电介质半空间中线结构导体电磁散射的直接时域分析方法

针对半空间中线结构导体电磁散射的时域电场积分方程,采用矩量法(MOM)结合时间步进算法(MOT)直接在时域求解导体上的瞬态电流以及空间的瞬态电场。该方法具有求解速度快,时域响应过程机理明晰的特点。针对计算实例的分析结果与文献结果相吻合。     

Surface-breaking crack in an elastic half-space

A semi-infinite crack terminating at the boundary of an elastic half-space is considered. It is assumed that the crack is subjected to a mode-I load applied in a finite region remote from the crack plane, and the boundary of the half-space and the crack surfaces are free of tractions. The problem is formulated in terms of a hypersingular integral equation with respect to the relative crack-face separation defined over the region occupied by the crack. The behaviour of the solution near the corner point where the crack edge intersects the boundary is analysed and results which show the dependence of the stress singularity exponent on the angle of inclination of the crack edge are presented.     

Slow vertical motions of an elliptic punch on an elastic half-space

The dynamic contact problem for a homogeneous, isotropic elastic half-space and a punch of an arbitrary base shape is studied. During the motion of the punch it is assumed that the contact area is fixed and there is no friction under the punch. An approximate solution to the problem is obtained under the assumption that the contact pressure under the punch is slightly varied during the time of travel of the Rayleigh wave along the distance equal to the diameter of the contact area. The solution of the problem of slow motions of a punch on an elastic half-space is reduced to the solution of the recurrent system of integral equations of the static contact problem. Asymptotic models of vertical motions of a flat-ended punch with an arbitrary base are constructed. The case of an elliptic punch is considered in detail.     

Numerical analysis for environmental effects in circular tanks

An efficient numerical method of analysis for environmental (thermal, shrinkage, and swelling) effects in circular, concrete, liquid storage thin-walled tanks under conditions of axial symmetry is outlined. Although the approach is based on individual analyses of wall and plate sub-structures, it yields the global solution that accounts for actual interaction between the wall and plate elements. This interaction between the tank main elements is introduced in a Force Method-type procedure by utilising conditions of compatibility of displacements at the wall-plate junctions. The analysis technique is applicable to a wide range of circular-cylindrical tank systems in contact with a variety of support media. The numerical treatment of the considered environmental effects presented herein extends the approach outlined earlier by the author [1 and 2] and is just a part of design analysis that includes also tank pre-stressing. The effectiveness and usefulness of the proposed method and of the computer software developed are tested with the included examples.     

饱和半空间中隧道衬砌对平面SV波的散射IBIEM求解

基于Biot两相介质理论,采用一种高精度的间接边界积分方程法(IBIEM),研究了平面SV波在饱和半空间中隧道衬砌周围散射的基本规律,并给出了不同参数下地表位移幅值、衬砌动应力集中因子及表面孔隙水压分布图和相应的频谱结果。数值分析表明:饱和半空间隧道衬砌对SV波的散射特征取决于围岩介质孔隙率、入射波的频率和角度、隧道埋深等因素;隧道外壁透水状态对地表位移和隧道应力影响不大;不同角度SV波入射下,隧道应力集中部位有很大差别,且随半空间介质孔隙率增大,应力集中越发显著;衬砌外壁孔隙水压峰值可达到入射波应力幅值的4倍,且30°斜入射下幅值明显大于0°垂直入射情况;衬砌上方附近不同点位位移频谱特征差异显著,斜入射情况位移放大效应明显;随埋深增大,地表位移幅值和衬砌表面动应力谱振荡更为剧烈,但幅值会有所降低。另外,按波速比等效的单相介质模型可以近似计算SV波入射下隧道–饱和围岩的位移场和应力场。     

Propagation of Radar Pulses from a Horizontal Dipole in Variable Dielectric Ground: A Numerical Approach

We numerically investigate the propagation of radar type short pulses from a horizontal dipole in the presence of some simple models of inhomogeneous ground with a flat surface. We use 3-dimensional (3-D) pseudospectral time domain (PSTD) and 2-D finite difference time domain forward modeling to determine the range and azimuth dependence of electric field components and to simulate events in a moveout profile. The models are: (i) a uniform half space with either high or low conductivity; (ii) a vertical dielectric wedge; (iii) a surface thin layer with a monocline wedge overlaid on the dielectric half space. Our homogeneous results agree with the analytical solutions, and more clearly show the significant vertical electric field component, which occurs for all models. The incorporation of an anomalous dielectric quadrant does not affect the air wave and only complicates ground wave propagation near the boundary. Modeling of a monocline dielectric wedge shows predictable subsurface reflections and refractions, some of which are highly dispersive events, depending on the direction of propagation. We present two field examples that appear to demonstrate some of our findings. We conclude that air waves make suitable references for moveout profiles regardless of dielectric complications, and that our results provide some insight into the interpretation of unique events seen in moveout profiles.     

粘弹性半空间在简谐分布荷载下的稳态响应

本文采用三参数分数导数粘弹性本构模型分析了粘弹性半空间在简谐分布荷载下的稳态响应。数值计算结果给出了衰减因子与频率和分数导数阶数之间的关系曲线。结果表明:当分数导数阶数在-1/2和1/3之间时,材料的阻尼效果最佳。这与 Rouse 的分子理论和由实验曲线拟合所得结果一致.     

频域内求解移动荷载作用下三维层状场地动力响应的理论推导

基于Hung教授所做移动荷载作用下弹性半空间的振动分析,给出了频域内求解移动荷载作用下三维层状场地动力响应的理论推导,得到弹性半空间动力刚度矩阵和单层土动力刚度矩阵;根据相邻层连接处的平衡条件和变形协调条件,得到具有对称性精确分析、且不受土层厚度影响的整体刚度矩阵。本理论分析方法可用于求解三维层状场地在车辆移动荷载作用下的动力响应问题。     

层合介质中平面SH波的传播

研究了平面SH波通过多层弹性层状介质时的传播特性,求得了透射波和反射波振幅的解析解表达式,并把本文表达式的特例与现有文献结果作了对比,结论一致,同时进行了含单一夹层时SH波的室内砂池模拟试验,试验结果与理论结果基本吻合。     

考虑桩底土层波动效应的饱和黏弹性半空间中摩擦桩竖向振动

为深化对饱和黏弹性半空间地基中摩擦桩竖向振动特性的认识,基于Boer多孔介质动力控制方程组,考虑桩底土层波动效应,采用Hankel积分变换和微分算子分解理论求解相关方程得到桩底、桩侧反力,进而建立饱和土中桩基竖向振动偏微分方程,结合桩土接触面混合边值条件推导得出了饱和黏弹性半空间地基中摩擦桩桩顶竖向动力阻抗解析表达式。并在此基础上进一步通过数值算例对比分析探讨了液固耦合系数、桩长径比、桩土模量比、地基土黏滞阻尼系数这些重要因素对所得桩顶动力阻抗的影响规律,得到了一些对工程实践有意义的结论。