液滴变形及表面张力模拟的光滑粒子动力学方法

光滑粒子动力学(smoothed particle hydrodynamics,SPH)方法是一种Lagrange无网格粒子方法,在多相流模拟方向有着巨大的潜力。液体表面张力是多相流动的一个很重要的作用力。该文采用连续表面力(continuum surface force,CSF)模型和粒子间相互作用力(inter-particle interaction force,IIF)模型在SPH方法中引入表面张力,比较了这两种模型对液滴变形过程的模拟。CSF模型与理论结果之间的比较表明,CSF模型很好地模拟表面张力的效应。而IIF模型虽然也可以用于计算表面张力,但与CSF模型相比,其模型参数的确定较为困难。

基于物理的海浪场景的真实感建模与绘制

提出一种基于物理的海浪场景的真实感建模与绘制算法.基于平滑粒子流体动力学模型,首先提出一种压力状态方程以取代传统的理想气体状态方程,从而在保证系统稳定性的同时,最大程度地保证液体的体积守恒;为了实现对水面浪花飞溅和泡沫的模拟,提出自适应的表面张力模型,通过制定3类流体粒子状态的转化规则,实现了飞溅粒子和主水体之间的无缝连接;并采用GPU图形硬件加速技术大大地提高了整个过程计算效率.最终绘制出海浪行进、翻卷、破碎及拍岸等真实感较强的动态效果.

溴化锂溶液垂直降膜过程中流动与传热的数值模拟

采用流体体积(VOF)法捕捉自由界面,并应用连续表面力(CSF)模型,建立了垂直降膜波动模型,研究了溴化锂溶液垂直降膜过程中的波动过程,根据波动模型得到的界面信息,建立了以波速为动坐标系的固定界面传热模型,同时考察了波动对传热的影响,并建立了垂直降膜波动模型和固定界面传热模型。结果表明:一定入口频率的扰动发展为孤波和毛细波的组合波,孤波波峰处出现了循环流动,且在第一个毛细波波谷处出现回流。波动强化机理与Pr数有关,Pr数较大时,对流起主要作用,Pr数较小时,液膜减薄起主要作用。

规整填料波纹结构上的二维两相流模拟方法

规整填料是由规则排列的波纹板组成的。液相是沿着波纹板壁面往下流动,而气相则是在波纹板之间形成的通道内与液相呈并流或逆流的状态。因此,气液两相的水力学特性决定着填料塔的操作弹性和质量传递效率。波纹板上的液膜流动状态因在很多应用领域都发挥作用而备受关注。本文从物理建模、自由界面处理方法、表面张力模型以及湍流模型等方面对规整填料波纹板上的二维液膜数值模拟方法作了详细的陈述,并且对该领域的研究现状作了进一步分析和总结。

倒装芯片封装中非牛顿流体下填充的数值仿真

倒装芯片封装中的下填充工艺可以有效地提高封装连接的可靠性,因而得到了广泛应用。含有硅填料的环氧树脂是常用的下填充胶料,在下填充流动过程中表现出明显的非牛顿流体特性。利用Fluent软件对具有非牛顿流体特性胶料的下填充过程进行了三维数值模拟。采用流体体积比函数(VOF)对流动前沿界面进行追踪,再用连续表面张力(CSF)模型来计算下填充流动的毛细驱动力,并用幂函数本构方程来体现下填充胶料的非牛顿流体特性。通过数值模拟,获得了下填充流动前沿位置随时间变化的数据,这些数据与实验结果有较好的吻合度。该数值方法可较好地预测具有非牛顿流体性质胶料的下填充过程。

金属/陶瓷润湿性的实验表征和理论预测研究进展

金属/陶瓷体系的润湿性研究在金属与陶瓷的连接、金属液的熔炼和提纯、浸渗法和液相法制备复合材料等领域都有着重要意义。金属熔体在陶瓷表面的润湿过程中,会出现基板在熔体中溶解、界面吸附和互相反应等,是一种较为复杂的物理化学现象。有关金属/陶瓷润湿性的实验和理论研究一直是国际上材料学领域的热点之一。目前金属/陶瓷润湿性主要通过测量接触角θ(借助Young s方程计算)来得出,润湿性表征方法存在较大局限性,特别是接触角对实验条件高度敏感,其往往难以准确反映润湿性,以及适用于高熔点合金与陶瓷体系的方法较为缺乏。因此,除对接触角测试方法进行改进外,很多研究者也试图通过理论计算来考察润湿性,但至今尚未发展出能够很好地应用于所有金属/陶瓷体系的理论预测模型。润湿性实验表征方法的近期研究主要集中在改良座滴法、滴定法、毛细上升法和感应熔化法等。其中,改良座滴法相比传统座滴法能够消除熔体表面氧化膜的影响。感应熔化法可以使高熔点合金(如Ti合金等)熔化,具有独特优势(相比之下其他几种方法只适用于Al系、Mg系等低熔点合金与陶瓷的体系)。在理论预测模型方面,除直接基于Young s方程,根据表面张力模型来研究润湿性外,也有学者尝试结合Young-Dupré方程,从热力学和原子键的角度揭示反应界面润湿性的内在规律。同时,将润湿视为一种反应现象,对界面反应吉布斯自由能变化和润湿过程中表面相的能量变化加以考虑,也形成了一种新的定性衡量润湿性的标准。此外,研究者还在润湿铺展动力学方面取得了一些重要成果,包括直接根据金属形核理论来计算润湿角,以及利用如流体动力学模型、分子动力学模型、反应控制模型和扩散控制模型等来预测金属/陶瓷体系的润湿速率。本文主要从润湿过程的机制、接触角的测试方法和用以预测润湿性的理论模型三个方面,综述了金属/陶瓷润湿性领域的实验和理论研究进展。

Calculating models on surface tension of RE_2O_3-Mg O-SiO_2(RE=La, Nd, Sm, Gd and Y) melts

A thermodynamic model was developed for determining the surface tension of RE2O3-MgO-SiO2(RE=La, Nd, Sm, Gd and Y) melts considering the ionic radii of the components and Butler's equation. The temperature and composition dependence of the surface tensions in molten RE2O3-MgO-SiO2 slag systems was reproduced by the present model using surface tensions and molar volumes of pure oxides, as well as the anionic and cationic radii of the melt components. The iso-surface tension lines of La2O3-MgO-SiO2 slag melt at 1873 K were calculated and the effects of slag composition on the surface tension were also investigated. The surface tensions of La2O3, Gd2O3, Nd2O3 and Y2O3 at 1873 K were evaluated as 686, 677, 664 and 541 m N/m, respectively. The surface tension of pure rare earth oxide melts linearly decreases with increasing cationic field strength, except for Y2O3 oxide, while Y2O3 has a much weaker surface tension. The evaluated results of the surface tension show good agreements with literature data, and the mean deviation of the present model is found to be 1.05% at 1873 K.

A Surface Tension Model for Liquid Mixtures Based on NRTL Equation

A new equation for predicting surface tension is proposed based on the thermodynamic definition of surface tension and the expression of the Gibbs free energy of the system. Using the NRTL equation to represent the excess Gibbs free energy, a two-parameter surface tension equation is derived. The feasibility of the new equation has been tested in terms of 124 binary and 16 multicomponent systems(13-ternary and 3-quaternary) with absolute relative deviations of 0.59% and 1.55% respectively. This model is also predictive for the temperature dependence of surface tension of liquid mixtures. It is shown that, with good accuracy, this equation is simple and reliable for practical use.

Estimation of surface tension of organic compounds using quantitative structure-property relationship

A novel quantitative structure-property relationship （QSPR） model for estimating the solution surface tension of 92 organic compounds at 20℃ was developed based on newly introduced atom-type topological indices. The data set contained non-polar and polar liquids, and saturated and unsaturated compounds. The regression analysis shows that excellent result is obtained with multiple linear regression. The predictive power of the proposed model was discussed using the leave-one-out （LOO） cross-validated （CV） method. The correlation coefficient （R） and the leave-one-out cross-validation correlation coefficient （Rcv） of multiple linear regression model are 0.991 4 and 0.991 3, respectively. The new model gives the average absolute relative deviation of 1.81% for 92 substances. The result demonstrates that novel topological indices based on the equilibrium electro-negativity of atom and the relative bond length are useful model parameters for QSPR analysis of compounds.

A Kinetic Model for Describing the Effect of Proteins on the Air-Water Interface Tension

The main objective of this work was to develop a kinetic model to describe the variation of the surface tension in an air-water interface due to the adsorption of proteins from different origins and to identify quantitatively the relevant parameters, it was considered that the processes of adsorption, unfolding and reordering of the protein molecule in the interface occur simultaneously. The model used in the present work to calculate the surface tension postulates the existence of two simultaneous processes, adsorption and protein rearrangement represented with an equation of first order with two exponential components. The relevant parameter of the equation are ka and kr-the rate constants of the two first order kinetic phases that correspond to both conformational states of the protein, adsorption and rearrangement during the process of variation of the surface tension, and the amplitude parameters Aa and Ar. The results suggest that the kinetic model for the variation of the surface tension of protein solutions proposed in this work, with two simultaneous first order processes, is more appropriate than previous models to describe such variation.

重力场下平板边界层内气液两相流动数值分析

通气减阻技术因具有降低能耗和环境污染小等效果,在工程领域内得到广泛关注。为研究重力场中气相在平板湍流边界层内流动演化过程及由此产生的减阻效应,该文耦合连续表面张力(CSF)的VOF多相流模型和标准k-?湍流模型,求解非定常RANS方程,对边界层内气液两相流动进行数值模拟。通过计算结果与实验结果的对比,验证了数值方法的有效性;进而对不同通气流量和来流雷诺数下,气泡当量直径、近壁区空隙率及流动减阻率进行定量分析。结果表明:减阻效应与近壁区空隙率密切相关;来流雷诺数和通气量的提高,均能增强减阻效应。

Experiments and model for the surface tension of carbonated monoethanolamine aqueous solutions

The surface tension of carbonated monoethanolamine aqueous solutions from 293.15 to 323.15 K was measured by using an automatic surface tension-meter.A model applicable for the surface tension of MEA-CO2-water mixtures was proposed and the calculated results agreed well with the experiments.The influences of temperature,MEA concentration and CO2 loading were demonstrated on the basis of experiments and calculations.

Study on asymmetric interior corner flow in microgravity condition

The capillary flow in asymmetric interior corner consisting of straight vane and curved wall is studied with analytical solution.The concept of equivalent interior corner angle is proposed to convert the asymmetric interior corner model into symmetric interior corner model.Then the governing equations of interior corner flow are established,and based on which the interior corner flow is calculated.This method is used to analyze the capillary flow in cylindrical vane-type surface tension tank with outer vanes.The research can provide beneficial reference to the design of vane-type surface tension tank.

Localization and macroscopic instability in nanoporous metals

Ductile fracture generally relates to microscopic voiding and to strain localization in metallic materials.When the void size is reduced to the nanoscale,size effects often lead to a different macroscopic plastic behavior from that established for the same material with larger voids.For example,irradiation of metallic materials can generate a large number of voids at the nanoscale,leading to complex deformation behaviors.The present work advances the understanding of strain localization in nanoporous metallic materials,connecting both the microscopic(nano-)and macroscopic scales.To explore the physical mechanisms at the nanoscale,molecular dynamics(MD)simulations were here carried out,capturing multiple nanovoids explicitly.Then,a homogenized continuum theory based in Gurson's constitutive framework is proposed,which enables us to explore how localized behavior at the macroscopic scale evolves.The homogenized model incorporates the surface tension associated with nanosized void.The importance of this surface tension is illustrated by several parametric studies on the conditions of localization,when a specimen is subjected to uniaxial tension.Our parametric studies show that for smaller nanovoid sizes,and for a hardening matrix material,shear localization onset is delayed.Our proposed homogenization model was then used to predict localization behavior captured by our MD simulation.The yield stress and the localization strain predicted by our continuum model are in general agreement with the trends obtained by MD simulation.Moreover,based on our present study,experimental results of shear failure strain vs.dose of irradiation for several metals could be qualitatively explained rather successfully.Our model can therefore help shed light on prolonging the operation limits and the lifetime of irradiated metallic materials under complex loading conditions.