RTM充模过程的数值模拟

本文首先建立了ＲＴＭ充模过程的二维数学模型。然后选用控制体积有限元法（ＦＥＭ／ＣＶ）确定了模拟ＲＴＭ充模过程的数值计算方法，最后进行了对恒流量充模过程的模拟计算，并通过将计算结果与Ｗ．Ｂ．Ｙｏｕｎｇ的试验结果比较验证了数学模型和数值方法的正确性。     

RTM工艺充模过程模拟研究进展

主要介绍了RTM工艺树脂充模过程的流动模式、充模过程模拟的流动模型和模拟方法。讨论了不同模拟情况下所需的合理假设、边界条件的设置以及采用的不同数值计算方法。同时,介绍了目前基于数值计算的RTM仿真软件,提出了RTM充模仿真研究的未来发展趋势。     

聚合物多相分层充模流动成型的粘性包围形成机理数值分析

基于聚合物多组分成型技术的工程背景，建立了全三维非稳态非等温多相分层充模流动的理论模型，提出了求解理论模型的稳定高效的数值算法。通过数值模拟，给出了不同流变性能参数、过程条件下多相分层充模流动成型时的粘性包围形成过程和其形貌的定量对比。在此基础上，通过理论分析，揭示了粘性包围的产生机理，并研究了流变性能参数和过程条件对分层界面形貌和粘性包围影响的规律性关系。模拟研究表明，模拟结果与Bamin Khomani等的实验研究结论相吻合。     

矩形腔中反应注射充模过程的数值模拟

<正>1 引言 反应注射充模（RIM）是由聚氨酯工艺发展起来的新型塑料成型方法,它具有模腔压力和进料温度低、节能、模具设备简单和产品性能优良等众多优点,特别适于生产大型塑料制件。近年来国际上已大量开展相关过程的流动和传热的数值模拟研究,以发展此一成型工艺的CAD/CAE工作。本文拟在过去对热注射充模（TIM）过程的流动和传热数值模拟研究的基础上,参考国外近年在RIM数值模拟方面的成就,对典型的端面进料矩形腔内RIM过程进行数值模拟研究。     

气体辅助注射成型充模流动模拟

本文建立了描述气体辅助注射成型充模流动过程的数学模型,并采用有限元/有限差分混合算法进行数值求解,在对移动边界的处理上采用控制体积法对充模过程中的两类移动边界:熔体前沿、熔体-气体边界进行跟踪,从而实现气体辅助注射成型充模过程的数值模拟。通过对一平板带厚筋结构进行数值分析验证了本文给出的理论算法及软件的可靠性。     

橡胶注射过程中压力变化的研究

对橡胶注射过程中的压力变化进行了理论与实验研究。充模流动模型的压力、能量控制方程分别为：选用高斯方法求解总体有限元方程。实验与计算分析对比证明．本文选用的数学模型和计算方法所得结果与实测结果基本吻合、该模型可用以代替大量的实验，对橡胶充模过程进行模拟，并用Ｇｒａｐｈｅｒ软件对数值结果进行处理，以图表直观地表达出各种因素对充模过程的影响。     

RIM充模过程数值模拟

用有限元法对RIM充模过程进行数值模拟．采取任意拉格朗日－欧拉法（ALE）处理流动前缘.并以边充模边划分网格的方法,使前缘边界条件得到较充分的满足．对不同操作参数下的RIM充模模拟结果进行了讨论、分析,得出选用薄腔、较快的充模速度以及适当较高的物料初始温度对RIM充模有利的结论,这对工业实践有重要的指导意义．     

注射充模过程的数值分析

本文在 E.Broyer 提出的简化有限元法的基础上推导出求解压力场和速度场的差分方程。并研制了充模过程分析软件。对聚苯乙烯在矩形型腔中的充模过程的数值模拟表明理论与实验吻合得较好。     

充模过程熔接缝形成的数值模拟

本文在分析注塑周期熔接缝形成过程的基础上，在充模阶段，利用前沿区喷泉流动的概念，建立“喷泉遭遇流”的物理模型和数学模型，并运用MAC的数值差分方法模拟了“喷泉遭遇流”的流场。为深入了解注塑充模阶段熔接缝的形成机理提供了理论基础。     

基于VOF方法的RTM充模非饱和流动仿真算法研究

充模过程是RTM工艺的关键环节之一。本文针对RTM充模环节中非饱和流动过程的两相流仿真预测技术进行研究。首先分析了充模过程非饱和流动的形成原因,建立起统一的双尺度多孔介质非饱和流动数学模型。然后建立了孔隙为微米级的微观模型,采用VOF方法对其流动前沿进行跟踪。采用VOF和主从单元法相结合的方法,对孔隙为毫米级的宏观模型中树脂非饱和流动进行数值模拟。利用FLUENT对法兰盘的充模过程进行数值求解,验证该仿真算法的可用性。     

颗粒增强复合材料有限覆盖技术数值模拟研究

本文将有限覆盖技术应用于颗粒增强复合材料的数值模拟。通过引入数学与物重网格,将有限元的插值域与积分域分别定义在两个不同的覆盖上,即在数学网格上进行插值函数的构造,在物理网格上完成系统能量泛函的积分运算,最后通过覆盖权函数将二者联结在一起。它的优点是单元网格划分随意,不受复杂边界形状和二相材料界面的限制,单元可以是任意形状,是较之于有限元方法更普遍的数值模拟方法。最后给出了有限元网格覆盖颗粒增强复合材料的数值模拟算例,并与现有的方法进行了比较和讨论。     

Use of orthogonal collocation on finite elements with moving boundaries for fixed bed catalytic reactor simulation

A numerical procedure for the solution of transient models for the simulation of fixed bed catalytic reactors is developed. The most general model examined includes axial dispersion in the external fluid phase, interphase mass and heat transfer resistances,intraphase mass resistance and any given kinetic scheme with complex reaction rate expressions. The solution technique is based on the method of lines, in which the space variables are discretized using the orthogonal collocation method on finite elements, with elemination of the node unknown functions, coupled with an integration method for stiff ordinary differential equations. An efficient procedure for updating during the integration the position of the finite element boundaries, in order to follow the movement of steep concentration and temperature profiles along the space variable during the reactor transient, is proposed. Application examples of the developed computer program are also given.     

层合板在固化全过程中瞬态温度场及固化度的有限元分析

本文根据固化动力学理论和热传导理论，采用有限元与有限差分相结合的方法，对复合材料层合板在固化工艺过程中板内温度和固化度的分布及其变化规律进行数值模拟；在分析过程中考虑了温度和固化度的耦合作用，并采用Ｅｕｌｅｒ－Ｃａｕｃｈ逐步迭代的方法进行解耦求解；通过算例，分析和讨论了层合板的温度边界条件，板厚度以及升温速率对层合板内温度和固化度分布的影响。     

An optimization procedure for the pultrusion process based on a finite element formulation

Composite materials are manufactured by different processes. In all, the process variables have to be analyzed in order to obtain a part with uniform mechanical properties. In the pultrusion process, two variables are the most important: the pulling speed of resin‐impregnated fibers and the temperature profile (boundary condition) imposed on the mold wall. Mathematical modeling of this process results in partial differential equations that are solved here by a detailed procedure based on the Galerkin weighted residual finite element method. The combination of the Picard and Newton‐Raphson methods with an analytical Jacobian calculation proves to be robust, and a mesh adaptation procedure is presented in order to avoid integration errors during the process optimization. The two earlier‐mentioned variables are optimized by the Simulated Annealing method with some constraints, such as a minimum degree of cure at the end of the process, and the resin degradation (the part temperature cannot be higher than the resin degradation temperature at any time during the whole process). Herein, the proposed objective function is an economic criterion instead of the pulling speed of resin‐impregnated fibers, used in the majority of papers.     

Material and finite element analysis of poly(tetrafluoroethylene) rotary seals

Abstract

The stress-strain characteristics of PTFE under uniaxial tension and compression have been measured at various temperatures. A new finite element analysis procedure using MARC is presented, which can simulate the different properties of PTFE from tension and compression data. This method is based on using the maximum principal stress value at the integration point of each element to define whether the element is under tension or compression at each increment, then using subroutines to specify the material properties. A positive value indicates a state of tension and a negative value indicates compression. It has been found that the finite element analysis results are in good agreement with those from experiment. Finally, a PTFE rotary seal was modelled using this new method, and results were obtained incorporating stress and lip loads of the rotary seal, with different temperature effects.     

TRANSPORE : A GENERIC HEAT AND MASS TRANSFER COMPUTATIONAL MODEL FOR UNDERSTANDING AND VISUALISING THE DRYING OF POROUS MEDIA

ABSTRACT

In this work a sophisticated numerical model is presented that describes the drying of porous media. This model, which is known as TransPore, has evolved over the years through the direct inputs of both authors. Nowadays, TransPore can be used to analyse the drying of media that are of completely arbitrary shape and size, under a variety of drying conditions. The engine of the computational model uses a number of state-of-the-art numerical methods that ensure the simulation results describe the particular drying process accurately, whilst guaranteeing the most efficient and effective usage of computer resources. For example, the numerical discretisation method is based on a completely conservative hybrid finite element control volume technique that uses a finite element mesh for its background gradient interpolation. Furthermore, flux limiting is used to reduce numerical dispersion in the drying kinetics and the generated non-linear system is resolved using the full Newton method for the outer iteration coupled together with a preconditioned conjugate gradient technique for the inner iteration. A graphical interface has been linked to the model to enable online visualisation of the drying process. The mathematical model allows both homogeneous and heterogeneous porous media to be simulated. The resultant software is an extremely powerful and effective tool for investigating existing dryer designs and for proposing new and innovative drying schedules that provide optimal drying quality in minimal drying time.     

Implementation of the DSPM model using a commercial finite element system

A solution procedure based on the use of the finite element method (FEM) was developed to solve the Donnan steric-partioning pore model (DSPM) for a nanofiltration membrane coupled with a boundary layer. The numerical solution of nanofiltration models like DSPM is usually carried out by combining an integration method like Runge-Kutta with an iterative procedure that starts from guessed permeate concentrations values. However, this approach may have problems of lack of convergence. As an alternative procedure, a finite element system is used to easily implement the transport equation for the membrane and the boundary layer with Donnan-steric conditions in both membrane sides. To test the solution method, an analytical solution was developed for the transport of an uncharged solute across a membrane with boundary layer. Afterwards, the method was applied to the calculation of binary and ternary ionic systems and its performance was compared with that obtained with the classical iterative method. The developed methodology benefits from the accuracy of FEM and the representation and analysis capabilities of the software used.     

Finite element analysis of switching domains using ferroelectric and ferroelastic micromechanical model for single crystal piezoceramics

Here, the domain switching in a ferroelectric and ferroelastic single crystal subjected to electrical, electromechanical, and mechanical loading condition is studied. An isoparametric 3D electromechanical hexahedral finite element introducing the micromechanical constitutive law for domain switching is proposed to investigate the non-linear response of single crystal piezoceramics. The micromechanical model considered here is based on thermodynamic approach and internal variables, accounting for the electromechanical interaction energy between the domains. The volume fractions of six distinct uni-axial variants are treated as the internal variables to describe the microscopic state of the material at any given loading level. Furthermore, the formulation includes a realistic phase transition from a cubic unit cell to tetragonal one in the single crystal piezoceramics under the application of external load. The non-linear electromechanical constitutive equations obtained are solved using an implicit integration technique employing the return-mapping algorithm. The model developed here is tested for its applicability considering variety of benchmarks, and it brings out the behaviour of piezoceramic materials as observed in experimental studies.The hexahedral finite element presented is also implemented in the commercial finite element code Abaqus via the User Element subroutine.     

Optimal curing for thermoset matrix composites: Thermochemical and consolidation considerations

A design sensitivity method is used to find optimal autoclave temperature and pressure histories for curing of thermoset-matrix composite laminates. The method uses a finite element simulation of the heat transfer, curing reaction, and consolidation in the laminate. Analytical sensitivities, based on the direct differentiation method, are used within the finite element simulation to find the design sensitivities, i.e., the derivatives of the objectives function and the constraints with respect to the design variables. Standard gradient-based optimization techniques are then used to systematically improve the design, until an optimal process design is reached. In this study the objective is to minimize the total time of the cure cycle, while the constraints include a maximum temperature in the laminate (to avoid thermal degradation) and a maximum deviation of the final fiber volume fraction from its target value (to achieve proper consolidation). The simulations of curing process are performed for EPON 862/W epoxy under a conventional cure cycle, for both thin and thick parts. Time-optimal cure cycles are found using the optimization program. Simulations of fast-curing cycles are also examined. The optimal cycles are similar in form to conventional cure cycles, but give substantially shorter cure times. The entire scheme works automatically and efficiently, simultaneously adjusting multiple design variables at each iteration.     

玻璃吹制成型熔体与模具传热耦合模拟

玻璃吹制成型过程中熔体与模具接触时间短,热交换迅速、剧烈,同时玻璃的黏度对温度极其敏感,微小的温度波动将会引起黏度的剧烈改变,并最终决定制品的厚度分布,因此熔体与模具传热的耦合求解是十分必要的。鉴于此,本文在熔体与模具接触面上引入了界面单元来处理接触面热阻区的热传递问题,建立了熔体流动与模具温度场耦合模拟的控制方程,完成了算法编制,实现了熔体流动与模具温度场的耦合模拟。算例证明,与耦合传热算法相比迭代结果不足以满足吹制成型对温度场准确性的要求;通过模拟与实验对比,在连续生产条件下模具绝大部分的温度保持稳定,但与熔体接触的型腔壁的温度却有大幅的周期性变化;模拟的最终产品壁厚较准确地反映了产品的实际壁厚分布,准确度达到88%以上。