A sharp interface method for high-speed multi-material flows: strong shocks and arbitrary materialpairs

A general framework is developed for solving high-speed and high-intensity multi-material interaction problems on adaptively refined Cartesian meshes. The framework is applicable for interfaces separating materials with very different properties and in the presence of strong shocks. A sharp interface treatment is maintained through a modified Ghost Fluid Method. The embedded boundaries are tracked and represented with level sets. A tree-based Local Mesh Refinement scheme is employed to efficiently resolve the desired physics. Results are shown for situations that cover varied combination of materials (fluids, rigid solids and deformable solids) with careful benchmarking to establish the validity and the versatility of the approach.     

微动磨损对过盈配合结构微动参量的影响

基于Archard磨损模型与Abaqus自适应网格技术建立了仿真分析过盈配合结构微动磨损的计算模型,对配合面轮廓随循环周次的变化进行了预测,并详细研究了微动磨损对接触压应力、摩擦剪切应力及微动滑移幅值等微动参量的影响.结果表明:该计算模型能够较为准确地对配合面轮廓随循环周次的变化进行预测;由于微动磨损的作用,配合边缘处接触压应力的峰值逐渐增大,且其位置逐渐向配合内部移动;摩擦剪切应力的最大值逐渐由黏着-滑移过渡位置向磨损-未磨损过渡位置移动;张开区域的宽度以及滑移区内各位置处的微动滑移幅值均随着循环周次的增加而增大.     

运动网格上的水下爆炸数值模拟方法

 在对水下爆炸过程的数值模拟中,把水-气介质界面当作一种特殊的内部边界,并且在该边界上的网格节点都有双重定义,分别对应边界两侧的不同介质状态,通过利用HLLC（Harten,Lax,van Leer,Contact）方法求解任意ALE（Arbitrary Largrangian Eulerian Method,拉格朗日-欧拉方程）方程组,以及运用界面跟踪和动网格方法,对一维球对称水下爆炸模型进行了数值模拟。结果表明,所得到的数值计算结果与实验结果吻合得较好,并且在扩展到二维柱对称水下爆炸模型时,同样得到了满意的结果。     

Effects of the particle Stokes number on wind turbine airfoil erosion

Under natural conditions, wind turbines are inevitably eroded by the action of sand-wind flow. To further investigate the effects of dust drift on the erosion of the wind turbine blades in sand-wind environments, the effects of the wind velocity, particle diameter, and particle density on the erosion of wind turbine airfoils are studied, and the effects of the particle Stokes number on the airfoil erosion are discussed. The results show that, when the angle of attack(AOA) is 6.1°, there will be no erosion on the airfoil surface if the particle Stokes number is lower than 0.013 5, whereas erosion will occur if the particle Stokes number is higher than 0.015 1. Therefore, there exists a critical range for the particle Stokes number. When the particle Stokes number is higher than the maximum value in the critical range, airfoil erosion will occur. The result is further confirmed by changing the particle diameter, particle density, and inflow speed. It is shown that the erosion area on the airfoil and the maximum erosion rate are almost equal under the same particle Stokes number and AOA. The extent of airfoil erosion increases when the particle Stokes number increases, and the critical particle Stokes number increases when the AOA increases. Moreover, the geometric shape of the airfoil pressure surface greatly affects the airfoil erosion, especially at the curvature near the leading edge.     

Effective electroelastic constants for three-phase confocal elliptical cylinder model in piezoelectric quasicrystal composites

A three-phase confocal elliptical cylinder model is proposed to analyze micromechanics of one-dimensional hexagonal piezoelectric quasicrystal (PQC) composites. Exact solutions of the phonon, phason, and electric fields are obtained by using the conformal mapping combined with the Laurent expansion technique when the model is subject to far-field anti-plane mechanical and in-plane electric loadings. The effective electroelastic constants of several different composites made up of PQC, quasicrystal (QC), and piezoelectric (PE) materials are predicted by the generalized self-consistent method. Numerical examples are conducted to show the effects of the volume fraction and the cross-sectional shape of inclusion (or fiber) on the effective electroelastic constants of these composites. Compared with other micromechanical methods, the generalized selfconsistent and Mori-Tanaka methods can predict the effective electroelastic constants of the composites consistently.     

基于ALE方法的3D充填流动模拟

基于任意拉格朗日-欧拉方法发展了三维充填流动的数值模拟方案.该方案采用ALE方法准确地追踪移动自由面的位置并避免了网格扭曲;基于移动最小二乘曲面拟合方法提出了移动自由面上网格节点重定位方法,将充填流动的网格更新过程简化为自由面附近的局部网格重划分过程,并通过分级多面体三角剖分实现,减小了网格划分的计算量,实现了实时网格生成.给出的数值算例结果表明了该数值模型对三维充填流动模拟的有效性.     

非线性流固耦合问题的ALE分步有限元数值方法

推导了一种基于ALE（Arbitrary Lagrangian-Eulerian,即任意的拉格朗日-欧拉）描述下的带有自由液面不可压液体与运动结构非线性耦合问题的一种有限元数值计算方法,在时间域上采用分步格式计算,这种方法与混合插值方法比较其优点是速度和压力可使用同阶线性插值,给数值计算带来很大方便,将所得到的方法应用到结构与TLD（调谐式（液体阻尼器）装置之间的耦合问题,数值计算结果验证了本文所推导的方法。     

Level set方法在自适应Cartesian网格上的应用

采用基于自适应Cartesian网格的level set方法对多介质流动问题进行数值模拟。采用基于四叉树的方法来生成自适应Cartesian网格。采用有限体积法求解Euler方程,控制面通量的计算采用HLLC（Hartern, Lax, van Leer, Contact）近似黎曼解方法。level set方程也采用有限体积法求解,采用Lax-Friedchs方法计算通量,通过窄带方法来减少计算量,界面的处理采用ghost fluid方法。Runge-Kutta显式时间推进,时间、空间都是二阶精度。对两种不同比热比介质激波管问题进行数值模拟,其结果和精确解吻合;对空气/氦气泡相互作用等问题进行模拟,取得令人满意的结果。     

激光线聚焦驱动平面银靶的二维数值模拟

介绍新研制的二维非平衡辐射流体力学程序XRL2D的物理方程以及计算方法,并对神光Ⅱ上典型的类镍银X光激光实验条件,用3种ALE计算方法模拟了预主脉冲线聚焦驱动银平面靶的流体运动.几种方法模拟给出的物理图像清晰且相似,类镍离子丰度分布呈弯月形,同实验上XRL场图呈弯月形分布一致.对3种计算方法给出的结果进行了细致的比较分析.     

Numerical modelling of step–strain for stretched filaments

This article addresses the modelling of filament-stretching/step–strain deformation under viscoelastic capillary break-up configurations of the CaBER-type. Start-up, prior to step–strain, is conducted under constant stretch-rate synchronous plate retraction with impulsive sessation of plate motion. The study encompasses variation in material rheology, appealing to Oldroyd, Geisekus and Phan-Thien/Tanner-type models, which display differences in shear and extensional viscosity properties (shear thinning/extension hardening). Two different viscosity ratio settings are considered to reflect high- and low-solvent viscosity constituent components; the former representing typical Boger fluids, the latter high-polymer concentration fluids. We compare and contrast results for three alternative filament aspect ratios at the onset of step–strain. Throughout the step–strain period, we have been able to successfully capture such physical features as drainage to the filament feet, necking at the filament centre, and periods with travelling waves through the axial filament length. In addition, we have identified the suppressive influence that larger capillary forces have upon radial fluctuations, and the minor impact that gravitational forces have upon the ensuing deformation. From this study, estimates for rheometrical data have been derived in terms of characteristic material relaxation time and apparent extensional viscosity. The computational techniques employed include a compressed-mesh (CM) procedure, an Arbitrary Lagrangian–Eulerian scheme (ALE) and a free-surface particle tracking technique. Spatial discretisation of the problem is accomplished through a hybrid finite element/finite volume algorithm implemented in the form of a time-stepping incremental pressure-correction formulation.