瓦斯爆炸诱导沉积煤尘爆炸的数值模拟

建立了描述瓦斯爆炸卷扬沉积煤尘参与爆炸的物理和数学模型,借助流场模拟平台,对瓦斯爆炸 卷扬沉积煤尘参与爆炸的过程进行了数值模拟;并把模拟值与实验值进行了对比;对爆炸过程中的速度场和 温度场进行了深入的分析。通过比较分析爆炸压力、速度场以及温度场,认为模拟结果清楚地展现了沉积煤 尘的扬起和爆炸过程,达到了瓦斯爆炸诱导沉积煤尘爆炸数值模拟的要求。     

靠近排列的两个交错方柱三维绕流的数值模拟

通过用时间分裂算法求解Navier－Stokes方程,对中等Reynolds数下靠近排列的两个交错方柱三维绕流进行了数值模拟,其中,中间速度场用四阶Adams格式计算,压力场通过结合近似因子分解方法AF1与稳定的双共轭梯度方法Bi-CGSTAB进行迭代求解．数值模拟发现当两个方柱靠得较近时,有互相吸引趋势,而且上游方柱的Strouhal数较大．方柱的交错排列方式对绕流影响明显．计算结果与实验定性吻合,而且比用MAC－AF1方法计算的结果好．     

氧化沟推流转轮速度对水流回流长度影响的数值模拟研究

氧化沟水下推流转轮是氧化沟中水流运动最主要的动力来源,转轮转速的大小对沟道内水流的流速以及流场结构有着重要的影响。在本文中湍流模型选用Realizable k-ε模型,并结合气液两相流模型,对氧化沟水力特性进行三维数值模拟,研究了转轮转速大小对氧化沟内直道段回流长度的影响。压力与速度的耦合采用SIMPLE算法,模拟自由水面采用了VOF(volume of fluid)法,采用了量纲分析法得到了在单一量变化时回流区长度与转速之间的关系式,并用数值模拟结果确定了各系数。该成果可为氧化沟工艺的运行与设计提供依据。     

基于CFD的河流弯道二次流的三维数值模拟

为了系统地研究河流弯道在二次流影响下水沙运动的特点,本文基于CFD(Computational Fluid Dynamics)数值模拟和物理模型实验的方法,对河流弯道二次流进行了模拟和测量;应用雷诺时均法模型,结合Eulerian两相流模型对河流弯道二次流及其泥沙冲淤规律进行了数值模拟;以SIMPLE方法对压力场和速度场进行了耦合计算,并对辽宁省阜新市细河某段支流河道进行了物理模型实验,数值模拟的结果与实验结果基本一致,表明了本文方法的正确性。在此基础上,对90°弯曲的梯形断面河道的二次流结构和冲淤变化进行了分析,为防洪和水利设施的建设提供理论依据。     

液体燃料空气炸药形成过程的数值模拟

对液体燃料的爆炸抛撒形成的云雾运动作了数值模拟。建立了多相流模型与算法，给出了云雾区的速度场与燃料浓度分布。云雾的外形变化与实验结果符合较好。     

高速钢球对水介质侵彻时瞬时空腔形成的数值模拟

采用二维有限差分非线性动力数值计算程序（Ａｕｔｏｄｙｎ－２Ｄ）对高速钢球侵彻水介质时瞬时空腔的形成及其发展过程进行了数值模拟，获得了钢球侵彻水介质过程中速度衰减的规律、水介质中速度场和压力场的分布等数值模拟结果。数值模拟的结果与实验结果及现象相符。数值模拟结果及其相关分析为从理论上深入分析研究高速投射物对生物的致伤机理提供了重要的依据。     

连续流式电泳浓度场的三维分析

本文研究含不同微粒的缓冲液通过方形连续流式电泳室时在横向电场作用下的分离问题,首次全面考虑了三维的温度场,速度场和浓度场的相互作用,通过数值模拟揭示了微重力环境及通常重力条件下各参数的影响。文中还提出一种拟三维算法,能使数值模拟的工作量大大减小而所得结果与三维算法的结果一致。     

稳态斜轧延伸过程的刚塑性伽辽金法模拟

将无网格伽辽金法(Element-Free Galerkin Method,EFGM)与三维刚塑性流动理论相结合,对斜轧延伸过程进行了数值模拟。详细推导了斜轧延伸过程EFGM数值模型的刚度方程,给出了初始速度场和速度边界条件的建立方法和刚性区域的处理技术。得到的轧件的物理形态和金属流动的速度场均与实际情况相符,证明了采用EFGM计算斜轧延伸过程的可行性与正确性,将无网格算法引入到了斜轧领域。并将轧制力和壁厚的计算结果与实验结果进行了比较,结果发现：实验得到的轧制力结果偏小而壁厚值却偏大,其主要原因是由于在建模时做了简化和假定,同时也受轧机弹跳的影响。     

含扰流装置的中心燃气式抛撒内弹道过程的数值模拟

为了研究扰流板对子母弹抛撒过程中子弹翻转角速度的影响规律,采用二维两相流模型对子母弹中心燃气式抛撒内弹道过程进行了数值模拟研究。通过计算结果和测试结果的对比,验证了数值模型的可行性和准确性。对流场结构和推弹装置受力状态的对比分析表明,当燃气发生器小孔集中于扰流板上侧时,提高扰流板位置可以有效增大推弹装置受到的翻转合力矩。可为同类型抛撒系统的设计和改进提供理论参考。     

爆炸焊接界面波物质点法三维数值模拟

基于冲击动力学和爆炸焊接理论,采用物质点法对爆炸焊接界面波的形成进行三维数值模拟。通过数值模拟结果与爆炸焊接实验结果的对比,对复合界面材料的塑性流动变形以及界面波形成的机理进行探讨。结果表明:界面波是因为在碰撞点处的金属材料发生熔化并产生涡旋流动形成的;同时也说明采用物质点法模拟爆炸焊接界面波的形成是可行的。     

一种基于直接计算高阶奇异积分的断裂力学双边界积分方程分析法

相对于有限元法,边界单元法在求解断裂问题上有着独特的优势,现有的边界单元法中主要有子区域法和双边界积分方程法.采用一种改进的双边界积分方程法求解二维、三维断裂问题的应力强度因子,对非裂纹边界采用传统的位移边界积分方程,只需对裂纹面中的一面采用面力边界积分方程,并以裂纹间断位移为未知量直接用于计算应力强度因子.采用一种高阶奇异积分的直接法计算面力边界积分方程中的超强奇异积分;对于裂纹尖端单元,提供了三种不同形式的间断位移插值函数,采用两点公式计算应力强度因子.给出了多个具体的算例,与现存的精确解或参考解对比,可得到高精度的计算结果.      

汶川地震诱发文家沟巨型滑坡 碎屑流基本特征及成因机制初步分析

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2008年5月12日,汶川M80地震在四川省绵竹市清平乡文家沟内诱发一巨型滑坡。通过现场调查得知,滑坡前后缘高差455m,厚度20～30m,滑面为基岩层面,初始方量2750×107m3。滑体在运动中转化为碎屑流。滑坡-碎屑流总的水平运动距离为4022m,垂直运动距离为1443m,遗留的堆积物体积达5×107m3。滑坡距映秀—北川断裂仅36km,位于其下盘,地震烈度达XI度。滑坡导致文家沟中48人遇害,并形成一条完整的地震次生地质灾害链。初步分析表明滑坡启动速度快,滑坡向碎屑流转化过程明显、地点明确。碎屑流运动过程复杂,伴有强烈的“气垫效应”和“前缘气浪冲击效应”。作者认为,文家沟滑坡的高启动速度是长持时强烈地震动作用的结果,与山体的猛烈碰撞是导致滑体解体并转化为碎屑流的原因。     

Preface: Orbits around asteroid

One of the core issues in modern celestial mechanics is the orbital dynamics in the near-regime gravitational field of as- teroids, which provides deep insights into the mathematical nature of a class of nonlinear systems, and plays as a critical basis for in situ explorations of different science goals. Lots of efforts have been made to reveal the characteristics of orbital motion in the vicinity of asteroids, and to improve the skills of asteroid research in methodology.     

Effet de l'anisotropie élastique cristalline sur la distribution des facteurs de Schmid à la surface des polycristauxInfluence of crystalline elasticity anisotropy on Schmid factor distribution at the free surface of polycrystals

Experimental studies of the plasticity mechanisms of polycrystals are usually based on the Schmid factor distribution supposing crystalline elasticity isotropy. A numerical evaluation of the effect of crystalline elasticity anisotropy on the apparent Schmid factor distribution at the free surface of polycrystals is presented. Cubic elasticity is considered. Order II stresses (averaged on all grains with the same crystallographic orientation) as well as variations between averages computed on grains with the same crystallographic orientation but with different neighbour grains are computed. The Finite Element Method is used. Commonly studied metals presenting an increasing anisotropy degree are considered (aluminium, nickel, austenite, copper). Concerning order II stresses in strongly anisotropic metals, the apparent Schmid factor distribution is drifted towards small Schmid factor values (the maximum Schmid factor is equal to 0.43 instead of 0.5) and the slip activation order between characteristic orientations of the crystallographic standard triangle is modified. The computed square deviations of the stresses averaged on grains with the same crystallographic orientation but with different neighbour grains are a bit higher than the second order ones (inter-orientation scatter). Our numerical evaluations agree quantitatively with several observations and measures of the literature concerning stress and strain distribution in copper and austenite polycrystals submitted to low amplitude loadings. Hopefully, the given apparent Schmid factor distributions could help to better understand the observations of the plasticity mechanisms taking place at the free surface of polycrystals. To cite this article: M. Sauzay, C. R. Mecanique 334 (2006).     

Nonlinear behavior of matrix-inclusion composites under high confining pressure: application to concrete and mortar

This paper is devoted to a micromechanics-based simulation of the response of concrete to hydrostatic and oedometric compressions. Concrete is described as a composite made up of a cement matrix in which rigid inclusions are embedded. The focus is put on the role of the interface between matrix and inclusion which represent the interfacial transition zone (ITZ). A plastic behavior is considered for both the matrix and the interfaces. The effective response of the composite is derived from the modified secant method adapted to the situation of imperfect interfaces. To cite this article: T.H. Le et al., C. R. Mecanique 336 (2008).     

Dynamics and Breakup of Viscoelastic Liquids (A Review)

The phenomena of hydrodynamic breakup of liquid jets, drops, films, bridges, and filaments are reviewed for liquids with viscoelastic properties. The reasons for breakup are capillary instabilities, collisions with rigid obstacles, and other forms of dynamic action. The relationship between the properties of the liquids and the features of the breakup process is discussed.     

Flow stability analysis and excitation using pulsating jets

Classical flow stability applied to transition from laminar to turbulent flow may also describe the behavior of vorticity fluctuations created by a pulsating jet placed along a solid boundary. A numerical laminar flow experiment involving a pulsating jet placed along the surface of a duct with flow separation downstream, resulted in eliminating most part of the separated flow region. Applying the same approach to a turbulent flow, it was possible to develop a turbulent stability flow formulation and apply successfully turbulent pulsating jet flow separation control. To cite this article: D. Skamnakis, K. Papailiou, C. R. Mecanique 333 (2005).