横向各向同性介质纵波非双曲线时差速度分析

在各向异性介质中，纵波反射旅行时具有非双曲线时差特性，随排列长度的增大非双曲线现象更加明显。显然，常规双曲线时距曲线方程已经不能满足描述地震勘探中日益复杂的地球介质模型的需求。为此，在时距关系中增加含炮检距的四次项，并采用分式展开法表示该四次项，同时引入远偏移距收敛因子。改进后的时距关系表达式在形式上接近于常规地震波双曲线型时距关系，清楚地描述了横向各向同性介质中速度随炮检距的变化。实例表明，该算法提高了各向异性介质速度分析精度，改善了剖面叠加效果。     

基于TiNi合金的超弹性对其相关磨损机制的FEM研究

本文在重点考虑TiNi合金高弹性变形量的前提下，采用等向强化模型，对不锈钢和超弹TiNi合金在法向接触载荷作用下的六种模型进行了有限元(FEM)分析。结果表明：在相同载荷条件下，超弹TiNi合金产生的von Mises弹性应变要高于不锈钢，但其von Mises应力和塑性应变却恰恰相反，在同一载荷下该合金发生塑性变形的区域要小于不锈钢；此外，超弹TiNi合金发生塑性变形要比不锈钢困难，所需的临界载荷值随其最大弹性变形量(屈服点处的应变值)的增加而增加。最后，基于本文的有限元计算结果对超弹TiNi合金的蘑粒磨损和疲劳磨损机制进行了讨论。     

横观各向同性功能梯度圆板弯曲问题的精确解

对周边为弹性支承边界条件下的横观各向同性功能梯度材料圆板轴对称弯曲问题进行了分析.将位移函数写成傅里叶-贝塞尔级数的形式,根据横观各向同性功能梯度材料基本方程,并针对指数函数形式的梯度分布情况,对功能梯度圆板轴对称弯曲问题的位移和应力进行了精确分析.并通过具体算例,分析了在圆板上、下表面荷载作用下,材料性质的不同梯度变化对圆板结构响应的影响.分析结果表明,材料性质的梯度变化对圆板的力学性能有显著影响.     

饱和粘土中球孔扩张问题弹塑性解析

为了研究静力触探试验及沉桩扩孔等工程问题,基于修正剑桥模型,推导了不排水条件下球孔扩张问题的半解析解。将扩张球孔周围土体分为临界状态区、塑性区以及弹性区三个区域。弹性区内,利用弹性理论得到应力和孔隙水压力的解答;临界状态区及塑性区内,利用相关联的流动法则、拉格朗日分析法建立了关于应力的一阶非线性常微分方程组,以弹塑性界面处的应力分量作为初值,求解微分方程组可得到应力和孔隙水压力的解答。研究结果表明：各向同性超固结比对扩孔压力、土体应力、超孔隙水压力以及塑性区范围均具有显著影响,且扩孔过程中土体剪切模量并非常量,其随扩孔半径、各向同性超固结比的变化而变化;同时通过与已有解答进行比较,对本文方法的可靠性进行了验证。     

Experimental measurements of the phase and group velocities of body waves in a transversely isotropic medium

In this study, we perform an experimental result for measurements of the body wave phase and group velocities in transversely isotropic media (TIM) by through-transmission technique. After comparing the experimental and theoretical first arrival times of the waves, a difference between the phase velocity and group velocity is observed. When the ratio between propagation distance (d) of the wave and the diameter (D) of transducer is 2.4 for measuring phase velocity and the point probes configuration for measuring group velocity, the accuracy in velocity estimation can reach the limit of system's resolution. However if d/D is 7.8, the wave will propagate with an intermediate velocity between the phase and group velocities. The rapid change of the wave velocity and waveform for qSV-wave propagation with the group velocity has been observed at the propagation direction near the cusps. Therefore, in order to reduce the error in group velocity estimation of qSV-waves, the optimum directions are suggested at 20 and 60°.     

基于无网格局部Petrov-Galekin法的板结构拓扑优化

为将无网格法的优势集成到结构拓扑优化中,基于无网格局部Petrov-Galerkin(Meshless Local Petrov-Galerkin,MLPG)法进行板结构的拓扑优化.基于带惩罚的各向同性固体微结构(Solid Isotropic Microstructure with Penalization,SIMP...     

压差矢量水听器阵波束形成的优化

以各向同性噪声作为背景噪声场,对矢量水听器阵波束形成的优化方法进行了系统的研究.在分析各向同性噪声场中声压、振速相关性的基础上,利用最大信噪比准则推导了基阵的最佳增益与噪声场特性和阵列流形之间的关系,提出利用最佳增益权对阵列接收信号进行波束形成处理.通过对矢量水听器阵进行分解,将最佳增益波束形成引入矢量阵信号处理中.以二维压差矢量水听器阵作为接收基阵进行了仿真计算和湖上试验,结果表明,矢量阵的最佳增益波束形成可以获得性能更优的波束和更大的空间处理增益.     

相关扩散方程在图像修补中的应用

图像修复是图像复原研究中的一个重要内容,可以用于旧照片中丢失信息的恢复、视频文字去除以及视频错误隐藏等。目前有很多图像修补算法对于灰度图像的修补已经取得了很好的修补效果,但存在着时间消耗大和应用到彩色图像修补中时修补效果不理想的缺点。将相关扩散方程引入到图像修补中,并进行改进,使得图像的修补效率和修补效果都得到了有效提高,而且可以很自然地应用到彩色图像修补中。大量的实验证明了该方法的有效性。     

Effect of undulation on SH-wave propagation in corrugated magneto-elastic transversely isotropic layer

This article delves to study the effect of corrugated boundary surfaces on the propagation of horizontally-polarized shear waves (SH-waves) in a magnetoelastic transversely isotropic layer under a hydrostatic state of stress lying over an elastic half-space under gravity. A dispersion equation has been derived in closed-form and is found to be in good agreement to the classical Love-wave equation. The effect of magnetoelasticity, hydrostatic state of stress, gravity, corrugation, position parameter, and undulation on the phase velocity of the SH-wave has been identified. Numerical computation along with graphical demonstration has been carried out for cadmium, magnesium, and zinc materials of hexagonal symmetry to highlight some significant facts.     

Effects of Hall current and two temperatures in transversely isotropic magnetothermoelastic with and without energy dissipation due to ramp-type heat

The present article is concerned with the investigation of disturbances in a homogeneous transversely isotropic thermoelastic rotating medium with two temperatures, in the presence of the combined effects of Hall currents and magnetic field. The formulation is applied to the thermoelasticity theories developed by Green-Naghdi theories of type-II and type-III. Laplace and Fourier transform techniques are applied to solve the problem. The analytical expressions of displacements, stress components, temperature change, and current density components are obtained in the transformed domain. A numerical inversion technique has been applied to obtain the results in the physical domain. Numerical simulated results are depicted graphically to show the effect of Hall current and two temperatures on resulting quantities. Some special cases are also deduced from the present investigation.