analytically is limited, it becomes also necessary to apply numerical methods, specifically the method of finite differences, in a time domain Finite Difference Time Domain method. The effects of the decameter wave dynamic reflection from structures with considerable spatial gradients (the scales of which are comparable with the sounding pulse wavelength) have been studied based on this method. It has been shown that the spectrum can broaden and a Doppler frequency shift of a reflected signal can originate can take place. 相似文献
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Subhas Dutta 《Pure and Applied Geophysics》1962,52(1):20-26
Summary The possibility of propagation of Rayleigh waves in a transversely isotropic medium resting on (i) a rigid base and (ii) a yielding base has been studied in this paper. In the former case the relation between the wave velocity and ratio of wave length to thickness has been found and in the latter case the frequency equation and its possible solutions are obtained. 相似文献
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本文应用Chisnell- no方法,求解了在理想介貭中,垂直磁流体冲激波在非均勻磁場中的传播問題。这种方法,把非均勻介貭分解成无限小的弱間断面,根据气体动力学中波与間断面相互作用的原理,算出激波通过弱間断面时的强度变化,然后用积分求得激波通过整个非均勻区时的强度变化。作者引入了激波的特征速度（它是激波在波前后介貭中传播速度的几何平均值）作为輔助参量,得到形式上比較簡单的激波传播方程。然后考虑了磁压力远大于气体压力的强磁介貭中的激波传播問題,并进行了数值积分。采用的介貭密度模型有三种:（1）阿尔芬波速为常数;（2）密度不变;（3）密度与磁場强度成正比。計算結果表明:当激波由弱磁場向强磁場传播时,激波的强度逐漸变弱。其中,在阿尔芬波速为常数的介貭中,激波强度的衰减最为緩慢;在密度不变的介貭中,激波强度的衰減最为迅速;而在密度与磁場成正比的介貭中,激波强度的衰減則介乎上述两种密度分布之間。作者联系磁流体冲激波在地球外层空間的传播問題进行了討論,密度的模型采取大气啃昔的观測結果（卽上述第三种密度分布）,并进行了适当的外推,估計了在十个地球半径处的磁流体冲激波传到地面时的强度,求出了激波在地面引起的磁場变化与激波初始速度之間的关系。根据上述簡化模型,計算結果表明,在十个地球半径处初始速度为108厘米/秒的激波,传到地面引起的磁場变化大約为60伽（亻馬）,这个数值的量級恰好与中低緯度强磁暴的急始变幅相符。 相似文献
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介质的黏滞性是普遍存在的.黏滞性介质中的真振幅成像需要校正由介质的黏滞性引起的振幅衰减与速度频散,然而常规的反Q偏移方法存在不稳定问题.本文在反演的框架下求解黏声介质成像问题,在有效避开不稳定的同时实现真振幅成像.首先将波动方程线性化,并依此建立黏声介质最小平方逆时偏移（LSRTM）的目标函数;然后推导波动方程伴随算子,并在此基础上借助伴随状态法推导迭代求解的具体算法;最后通过引入动态相位编码技术将计算量降至与常规逆时偏移相同的数量级.该方法在真振幅成像过程中考虑了介质黏滞性的影响,更接近实际情况,具有更好的振幅保持性.相对于常规逆时偏移,该方法能够自动压制成像噪声,具有更高的成像分辨率及精度.通过模型试算验证了方法的正确性. 相似文献
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本文以波动理论为基础, 半解析化求解地震勘探中常用的SH波方程. 获得的主要结果包括: 给出了二维均匀介质中SH波方程的解析解; 利用Cagniard-de Hoop方法详细推导了二维双层介质中SH波方程的解析解, 获得了透射波的解析解表达式. 同时, 基于SH波方程的解析表达式, 给出了包含各种波(如直达波、反射波、首波以及透射波)的解析解和波形图. 对于比较复杂的积分型解析解, 利用数值积分方法给出了数值结果, 并与优化的近似解析离散化方法(ONADM)和4阶Lax-Wendroff修正方法(LWC)的数值结果进行了比较, 以验证解析解的正确性. 本文的研究成果有望在检验波动方程数值新方法的有效性、波传播理论分析等方面得到应用. 相似文献
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基于BISQ模型的三维双相各向异性介质数值模拟 总被引：5，自引：2，他引：3
Biot-flow and squirt-flow are the two most important fluid flow mechanisms in porous media containing fluids. Based on the BISQ （Biot-Squirt） model where the two mechanisms are treated simultaneously, the elastic wave-field simulation in the porous medium is limited to two-dimensions and two-components （2D2C） or two-dimensions and three-components （2D3C）. There is no previous report on wave simulation in three- dimensions and three-components. Only through three dimensional numerical simulations can we have an overall understanding of wave field coupling relations and the spatial distribution characteristics between the solid and fluid phases in the dual-phase anisotropic medium. In this paper, based on the BISQ equation, we present elastic wave propagation in a three dimensional dual-phase anisotropic medium simulated by the staggered-grid high-order finite-difference method. We analyze the resulting wave fields and show that the results are an improvement. 相似文献