The multi-parameter inversion of elastic wave in half-space

The multi-parameter inverse scattering problem of elastic wave equation with single frequency is investigated within Born approximation. By use of a wideband measuring scheme in which both transmitters and receivers scan over the half-space surface, the formula of the scattering field of elastic wave is derived. Four types of mode conversion of elastic wave (P→P,P→S,S→P,S→S) are separated from the scattering field. These components contain sufficient information for us to reconstruct the configurations of the density and Lamé parameters of the medium. The inverse formulas have the form of filtered back-propagation as in the acoustic diffraction tomography. Computer simulations are also obtained. Supported by Foundation of Ph.D Program of the State Education Commission of China.     

成层半空间出平面自由波场的一维化时域算法

提出了一种计算出平面SH波斜入射时弹性水平成层半空间中自由波场时域计算的一维化有 限元方法. 在进行有限元网格划分时,竖向单元取满足有限元模拟精度的任意尺寸,水平向 网格尺寸由时间离散步长和水平视波速确定,并自动进行虚拟网格划分. 基底设置人工边界, 并将波动输入转化为等效荷载施加在边界节点上. 然后将集中质量有限元法和中心差分法相 结合建立节点运动方程,并将水平方向相邻节点的运动用该节点相邻时刻的运动表示,从而 将求解节点运动的二维方程组转化为一维方程组. 求解此方程组,即得到自由场中竖向一列 节点的运动. 最后根据行波传播的特点,可方便地确定全部自由波场. 理论分析和数值算例 表明,该方法具有较高的精度和良好的稳定性.     

基于弹性波反演的压力管道损伤识别

基于弹性波的波动方程反演提出压力管道的损伤检测方法，根据直杆的波动方程，用直杆的横截面积作为反演参数模拟管道损伤，在优化思想下利用序列二次规划对其进行数值反演，达到损伤识别。     

基于子结构的非线性参数系统动力反演方法研究

研究了输入、输出不完备情况下的非线性参数系统动力反演问题.将子结构技术与分解算法相结合,引入广义逆,无需迭代.直接求得待识别参数的极小范数最小二乘解,反演获得未知输入荷载.本文从理论上论证了该方法的收敛性和严格的适用条件,为有限测点条件下非线性参数系统的动力反演问题提供了一个较好的解决方法.与全量补偿算法相比,计算效率大大提高,具有广泛的工程实际应用前景.数值算例表明该方法具有很好的参数识别精度及荷载反演效果.     

Interaction of slowly moving punches with an elastic half-space

The problem of slow dynamic contact interaction of a system of punches remote from each other with an elastic half-space surface in the absence of friction is studied under the assumptions that the diameters of the contact areas are smaller than the minimum distance between the punches and the time required for the shear wave to travel the distance equal to the punch diameter is comparable to the time scale of the process. A first-order asymptotic model is constructed. As an example, the case of steady-state vibrations of a system of two punches is considered. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 198–206, November–December, 2008.     

非饱和弹性半空间地基的稳态响应半解析法研究

应用半解析法研究简谐荷载下非饱和弹性半空间地基的稳态响应。基于非饱和土的动力控制方程以及非饱和弹性半空间的边界条件,建立地基层单元的半解析函数,应用加权残数法得到在简谐荷载下非饱和弹性半空间地基的稳态响应半解析方程。对半解析方程求解,得到了竖向简谐荷载作用下非饱和弹性地基水平位移和竖向位移幅值,数值分析了饱和度和地基深度等参数对孔压和位移幅值的影响。研究结果表明,应用本文方法研究非饱和弹性半空间地基的稳态响应是切实有效的。     

THE ELASTIC FIELD INDUCED BY A HEMISPHERICAL INCLUSION IN THE HALF—SPACE

The elastic field induced by a hemispherical inclusion with uniform eigeustralns in asemi-infinite elastic medium is solved by using the Green‘s function method and series expansion tech-nique. The exact solutions axe presented for the displacement and stress fields which can be expressedby complete elliptic integrals of the first, second, and third kinds and hypergeometric functions. Thepresent method can be used to determine the corresponding elastic fields when the shape of the inclusionis a spherical crown or a spherical segment. Finally, numerical results axe given for the displacementand stress fields along the axis of symmetry (x3-axis).     

Contact interaction of an elastic punch and an elastic half-space with initial (residual) stresses

The contact interaction of an elastic punch of arbitrary cross-section and an elastic semi-space with initial (residual) stresses is studied. A general method to solve the problem is proposed. It allows solving contact problems for bodies with initial (residual) stresses when the solution of the corresponding elastic problem is known __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 12, pp. 28–40, December 2007.     

Response of an elastic half-space with power-law nonhomogeneity to static loads

In this paper a series of problems for an isotropic elastic half-space with power-law nonhomogeneity are considered. The action of surface vertical and horizontal forces applied to the half-space is studied. A part of the paper deals with the case of zero-valued surface shear modulus (for positive values of the power determining the nonhomogeneity). This condition leads to simple solutions for two-dimensional (2D) case when radial distribution of stresses exists for surface loads concentrated along an infinite line. Corresponding results for the three-dimensional (3D) case are constructed on the basis of the relationships between 2D and 3D solutions developed in the paper. A more complicated case, in which the shear modulus at the surface of the half-space differs from zero, is treated using fundamental solutions of the differential equations for Fourier–Bessel transformations of displacements. In the paper the fundamental solutions are built in the following two forms: (a) a combination of functions expressing displacements of the half-space under the action of vertical and horizontal forces in the case of zero surface shear modulus, and (b) a representation of the fundamental solutions using confluent hypergeometric functions. The results of numerical calculation given in the paper relate to Green functions for the surface vertical and horizontal point forces.     

Rayleigh-type waves in a water-saturated porous half-space with an elastic plate on its surface

The paper deals with the plane problem of steady-state time harmonic vibrations of an infinite elastic plate resting on a water-saturated porous solid. The displacements of the plate are described by means of the linear theory of small elastic oscillations. The motion of the two-phase medium is studied within the framework of Biot's linear theory of consolidation. The main interest is focused on the investigation of properties of the Rayleigh-type waves propagating alongside of the contact surface between the plate and the porous half-space. In particular, the dependence of the phase velocity and attenuation of the waves on the plate stiffness, mass coupling coefficient, and degree of saturation of the medium is studied. Besides, for the limiting case of an infinitely thin plate, the comparison of the wave characteristics is carried out with those of the pure Rayleigh waves.     

On the possibility of local buckling of the surface of an elastic half-space under compression

The possibility of local buckling of the free surface of the lower half-plane under compression is studied in a static formulation within the framework of plane deformation. It is shown that in some media small subcritical strains can lead to local buckling of the half-plane surface. It is found that two forms of local surface buckling correspond to one critical compression load. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 3, pp. 149–152, May–June, 2005.     

波数-频率域内地基土表面位移Green函数的理论分析

建立了柱面坐标系下分层弹性半空间地基土模型。利用钟阳刚度矩阵法和Haskell-Thomson传递矩阵法推导出所有分层土体之间的振动传递关系;根据Helmholtz定理将土体的位移向量分解成势函数的形式,推导出弹性半空间表面应力与位移之间的关系;再将分层土体和半空间地基土通过位移与应力之间的关系进行耦合,得到分层弹性半空间地基土模型表面位移与应力之间的关系。结合单位脉冲荷载作用下地基土表面的边界条件,推导出波数-频率域内地基土表面位移Green函数的解析解,用Matlab程序语言对理论进行实现并通过算例对地基土表面位移Green函数的特征进行了分析和总结。     

Application of transition matrix to scattering of elastic waves in half-space by a surface scatterer

A transition matrix formulism for the scattering problems of elastic waves using a surface scatterer of three-dimensional half-space is derived by applying Betti's third identity and orthogonality conditions. The basis functions and their corresponding regular parts are derived from Lamb's singular solutions. The new orthogonal functions are constructed based on the linear transform. The intrinsic properties of the scattering and transition matrices derived in this paper are investigated. Numerical results for verification are presented and discussed.     

半无限横观各向同性体中共面双裂纹边界元分析

基于双横观各向同性材料基本解的对偶边界元方法,分析了半无限横观各向同性材料中两条共面裂纹的相互作用问题。裂纹面上分别作用着法向和切向两种均布荷载,材料的各向同性面及裂纹面平行于半无限域自由面。数值计算得到了该类裂纹的应力强度因子(SIF)值和两条共面裂纹相互作用的SIF值影响系数。根据数值结果分析了自由面对该类裂纹SIF值的影响,以及裂纹间距与形状、自由面对SIF值影响系数的影响。结果表明,自由面对作用法向力时的该类裂纹SIF值有明显的影响,裂纹间距与形状对SIF值影响系数影响较大,但自由面对SIF值影响系数基本无影响。     

The general solution of second order effects in elastic half-space acted upon by a non-uniform shear load

I.IntroductionInfiniteelasticitytheorythemathematicalequationsgoverningthedeformationofanisotropiccompressibleelasticmaterialarehighlynonlinear.Asaresult,theexactsolutionsoftheboundaryvalueproblemshavebeenpossibleonlyinsomerestrictedcasesand,oftenapproxim…     

The illustration calculations of second order effects in elastic half-space acted upon by a non-uniform shear load

I.IllustrationsThegeneralsolutionofsecondordereffectsinelastichalfspaceacteduponbyanon-uniformshearloadpresentedbypaperIl]areapplicableforallvalueof6>-l,butareverycomplicated.Asani1lustrationofthemethodwegivebelowthelinearandsecondordersolutionsfor8=l/2.T…     

Rayleigh waves in an isotropic elastic half-space coated by a thin isotropic elastic layer with smooth contact

In the present paper, we are interested in the propagation of Rayleigh waves in an isotropic elastic half-space coated with a thin isotropic elastic layer. The contact between the layer and the half space is assumed to be smooth. The main purpose of the paper is to establish an approximate secular equation of the wave. By using the effective boundary condition method, an approximate, yet highly accurate secular equation of fourth-order in terms of the dimensionless thickness of the layer is derived. From the secular equation obtained, an approximate formula of third-order for the velocity of Rayleigh waves is established. The approximate secular equation and the formula for the velocity obtained in this paper are potentially useful in many practical applications.     

Nonlinear time transformation method for strong nonlinear oscillation systems

In this paper, a nonlinear time transformation method is presented for the analysis of strong nonlinear oscillation systems. This method can be used to study the limit cycle behavior of the autonomous systems and to analyze the forced vibration of a strong nonlinear system. The project partly supported by the Foundation of Zhongshan University Advanced Research Center     

Linearized inverse scattering for elastic parameters in a half-space with reflection data

ＩｎｔｒｏｄｕｃｔｉｏｎＭｕｌｔｉｐａｒａｍｅｔｅｒｉｎｖｅｒｓｅｓｃａｔｔｅｒｉｎｇｆｏｒｅｌａｓｔｉｃｍｅｄｉｕｍｉｓａｆｏｕｎｄａｔｉｏｎａｌｐｒｏｂｌｅｍｉｎｓｅｉｓｍｏｌｏｇｙａｎｄｎｏｎｄｅｓｔｒｕｃｔｉｖｅｔｅｓｔｉｎｇ .ＷｉｔｈｉｎｔｈｅＢｏｒｎａｐｐｒｏｘｉｍａｔｉｏｎ ,ｔｈｉｓｐｒｏｂｌｅｍｈａｓｂｅｅｎｉｎｖｅｓｔｉｇａｔｅｄｂｙｓｅｖｅｒａｌａｕｔｈｏｒｓ.Ｂｌａｃｋｌｅｄｇｅｅｔａｌ.[1]ｈａｖｅｅｘｔｅｎｄｅｄｔｈｅＸ＿ｒａｙｔｏｍｏｇｒａｐｈｙｓｃｈｅｍｅｔｏｔｈｅｄ…     

Abel inversion of axially-symmetric shock wave flows

Finite-fringe interferograms produced for axisymmetric shock wave flows are analyzed by Fourier transform fringe analysis and an Abel inversion method to produce density field data for the validation of numerical models. For the Abel inversion process, we use basis functions to model phase data from axially-symmetric shock wave structure. Steady and unsteady flow problems are studied, and compared with numerical simulations. Good agreement between theoretical and experimental results is obtained when one set of basis functions is used during the inversion process, but the shock front is smeared when another is used. This is because each function in the second set of basis functions is infinitely differentiable, making them poorly-suited to the modelling of a step function as is required in the representation of a shock wave.Received: 12 November 2003, Accepted: 21 October 2004, Published online: 31 March 2005[/PUBLISHED]PACS: 47.40.-x, 42.40.Kw, 02.30.Zz