A lattice Boltzmann equation for waves

We propose a lattice Boltzmann model for the wave equation. Using a lattice Boltzmann equation and the Chapman-Enskog expansion, we get 1D and 2D wave equations with truncation error of order two. The numerical tests show the method can be used to simulate the wave motions.

Influence of Obstacle-Produced Turbulence on Development of Premixed Flames

An investigation into influence of obstructions on premixed flame propagation has been carried out in a semi-open tube. It is found that there exists flame acceleration and rising overpressure along the path of flame due to obstacles. According to the magnitude of flame speeds, the propagation of flame in the tube can be classified into three regimes: the quenching, the choking and the detonation regimes. In premixed flames near the flammability limits, the flame is observed first to accelerate and then to quench itself after propagating past a certain number of obstacles. In the choking regime, the maximum flame speeds are somewhat below the combustion product sound speeds, and insensitive to the blockage ratio. In the more sensitive mixtures, the transition to detonation (DDT) occurs when the equivalence ratio increases. The transition is not observed for the less sensitive mixtures. The dependence of overpressure on blockage ratio is not monotonous. Furthermore, a numerical study of flame acceleration and overpressure with the unsteady compressible flow model is performed, and the agreement between the simulation and measurements is good.

Micro-systems for Optical Protein-Chip

Protein-Chip as micro-assays for the determination of protein interaction, the analysis, the identification and the purification of proteins has large potential applications. The Optical Protein-Chip is able to detect the multi-interaction of proteins and multi-bio-activities of molecules directly and simultaneously with no labeling. The chip is a small matrix on solid substrate containing multi-micro-area prepared by microfabrication with photolithography or soft lithography for surface patterning, and processed with surface modification which includes the physical, chemical, and bio-chemical modifications, etc. The ligand immobilization, such as protein immobilization, especially the oriented immobilization with low steric hindrance and high bio-specific binding activity between ligand and receptor is used to form a sensing surface. Each area of the pattern is corresponding to only one bioactivity. The interval between the areas is non-bioactive and optically extinctive. The affinity between proteins is used to realize non-labeling microassays for the determination of protein identification and protein interaction. The sampling of the chip is non-disturbing, performed with imaging ellipsometry and image processing on a database of proteins.

Examination of the LBM in simulation of microchannel flow in transitional regime

The gas flows in micro-electro-mechanical systems possess relatively large Knudsen number and usually belong to the slip flow and transitional flow regimes. Recently the lattice Boltzmann method (LBM) was proposed by Nie et al. in Journal of Statistical Physics, vol. 107, pp. 279-289, in 2002 to simulate the microchannel and microcavity flows in the transitional flow regime. The present article intends to test the feasibility of doing so. The results of using the lattice Boltzmann method and the direct simulation Monte Carlo method show good agreement between them for small Kn (Kn = 0.0194), poor agreement for Kn = 0.194, and large deviation for Kn = 0.388 in simulating microchannel flows. This suggests that the present version of the lattice Boltzmann method is not feasible to simulate the transitional channel flow.

跨声速翼型激波/边界层干扰被动控制的数值模拟计算

本文应用数值计算的方法着重研究了跨声速翼型开孔壁的减阻效果。计算采用了边界层与位流相互作用的模型,藉以了解开孔壁对激波强度及结构的影响和对边界层控制的效果。通过对NACA0012翼型的计算表明,本文采用的自然吹吸的开孔模型能够显著地削弱激波的强度,改善激波的结构,但会使粘性损失增加。在马赫数较小时,翼型开孔后总阻力会增加,而在大马赫数时,开孔翼型的减阻效果才表现出来。这种趋势是与实验结果相吻合的。

缺陷连续统理论及其在本构方程研究中的应用 Ⅱ.缺陷的规范场理论

详细评述了缺陷连续统的规范场理论,该理论是近代材料科学和固体力学中新发展起来颇有意义的一个分支。首先强调了Noether定理及其逆定理在构造缺陷规范场理论中的重要性。同时基于Yang-Mills普适规范场构造,包括对SO(3)T(3)群的最小替换和最小耦合原理,系统地介绍了Golebiewska-Lasota,Edelen,Kadic和Edelen等人的原始性工作及他们的贡献。本文表明,Kadic和Edelen的理论是基于一组缺陷动力学的线性连续性方程发展起来的,不能和关于缺陷场的现有几何理论完全协调起来。考虑到这一点,本文提供了另一种方法来建立非线性弹性规范场的相应理论,这里考虑了Poincaré规范群SO(3)T(3).采用类似于研究引力场理论的Kibble方法,导出了缺陷连续统的拉氏密度。非完整坐标变换和非欧联络系数在数学上完全等价于子Poincaré群SO(3)T(3)的规范场。因此,本文的规范场理论和4维物质流形的缺陷场的非线性几何理论是完全一致的,并证明在弱缺陷条件下,可以简化到Kadic和Edelen的结果。

生物力学——进展和趋向

<正> 今天,生物力学的发展似乎进入了一个新的时期。它有什么特点?未来如何?这是一个引人关注的问题。要回答这个问题,回顾一下它的过去是必要的。 生物力学的发展大体可分三个时期。 Ⅰ.“前学科”时期 生命现象中力学问题的研究由来已久,可以追溯到亚里士多德.但成为一门独立的学

平面应变Ⅰ型非线性裂纹问题的高阶渐近解

本文给出了平面应变情况下Ⅰ型问题裂纹尖端附近二阶渐近场的定解方程、求解方法和计算结果,并以某些细致的有限无解为依据,估计了二阶渐近场的幅值系数k_2,分析了它对应力、应变分布和三轴张力的影响,变化规律以及在弹塑性断裂准则中的作用。

根据爆轰产物的微观描述预估凝聚炸药的爆轰压力

<正> 40年代以来,从凝聚炸药的化学成分和密度直接计算它的爆轰性质有几种不同的方法,它们的共同点都是采用稳定流动的守恒定律和在爆轰的不连续面上的CJ条件,不同点在于对爆轰产物这样的非常稠密的气体和固体的混合物用什么样的状态方程来描述,本文综述几种状态方程的特点和它们所预估的爆轰压力值之间的差异。

塑料及纤维增强塑料形变过程的热象研究

<正> 塑料和纤维增强塑料极低的热传导系数使它具备了应用热象技术研究形变过程的特殊的有利条件。本文简要叙述了用红外热象技术研究聚丙烯、聚碳酸脂及短纤维增强聚丙烯拉伸形变过程的研究结果。用上述材料注射成标准拉伸样条,夹装在Instron 1195万能材料试验机上,以指定速度进行拉伸直至断裂。同时用AGA-780红外热象仪记录试件拉伸过程的热图。为考察拉伸速度对形变热的影响,拉伸速度在2～50 mm/m范围内。通过对不同拉伸速度、不同时刻的试件样条热图的分析,得到了试件在拉伸过程中的温升及形变信息,给出了试件样条断裂瞬间的热图和拉伸过程中各时刻的试件温度分布图。实验结果表明,对于所研究的两种塑料,形变热软化效应在屈服和颈缩形成阶段不起主要作

煤浆的流变性和稳定性

<正> 随着工农业和交通运输业的迅速发展,人类社会对矿物燃料的需求越来越大。石油既是一种比较清洁而又使用便利的通用燃料,又是可贵的化工原料,其需求量增长尤为迅速。石油资源最终枯竭的前景是意料中的事。矿物燃料中得天独厚,储量最大的是煤。仅以我国而论,现已探明的煤的天然储量有几千亿吨,按现在的年产量估计,可供开采一千多年。但是,煤既不适用于原有的烧油锅炉、各种动力装置和输送系统,燃烧后排放的废气和粉尘又

A new formulated method of a quasi-compatible finite-element and its application in fracture-mechanics

Based on the local properties of a singular field, the displacement pattern of an isoparametric element is improved and a new formulated method of a quasi-compatible finite element is proposed in this paper. This method can be used to solve various engineering problems containing singular distribution, especially, the singular field existing at the tip of cracks. The singular quasi-compatible element (SQCE) is constructed. The characteristics of the elements are analysed from various angles and many examples of calculations are performed. The results show that this method has many significant advantages, by which, the numerical analysis of brittle fracture problems can be solved.

波浪场中水中悬浮隧道动力响应的研究

针对水中悬浮隧道在波浪力作用下动力响应的问题,通过Hamilton原理推导得到了悬浮隧道管段和锚索的运动控制方程,同时考虑了锚索横向和轴向变形之间的耦合作用,建立了悬浮隧道的动力响应模型,在时间域内采用逐步积分法迭代求解其运动控制方程.波浪力采用Airy线性波理论和Morison方程计算.计算结果表明:当锚索长细比较大时,锚索的自振模态会被激发,其横向和轴向变形之间的耦合作用不可忽略.随着入射波高或悬浮隧道重浮比的增加,悬浮隧道的横荡位移以及横摇角增大,但结构的垂荡位移以及锚索中的应力受波浪的影响较小.

瑞利泰勒不稳定性中尺度效应的数值模拟研究(英文)

　瑞利 泰勒不稳定性是一种由于密度梯度引起的界面不稳定性,在惯性约束聚变中具有重要的意义。利用被动标量输运模型对包含不同尺度初始扰动的界面演化过程进行数值模拟。计算结果表明界面的初始形状对不稳定性的发展具有很大的影响,狭长型扰动比正方型扰动发展慢。另外,不同尺度扰动的相互作用一般会减小沿界面发展方向运动的动能,使能量更多地用于平行于界面方向的运动。