金属晶界力学性质的计算机模拟

本文扼要介绍了基于原子间相互作用的计算机模拟方法以及它们应用于研究金属晶界上所取得的成功.文中列举了晶界的生成、原子弛豫结构、杂质偏聚和空位迁移等几个方面的工作作为例证.此外,对这种模拟方法的局限性作了评论.

变截面圆轴扭转问题用非正交曲线坐标的新解法

本文是在飞机发动机涡轮轴应力分析的基础上提高为变截面圆轴扭转问题的一个新解法.利用向量的散度和旋度对不同坐标系是不变量的特点,通过张量分析推导出在任意非正交曲线坐标系中变截面圆轴扭转问题的平衡和协调方程,包括用应力函数表达的协调方程和应力函数与应力分量的关系式.用任意非正交曲线坐标和差分法求解应力函数.本文计算得到了全轴的等应力函数线和剪应力分布,并得到沿小凹槽边任意点的应力,计算结果和光弹试验结果接近.本文还计算了有解析解的空心锥轴,误差小于百分之一.通过计算说明本文提出的新解法收敛性很好,并且所需计算机容量少(可在容量32k的TQ-16机上同时计算800多个节点),应用方便,便于编排通用程序,计算量较有限元法少;另一方面,由于采用了任意非正交曲线坐标,因此,适用于解决复杂曲线边界的问题,提高了通常用的差分法的适应性和灵活性;此外,本方法用应力函数作为未知量,从所得的等应力函数线和等位移函数线图可以看出全轴应力分布的概况,对于改进设计很有帮助.

东方红-60推土机车架强度分析

<正> 一、问题的提出推土机车架是按装推土机各部件(发动机、减速器、后桥和驾驶座等)的基础。车架除承受这些部件的重量以及由此引起的动负荷外,还承受相当大的履带工作张力以及地面作用于车轮正向和侧向的阻力。因此在实际工作中,车架各杆件均处于拉、扭、弯、压同时作用的这一复杂而又繁重的工作载荷条件下。由于车架是推土机的基础,不管车架是变形还是损坏都会直接影响到推土机的正常使用。因此,必须保证车架有足够的强度和刚度。

关于弹性体固有频率的两个变分原理

<正> 对于几何形狀较复雜的彈性体,要嚴格地根据彈性体力学的全部方程來决定它的固有频率是有很大的困难的,因此在实际上常常采用了各式各样的近似解法,其中最有名的近似解法要算根据萊瑞原理的变分解法(称为萊瑞黎茲法)。在許多問題中,萊瑞黎兹法給出了滿意的結果。但是这个方法在实用上及理論上遺留下两个問題:第一、在許多問題中,我們往往能对应力分布的情況作适当的估計,可是这些估計在萊瑞黎兹法中不能加以充分利用;第二、在各种近似理論中,例如在梁、板、壳的近似理論中,虽然都各有自己的萊瑞原理,可是这些原理并不是彈性体力学中的萊瑞原理的直接的特殊形式。

Diffusion dominated process for the crystal growth of a binary alloy

The pure diffusion process has been often used to study the crystal growth of a binary alloy in the microgravity environment. In the present paper, a geometric parameter, the ratio of the maximum deviation distance of curved solidification and melting interfaces from the plane to the radius of the crystal rod, was adopted as a small parameter, and the analytical solution was obtained based on the perturbation theory. The radial segregation of a diffusion dominated process was obtained for cases of arbitrary Peclet number in a region of finite extension with both a curved solidification interface and a curved melting interface. Two types of boundary conditions at the melting interface were analyzed. Some special cases such as infinite extension in the longitudinal direction and special range of Peclet number were reduced from the general solution and discussed in detail.

Experiment on the thermocapillary convection of a mercury liquid bridge in a floating half zone

A liquid bridge of a floating half zone consisting of liquid mercury sealed in a glass tube with nitrogen atmosphere was used for the experiment of thermocapillary convection with a low Prandtl number liquid. A non-contacted diagnostic method was developed to monitor the surface flow and the surface oscillation. A growing surface film (or skin) is a crucial source to suppress thermocapillary convection, and is discussed in this paper. For the case of a mercury Liquid bridge, the critical Marangoni number was obtained as 900, and the oscillatory frequency was around 5 Hz.

Internal resonance of an L-shaped beam with a limit stop .1. Free vibration

Real-life structures often possess piecewise stiffness because of clearances or interference between subassemblies. Such an aspect can alter a system's fundamental free vibration response and leads to complex mode interaction. The free vibration behaviour of an L-shaped beam with a limit stop is analyzed by using the frequency response function and the incremental harmonic balance method. The presence of multiple internal resonances, which involve interactions among the first five modes and are extremely complex, have been discovered by including higher harmonics in the analysis. The results show that mode interaction may occur if the higher harmonics of a vibration mode are close to the natural frequency of a higher mode. The conditions for the existence of internal resonance are explored, and it is shown that a prerequisite is the presence of bifurcation points in the form of intersecting backbone curves. A method to compute such intersections by using only one harmonic in the free vibration solution is proposed. (C) 1996 Academic Press Limited

H4 exponential finite-difference scheme for convective diffusion-equations

Perturbations are applied to the convective coefficients and source term of a convection-diffusion equation so that second-order corrections may be applied to a second-order exponential scheme. The basic Structure of the equations in the resulting fourth-order scheme is identical to that for the second order. Furthermore, the calculations are quite simple as the second-order corrections may be obtained in a single pass using a second-order scheme. For one to three dimensions, the fourth-order exponential scheme is unconditionally stable. As examples, the method is applied to Burgers' and other fluid mechanics problems. Compared with schemes normally used, the accuracies are found to be good and the method is applicable to regions with large gradients.

NaClO_3晶体生长过程光学诊断与数值模拟

运用光学干涉诊断方法实时观测NaClO3晶体生长过程,得到晶体生长过程中溶液浓度,晶体尺寸等物理参量.将这些参量与数值模拟得到的结果进行比对,研究重力条件下NaClO3晶体溶液生长过程中速度场、浓度场的分布与演化,尝试提出符合实际情况的晶体生长理论模型.对比两种方法得到的浓度边界层厚度,数值模拟得到了与实验数据相一致的结论.