论陀螺的迴转稳定准则及其应用

本文以卡尔丹角为方位参量,建立了轴对称刚体(陀螺)永久转动情形的非线性稳定方程组。应用直接方法证明了具有完全耗散情形的陀螺迴转稳定准则:陀螺绕对称轴自由迴旋稳定的充要条件是转子呈扁形。这一准则不仅为陀螺仪设计提供理论依据,而且为飞行器用自旋稳定实现姿态控制提供理论依据。美国发射的Fxplorer-1号绕长轴自旋失稳和第一颗通讯卫星Syncon号绕短轴自旋取得姿态控制成功的事实都能依据这一准则得到合理解释。

论侧向应力与疲劳裂纹扩展

本文通过对Ⅰ型平裂纹及复合型斜裂纹的疲劳试验说明:虽然平行于裂纹面的正应力(侧向应力)对应力强度因子不起作用,但是对裂纹顶端的塑性变形,从而对疲劳裂纹扩展速率却有明显的影响.相应于同样的应力强度因子幅值,当双轴载荷比λ=1时,侧向应力为零,裂纹扩展最慢;随着λ值减小,裂纹扩展速率增大.因此,在估算疲劳寿命时,如果只考虑应力强度因子幅值的作用,而忽略实验加载条件和实际加载条件下侧向应力差别的影响,必然会带来较大的误差,甚至是不安全的.

含稀疏分布杂质的复合材料中的均匀化稳恒热传导方程

本文应用双空间尺度法导出了含稀疏分布椭圆柱形杂质的复合材料柱中的均匀化稳恒热传导方程,求得了等效导热系数的具体形式,并指出,当杂质枉截面单向分布时,宏观热传导是各向异性的,而当杂质枉截面按方向均匀分布时,宏观热传导是各向同性的.

太阳耀斑可能的储能过程

一般看法是,太阳耀斑的能量源于对流层和光球层,然后逐步堆积到外层的色球和日冕活动区中。所以,分析太阳大气中能量是如何从低层转移到上层的过程,以及分析太阳活动区中无力场能量是怎样堆积起来的机制,显然是讨论耀斑储能过程的中心问题之一。本文从冻结型无力场的基本方程组出发,不仅仅考虑旋转的环形流场,更考虑子午流场之间的相互作用,并具体推算了非定常的时间演化过程。

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.

Crack growth by grain boundary cavitation in the transient and extensive creep regimes

Crack growth due to cavity growth and coalescence along grain boundaries is analyzed under transient and extensive creep conditions in a compact tension specimen. Account is taken of the finite geometry changes accompanying crack tip blunting. The material is characterized as an elastic-power law creeping solid with an additional contribution to the creep rate arising from a given density of cavitating grain boundary facets. All voids are assumed present from the outset and distributed on a given density of cavitating grain boundary facets. The evolution of the stress fields with crack growth under three load histories is described in some detail for a relatively ductile material. The full-field plane strain finite element calculations show the competing effects of stress relaxation due to constrained creep, diffusion and crack tip blunting. and of stress increase due to the instantaneous elastic response to crack growth. At very high crack growth rates the Hui-Riedel fields dominate the crack tip region. However. the high growth rates are not sustained for any length of time in the compact tension geometry analyzed. The region of dominance of the Hui-Riedel field shrinks rapidly so that the near-tip fields are controlled by the HRR-type field shortly after the onset of crack growth. Crack growth rates under various conditions of loading and spanning the range of times from small scale creep to extensive creep are obtained. We show that there is a strong similarity between crack growth history and the behaviour of the C(t) and C(t) parameters. so that crack growth rates correlate rather well with C(t) and C(t). A relatively brittle material is also considered that has a very different near-tip stress field and crack growth history.

过冷核态池沸腾中的Marangoni效应

分析了过冷核态池沸腾过程中气泡横向运动现象,指出其成因在于相邻气泡界面温度差引起的Mara- ngoni对流对周围液体的吸引.通过对该流动的尺度分析,得到了气泡横向运动特征速度及其可观测度的估算公式,其预测结果与实验观测相一致.特别是对极细小的初始核化气泡,该公式预测了强烈的横向Marangoni对流会导致气泡顶端微射流的形成.该效应在加热面水平向下或微重力沸腾等气泡脱落频率较低的情形中尤为重要.

汽车模具复杂棱脊和沟槽的数字化及激光加工轨迹规划

针对大型汽车冲压模具复杂棱脊和沟槽的数字化问题提出了三维自适应测量算法。为适应于激光表面强化加工的特殊要求,在后续测量数据处理过程中建立了复杂棱脊和沟槽的简化数学模型,提出了六维激光加工轨迹规划算法,并进行了测量和加工试验验证。上述算法都已应用到集成化柔性激光加工系统中。

Rarefied gas dynamics: fundamentals, simulations and micro flows

Determination Of Interfacial Properties Between Metal Film And Ceramic Substrate With An Adhesive Layer

Peel test measurements and inverse analysis to determine the interfacial mechanical parameters for the metal film/ceramic system are performed, considering that there exist an epoxy interface layer between film and ceramic. In the present investigation, Al films with a series of thicknesses between 20 and 250 mu m and three peel angles of 90, 135 and 180 degrees are considered. A finite element model with the cohesive zone elements is used to simulate the peel test process. The finite element results are taken as the training data of a neural network in the inverse analysis. The interfacial cohesive energy and the separation strength can be determined based on the inverse analysis and peel experimental result. (C) 2008 Elsevier Ltd. All rights reserved.

应用于PLC控制程序的Petri网执行模型

在现有的工业控制系统中经常使用PLC实现顺序控制、定时等功能.控制程序经常需要执行同步操作且输入开关量的触发时机具有不确定性,因此无法充分描述真实的执行过程.为此提出下述解决方法:首先在控制程序的编译阶段,使用Petri网建立网模型以表示程序执行逻辑,其次在控制程序的执行阶段,根据程序真实执行状况动态运行上述网模型,当程序运行结束时网模型停止执行,由此判断程序中存在的逻辑错误.

Transparent Ni2+-doped ZnO-Al2O3-SiO2 system glass-ceramics with broadband infrared luminescence

We report transparent Ni2+-doped ZnO-Al2O3-SiO2 system glass-ceramics with broadband infrared luminescence. After heat-treatment, ZnAl2O4 crystallite was precipitated in the glasses, and its average size increased with increasing heat-treatment temperature. No infrared emission was detected in the as-prepared glass samples, while broadband infrared luminescence centered at 1310 nm with full width at half maximum (FWHM) of about 300 nm was observed from the glass-ceramics. The peak position of the infrared luminescence showed a blue-shift with increasing heat-treatment temperature, but a red-shift with an increase in NiO concentration. The mechanisms of the observed phenomena were discussed. These glass-ceramics are promising as materials for super broadband optical amplifier and tunable laser. (c) 2006 Elsevier Ltd. All rights reserved.

Motion simulation of annular polishing

Based on the Coulomb friction model, the frictional motion model of workpiece relating to the polishing pad was presented in annular polishing. By the dynamic analysis software, the model was simulated and analysed. The conclusions from the results were that the workpiece did not rotate steadily. When the angular velocity of ring and the direction were the same as that of the polishing pad, the angular velocity of workpiece hoicked at the beginning and at the later stage were the same as that of the polishing pad before contacting with the ring. The angular velocity of workpiece vibrated at the moment of contacting with the ring. After that the angular velocity of workpiece increased gradually and fluctuated at a given value, while the angular velocity of ring decreased gradually and also fluctuated at a given value. Since the contact between the workpiece and the ring was linear, their linear velocities and directions should be the same. But the angular velocity of workpiece was larger than that of the polishing pad on the condition that the radius of the workpiece was less than that of the ring. This did not agree with the pure translation principle and the workpiece surface could not be flat, either. Consequently, it needed to be controlled with the angular velocity of ring and the radii of the ring and the workpiece, besides friction to make the angular velocity of workpiece equal to that of the polishing pad for obtaining fine surface flatness of the workpiece. Copyright © 2007 Inderscience Enterprises Ltd.}

用于机载激光测深系统的时间间隔测量模块

机载海洋激光测深系统不仅要求精确测量激光从海表的入射点到海底目标点之间的距离，还要精确测定飞机到海表入射，点之间的距离，为水深数据的海浪校正而确定平均海平面以及波高。为此设计和研制了一高精度时间间隔测量器，该单元基于专用时间数字转换芯片开发，采用延迟线插入法技术，双通道工作，具有高时间分辨率(最高可达250ps)和高测量重复率的特性。给出硬件和软件设计方法以及单元的测试结果。