Structural Failure Analysis and Numerical Simulation of Micro-Accelerometers under Impulsive Loading

Micromachined accelerometer is a kind of inertial MEMS devices, which usually operate under intensive impact loading. The reliability of micromachined accelerometers is one of the most important performance indices for their design, manufacture and commer

关于热传导测温中动态测温响应与误差估计

从理论上给出了关于热传导测温中动态测温响应与误差估计。温度测量敏感元件的温度滞后于外界温度的变化，其滞后时间不超过敏感元件的半个特征时间L2/α,所以温度测量误差不超过βL2 /2α，也就是说，在热传导动态温度测量中，温度测量敏感元件的热响应时间可估为 L2/2α，最大温度测量误差可估为βL2 /2α。

An experimental study on turbulent coherent structures near a sheared air-water interface

The turbulence structures near a sheared air-water interface were experimentally investigated with the hydrogen bubble visualization technique. Surface shear was imposed by an airflow over the water flow which was kept free from surface waves. Results show that the wind shear has the main influence on coherent structures under air-water interfaces. Low- and high- speed streaks form in the region close to the interface as a result of the imposed shear stress. When a certain airflow velocity is reached, "turbulent spots" appear randomly at low-speed streaks with some characteristics of hairpin vortices. At even higher shear rates, the flow near the interface is dominated primarily by intermittent bursting events. The coherent structures observed neat sheared air-water interfaces show qualitative similarities with those occurring in near-wall turbulence. However, a few distinctive phenomena were also observed, including the fluctuating thickness of the instantaneous boundary layer and vertical vortices in bursting processes, which appear to be associated with the characteristics of air-water interfaces.

液–固脉冲流化床中浓度波传播与衰减

采用数值计算和实验验证相结合的方法研究液一固脉冲流化床中浓度波的传播和衰减。当脉仲开半周期乃和闭半周期乃都远大于颗粒弛豫时间吊时,两相的惯性力之差在一个周期的绝大部分时间中相对于重力很小,可忽略,这时由双流体模型的动量方程可推导出推广的Richardson-Zaki公式,双流体模型简化为局部平衡模型。采用五阶精度WENO格式求解浓度波传播方程,得到了脉冲流化过程中浓度波传播与衰减的规律,与实验结果符合良好。

Net-like Ferromagnetic Mnsb Film Deposited on Porous Silicon Substrates

MnSb films were deposited on porous silicon substrates by physical vapor deposition (PVD) technique. Modulation effects due to the substrate on microstructure and magnetic properties of the MnSb film's were studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and measurements of hysteresis loops. SEM images of the MnSb films indicate that net-like structures were obtained because of the special morphology of the substrates. The net-like MnSb films exhibit some novel magnetic properties different from the unpatterned referenced samples. For example, in the case of net-like morphology, the coercive field is as low as 60 Oe.

障碍物管道中湍流火焰发展的数值模拟

应用湍流马赫数修正的非稳态可压缩性K-ε-f-gr四方程湍流模型，模拟了半开口狭长管道中重复布置的障碍物引起的湍流火焰加速现象。结果表明，障碍物产生的扰动对加强燃烧和湍流输运的影响很大。随着火焰向前传播，火焰穿过障碍物时发生变形，反应区越来越长，且火焰速度逐渐上升。同时，火焰速度和管内压力的计算结果与实验测量值吻合良好，修正后的湍流模型能较真实地模拟障碍物管内预混火焰的发展过程。

表面具有流向微槽叶片的传热性能分析

在综合考虑了流向微槽表面强化的传热特性和流向微槽表面减阻机理研究结果垢基础上，分析了表面具有流向微槽的叶片的传热性能，提出了与已有的叶片冷却技术完全不同的，全新的叶片冷却技术－叶片外部冷却技术。

圆域内双柱整流现象的数值模拟

基于Reyleigh整流定律，利用ψ－ε形式的定常不可压N-S方程，数值模拟了双柱在圆域内 作高频小振幅振动时所产生的定常整流流动。揭示了流动随整流雷诺数的演化特性。此外就求解ψ－ε形式的N-S方程所涉及的定解边界条件问题，亦进行了必要的讨论。

LEVEL SET输运方程的求解方法及其对气-液两相流运动界面数值模拟的影响

用数值模拟方法来研究气-液两相流动与传热现象是当今多相流领域的一个热门课题.由于两相流固有的复杂性,气-液两相流界面迁移现象的数值模拟一直是两相流研究中的一大难点.本文介绍了捕捉气-液两相流相界面运动的水平集方法(Level Set)及其研究进展,介绍了求解Level Set输运方程的3种方法,即一般差分格式、Superbee-TVD格式和Runge-Kutta法-5阶WENO组合格式.结合主流场的求解,分别用这3种方法对4种典型相界面在5种流场中的迁移特性进行了模拟计算,并对计算结果进行了比较和分析.结果表明,Runge-Kutta法-5阶WENO组合格式求解Level Set输运方程的效果最好,在以后的计算中将主要采用这种组合格式来进行气-液相界面输运方程的求解.

激光熔覆Fe—Cr—W—Ni—C合金的微观组织及其演化

用ＳＥＭ，ＡＴＥＭ及化学分析、显微硬度测定等手段，对激光熔覆Ｆｅ－Ｃｒ－Ｗ－Ｎｉ－Ｃ（其质量比为１０：５：１：１：１）合金的微观组织进行了研究。结果表明，该合金经激光熔覆后可得到亚共晶和过共晶两类熔覆组织为γ＋（γ＋Ｍ７Ｃ３）及Ｍ７Ｃ３＋（γ＋Ｍ７Ｃ３），存在领先相的竞争与选择，γ为亚稳奥氏体，具有较高的合金元素过饱和含量；Ｍ７Ｃ３（Ｍ＝Ｃｒ，Ｆｅ，Ｗ等）为Ｃｒ基合金碳化物。存在层片状、蜂窝状、网…

General Relationship Between Contact Stiffness, Contact Depth, and Mechanical Properties for Indentation in Linear Viscoelastic Solids Using Axisymmetric Indenters of Arbitrary Profiles

We derive a relationship between the initial unloading slope, contact depth, and the instantaneous relaxation modulus for indentation in linear viscoelastic solids by a rigid indenter with an arbitrary axisymmetric smooth profile. Although the same expression is well known for indentation in elastic and in elastic-plastic solids, we show that it is also true for indentation in linear viscoelastic solids, provided that the unloading rate is sufficiently fast. Furthermore, the same expression holds true for both fast loading and unloading. These results should provide a sound basis for using the relationship for determining properties of viscoelastic solids using indentation techniques.

损伤统计演化方程的性质和数值模拟

通过对一种含成核尺寸效应的损伤统计演化方程性质的分析和数值模拟，揭示了损伤率主要是由微损伤在二维相空间中的前沿的运动所决定的。这也就是Kachanov提出的损伤率演化方程的物理基础。数值结果进一步显示了含成核尺寸效应模型在损伤发展上与一维模型的区别。而且，由几种形式的细观动力学算出的损伤率与损伤的关系简单，可近似拟合为宏观上封闭的形式。

球铁材料脉冲激光表面强化的实验研究

采用经过二元光学变换后呈二维点阵分布的脉冲激光束对球铁试样作了表面强化处理。对强化前后试样表面的粗糙度、强化层深度、强化层显微硬度分布和耐磨性进行了研究。结果表明，在保证试样表面粗糙度（表面微熔或不熔）的前提下，随脉宽增加强化区层深增加。耐磨性测试表明，脉冲激光强化处理可提高材料耐磨性1.8倍以上.

Chaotic dynamic analysis of viscoelastic plates

The dynamic buckling of viscoelastic plates with large deflection is investigated in this paper by using chaotic and fractal theory. The material behavior is given in terms of the Boltzmann superposition principle. in order to obtain accurate computation results, the nonlinear integro-differential dynamic equation is changed into an autonomic four-dimensional dynamical system. The numerical time integrations of equations are performed by using the fourth-order Runge-Kutta method. And the Lyapunov exponent spectrum, the fractal dimension of strange attractors and the time evolution of deflection are obtained. The influence of geometry nonlinearity and viscoelastic parameter on the dynamic buckling of viscoelastic plates is discussed.

对达曼光栅进行二维扩展的矩形孔径光栅设计

介绍一种二元光学元件的设计方法.为了克服达曼光栅在二维设计上的局限性,采取均匀采样的矩形孔径编码方式进行优化设计.结果表明:与达曼光栅相比,不仅可将总衍射效率提高10%以上,还可得到更多样的二维设计图样,只是输出点阵均匀度略低于达曼光栅.因此,在均匀度要求不太高的高强光束变换中,这种二值型位相光栅的设计方法对于设计二维衍射图样十分简便有效,且其计算结果易于加工制作,具有很高的应用价值.