半空间内圆孔对稳态入射平面SH波的散射

利用复变函数方法、多极坐标移动技术和Graf加法公式讨论半空间内圆孔对稳态入射平面SH( shearing horizontal)波的散射问题.首先写出介质内的自由波场和散射波场,它们能够预先满足半空间边界自由应力条件;其次,利用Graf(格喇夫)加法公式,将虚源波函数进行数学变换,使之与圆孔产生的波函数共同表示为同一个无穷正交函数级数的形式;最后利用圆孔边界处的应力自由条件,得出确定散射波函数中未知系数的无穷线性代数方程组,该方法避免了散射波函数傅里叶级数展开中积分的数值计算,因而显著地提高收敛速度和计算精度.算例结果表明方法的可行性.     

弹性波散射反演的一种新思路

针对半空间界面半圆形凹陷和介质内圆孔对SH(shearing horizontal)波散射的反演问题提出一种优化求解方法.具体分析两种情况下弹性波散射反演问题的模型和特点,给出反演目标函数和反演数学模型,利用黄金分割法或对分法进行寻优求解.算例结果表明方法的可行性.文中方法对研究得比较成熟的弹性波散射正演问题对应的反演问题的求解具有应用价值和理论指导意义.     

四分之一空间内椭圆孔对SH(shearing horizontal,反平面剪切)波的散射

利用保角变换和多极坐标移动技术,求解四分之一空间内含有椭圆孔时椭圆孔对入射平面SH(shearing hori-zontal)波的稳态散射问题。首先利用四分之一空间两垂直边界处的应力自由条件,写出不含椭圆孔时空间介质内的反射波场;其次,通过保角映射技术考虑空间介质内含有任意主轴方向的椭圆孔时,由于椭圆孔对入射和反射波场的散射作用而产生的散射波场,并预先使得该散射波场满足四分之一空间介质两垂直边界处的应力自由条件,利用叠加原理,将入射波场、反射波场和散射波场叠加起来,即可得到问题的总位移波场。最后借助于椭圆孔边界处的应力自由条件和傅里叶级数展开列出求解散射波解中未知系数的无穷代数方程组,在满足计算精度的前提下将方程组进行有限项截断,得到一个有限线性方程组并求解。通过算例具体讨论四分之一空间内椭圆孔边界处的环向动应力集中系数随入射波入射角、无量纲波数、椭圆孔方位参数的变化情况。     

二维直角平面内偏心圆形衬砌对稳态入射平面SH波的散射

利用复变函数法、多极坐标变换及傅里叶级数展开技术求解二维直角平面内偏心圆形衬砌对稳态入射平面SH(shearing horizontal)波的散射问题.首先构造出介质内不存在偏心圆形衬砌时的入射波场和反射波场;其次建立介质内存在偏心圆形衬砌时由衬砌外边界产生的能够自动满足直角边应力自由条件的散射波解和衬砌外边界向衬砌介质内的折射波解以及衬砌内边界的散射波解,从而利用叠加原理可写出衬砌介质内外的总波场.利用衬砌外边界处应力位移的连续条件和内边界处应力自由条件以及傅里叶级数展开方法列出求解波解中未知系数的无穷代数方程组,在满足计算精度的前提下通过有限项截断,得到相应有限代数方程组的解,最后通过算例具体讨论衬砌内边界处的动应力集中系数和水平直边界位移幅度比及其相位随无量纲波数、入射波入射角、衬砌位置及其偏心度的不同而变化的情况,结果表明文中算法的有效实用性.     

半空间界面弹性柱支撑体对反平面SH波的动态响应

利用波函数展开法和格林(Green)函数法讨论半空间水平界面上弹性柱支撑体对入射反平面SH(shearinghorizontal)波的散射效应。首先解一个双曲偏微分方程定解问题,确定出不含界面弹性柱支撑体的完整半空间内的自由位移场及其对应的格林函数解;其次,利用叠加原理得到含界面弹性柱支撑体时半空间内的总位移场,并通过牛顿定律列出弹性柱支撑体的动态响应方程;最后借助于问题的位移边界条件和力边界条件写出未知力满足的定解积分方程,并给出其解析解。通过一个算例的数值解说明方法的可行性。     

直角平面内圆形弹性夹杂对稳态入射平面SH波的模糊散射

用多极坐标移动技术、格拉夫(Graf)加法公式和扩张原理研究含模糊波数直角平面内圆形弹性夹杂对稳态入射平面SH(shearing horizontal)波的模糊散射问题。首先利用直角平面两直角边界应力自由条件写出介质内的自由波场和散射波场;其次,利用圆形弹性夹杂边界处的应力和位移连续条件、傅里叶级数展开和Graf加法公式得到确定散射波函数中未知系数的无穷线性代数方程组。为了利用模糊波数的模糊信息,将模糊波数理解为模糊参数,将其支集等距划分,利用扩张原理通过确定性方法间接得到划分节点处的模糊波场值及其隶属度。实际计算表明,该算法收敛速度快,计算精度高,数值结果稳定,且能克服求解模糊波响应隶属度信息的困难。     

圆形区域内圆孔对SH波的散射

圆形截面区域内圆孔对弹性波的散射问题是无损探伤等应用领域内的主要研究对象之一,一直未在理论上给予解决。利用复数法、特殊函数加法公式和波函数展开法研究了圆形区域内圆孔缺陷对区域外边界反平面分布载荷的动态响应问题,给出了圆域内的位移场和圆孔缺陷边界处应力集中系数的计算方法,讨论了缺陷边界处应力集中系数随扰动频率、偏心距和方位角的变化关系,并通过数值算例分析验证了理论的研究结果,说明了边界和载荷对集中系数的影响。     

无限长带形域内圆孔的反平面响应

无限大带形区域内含圆孔的弹性波散射问题,由于涉及到两条直边界,在理论研究上一直是没有解决的问题,而只能借助于数值求解的办法。利用复变函数法、虚源法和Graf加法公式给出了该问题的散射波解析解,它能够预先满足两条边界上的应力自由条件,利用圆孔边界处的应力边界条件和傅立叶级数展开来确定散射波函数中的未知系数,从而确定出带形区域内的波场,最后通过一个算例计算了圆孔边界处的环向动应力集中系数,说明了文中结论和算法的正确性。     

半空间边界半圆形凹陷对SH波散射的模糊响应

利用波函数展开法考虑半空间边界半圆形凹陷对SH(shearing horizontal)波的(模糊)散射问题,得到边界半圆形凹陷处环向动应力集中系数和位移放大系数与波数之间的非线性关系式,考虑到波数的模糊性,为避免区间算法的不可逆性以及非线性方程求解的困难,特将模糊量隶属函数分段处理,使隶属度与模糊量一一对应,从而将原来的模糊问题转化为分段处理的确定性问题.给出的算例具体讨论凹陷边界处环向动应力集中系数和位移放大比率由于波数的模糊性而带来的模糊变化分布情况.     

嵌地半圆形刚平台双自由度传感系统地动响应

利用波函数展开法和振动理论讨论了半空间界面半圆形刚性平台上双自由度振动系统的反平面响应问题。利用弹性波动理论写出半空间介质内的总位移波场,应用振动理论列出双自由度振动系统满足的二阶常系数微分方程组,通过半圆形刚性平台与介质界面之间的位移和应力连续条件求出散射波函数中未知系数,最后确定出振子和半圆形刚性平台分别相对于入射波振幅的位移振幅比以及刚性平台边界处介质内的环向应力集中系数的变化规律,并通过数值算例给出了计算结果,说明了分析结论的正确性。     

Study on the scattering of 2-D Rayleigh waves by a cavity based on BEM simulation

A frequency domain boundary element method is introduced in this paper to simulate the scattering of two-dimensional Rayleigh waves by a cavity on the surface of an elastic half-space. This numerical method allows the Rayleigh wave to escape the truncated boundary without producing any spurious reflections. The numerical results of the displacements and stresses of a 2-D Rayleigh wave which travels along a flat surface of an elastic half-infinite medium are in good agreement when compared with theoretical ones. The problem of a Rayleigh wave scattering by a cavity on the surface of an elastic half-infinite medium is simulated by the proposed numerical method. The result is taken as the benchmark to introduce an approximate analytical method for such problems of scattering by a cavity on the surface. This numerical method is formulated for a two-dimensional homogeneous, isotropic, linearly elastic half-space and its implementation in a frequency domain boundary scheme is discussed in detail.     

直角平面内圆形刚性动夹杂对边界出平面点源载荷的动态响应

采用复变函数法和多极坐标移动技术研究二维直角平面区域内可动圆形刚性夹杂在边界出平面点源载荷作用下的动态响应问题.首先构造出直角平面区域内不含有夹杂时满足直角边界应力条件的格林(Green)函数解;其次求解波动方程边值问题,建立直角平面区域内含有夹杂时满足直边界应力自由条件的散射波解,利用叠加原理写出问题的总波场.借助于夹杂边界处的位移条件和夹杂运动的动力学条件,确定夹杂运动的位移幅度和散射波解中的未知系数.给出的算例结果表明本文方法的有效实用性.     

Impression creep: Effects of slip, stick and cavity depth

The impression creep of a power-law material by pushing a rigid cylindrical punch into an existing cavity of the same diameter as the punch located in the surface of a half-space was studied by using finite element method. For both the slip and stick conditions at the interface of the punch and the half-space, there is a well-defined steady punch penetration velocity after a transient stage. The steady penetration velocity is a power function of the applied load, which has the same stress exponent as by conventional creep tests. It increases with the stress exponent but decreases with increasing cavity depth, and is the largest for all slip condition and the smallest for both stick condition on the circular interface between the punch and the cavity and all stick condition.     

A magnetostatic problem for a half-space with a spherical flaw in the field of a coil

A magnetostatic problem for a half-space with a constant magnetic permeability and an internal spherical cavity has been solved. The external field is produced by a coil with a constant current, the axis of which is perpendicular to the surface of the half-space. The results of calculations are used to construct the dependences of the Cartesian components of the resulting field on the coordinates and parameters of the problem.     

Solution of a plane contact problem of the theory of elasticity on the basis of an elastic half-space model

A theoretical solution of a plane contact problem of the theory of elasticity based on a method of determination of the convergence of elastic bodies using an elastic half-space model is presented, and the contact deformation (diameter change) of circular cylinders with parallel axes is deter-mined on its basis. The possibility of obtaining a precise solution for the problem, using an elastic half-space model based on the Hertz theory, is demonstrated for the first time. It is shown that the known Kovalskii solution for contact deformation of circular cylinders with parallel axes is a rough approximation of a more precise solution of the problem. It is found that the obtained result agrees well with the Dinnik’s experimental data.     

Tensionless contact of a flexible plate and annulus with a smooth half-space under axisymmetric loads by integral equations

In this paper, a new hybrid method of analysis is presented for the problem of a frictionless circular plate or annulus in tensionless contact with a half-space. By virtue of a set of analytically explicit Green's functions for the two interacting continua, an exact but compact integral equation formulation with closed-form kernels is derived. With the incorporation of a newly developed adaptive-gradient (AG) element capable of capturing regular-to-singular solution transitions smoothly, an accurate numerical procedure is developed and validated in a number of benchmark cases of nonlinear plate–annulus–half-space interaction. From the simplicity and rate of convergence demonstrated, the hybrid method is apt to be an attractive analytical–numerical platform that can be extended to a large class of contact problems.     

Analytical and numerical methods of solution of three-dimensional problem of elasticity for functionally graded coated half-space

In the present paper, a three-dimensional problem of elasticity for homogeneous half-space with gradient coating is considered. Poisson's ratio of the layer is constant and its Young's modulus is a power function of the distance from the surface of the half-space. The surface of non-homogeneous half-space is under tangential loading applied in circular area. Analytical solution is obtained using Fourier integral transform technique. The analytical solution of the problem in continuous dependence of the Young modulus is compared with the solution of the problem in which the inhomogeneous layer is modeled by the package of homogeneous layers. In sub-layers of a package and in substrate is constructed an analytical solution satisfying the conditions of ideal mechanical contact at interlines. Good agreement between results is obtained.