Predicting the Mechanical Properties of Binary Blends of Immiscible Polymers

We couple a morphological study of an immiscible binary AB mixture with a micromechanical simulation to determine how the spatial distribution of the A and B domains and the interfacial region (interphase) affects the mechanical behavior of the blend. The morphological studies are conducted through a three-dimensional Cahn-Hilliard (CH) simulation. Through the CH calculations, we obtain the size and structure of the domains for different blend compositions. The output of the CH model serves as the input to the Lattice Spring Model (LSM), which consists of a three-dimensional network of springs. In particular, the location of the different phases is mapped onto the LSM lattice and the appropriate force constants are assigned to the LSM sites. A stress is applied to the LSM lattice and we calculate the elastic response of the material. We find that the local stress and strain fields are highly dependent on the morphology of the system. By integrating the morphological and mechanical models, we can isolate how modifications in the composition of the mixture affect the macroscopic behavior. Thus, we can establish how choices made in the components affect the ultimate performance of the material.     

不同倾角的脉管制冷机内自然对流影响的研究

本文通过对脉管内自然对流的数值模拟，讨论了当脉管冷端处在不同方向时，脉管内的自然对流对脉管制冷机性能的影响．数值模拟结果表明，当冷端在下时获得的制冷温度最低；当热端在下并与重力方向成３０°时制冷温度最高．结论与实验测量结果定性一致．所做的理论分析对实现脉管制冷机的良好运行有指导意义。     

Experimental verification of drop/impact simulation for a cellular phone

Conducting drop tests to investigate impact behavior and identify failure mechanisms of small-size electronic products is generally expensive and time-consuming. Nevertheless, strict drop/impact performance criteria for hand-held electronic products such as cellular phones play a decisive role in the design because they must withstand unexpected shocks. The design of product durability on impact has heavily relied on the designer's intuition and experience. In this study, a reliable drop/impact simulation for a cellular phone is carried out using the explicit code LS-DYNA. Subsequently globallocal experimental verification is accomplished by means of high-speed photography and impact response measurement. Using this methodology, we predict potential damage locations in a cellular phone and compare them with real statistical data. It is envisaged that development of a reliable methodology of drop/impact simulation will provide us with a powerful and efficient vehicle for improvement of the design quality and reduction of the product development cycle.     

双组元姿控发动机反流特性的DSMC模拟

为准确获得双组元姿控发动机的羽流及其反流特性,采用直接模拟蒙特卡罗(DSMC)方法结合可变软球(VSS)模型数值模拟以N2O4/MMH为推进剂的真空羽流。喷口参数由喷管流动的DSMC法计算得到。与文献比较表明本文计算程序可信。模拟结果表明,分子质量越小的气体越容易进入反流区;本文的计算条件下,在偏离X轴正向116°~140°范围内,组分数密度和质量流率以及温度均出现了最大值。     

狭义相对论效应──运动时钟变慢的计算机模拟演示实验

利用精炼的C语言进行程序设计，定量模拟狭义相结论的运动时钟变慢，并对处于两种不同时空观的时钟运行进行对比，使得时间膨胀效应变得直观。     

Numerical Analysis and Simulation Analysis for Space‐Time Data

Spatio temporal dynamics of the positive column of a dc neon glow discharge is studied and investigated experimentally and theoretically. Spatio temporal analysis by means of biorthogonal decomposition method (BOD) gives insights into the mechanism of irregularity and can be employed for characterization of spatio‐ temporal complexity. In the weak nonlinear region, the wave dynamics is approximated by an amplitude equation of the Ginzburg‐Landau equation (CGLE) with complex coefficients and an additional integral term based on a fluid model. In the present work we deal with irregular spatio‐temporal data. A comparison between the numerical analysis of the experimental data and simulation results are studied. A good agreement between the dynamical behaviour for experimental space‐time data and theoretical simulation space‐time results was obtained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A tentative approach to the direct simulation of drag reduction by polymers

An efficient technique for drag reduction uses dilute solutions of a few p.p.m. of polymers. A possible reduction in drag of up to 80% is achieved. Several experimental observations have been made which tend to indicate that the polymers modify the turbulence structures within the buffer layer. Flow visualisations have shown that the changes consist of a weakening of the strength of the streamwise vortices. Existing literature reveals no attempts of numerical simulation of this phenomenon. In this paper an approach is pursued by using a constitutive equation which relates the elongation viscosity to the local properties of the flow. According to this model this viscosity is large in zones where the amount of strain rate is greater than the amount of vorticity, and is zero when the vorticity exceeds the strain rate. Simulations have been performed in a “minimal channel” to give good resolution with a limited number of grid points. The accuracy of the method is tested by comparison with the results of other techniques. For simulations with polymers, quantitative comparisons cannot be made, but the results reproduce the qualitative outputs of the experiments. The mean streamwise velocity is modified in the buffer layer; the peak of the streamwise turbulent intensity, in wall units, increases and its maximum moves far from the wall; and the vertical turbulent intensity is largely reduced in the wall region. An interesting outcome from both the simulation and the experiments is that the strength of the longitudinal vortices is reduced when the polymers are present.     

Meshless simulation of equilibrium swelling/deswelling of pH‐sensitive hydrogels

Hydrogels have been widely used in microelectromechanical systems (MEMS) and Bio‐MEMS devices. In this article, the equilibrium swelling/deswelling of the pH‐stimulus cylindrical hydrogel in the microchannel is studied and simulated by the meshless method. The multi‐field coupling model, called multi‐effect‐coupling pH‐stimulus (MECpH) model, is presented and used to describe the chemical field, electric field, and the mechanical field involved in the problem. The partial differential equations (PDEs) describing these three fields are either nonlinear or coupled together. This multi‐field coupling and high nonlinear characteristics produce difficulties for the conventional numerical methods (e.g., the finite element method or the finite difference method), so an alternative—meshless method is developed to discretize the PDEs, and the efficient iteration technique is adopted to solve the nonlinear problem. The computational results for the swelling/deswelling diameter of the hydrogel under the different pH values are firstly compared with experimental results, and they have a good agreement. The influences of other parameters on the mechanical properties of the hydrogel are also investigated in detail. It is shown that the multi‐field coupling model and the developed meshless method are efficient, stable, and accurate for simulation of the properties of the stimuli‐sensitive hydrogel. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 326–337, 2006     

湍流燃烧二阶矩模型的大涡模拟验证

对美国Sandia国家实验室测量的甲烷-空气湍流射流火焰进行了三维大涡模拟(LES),其统计的时均量以及脉动量符合实验测量值,且和RANS代数二阶矩湍流燃烧模型模拟结果大致符合。LES统计得到的化学反应率系数脉动和甲烷浓度脉动的互关联与对应的时均量梯度的乘积分布趋势相同,大小幅值的位置也相对应,与二阶矩湍流燃烧模型的封闭假设相符,验证了二阶矩代数燃烧模型的合理性。     

Combinational simulations of free energy of polymer solution

It is conceptually proposed that the total entropy of polymer solution is contributed from two distinct parts: the positional and the oomformational. The former can be represented analytically, while the latter can be simulated with the random self-avoiding walk model on the simple cubic lattice for multichain systems. The obtained results indicated that both the conformational entropy and the mixing heat are consistent with the scaling laws wry well.