Numerical simulation of two-dimensional granular shearing flows and the friction force of a moving slab on the granular media

This paper studies some interesting features of two-dimensional granular shearing flow by using molecular dynamic approach for a specific granular system.The obtained results show that the probability distribution function of velocities of particles is Gaussian at the central part,but diverts from Gaussian distribution nearby the wall.The macroscopic stress along the vertical direction has large fluctuation around a constant value,the non-zero average velocity occurs mainly near the moving wall,which forms a shearing zone.In the shearing movement,the volume of the granular material behaves in a random manner.The equivalent friction coefficient between moving slab and granular material correlates with the moving speed at low velocity,and approaches constant as the velocity is large enough.     

缝合复合材料层板低速冲击损伤研究

通过三维动力学有限元法,以空间杆单元模拟缝线的增强作用,建立了缝合复合材料层板在横向低速冲击载荷作用下的渐近损伤分析模型。该模型考虑了缝合层板受低速冲击时的纤维断裂、基体开裂及分层等五种典型损伤形式,采用基于应变描述的Hashin失效准则和Yeh分层失效准则,并将其嵌入ABAQUS/Explicit用户子程序以实现相应损伤类型的判断及其材料性能退化。针对相同铺层的缝合与未缝合层板,模拟了低速冲击作用下的冲击响应和渐进损伤过程,数值结果与试验吻合较好,证明了该方法的合理有效性。同时探讨了冲击速度、缝合密度等对缝合层板冲击响应和损伤的影响。结果表明：有、无缝合层板的低速冲击响应具有类似的变化规律,缝合能够有效减小冲击损伤面积。随着缝合密度和缝线强度的增大,缝合对冲击损伤的抑制作用更为明显。     

布朗动力学理论模拟动态肌动蛋白纤维的增长

肌动蛋白的聚合耦合三磷酸腺酐(ATP)分子水解成二磷酸腺苷(ADP)分子和磷酸(Pi)的释放两个过程. 因此, 肌动蛋白纤维上的原聚体存在三种不同状态, 即分别结合ATP, ADP/Pi和ADP分子. 原聚体的不同状态导致纤维具有不同的空间图谱, 这些状态的空间分布将影响纤维的各种行为. 为此,建立了相应的分子模型,在布朗动力学模拟中实现了遵循时间演化的连续马尔可夫随机过程的解聚和水解反应; 重点阐述了如何实现纤维两端的聚合和解聚达到化学平衡的方法, 并系统研究了纤维在结合ATP分子的肌动蛋白单体溶液中的增长行为.     

嵌段共聚物组成对薄膜形貌影响的多体耗散粒子动力学研究

利用多体耗散粒子动力学(Multibody Dissipative Particle Dynamics, Multibody DPD)方法研究了在溶剂蒸发条件下, 嵌段共聚物在表面自组装形成薄膜的过程, 分别考虑了两嵌段共聚物和三嵌段共聚物及不同组成对薄膜形貌的影响. 模拟得到了无序状薄膜和层状薄膜, 并计算了这些薄膜的序参量和薄膜厚度随时间的演化. 结果表明, 嵌段共聚物的组成对薄膜厚度几乎没有影响, 当某种组分的链段很短时, 只能形成序参量较小的无序薄膜, 相反, 则可以得到序参量较大的层状薄膜.     

分子动力学模拟BCC铁中级联碰撞产生的缺陷结构及其演变(英文)

用分子动力学模拟BCC铁中级联碰撞原子的演变过程.结果显示,级联碰撞的原子不仅可以临时地产生自间隙原子、空位、以及<100>,<110>和<111>哑铃型缺陷,也可以产生<110>和<111>,以及<110>和<110>哑铃型缺陷的复合缺陷.模拟显示在模拟的能量范围内,如果初级碰撞原子的能量越大,该原子引起的级联碰撞覆盖区域会越大.发现具有几千电子伏特初级碰撞能量的原子引起的级联碰撞覆盖区域大约为11~15个晶格常数大小.同时还发现在级联碰撞的初始阶段(0.0~0.75 ps)不仅会有自间隙原子与空位的生成,同时也会有少量的自间隙原子与空位缺陷复合而消失.     

RDX/AMMO推进剂的分子动力学

Molecular dynamics simulations have been performed to investigate well-known ener-getic material cyclotrimethylene trinitramine (RDX) crystal, 3-azidomethyl-3-methyloxetane (AMMO) and RDX/AMMO propellant. The results show that the binding energies on differ-ent crystalline surface of RDX changes in the order of (010)>(100)>(001). The interactions between RDX and AMMO have been analyzed by means of pair correlation functions. The mechanical properties of RDX/AMMO propellant, i.e. elastic coefficients, modulus, Cauchypressure, and Poisson's ratio, etc., have been obtained. It is found that mechanical properties are effectively improved by adding some amounts of AMMO polymers, and the overall effect of AMMO on three crystalline surfaces of RDX changes in the order of (100)>(010)>(001). The energetic properties of RDX/AMMO propellant have also been calculated and the results show that compared with the pure RDX crystal, the standard theoretical specific impulse of RDX/AMMO propellant decrease, but they are still superior to those of double base propellant.     

对流扩散方程QUICK格式的数值摄动高精度重构格式

利用高智提出的数值摄动算法, 把对流扩散方程的常用QUICK格式(黏性和对流项分别用二阶中心和QUICK格式离散)进行了高精度重构, 包括利用离散单元内所有结点的全域重构和分别利用离散单元内上下游结点的上下游重构, 得到两类新的更高阶精度的数值摄动重构格式, 称为高的QUICK格式(G-QUICK格式). G-QUICK格式与QUICK格式相比简单性相当, 但精度更高; 全域重构G-QUICK格式和QUICK格式均为条件稳定, 上下游重构得到一些绝对稳定的G-QUICK格式. 解析分析和数值算例均证实了G-QUICK格式的优良性能, 上下游重构的G-QUICK格式为在对流扩散方程的QUICK格式中避免使用人工黏性提供了新途径.      

Influence of Solid-liquid Interaction and Temperature on the Dynamic Dewetting of a Thin Polymer Film:A Molecular Dynamics Study

Coarse-grained molecular dynamics simulations were carried out to investigate the dewetting behavior of a polymer thin film on partial wetting solid surface at the early stage of the dewetting process. Spontaneous dewetting is initiated by removing a band of strip from both the ends of the liquid polymer film which has achieved equilibrium. The solid-liquid interaction and temperature were varied to show their influence on the dewetting dynamics during dewetting as well as the shape evolution of the liquid ...     

Entanglement Dynamics of Three Superconducting Charge Qubits Coupled to a Cavity

We investigate the entanglement dynamics of a quantum system consisting of three superconducting charge qubits (SCQs) interacting with a microwave field. For separable and entangled states of the SCQs, the evolutions are studied under various photon numbers of cavity field. The results show that the amplitude and period of the bipartite entanglement square concurrences can be controlled by the choice of initial states of SCQs and photon numberof cavity field, respectively. This simple model of a quantum register allows us to understand the dynamic process of the quantum storage of information carried by charge qubit.     

柔性多体碰撞问题的多变量方法

针对柔性多体系统碰撞问题的特点, 提出了柔性多体系统碰撞问题的多变量方法. 在未碰撞阶段和分离后的阶段, 多变量方法考虑了物体大范围运动与变形的耦合.在碰撞阶段, 考虑非碰撞区域的变形, 对非碰撞区域用浮动参考系方法求解, 对发生碰撞的局部区域用非线性有限元方法求解. 非碰撞区域采用浮动基位形坐标和柔性体相对浮动基的变形模态坐标描述, 大大减缩了变量的维数,提高了计算效率. 碰撞局部区域采用非线性有限元节点坐标描述, 可以得到碰撞局部区域高精度的应力、应变响应, 而且可以反映碰撞局部区域的大变形、塑性等非线性响应. 该方法既能体现碰撞对系统大范围运动和长期动力学仿真的影响, 又能精确反映出碰撞发生的微小时间段内物体碰撞局部区域的应力、应变响应, 表现出碰撞过程中物体接触区域的演化历程.介绍了两杆正碰撞与铅垂面内双摆撞击自由圆盘的算例, 设计了两柔性杆正碰撞实验,多变量方法的数值仿真结果与实验测量结果很好地吻合.