Saltation in wind blown sand

The Boltzmann equation of the sand particle velocity distribution function in wind-blown sand two-phase flow is established based on the motion equation of single particle in air. And then, the generalized balance law of particle property in single phase granular flow is extended to gas-particle two-phase flow. The velocity distribution function of particle phase is expanded into an infinite series by means of Grad's method and the Gauss distribution is used to replace Maxwell distribution. In the case of truncation at the third-order terms, a closed third-order moment dynamical equation system is constructed. The theory is further simplified according to the measurement results obtained by stroboscopic photography in wind tunnel tests.

飞行器跨声速气动弹性数值分析

将流体和结构运动方程分别构造为含子迭代的计算格式，发展了一种紧耦合气动弹性分析方法．其中流体计算的空间离散采用改进的HLLEW（Harten-Lax-van Leer-Einfeldt-Wada）格式．TFI（transfinite interpolation）方法用于生成随结构变形的自适应多块动网格．利用所发展的方法，对一翼-身-尾气动外形，数值预测了马赫数在0．3-1．3范围内的气动颤振边界．并详细研究了时间步长、子迭代步数、初始流场、耦合方法、疏密网格对颤振计算结果的影响．

Study on flow characteristics of solid/liquid system in lysozyme crystal growth

During the process of lysozyme protein crystallization with batch method, the macroscopic flow field of solid/liquid system was observed by particle image velocimetry (PIV). Furthermore, a normal growth rate of (110) face and local flow field around a single protein crystal were obtained by a long work distance microscope. The experimental results showed that the average velocity, the maximal velocity of macroscopic solid/liquid system and the velocity of local flow field around single protein crystal were fluctuant. The effective boundary layer thickness delta(eff), the concentration at the interface Q and the characteristic velocity V were calculated using a convection-diffusion model. The results showed that the growth of lysozyme crystal in this experiment was dominated by interfacial kinetics rather than bulk transport, and the function of buoyancy-driven flow in bulk transport was small, however, the effect of bulk transport in crystal growth had a tendency to increase with the increase of lysozyme concentration. The calculated results, also showed that the order of magnitude of shear force was about 10(-21) N, which was much less than the bond force between the lysozyme molecules. Therefore the shear force induced by buoyancy-driven flows cannot remove the protein molecules from the interface of crystal.

Spall damage in aluminum-alloy

A void growth relations for ductile porous materials under intense dynamic general loading condition is presented. The mathematical model includes the influence of inertial effects, material rate sensitivity, as well as the contribution of void surface energy and material work-hardening. Numerical analysis shows that inertia appears to resist the growth of voids. The inertial effects increase quickly with the loading rates. The theoretical analysis suggests that the inertial effects cannot be neglected at high loading rates. Plate-impact tests of aluminum alloy are performed with light gas gun. The processes of dynamic damage in aluminum alloy are successfully simulated with a finite-difference dynamic code in which the theoretical model presented in this paper is incorporated.

近壁湍流脉动的概率分布函数

采用大涡模拟方法，模拟槽道湍流，获得了不同雷诺数情形下的槽道流大涡模拟数据库．在此基础上，获得了流向和垂向脉动速度的概率分布函数，并运用假设检验，分析了其与正态分布的定量差别．进一步计算了流向和垂向脉动速度的偏斜度、平坦度，讨论了二者在粘性子层、过渡区和对数律区的变化．同时，讨论了粘性子层、过渡区和对数律区流向和垂向脉动速度概率分布函数的特点及其与湍流猝发的高速流下扫和低速流喷发事件的关系．最后，分析了雷诺数对流向、垂向脉动速度分布的影响。

双材料界面裂纹平面问题的半权函数法

应用半权函数法求解双材料界面裂纹的平面问题.由平衡方程、应力应变关系、界面的连续条件以及裂纹面零应力条件推导出裂尖的位移和应力场,其特征值为lambda及其共轭.设置特征值为lambda的虚拟位移和应力场,即界面裂纹的半权函数.由功的互等定理得到应力强度因子KⅠ和KⅡ以半权函数与绕裂尖围道上参考位移和应力积分关系的表达式.数值算例体现了半权函数法精度可靠、计算简便的特点.