二维磁通随机钉扎系统动力学行为的数值模拟

本文利用数值模拟的方法,研究在Ｌｏｒｅｎｔｚ 驱动力作用下,随机钉扎环境中运动的二维磁通点阵的动力学行为．通过对不同随机分布点钉扎中心密度和不同磁通间相互作用强度的研究,发现磁通点阵存在从弹性区向塑性区的渡越（ｃｒｏｓｓｏｖｅｒ） , 并且这种渡越强烈依赖于磁通之间及磁通与钉扎之间的相互作用．随着钉扎中心密度的增加及磁通间相互作用强度的减弱,临界钉扎力增强．模拟结果与最近实验结果定性一致．部分结果偏离集体钉扎理论     

二维二相不规则网格的油藏数值模拟

本文采用不规则网格的差分方法,对平面油水模型进行了数值模拟,并用IMPES方法计算了两个实例。例1的计算结果与精确解吻合良好,比Pedrosa的局部加密网格法使用的网格数少而且计算更简便。例2为矩形网格难以计算的问题,应用本文方法也得出了较好的结果。这表明本文的不规则网格差分方法是可靠而简便的,它可以有效地应用于复杂外边界和复杂地层结构的油藏模拟问题。     

二维高速碰撞问题欧拉数值模拟的混合网格计算

提出了适用于二维平面或轴对称多介质流体力学两步欧拉数值方法中输运计算的混合网格界面处理.在一个混合网格中,将界面近似看作直线.整个方法分为3步:①用混合网格周围的8个网格的介质面积份额确定界面的法线方向;②用混合网格的介质面积份额或体积份额确定界面的直线方程;③用此直线方程求出通过网格边界的流.给出了用此方法所做的测试、数值计算及与其它算法的比较.     

随机稀释基底上刻蚀模型动力学标度行为的数值模拟研究

表面界面动力学粗化过程是凝聚态物理领域重要的研究内容,为研究基底不完整性对刻蚀模型动力学 标度行为的影响,本文采用Kinetic Monte Carlo(KMC)方法,分析研究了在随机稀释基底上刻蚀模型(Etching model)生长表面的动力学标度行为.研究发现:尽管随机稀释基底的不完整性会对刻蚀表面的动力学 行为产生显著的影响,导致刻蚀表面粗糙度指数和生长指数有明显的增加, 但其仍基本满足原有的动力学标度规律.此外,本文还对刻蚀表面动力学标度指数的有限尺寸效应进行了 分析讨论.     

激光相变烧蚀二维结构网格程序的数值计算

研究激光相变烧蚀二维结构网格程序,对液-气相变、固液汽三相物质进行整体模拟.激光相变烧蚀二维结构网格程序采用气化相变开始后在迎激光方向局部加密的重分方法,动量守恒方程采用Wilkins三角形回路积分法,能量守恒方程采用基于节点重构的扩散方程有限体积格式.     

电磁量计随爆轰波运动惯性性质的二维数值模拟

 利用二维非线性有限元动力分析程序,对金属电磁测速量计在爆轰波质速测量中随爆轰波运动的惯性性质进行了二维数值模拟。     

二维映射神经元模型中频率依赖的随机共振

通过数值模拟方法, 研究了在具有稳定次阈值振荡特性的二维映射神经元体系中, 噪声对体系非线性动力学的调控作用. 通过计算发现了噪声诱导的动作电位和随机共振现象. 另外,还研究了体系的控制参数及输入信号的频率对体系动力学的影响, 发现了该体系中频率依赖的随机共振现象. 关键词： 二维映射神经元模型 次阈值振荡 高斯白噪声 随机共振     

二维冰相I的电子和光学性质

二维冰是典型的原子制造技术获得的新型原子级材料,其结构和成核生长在材料科学、摩擦学、生物学、大气科学和行星科学等众多领域具有至关重要的作用.虽然二维冰的结构性质已被广泛研究,但对其电学和光学性质知之甚少.本文通过密度泛函理论和线性响应理论计算了二维冰相I在零温时的主要电学、光学、介电性质和红外光谱.其次,利用从头算分子...     

锶热原子束二维准直的动力学过程的蒙特卡罗模拟及实验研究

在考虑随机因素的情况下, 应用蒙特卡罗方法在理论上详细研究了锶原子束二维激光准直的动力学过程. 综合考虑原子横向发散角、初始原子位置、纵向速度分布、同位素等因素, 获得了激光二维准直后的原子横向空间分布的模拟结果以及随准直光失谐、光功率等参量因素的变化. 通过与实验数据比较, 理论值和实验值很好相符, 显示蒙特卡罗方法可以精确地描述锶原子束二维准直的动力学过程. 为原子束激光二维准直的精确控制, 高精度原子钟系统的优化, 提供了一种理论分析方法. 关键词： 二维准直 蒙特卡罗方法 横向空间分布     

双层多孔介质内预混燃烧的实验和二维数值模拟

对双层多孔介质燃烧器内丙烷/空气预混燃烧进行实验和数值研究.实验对多孔介质燃烧器内固体温度场分布进行测量分析;数值计算利用商业软件FLUENT6.2,通过添加用户自定义标量方程和用户自定义函数,对有壁面散热的双层多孔介质内预混燃烧进行了二维模拟,并与实验结果进行了比较.结果表明,双层多孔介质燃烧器具有良好的稳定燃烧范围和较低的污染物排放;壁面散热对多孔介质燃烧的影响不可忽视.     

Exact solution of a three-component system on the honeycomb lattice

A model three-component system is considered in which the bonds of a honeycomb lattice are covered by rodlike molecules of typesAA, BB, andAB. The ends of molecules near a common lattice site interact with energies _AA, _BB, and _AB. The model is equivalent to an Ising model on the 3–12 lattice. Exact results are obtained for the two-phase coexistence curves in the isothermal composition plane.     

Computer simulation study of a two-dimensional dipolar lattice

Summary The present work reports Monte Carlo calculations on a classical square lattice, consisting of purely dipolar plane rotators with identical dipole moments. Dipolar interactions are known not be essential for nematic ordering, but they can play a significant role in some specific cases; along the lines of the lattice model approximation already used in simulation work on liquid crystals, our system can be considered as an extreme case of nematogenic potential model. The system possesses an antiferroelectric ground state and, at higher temperature, it undergoes a transition to an orientationally disordered phase; comparison with the mean-field treatment of the transition is also reported. The structural properties were investigated by calculating orientational correlation functions, and found to exhibit some qualitative differences with respect to other potential models previously investigated for nematics. Simulation results indicate a close qualitative similarity with a three-dimensional analogue investigated in our previous work.

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Riassunto Il presente lavoro riporta calcoli Monte Carlo per un reticolo classico quadrato, costituito da rotatori piani puramente dipolari, con identici momenti. è noto che le interazioni dipolari non sono essenziali per l'ordinamento nematico, ma esse possono avere un ruolo significativo in alcuni casi specifici; lungo le linee dell'approssimazione a modello reticolare già applicata in lavori di simulazione per cristalli liquidi, il nostro sistema può pertanto venire considerato come un caso estremo di modello di potenziale nematogenico. Il sistema possiede stato fondamentale antiferroelettrico ed, a temperatura piú elevata, transisce ad una fase orientazionalmente disordinata; si riportano per confronto i risultati della trattazione a campo medio per tale transizione. Le proprietà strutturali furono investigate calcolando funzioni di correlazione orientazionale, e si è trovato che esse mostrano qualche differenza qualitativa rispetto ad altri modelli di potenziale previamente studiati per nematici. I risultati di simulazione indicano una stretta somiglianza qualitativa con un analogo tridimensionale investigato in nostri precedenti lavori.

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Резюме В этой работе предлагаются вычисления по методу Монте-Карло для классической квадратичной решетки, состоящей нз чнсто дипольных плоских ротаторов с тождественными дипольными моментами. Известно, что дипольные взаимодействия не являются существенными для нематического упорядочения, но они могут играть существенную роль в некоторых специфических случаях: в частности, в приближении модельной решетки, уже использованном при моделировании на жидких кристаллах, наша система может рассматриваться как предельный случай модели немтическочо потенциала. Рассмотренная система обладает антиферромагнитным основным состоянием и при высоких температурах она претерпевает переход в ориентационно разупорядоченную фазу; также проводится сравнение с рассмотрением этого перехода с помощью среднего поля. Исследуются структурные свойства, вычисляя ориентационные корреляционные функции. Обнаружено существование некоторых качественных различий по сравнению с моделями потенциалов, ранее использованных для нематиков. Результаты моделирования обнаруживают качественное подобие с трехмерным аналогом, исследованным в нашей предыдущей работе.

     

Construction of phase diagrams for nanoscaled Ising thin films on the honeycomb lattice using cellular automata simulation approach

The phase diagrams of the three-layer Ising model on the honeycomb lattice with a diluted surface have been constructed using the probabilistic cellular automata based on Glauber algorithm. The effects of the exchange interactions on the phase diagrams have been investigated. A general mathematical expression for the critical temperature is obtained in terms of relative coupling r = J₁/J and Δ_s = (J_s/J) ? 1, where J and J_s represent the nearest neighbor coupling within inner- and surface-layers, respectively, and each magnetic site in the surface-layer is coupled with the nearest neighbor site in the inner-layer via the exchange coupling J₁. In the case of antiferromagnetic coupling between surface-layer and inner-layer, system reveals many interesting phenomena, such as the possibility of existence of compensation line before the critical temperature.     

高速气流作用下能量加载金属蜂窝板数值模拟

数值模拟研究了高速气流作用下能量加载金属蜂窝板温度场。针对金属蜂窝典型单元,构造了蜂窝核细观导热数值计算分析模型。采用流固耦合计算方法,使用两相流模型和凝固/熔化模型模拟气流对烧蚀物的剥蚀,较完整地模拟了能量加载金属蜂窝板的物理变化过程,计算得到了金属蜂窝板的温度分布以及烧蚀形貌。结果表明两相流方法能够较全面地模拟能量加载金属蜂窝板过程中的对流换热、熔化与凝固过程以及金属液体在气流冲刷下的动力学过程,能获得较为合理的物理图像。     

Monte Carlo study of the antiferromagnetical Ising model on a centred honeycomb lattice

We use the Monte Carlo method to study an antiferromagnetical Ising spin system on a centred honeycomb lattice, which is composed of two kinds of 1/2 spin particles A and B. There exist two different bond energies J_A-A and J_A-B in this lattice. Our study is focused on how the ratio of J_A-B to J_A-A influences the critical behaviour of this system by analysing the physical quantities, such as the energy, the order parameter, the specific heat, susceptibility, {etc} each as a function of temperature for a given ratio of J_A-B to J_A-A. Using these results together with the finite-size scaling method, we obtain a phase diagram for the ratio J_A-B / J_A-A. This work is helpful for studying the phase transition problem of crystals composed of compounds.     

Stages of melting of graphene model in two-dimensional space

Spontaneous melting of a perfect crystalline graphene model in 2D space is studied via molecular dynamics simulation. Model containing 10⁴ atoms interacted via long-range bond-order potential (LCBOP) is heated up from 50 to 8,450 K in order to see evolution of various thermodynamic quantities, structural characteristics and occurrence of various structural defects. We find that spontaneous melting of our graphene model in 2D space exhibits a first-order behaviour of the transition from solid 2D graphene sheet into a ring-like structure 2D liquid. Occurrence and clustering of Stone–Wales defects are the first step of melting process followed by breaking of C–C bonds, occurrence/growth of various types of vacancies and multi-membered rings. Unlike that found for melting of a 2D crystal with an isotropic bonding, these defects do not occur homogeneously throughout the system, they have a tendency to aggregate into a region and liquid phase initiates/grows from this region via tearing-like or crack-propagation-like mechanism. Spontaneous melting point of our graphene model occurs at T_m = 7,750 K. The validity of classical nucleation theory and Berezinsky–Kosterlitz–Thouless–Nelson–Halperin–Young (BKTNHY) one for the spontaneous melting of our graphene model in strictly 2D space is discussed.     

Transport properties in the photonic super‐honeycomb lattice — a hybrid fermionic and bosonic system

We report on the transport properties of the super‐honeycomb lattice, the band structure of which possesses a flat band and Dirac cones, according to the tight‐binding approximation. The super‐honeycomb model combines the honeycomb lattice and the Lieb lattice and displays the properties of both. It also represents a hybrid fermionic and bosonic system, which is rarely seen in nature. By choosing the phases of input beams properly, the flat‐band mode of the super‐honeycomb lattice will be excited and the input beams will exhibit strong localization during propagation. On the other hand, if the modes of Dirac cones of the super‐honeycomb lattice are excited, one will observe conical diffraction. Furthermore, if the input beam is properly chosen to excite a sublattice of the super‐honeycomb lattice and the modes of Dirac cones with different pseudospins, e.g., by the three‐beam interference pattern, the pseudospin‐mediated vortices will be observed.

     

Numerical simulation of two-dimensional soap froth

The temporal evolution of two-dimensional foam is studied by event-driven numerical simulations based on different types of models. It is shown that most of the dynamical and topological features seen in experimental measurements can be reproduced. The average area of cells scales linearly with time and the distribution of n-sided cells can be compared with known results. The topological models regarding the lengths of the boundaries yield the best results among the models studied.     

The dissociated properties of dislocation in two-dimensional triangular lattice

The dissociated core structure of dislocation in two-dimensional triangular lattice is determined by the variational method within lattice theory. The dissociation effect leads to a narrower core width of partial dislocations than the compact one. The equilibrium separation between two partial dislocations is not very sensitive to the intrinsic stacking fault energy and there exists deviation from the intrinsic stacking fault energy criterion in the continuous elastic theory of dislocation. The relationship between the equilibrium separation and intrinsic stacking fault energy is analogous in lattice theory and the Peierls-Nabarro model. But the equilibrium separation obtained in lattice theory is wider than that obtained in the Peierls-Nabarro model for the same intrinsic stacking fault energy.