点格自动机

点格自动机(或译细胞自动机,cellular automata)是一种数学模型,J.von Neumann在40年代提出时,想用它来在计算机上模拟生物系统中某些自组织(self-organization)现象。八十年代以来,由于计算机技术和计算机科 ...     

嵌段共聚物相容剂对聚合物共混体系力学性能影响的连续介观模拟

结合介观动力学方法和三维弹簧格子模型, 研究了嵌段共聚物相容剂对相容性较差的聚合物二元共混体系力学性能的影响. 在适当范围内不断增加嵌段共聚物相容剂的用量, 研究了相容剂含量对体系杨氏模数及拉伸强度的影响, 同时也对不同体系材料的破碎位点进行了分析. 结果表明, 未加入相容剂的二元共混体系在拉伸模拟中表现出较低的拉伸强度, 而适量添加相容剂可以显著提升材料的拉伸强度, 随着相容剂含量的增加, 共混体系的破碎位点会发生转移并最终改善材料的整体性能. 而相容剂的加入对体系杨氏模数的影响较小. 该连续模拟方法为关联聚合物复合体系的微观结构和宏观力学性能提供了一条高效的途径.     

充分发展湍流场中Pr数对被动标量输运的影响

采用直接数值模拟方法,研究壁湍流中分子Pr数对湍流被动标量输运的影响.发现在槽道湍流的外层,湍流雷诺平均普朗特数PrT与分子普朗特数的倒数呈线性关系;湍流亚格子普朗特数PrT与分子普朗特数的关系较为复杂,在分子普朗特数为1附近时,湍流亚格子Prt数出现极小值.     

亚临界雷诺数下圆柱绕流的大涡模拟

本文应用Smagorinsky涡粘性模式和二阶精度的有限体积法对圆柱绕流的流场进行大涡模拟．求解了非正交曲线坐标系下的N-S方程,对雷诺数为100和20000的工况进行了计算．计算结果与实验及动力涡粘性模式的结果进行了比较,表明计算对于层流及高亚临界雷诺数的湍流流动是合理的     

Theoretical statistical solution and numerical simulation of heterogeneous brittle materials

The analytical stress-strain relation with heterogeneous parameters is derived for theheterogeneous brittle materials under a uniaxial extensional load, in which the distributions of theelastic modulus and the failure strength are assumed to be statistically independent. This theoreticalsolution gives an approximate estimate of the equivalent stress-strain relations for 3-D heterogeneousmaterials. In one-dimensional cases it may provide comparatively accurate results. The theoreticalsolution can help us to explain how the heterogeneity influences the mechanical behaviors, Further, anumerical approach is developed to model the non-linear behavior of three-dimensional heterogeneousbrittle materials. The lattice approach and statistical techniques are applied to simulate the initialheterogeneity of heterogeneous materials. The load increment in each loading stage is adaptivelydetermined so that the better approximation of the failure process can be realized. When the maximumtensile principal strain exceeds the failure strain, the elements are considered to be broken, which canbe carried out by replacing its Young‘s modulus with a very small value. A 3-D heterogeneous brittlematerial specimen is simulated during a full failure process. The numerical results are in good agreementwith the analytical solutions and experimental data.     

Validation of EMMS-based drag model using lattice Boltzmann simulations on GPUs

Interphase momentum transport in heterogeneous gas–solid systems with multi-scale structure is of great importance in process engineering. In this article, lattice Boltzmann simulations are performed on graphics processing units (GPUs), the computational power of which exceeds that of CPUs by more than one order of magnitude, to investigate incompressible Newtonian flow in idealized multi-scale particle–fluid systems. The structure consists of a periodic array of clusters, each constructed by a bundle of cylinders. Fixed pressure boundary condition is implemented by applying a constant body force to the flow through the medium. The bounce-back scheme is adopted on the fluid–solid interfaces, which ensures the no-slip boundary condition. The structure is studied under a wide range of particle diameters and packing fractions, and the drag coefficient of the structure is found to be a function of voidages and fractions of the clusters, besides the traditional Reynolds number and the solid volume fractions. Parameters reflecting multi-scale characters are, therefore, demonstrated to be necessary in quantifying the drag force of heterogeneous gas–solid system. The numerical results in the range 0.1 ≤ Re ≤ 10 and 0 < ? < 0.25 are compared with Wen and Yu's correlation, Gibilaro equation, EMMS-based drag model, the Beetstra correlation and the Benyahia correlation, and good agreement is found between the simulations and the EMMS-based drag model for heterogeneous systems.     

基于格子Boltzmann方法的液滴沿固壁铺展动态过程模拟

矿井喷雾降尘是利用水雾使粉尘润湿沉降的过程,考虑到固体与液体间分子作用力,本文采用格子Boltzmann方法对液滴沿固壁铺展的动力学行为进行了数值模拟,结果发现铺展直径及动态接触角随时间呈指数规律,确定了液滴表面张力与铺展最大直径间的关系,固壁润湿性对铺展最大速度值影响较大,这些与物理试验及文献结果符合良好. 进一步考察了疏水性强的固壁,发现当液滴表面张力足够小时,铺展接触角可以在90°以下,与理论公式符合. 研究发现铺展过程中伴随着振荡,且铺展到最大时液膜有回缩趋势. 关键词： 液滴 格子Boltzmann方法 铺展 数值模拟     

椭圆柱体在牛顿流体中运动的格子Boltzmann方法模拟

用格子Boltzmann方法建立了椭圆柱体的二维动力学模型，利用所建立的模型，数值模拟了 牛顿流体中不同形状的椭圆柱体在相同初始条件下的运动和同一椭圆柱体在不同初始条件下 的运动，并通过比较相同条件下圆柱体的运动，讨论了椭圆柱体二维运动的特征，得到了一 些有意义的结果. 关键词： 格子Boltzmann方法 椭圆柱体 牛顿流体     

A Hierarchy of Integrable Nonlinear Lattice Equations and New Integrable Symplectic Map

A discretespectral problem is discussed.and a hierarchy of integrable nonlinear lattice equations related to this spectral problem is devised.The new integrable symplectic map and finite-dimensional integrable systems are given by nonlinearization method.The binary Bargmann constraint gives rise to a Baecklund transformation for the resulting integrable lattice equations.