共查询到20条相似文献，搜索用时 836 毫秒
1.
S. A. Gil-Zepeda J. C. Montalvo-Arrieta R. Vai F. J. Snchez-Sesma 《Soil Dynamics and Earthquake Engineering》2003,23(1):77-86
A hybrid indirect boundary element – discrete wavenumber method is presented and applied to model the ground motion on stratified alluvial valleys under incident plane SH waves from an elastic half-space. The method is based on the single-layer integral representation for diffracted waves. Refracted waves in the horizontally stratified region can be expressed as a linear superposition of solutions for a set of discrete wavenumbers. These solutions are obtained in terms of the Thomson–Haskell propagators formalism. Boundary conditions of continuity of displacements and tractions along the common boundary between the half-space and the stratified region lead to a system of equations for the sources strengths and the coefficients of the plane wave expansion. Although the regions share the boundary, the discretization schemes are different for both sides: for the exterior region, it is based on the numerical and analytical integration of exact Green's functions for displacements and tractions whereas for the layered part, a collocation approach is used. In order to validate this approach results are compared for well-known cases studied in the literature. A homogeneous trapezoidal valley and a parabolic stratified valley were studied and excellent agreement with previous computations was found. An example is given for a stratified inclusion model of an alluvial deposit with an irregular interface with the half-space. Results are displayed in both frequency and time domains. These results show the significant influence of lateral heterogeneity and the emergence of locally generated surface waves in the seismic response of alluvial valleys. 相似文献
2.
采用有限元模拟方法建立了建筑群-沉积谷地二维模型,并在土体截断边界上施加粘弹性人工边界,在频域与时域中对比分析此体系和单独沉积谷地的地震反应,观察地震时沉积谷地与建筑群之间的动力相互作用规律。分析表明,沉积谷地中建筑群对谷地本身的地震反应具有显著影响。入射波频率较低时,由于共振效应的存在,在部分区域处建筑群-沉积谷地体系的地表位移响应幅值会大于单独沉积谷地,但随着入射波频率的增加,建筑群的存在又会对地震反应产生明显的减弱效果;建筑群对谷地的影响还与建筑高度和建筑间距有关,且不同位置处的响应也存在很大差异。计算结果可为沉积谷地中设防烈度的设置以及工程抗震设计提供部分理论依据。 相似文献
3.
Diffraction of seismic waves in an elastic, cracked halfplane using a boundary integral formulation 总被引：1，自引：0，他引：1
A. Rodríguez-Castellanos F. Luzn F.J. Snchez-Sesma 《Soil Dynamics and Earthquake Engineering》2005,25(11):827-837
The presence of subsurface cracks in a halfspace excited by elastic waves may give rise to scattered body and surface waves. For many engineering applications, such as non-destructive testing or oil exploration, the scattered field may yield valuable information to detect cracks and other scatterers. We use the Indirect Boundary Element Method (IBEM) to study the diffraction of P, SV waves with various incidence angles and Rayleigh surface waves. This approximate boundary integral technique is based upon the integral representation for scattered elastic waves using single-layer boundary sources. Our approach is usually called indirect BEM as the sources' strengths should be obtained as an intermediate step. This indirect formulation can give to the analyst a deep physical insight on the generated diffracted waves because it is closer to the physical reality and can be regarded as a realization of Huygens' Principle. In any event, mathematically it is fully equivalent to the classical Somigliana's representation theorem. In order to gauge accuracy we test our method by comparing with previous results in the literature. Various crack configurations, including multiple cracks, are investigated. Results in frequency and time domains are displayed. Under certain conditions the amplitude spectra of those waves clearly show conspicuous resonance peaks. 相似文献
4.
Scattering of elastic waves by inhomogeneous and anisotropic bodies in a half space is considered. The integral equation method is formulated by using the fundamental solution of a homogeneous isotropic body in elastostatics and regarding the resulting inhomogeneous terms as equivalent body forces. Numerical examples are presented for the wave scattering by inhomogeneous and/or anisotropic alluvial valleys and for the dynamic analysis of an inhomogeneous dam. The effect of inhomogeneities and anisotropy on the dynamic behaviour of alluvial valley and dam is discussed. 相似文献
5.
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
6.
Surface motion of multiple alluvial valleys for incident plane SH-waves by using a semi-analytical approach 总被引：1，自引：0，他引：1
Jeng-Tzong Chen Po-Yuan Chen Chia-Tsung Chen 《Soil Dynamics and Earthquake Engineering》2008,28(1):58-72
In this paper, the degenerate kernels and Fourier series expansions are adopted in the null-field integral equation to solve the exterior Helmholtz problems with alluvial valleys. The main gain of using degenerate kernels in integral equations is free of calculating the principal values for singular integrals by locating the null-field point exactly on the real boundary. An adaptive observer system is addressed to fully employ the property of degenerate kernels for circular boundaries in the polar coordinate. Image concept and technique of decomposition are utilized for half-plane problems. After moving the null-field point to the real boundary and matching the boundary conditions, a linear algebraic system is obtained without boundary discretization. The unknown coefficients in the algebraic system can be easily determined. The present method is treated as a “semi-analytical” solution since error only attributes to the truncation of Fourier series. Earthquake analysis for the site response of alluvial valley or canyon subject to the incident SH-wave is the main concern. Numerical examples including single and successive alluvial valleys are given to test our program. Limiting cases of a single canyon and two successive canyons are also addressed. Amplification of soft basin is also observed in this study. The validity of the semi-analytical method is verified. Our advantages, well-posed model, principal value free, elimination of boundary-layer effect and exponential convergence and mesh-free, by using the present method are achieved. 相似文献
7.
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
8.
SH波入射时多个半圆形沉积谷地附近浅埋圆形孔洞的动力分析 总被引：3，自引：0，他引：3
本文采用辅助函数的思想,利用复变函数和多级坐标的方法给出了SH波入射条件下多个半圆形沉积谷地附近浅埋圆形孔洞动力分析问题的解答。将整个求解区域分割成两部分来处理,区域I为多个半圆形沉积谷地,区域II为浅埋圆形孔洞附近带半圆形凹陷的半无限弹性空间。在区域I和II中分别构造位移解,并在二个区域的“公共边界”上实施位移应力的连续条件,建立求解该问题的无穷代数方程组。最后,本文给出了算例和数值结果,并对其进行了讨论。 相似文献
9.
An extensive numerical analysis on the seismic site effects due to local topographical and geotechnical characteristics is carried out. 2D configurations under incidence of vertically propagating SV waves is modeled with the aid of HYBRID program, combining finite elements in the near field and boundary elements in the far field. The filling ratio and the impedance ratio effects on the modification of the seismic response of alluvial valleys are underlined. Parametric analysis is done on the central point of alluvial valleys where the critical point of response under existence of sediments stands. Specifying the amplification pattern under filling ratio effects, effective geometrical parameters are introduced. Subsequently, to assess the effect of the type of sediments on the seismic response, mechanical properties of materials are changed and impedance contrast coefficient is considered in combination with geometrical parameters. Finally, practical curves are presented for engineering applications. 相似文献
10.
It is well-known that the response of a site to a seismic solicitation depends on local topographical and geotechnical characteristics. Many aspects of seismic site effect still need to be studied in more detail and they can be incorporated in the seismic norms after quantification. The purpose of this paper is to contribute to establishment of a simple method to include complex site effects in a building code. Horizontal ground movements in various points of two-dimensional (2D) irregular configurations subjected to synthetic SV waves of vertical incidence are calculated. The parametric studies are achieved by means of HYBRID program combining finite elements in the near field and boundary elements in the far field (FEM/BEM). The results are shown in the form of pseudo-acceleration response spectra. For the empty valleys, we can classify the spectral response according to a unique geometric criterion: the “surface/angle” ratio, where surface is the area of the valley opening, and angle denotes the angle between the slope and horizontal line in the above corner. To assess the influence of the 2D effect on the spectral response of filled valleys, the response of alluvial basins are compared with the response of one-dimensional columns of soil. Finally, an offset criterion is proposed to choose a relevant computation method for the spectral acceleration at the surface of alluvial basins. 相似文献
11.
Wei-Lung Chang 《地震工程与结构动力学》1993,22(9):773-789
An alternate formulation of the ‘substructure deletion method’ suggested by Dasgupta in 19791 has been successfully implemented. The idea is to utilize simple Green's functions developed for a surface problem to replace the more complicated Green's functions required for embedded problems while still being able to generate an accurate solution. Since the exterior medium is usually represented by a continuum model, the interior medium in the present approach will also be represented by a continuum model rather than a finite element model as suggested originally, thereby eliminating the incompatibility between the solutions of the interior and exterior media. Detailed studies of the method's accuracy and limitations were performed using two-dimensional examples in wave scattering of canyons and alluvial valleys, problems which are more suitable for this method than the embedded foundation problem. The results obtained indicate that the alternate formulation gives accurate results only when the vertical dimension of the scattering object is not too large; if the aspect ratio (vertical over lateral) exceeds a certain limit, the results will not approach the known results given by boundary integral equation solutions or indirect boundary integral equations no matter what the refinement of the model may be. The greatest advantage of the present method is that the task of calculating Green's functions is reduced significantly; computational time using this new formulation is approximately five times less than for conventional boundary integral equation methods. 相似文献
12.
This paper presents an analytical solution for two-dimensional scattering and diffraction of plane P waves by circular-arc alluvial valleys with shallow saturated soil deposits. The solution is based on Biot's dynamic theory for saturated porous media, and derived by employing Fourier–Bessel series expansion technique. In this analysis, soil deposits in the circular-arc valley are modeled as saturated porous media based on Biot's dynamic theory, and the circular-arc valley is assumed to be imbedded in an infinite half-space, filled with elastic single-phase media. Numerical results from this solution show that the amplitudes of displacement at the surface of an alluvial valley are mainly relative to the angle of incidence, the dimensionless frequency of incident P wave, the degree of saturation and porosity of soil deposits, and the stiffness and Poisson's ratio of the solid skeleton of the soil deposits. Furthermore, the proposed solution is compared with the previous solution, in which the soil deposit was modeled as an elastic single-phase solid. 相似文献
13.
Elastic wave propagation in an irregularly layered medium 总被引：1，自引：0，他引：1
Rossana Vai Jos Manuel Castillo-Covarrubias Francisco J. Snchez-Sesma Dimitri Komatitsch Jean-Pierre Vilotte 《Soil Dynamics and Earthquake Engineering》1999,18(1):385
The indirect boundary element method (IBEM) is used to simulate wave propagation in two-dimensional irregularly layered elastic media for internal line sources. The method is based on the integral representation for scattered elastic waves using single layer boundary sources. Fulfillment of the boundary conditions leads to a system of integral equations. Results are obtained in the frequency domain and seismograins are computed through Fourier synthesis. In order to test and validate the method we present various comparisons between our results and the time series obtained analytically for a buried line source in a half-space and by using the recently developed spectral element method (SEM). 相似文献
14.
Michel Bouchon 《Pure and Applied Geophysics》1996,148(1-2):3-20
We review the application of the discrete wave number method to problems of scattering of seismic waves formulated in terms of boundary integral equation and boundary element methods. The approach is based on the representation of the diffracting surfaces and interfaces of the medium by surface distributions of sources or by boundary source elements, the radiation from which is equivalent to the scattered wave field produced by the diffracting boundaries. The Green's functions are evaluated by the discrete wave number method, and the boundary conditions yield a linear system of equations. The inversion of this system allows the calculation of the full wave field in the medium. We investigate the accuracy of the method and we present applications to the simulation of surface seismic surveys, to the diffraction of elastic waves by fractures, to regional crustal wave propagation and to topographic scattering. 相似文献
15.
P. Galvín S. François M. Schevenels E. Bongini G. Degrande G. Lombaert 《Soil Dynamics and Earthquake Engineering》2010
Ground vibrations induced by railway traffic at grade and in tunnels are often studied by means of two-and-half dimensional (2.5D) models that are based on a Fourier transform of the coordinate in the longitudinal direction of the track. In this paper, the need for 2.5D coupled finite element-boundary element models is demonstrated in two cases where the prediction of railway induced vibrations is considered. A recently proposed novel 2.5D methodology is used where the finite element method is combined with a boundary element method, based on a regularized boundary integral equation. In the formulation of the boundary integral equation, Green's functions of a layered elastic halfspace are used, so that no discretization of the free surface or the layer interfaces is required. In the first case, two alternative models for a ballasted track on an embankment are compared. In the first model, the ballast and the embankment are modelled as a continuum using 2.5D solid elements, whereas a simplified beam representation is adopted in the second model. The free field vibrations predicted by both models are compared to those measured during a passage of the TGVA at a site in Reugny (France). A very large difference is found for the free field response of both models that is due to the fact that the deformation of the cross section of the embankment is disregarded in the simplified representation. In the second case, the track and free field response due to a harmonic load in a tunnel embedded in a layered halfspace are considered. A simplified methodology based on the use of the full space Green's function in the tunnel–soil interaction problem is investigated. It is shown that the rigorous finite element-boundary element method is required when the distance between the tunnel and the free surface and the layer interfaces of the halfspace is small compared to the wavelength in the soil. 相似文献
16.
17.
A. Rodríguez-Castellanos F.J. Sánchez-Sesma C. Ortiz-Alemán M. Orozco-del-Castillo 《Soil Dynamics and Earthquake Engineering》2011
In earthquake engineering and seismology it is of interest to know the surface motion at a given site due to the incoming and scattered seismic waves by surface geology. This can be formulated in terms of diffraction of elastic waves and then the indirect boundary element method (IBEM) for dynamic elasticity is used. It is based on the explicit construction of diffracted waves at the boundaries from which they radiate. This provides the analyst with insight on the physics of diffraction. The IBEM has been applied to study the amplification of elastic waves in irregular soil profiles. From the strong or weak satisfaction of boundary conditions and a simple analytical discretization scheme a linear system of equations for the boundary sources is obtained. Here, we explore the use of a weak discretization strategy with more collocation points than force densities. The least squares enforcement of boundary conditions leads to a system with reduced number of unknowns. This approach naturally allows one to use both coarser and finer boundary discretizations for smooth and rapidly varying profiles, respectively. A well studied semicircular canyon under incident P or SV in-plane waves is used to calibrate this method. Several benefits are obtained using mixed meshing that leads to the least squares condensation of the IBEM. 相似文献
18.
A comprehensive numerical analysis of the seismic response and site period of curved alluvial valleys was performed by taking into account the characteristics of sedimentary materials. This study presents a criterion as a combination of the three following geometrical and geotechnical characteristics of curved valleys in order to provide a simple method for code implementation of complex site effects: depth ratio, filling ratio and impedance ratio. The parametric studies were performed by a HYBRID program combining finite elements in the near field and boundary elements in the far field (FEM/BEM). The amplification patterns under above-mentioned characteristics were determined at the central point of valleys. The results are shown in the form of response spectra. Different impedance coefficients of materials were considered to evaluate effects resulting from combination with filling ratio and geometrical parameters. Finally, a criterion is proposed in terms of engineering applications to assess the spectral response at the surface of curved alluvial valleys. 相似文献
19.
Marijan Dravinski 《地震工程与结构动力学》2003,32(5):653-670
Scattering of plane harmonic waves by a three‐dimensional basin of arbitrary shape embedded within elastic half‐space is investigated by using an indirect boundary integral equation approach. The materials of the basin and the half‐space are assumed to be the most general anisotropic, homogeneous, linearly elastic solids without any material symmetry (i.e. triclinic). The unknown scattered waves are expressed in terms of three‐dimensional triclinic time harmonic full‐space Green's functions. The results have been tested by comparing the surface response of semi spherical isotropic and transversely isotropic basins for which the numerical solutions are available. Surface displacements are presented for a semicircular basin subjected to a vertical incident plane harmonic pseudo‐P‐, SV‐, or SH‐wave. These results are compared with the motion obtained for the corresponding equivalent isotropic models. The results show that presence of the basin may cause significant amplification of ground motion when compared to the free‐field displacements. The peak amplitude of the predominant component of surface motion is smaller for the anisotropic basin than for the corresponding isotropic one. Anisotropic response may be asymmetric even for symmetric geometry and incidence. Anisotropic surface displacement generally includes all three components of motion which may not be the case for the isotropic results. Furthermore, anisotropic response strongly depends upon the nature of the incident wave, degree of material anisotropy and the azimuthal orientation of the observation station. These results clearly demonstrate the importance of anisotropy in amplification of surface ground motion. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
20.
Scattering of elastic waves by a three‐dimensional transversely isotropic basin of arbitrary shape embedded in a half‐space is considered using an indirect boundary integral equation approach. The unknown scattered waves are expressed in terms of point sources distributed on the so‐called auxiliary surfaces. The sources are expressed in terms of the full‐space Green's functions with their intensities determined from the requirement that the boundary and the continuity conditions are to be satisfied in the least‐squares sense. Steady‐state results were obtained for incident plane pseudo‐P‐, SH‐, SV‐, and Rayleigh waves. Using the Radon transform the Green's functions are obtained in the form of finite integrals over a unit sphere or a unit circle which can be numerically evaluated very efficiently. Detailed analysis of the method includes the discussion on the shape of the auxiliary surfaces and the distribution of the collocation points and sources. The convergence criteria is defined in terms of transparency tests, isotropic limit test, and minimization of a certain norm. The isotropic limit tests show excellent agreement with the isotropic results available in literature. For anisotropic materials the numerical results are given for a semispherical basin. The results show that presence of an anisotropic basin may result in significant amplification of surface motion atop the basin. While the amplitude of peak surface motion may be similar to the corresponding isotropic results, the difference in the displacement patterns may be quite different between the two. Therefore, this study clearly demonstrates that material anisotropy may be very important for accurate assessment of surface ground motion amplification atop basins. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献