用迭代法模拟注塑成型的三维流动

Hele-Shaw模型是模拟注塑成型过程的常用模型,它的主要缺点是不能模拟一些重要的物理现象及引入实际制件中并不存在的“中面”概念,为了消除这些不足,本文开发了真三维的流动分析程序。建立了粘性、不可压缩的非牛顿流体流动的控制方程,为了避免同时求解耦合的压力场、速度场,本文引入拟稳定技术独立地求解这些方程,用迭代法求耦合方程的解。这种方法可以减少内存并提高数值方法的稳定性。算例表明数值结果与实验结果吻合较好,这种方法成功地模拟了注塑成型流动过程中的重要特征。     

黏性不可压缩流体流动前沿的数值模拟

提出了模拟注射成型中黏性、不可压缩流体流动前沿的新方法. 将Hele-Shaw流动应用于非 等温条件下的黏性、不可压缩流体，建立了流动分析模型，用充填因子的输运方程描述流动 前沿. 应用高阶Taylor展开式计算每一时间步长的充填因子，用Galerkin方法导出了计算 充填因子各阶导数的递推公式. 给出了时间增量的选取方法，证明了它的稳定性. 针对Han 设计的试验模具，用相同的材料及工艺条件模拟充填过程，比较了传统方法和该方法的模 拟结果与实验结果的差异. 算例分析表明，该方法可以有效地提高注射成型中流动前沿的 模拟精度和计算效率.     

成型充填过程的ALE有限元模拟

在ALE框架中提出了一个用于成型充填过程有限元数值模拟的模型。应用ALE参考构形及ALE参考粒子速度描写充填过程中的熔体质量运动。摒弃了Hele-Shaw近似假定,因而所提出的模型能用于非薄壁型腔中高分子材料充填过程的数值模拟。应用基于时域分步算法的Taylor-Galerkin方法,对控制成型充填过程的守恒方程建立了弱形式。对移动自由面附近的充填材料区构造了网格生成算法与网格重划分方案。给出了在几种不同形状的典型腔体中充填过程的数值模拟结果,表明了所提出的ALE有限元模型模拟充填过程的有效性。     

注塑成型充模过程的温度场计算

对注塑成型过程中充填阶段的非等温效应的数值模拟进行了研究 ,模拟了非牛顿流体在任意形状型腔内的流动。这里 ,数学模型是基于非牛顿流体在非等温状态下的广义 Hele-Shaw流动 ,利用有限元 /有限差分混合数值方法求解流场中的压力和温度分布     

注塑模充模过程动态分析

注塑成型是利用型腔模制造理想制品主要的成型加工方式 ,塑料熔体的流动行为将直接影响着最终塑件的质量 ,塑料熔体在三维薄壁型腔内的流动属于带有运动边界的粘性不可压缩流体的流动 ,本文针对塑料注塑成型特点 ,经过量纲分析和引入合理而必要的假设 ,得到了适合于充模分析的数学模型。控制方程的求解主要包括三个阶段 :压力场、温度场和流动前沿位置的确定。数值求解采用有限元法求解压力场、有限差分法求解温度场、并利用控制体积法跟踪熔体前沿 ,实现了充模过程的动态模拟     

注塑成型喷射现象数值模拟及机理分析

喷射是熔体充填过程中一种特殊流动形态,也是注塑成型的不良现象,为了预测射流长度、形态演化,揭示喷射的产生机理,建立了粘性、非等温的熔体三维流动模型,构造了熔体流动前沿演化的输运方程。用有限体积法离散控制方程,提出了压强与速度及速度与温度的两重解耦合方案,开发了模拟程序,分析了模拟成型过程中粘性力、惯性力、速度、温度、压力等物理量的大小及变化规律。基于模拟结果分析了粘性力、惯性力的大小对喷射的影响,发现:当惯性力大于粘性力时产生喷射现象,随着粘性力增大,射流变为蛇形流;射流长度依赖于注射速度,速度越大,射流越长,熔体温度对射流长度基本没有影响。此外,实验结果表明,注塑成型喷射现象数值模拟及机理分析方法可以较好地预测射流长度、蛇形流的形态以及蛇形流中、后端摆动幅度。     

非等温黏弹性复杂流动的改进SPH方法模拟

非等温黏弹性流体广泛存在于自然界和工业生产中,准确预测黏弹性流体的非等温流动机理和复杂流变特性有着重要的应用价值.文章提出一种改进的光滑粒子流体动力学(smoothed particle hydrodynamics,SPH)方法对非等温黏弹性复杂流动进行了数值模拟,其中流体的黏弹特性通过eXtended Pom-Pom本构模型来表征.为了提高模拟结果的精度,采用了一种核函数梯度的修正算法;为了灵活地施加边界条件,发展了边界粒子和虚拟粒子相联合的边界处理方法;为了消除流动过程中的拉伸不稳定性,施加了粒子迁移技术.运用改进SPH方法数值模拟了液滴撞击固壁和F型腔注塑成型问题,通过与Basilisk软件得到的结果进行比较验证了改进SPH方法求解非等温黏弹性流体的有效性.通过利用不同粒子初始间距进行计算,评价了改进SPH方法的数值收敛性.研究了非等温流动相较于等温流动的不同流动特征,深入分析了不同热流变参数对流动过程的影响.数值结果表明,文章提出的改进SPH方法可稳定、准确地描述非等温黏弹性复杂流动的传热机理、复杂流变特性和自由面变化特性.     

水平井砾石充填数值模拟研究进展

综述了水平井数值模拟研究的最新进展,内容包括：水平井砾石充填 机理及技术难题、充填过程中平衡砂床高度、临界流速的计算模型,描述了筛管/井筒环空砂 浆流动、冲管/筛管环空纯携砂液流动以及它们之间流体的交换和向地层的滤失过程. 重点介 绍了$\alpha$波充填过程中流动数学模型的研究现状及影响水平井砾石充填的各个 因素和存在的问题.     

基于实体的注射成型流动模拟

提出了应用中面模型技术模拟实体模型的注射成型流动过程的新方法。对实体模型的表面进行二维网格划分，将结点在厚度方向上配对．配对点之间添加虚拟热流道单元，建立二维有限元分析的网格模型。将HeleShaw流动应用于非等温条件下的粘性、不可压缩流体，建立基于中面模型流动分析的数学模型，用充填园子的输运方程描述流动前沿。用有限元计算充填过程的压力场．有限差分计算温度场，高阶的Taylor展开式计算每一时间步长的充填因子。针对Han设计的试验模具，用相同的材料及工艺条件，比较中面模型和实体模型的模拟结果。算例分析表明，这种方法可以有效地模拟基于实体模型的注射成型流动过程。     

井内流动与传热的三维耦合数值模型

钻井过程中,井内的压力、流场及温度分布是钻井作业必需的重要参数。本文提出了一个描述井内流动和传热的三维数学模型,用SIMPLER方法获得了该数学模型的数值解。该数值模型考虑了温度、压力对钻井液的流变性、密度以及各种介质的热物理参数的影响。现场试验数据与数值模拟结果的对比表明：本文提出的数学模型及采用的数值计算方法是可行的。     

两相临界流

由于两相临界流在压水反应堆安全分析中的重要性，在过去的４０年内，两相临界流一直是一个活跃的分支学科。本文对压水堆失水事故常用的两相临界流均匀平衡模型、滑移模型、考虑相间热力学非平衡效应的简化模型及两流体模型做了综述。结论是到目前为止，没有一个数学模型能准确预测各种参数范围、各种通道形状的临界流量。特定的模型只能适用于特定的情况。本文对非平衡两相流中汽泡成核、汽泡生长、相界面间质量、动量、能量交换的机理给予了更多的关注。     

Numerical simulation of flow boiling for organic fluid with high saturation temperature in vertical porous coated tube

A semi-analytical model is developed for the prediction of flow boiling heat transfer inside vertical porous coated tubes. The model assumes that the forced convection and nucleate boiling coexist together in the annular flow regime. Conservations of mass, momentum, and energy are used to solve for the liquid film thickness and temperature. The heat flux due to nucleate boiling consists of those inside and outside micro-tunnels. To close the equations, a detailed analysis of various forces acting on the bubble is presented to predict its mean departure diameter. The active nucleation site density of porous layer is determined from the pool boiling correlation by introducing suppression factor. The flow boiling heat transfer coefficients of organic fluid (cumene) with high saturation temperature in a vertical flame-spraying porous coated tube are studied numerically. It is shown that the present model can predict most of the experimental values within ±20%. The numerical results also indicate that the nucleate boiling contribution to the overall heat transfer coefficient decreases from 50% to 15% with vapor quality increasing from 0.1 to 0.5.     

热流体力学及其应用

热流体力学是一门涉及传热学、流体力学和热力学的交叉学科,并把重点放在讨论热过程对流体流动的影响。它由5部分组成:①热阻力。在某些情况下热阻力的存在对通道中的流体流量和换热系数有重大影响。借助于热阻力系数的定义和分析表达式,不仅可以预示单相通道流中的压力降,而且能用简便的方法预示气-液两相通道流中的压力降和临界热流。②热绕流。运用“虚质量源”和“热偶极子”的概念,对热绕流现象进行了分析和数值研究。它可在热除尘、粒子样品收集和热设备中流量分配等方面获得广泛的应用。③热驱动。不仅在重力场中,而且在如离心力场、表面张力场和电磁力场中也存在着热驱动流。着重讨论了流体运动的起因及其带来的后果,它包括环境污染、传热强化和同位素分离系数的提高等,④热不稳定性。重点讨论了热不稳定性的物理机理。用各种动力学方法所得到的流动不稳定性的临界准则对材料加工、热减阻、水源热污染等都是十分重要的。⑤热优化。研究了基于熵产生最小(热力学第二定律)为目标函数的流动和传热过程的优化。探讨了在一定条件下热力学第一定律效率和第二定律效率的内在联系。     

Nucleate boiling heat transfer: possibilities and limitations of theoretical analysis

The paper considers the different ways of nucleate boiling investigation, and in particular, presents the analysis of the latest numerical studies of the nucleate boiling primary processes (isolated bubble growth, thin liquid film flow and evaporation near the nucleation site). Many features of the process that were only the hypothesis became established facts after the direct numerical simulation. However, in spite of their undoubted usefulness these investigations cannot be applied for practical calculations. The high complexity of the phenomena comprising nucleate boiling excludes practically the possibility of strict theoretical analysis of the process. Under this situation development of an approximate theory of nucleate boiling retains its validity at present. Such a theory has been developed by the author in 1988. It reveals the main regularities of the nucleate boiling and leads to the predicting equation for heat transfer, which includes two empirical numerical factors. On the basis of the model developed the method of calculation of heat transfer in boiling of binary mixtures is proposed. To improve the existing predicting equations for boiling heat transfer it seems to be especially important to ground theoretically the nucleation sites density dependence on the wall superheat and liquid properties.     

Effect of Moisture Movement on Tested Thermal Conductivity of Moist Aerated Autoclaved Concrete

The purpose of this work was to study both theoretically and experimentally the process of moisture redistribution and heat transfer due to phase changes during the tests of thermal conductivity in aerated autoclaved concrete (AAC) moist specimens. The different moisture contents of the test samples were obtained in climatic chamber at equilibrium conditions reached with constant air temperature and variable relative humidity. The moist specimens were sealed inside highly impermeable polyethylene bag, as required by UNI 10051, and placed in a heat flow meter apparatus. During the experimental thermal conductivity measurements, the temperature and heat flow rate were measured under transient and steady state conditions. A theoretical analysis of the heat and mass transfer process was performed and then a suitable numerical model was used to predict the moisture redistribution and heat transfer due to the phase changes. The theoretical model has been compared against the experimental data. Substantial agreement between numerical results and experimental data was found. Then several numerical simulations have been performed to study the influence of the errors due to phase changes and non-uniform moisture distribution during the test of thermal conductivity of moist AAC specimens.     

Numerical and Experimental Evaluation of Dispersion Coefficient for Resin Transfer Modeling

Resin transfer molding (RTM) is a composite manufacturing process. A preformed fiber is placed in a closed mold and a viscous resin is injected into the mold. In this article, a model is developed to predict the flow pattern, extent of reaction, and temperature change during the filling and curing in a thin rectangular mold. A numerical simulation is presented to predict the free surface and its interactions with heat transfer and cure for flow of a shear-thinning resin through the preformed fiber.To simulate this process, using local thermal equilibrium assumption, it is essential to include the thermal dispersion term in energy equation. The best method to achieve this result is experimental simulation and preparing proportionate system at simple conditions without curing. By comparison of recorded temperature values (using installed instruments at various locations), and the corresponding results from numerical solution for different estimated values of dispersion coefficient, this coefficient has been evaluated based on the best matching estimate. The results show that, to simulate composite manufacturing process by RTM method, the effect of dispersion term in energy equation shall not be neglected.     

Computational Modeling of the Structure of a High-Current Discharge in a Magnetogasdynamic Channel

A two-dimensional computational model is proposed to calculate radiative-convective heat transfer in gas flows with large gradients of physical properties. The model is based on the numerical solution of the unsteady dynamic equations for a compressible inviscid gas and the radiative transfer equations. Flow calculations for the magnetogasdynamic channel of a rail accelerator show that the dynamics of the process is substantially affected by the flow in the discharge region and hydrodynamic instability, resulting in the nonstationarity and nonuniformity of the flow and discharge structure. During the process, the discharge can exist both in the form of several current-carrying channels and in the form of a unified plasma formation. Results of the numerical calculations agree qualitative with experimental data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 6, pp. 5–13, November–December, 2005.