共查询到20条相似文献，搜索用时 546 毫秒
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针对具有饱和土沉积层的充水河谷对平面瑞雷波的散射问题,把半空间场地用单相弹性介质模拟,河谷中的饱和土沉积层用Biot饱和多孔介质动力理论模拟,河谷中的水假定为无黏性流体（理想流体）,利用波函数展开法在频域内给出了具有饱和土沉积层的圆弧形充水河谷对平面瑞雷波散射问题的解析解答.文中给出了算例,计算了不同输入频率和高宽比时河谷谷底的位移幅值.算例表明由于具有饱和土沉积层的充水河谷存在,使得河谷谷底的位移幅值放大4倍多,并且它的幅值随着河谷谷底位置的不同而产生较大的变化. 相似文献
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本文将普遍声逆散射微扰论应用于弹性波层析成像问题,在Born变换下推出了以旋转角为补偿参数的各阶微扰重建公式,实现了对非均匀各向同性散射体内3个参数（质量密度ρ和两个Lamé系数λ,μ）的同时重建. 对于层析成像问题,在弹性波的传播过程中P波与SV波有耦合,但它们不会和SH波发生耦合,于是可以得到3个形式相对简单的标量方程. 在Born变换下,在散射波中引入微扰参数,将散射体的3个参数分别按该微扰参数展开,然后利用二维自由空间的Green函数分别得到散射的P波、SV波和SH波的积分表示. 最后,经一维傅氏变换后,得到Born变换下散射体3个参数的各阶微扰重建公式. 相似文献
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平面SH波在相邻多个半圆形凹陷地形上的散射 总被引：13，自引：0，他引：13
本文利用复变函数和多极坐标方法研究平面SH波对相邻多个半圆形凹陷地形的散射问题。文中首先给出了相邻多个半圆形凹陷地形对SH波散射的波函数,进一步利用移动坐标的方法逐一地满足凹陷地形的边界条件。最后将解的问题归结为对一组无穷代数方程组的求解。作为算例,对具有两个半圆形凹陷地形的问题进行了分析,给出了数值结果,并进行了一些讨论。 相似文献
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半无限空间界面附近SH波对圆形衬砌的散射 总被引：6，自引：2，他引：6
建立了求解半无限空间中SH波对浅埋圆形衬砌结构的散射与动应力集中问题的解析方法。利用SH波散射的对称性和多极坐标的方法，在复平面上构造出了一个可以预先满足半空间自由表面上应力自由的边界条件的浅埋圆形衬砌对稳态SH波散射的波函数，并构造出衬砌内的散射波函数。然后根据衬砌周围的边界条件，将该问题转化为对一组无穷代数方程组的求解。最后给出了具体算例，并讨论了其数值结果。 相似文献
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各向异性介质中圆柱体对SH波散射的射线理论 总被引：1，自引：0，他引：1
本文建立了各向异性介质中SH波传播的几何射线理论并由此得到圆柱体对平面SH波散射的解析解。在远处,散射场的波阵面趋于点源产生的扰动的椭圆阵面,但振幅的角分布与入射波的方向以及观测点的方位有关。 相似文献
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采用波函数展开法及边界离散的方法给出了任意断面形状的地下夹塞对平面SH波散射的半解析解; 利用蒙特卡罗方法随机模拟产生了30组夹塞断面样本, 通过对该样本在平面SH波入射下地表位移幅值的统计分析, 研究了夹塞断面形状随机性对平面SH波散射的影响. 结果表明, 夹塞断面形状随机性对平面SH波的散射具有重要影响. 以圆形夹塞为例, 当断面半径的变异系数为0.1时, 地表位移响应幅值变异系数可达0.71. 随着入射频率的升高, 变异系数逐渐增大; 随着夹塞刚度的降低, 变异系数逐渐增大; 随着夹塞埋深的增加, 变异系数逐渐减小. 相似文献
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SH波作用下浅埋裂纹附近半圆形凸起的地震动 总被引：2，自引：0，他引：2
利用Green函数、复变函数及多极坐标法研究了浅埋裂纹附近的半圆形凸起地形对SH波的散射问题。首先求解出适合本问题的Green函数,即含有半圆形凸起的弹性半空间内任意一点承受时间谐和的出平面线源荷载作用时位移场的解答。然后,从半圆形凸起地形对SH波的散射问题出发,利用本问题的Green函数在基体内构造裂纹。最后给出了浅埋裂纹附近的半圆形凸起地形对SH波散射的位移场。通过算例讨论了裂纹对地表位移幅值的影响,结果表明裂纹在一定情况下具有减震作用。 相似文献
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圆弧状沉积盆地与软土单覆盖层出平面地表运动对比 总被引：2，自引：0，他引：2
采用解析方法，通过圆弧状沉积盆地与同样参数的软土均匀单覆盖层的对比，研究沉积盆地对平面SH波二维散射效应和其出平面地表运动。数值对比结果表明：（1）波垂直入射时盆地中央地表位移幅值反应，其随频率变化形式与软土单覆盖层的地表运动有较强的对应性，且此时单覆盖层地表位移幅值为其下降；（2）盆地的二维散射效应特点显著波的汇聚作用使盆地中的地表运动显著放大，总体上较软土单覆盖层的地表位移幅值要大，其频域内的最大反应则明显大于单覆盖层情况，但最大反应在盆地表面出现的位置依赖于入射波角度、盆地深宽比和盆地的软硬程度；（3）沉积盆地中地表位移运动有强烈扭转效应，且随盆地变软和入射波频率增高而增强。 相似文献
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弹性层状半空间中沉积谷地对入射平面SH波的放大作用 总被引：6，自引：3，他引：6
对Wolf理论进行拓展,使之可解决沉积谷地对波的散射问题,进而利用间接边界元法,求解了弹性层状半空间中沉积谷地对入射平面SH波的放大作用问题。通过自由场反应分析,求得假想边界上各点的位移和各单元的应力反应。施加虚拟均布荷载,求得位移和应力的格林函数。根据应力和位移连续边界条件确定虚拟分布荷载,将自由场反应和虚拟分布荷载产生的反应叠加起来,即得到问题的解答。最后,以基岩上单一土层中沉积谷地对入射平面SH波的放大作用为例进行了数值计算分析,结果表明,层状半空间中沉积谷地和均匀半空间中沉积谷地对波的放大作用存在显著差别。文中分析了造成差别的原因,并讨论了覆盖层厚度和刚度对放大作用的影响。 相似文献
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Three-dimensional scattering of seismic waves by a cylindrical alluvial valley embedded in a layered half-space is investigated by using the combination of the boundary integral representation and the finite element method. The surface displacements due to incident plane harmonic body waves (P, SV and SH) propagating at an arbitrary angle to the axis of the cylindrical valley are evaluated numerically for two semi-elliptical alluvial valleys. The presence of the layer is found to have a strong effect on the amplification of the surface displacements in some cases. The three-dimensional motion seems to be quite critical and may cause large amplification. The surface ground motion becomes significant when compared with corresponding free-field motion as the wavelengths become comparable to the characteristic length of the valley. The maximum amplification always occurs atop the valley. Numerical results show that the amplitude and the amplification pattern of the surface displacement strongly depend upon the frequency, the angle and the type of the incident waves. 相似文献
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A closed-form solution of two-dimensional scattering of plane SH waves by a cylindrical alluvial valley of circular-arc cross-section in a half-space is presented using the wave functions expansion. The solution is reduced to solving a set of infinite linear algebraic equations using the exterior region form of Graf's addition theorem. Numerical solutions are obtained by truncation of the infinite equations and their accuracies are demonstrated by convergence of the numerical results to the exact boundary condition with the increasing of the truncation order. The present solution is compared with the existing one presented by Todorovska and Lee for the same problem and their differences are analysed. Complicated effects of the depth-to-width ratio of the alluvial valley on surface ground motion are finally illustrated. 相似文献
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Introduction The effect of local site conditions on wave propagation is one of the most attractive topics in engineering seismology. It may be resolved by either a numerical method or an analytical method. Numerical methods include the finite difference, finite element, boundary element method, etc. The analytical method is the wave function expansion method. The advantage of these numerical methods is that they can be applied to local inhomogeneity of arbitrary shapes, but analytical method … 相似文献
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平面SV波在饱和半空间中沉积谷地周围的散射 总被引：1，自引：0，他引：1
采用一种特殊的间接边界积分方程法,求解了平面SV波在饱和半空间中任意形状沉积谷地周围的二维散射问题。结合饱和半空间中膨胀波源和剪切波源格林函数,由分布在沉积和半空间交界面附近两虚拟波源面上的波源分别构造沉积内外的散射波场,由交界面连续条件建立方程并求解确定虚拟波源密度,总波场反应即可由自由波场和散射波场叠加而得。然后通过边界条件验算、退化解答与现有结果的比较以及稳定性检验,验证了方法的计算精度。通过一组典型算例,研究了平面SV波在饱和半空间中沉积谷地周围散射的基本规律,详细给出了不同参数情况沉积谷地附近地表位移幅值和孔隙水压,着重分析了入射SV波频率和角度、边界渗透条件、沉积孔隙率等因素对场地反应的影响,得出了一些有益的结论。 相似文献
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Azimuth dependent wave amplification in alluvial valleys 总被引：1，自引：0，他引：1
An extension of the indirect boundary element method (IBEM) to three-dimensional scattering by two-dimensional alluvial valleys is presented. While the valley is two-dimensional, the incident plane waves can arrive outside the 2D plane so the scattering is three-dimensional with coupling of P---SV---SH waves. Such a method makes it possible to take earthquake location into account in the estimation of site effects in alluvial valleys. The method is validated by transparency tests, by comparison with 2D simulations, and by comparison with results of other authors. The advantage of the method is that is combines high accuracy with cost-efficiency in terms of computer-time. It is applied to theoretically estimate site effects across a simplified model of an alluvial valley in the French Alps where azimuth dependence of local amplification has been observed. A parametric study with simulations for a range of azimuths and incidence angles shows that (1) the local amplification depends strongly on both azimuth and incidence of the incoming waves, (2) the global pattern of amplification across the valley is very complex for all azimuths, and (3) it is not possible to predict the 3D response of the valley from 2D modeling. Theoretical spectral ratios are in approximate agreement with observed ones for a station in the center of the valley where the local structure justifies use of a simplified model for the comparison. 相似文献
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场地效应通常包含土层放大效应和地形放大效应，为了揭示二者的相对贡献，本文构造了平面SH波作用下部分充填沉积谷的解析模型，借助于区域分解策略，在波函数展开法的框架下，提出了超定方程组解法，得到了部分充填圆弧形沉积谷对平面SH波散射的波函数级数解，而且级数解的收敛测试表明了超定方程组解法的必要性.通过与文献结果进行对比，验证了本文方法的正确性.通过调整解析模型中两个子区域内的材料参数，计算了沉积谷引起的场地放大效应和相应的空河谷引起的地形放大效应.对二维土层与地形效应进行对比分析，结果显示，在沉积谷内二维土层放大效应通常强于地形放大效应，而地形放大效应决定了沉积谷外的地面运动放大形态.针对最大地面运动，进行了沉积谷和相应空河谷的参数分析，进一步描述了二维土层放大效应，研究结果表明二维土层放大效应引起的最大地面运动通常远远大于地形放大效应引起的最大地面运动，并且二维土层效应通常随着土层与基岩的阻抗比的增大而增大，但不是一维土层放大效应与二维地形放大效应的简单线性叠加. 相似文献
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To improve the understanding of the near-field soil and topographic amplification effects, an analytical solution by the authors for the scattering of plane SH waves by a radially inhomogeneous semi-cylindrical valley is extended to the case of a line source of cylindrical SH waves. Upon confirmation of its accuracy with past exact solutions for a homogeneous and an inhomogeneous semi-cylindrical valley under far-field plane SH waves, the extended solution is used to calculate the ground motion amplification factors for both the homogeneous and inhomogeneous valleys subjected to near-field waves. A comprehensive parametric study is conducted with respect to the location of the wave source, the dimensionless frequency of the incident waves, and the inhomogeneity degree of the covering soil layer. It is found that more amplifications and reductions of ground motions will occur within a certain range in and around the valley as the sources are located further. Consistent with the far-field case, it is confirmed that an increase of the degree of inhomogeneity of the covering soil layer generally amplifies the ground motions significantly. 相似文献