气体辅助注射成型工艺及充模过程CAE分析

描述了气体辅助注射成型的工艺过程及熔体充填和气体穿入的数学模型，采用有限元／有限差分／控制体积法计算充填阶段的压力场和温度场，确定两类移动边界—熔体前沿和熔体／气体边界。并对典型制件进行模拟以验证模型的可行性。     

三维塑料注射成形可压缩充模过程数值模拟

在塑料注射成形充填过程即将结束时,塑料熔体逐步压实,可压缩性不可忽略。基于PG(Petrov-Galerkin)原理的PSPG(Pressure-Stabilizing/Petrov-Galerkin)法可抑制动量控制方程求解中速度与压力插值空间不匹配造成的虚假数值振荡,SUPG(Streamline-Upwind/Petrov-Galerkin)/GGLS(Galerkin gradient least-squares)法可实现对具有对流占优和小导热系数的能量场控制方程的稳定数值求解,由此采用PSPG法和SUPG/GGLS法建立了注射成形可压缩熔体充模流动的稳定有限元计算格式,并对充模过程进行了模拟。数值算例表明:充填过程中熔体的可压缩性一般情况下可以忽略,但在填充即将结束时熔体可压缩流动对计算结果影响较大,基于可压缩性模型模拟得到的填充结束时注射压力比较缓慢的上升,流动平衡更加真实。     

树脂膜熔渗工艺充模过程的模拟与分析

树脂膜熔渗工艺(RFI)是一种新型的复合材料成型工艺.为了更深入了解树脂膜熔渗工艺过程中充模阶段的控制参数对制品质量的影响,避免制品出现空斑、充模不完全等问题,针对该工艺过程中树脂在复杂形状预制件中的流动行为进行了分析,在达西定律基础上建立了二维等温流动控制方程,利用有限元/控制体方法建立了数值分析模型,编制了FORTRAN程序进行模拟运算,并讨论了流动过程中施加的压力对充模时间的影响.由计算实例可见,所编制程序能够很好地预测树脂膜熔渗工艺过程中充模时间、各个时刻树脂的流动前沿位置及模腔中的压力分布.     

水润滑动压滑动轴承建模

分析水润滑动压滑动轴承的特点,并建立相关方程和边界条件,对其进行量纲一化。为精确求解紊流状态下微小润滑水膜的压力场、速度场、温度场建立数学模型,为该轴承的进一步数值计算和流场的热动力学分析奠定理论基础。     

聚合物熔体的非等温平板收缩流动的数值模拟

用有限元法模拟了Carreau流体在4：1平板收缩口模中的非等温挤出流动，采用3节点的三角形单元对速度、压力和温度进行等阶插值，运用特殊的罚函数处理流体的不可压缩条件，解决了压力场的数值振荡问题，并用改进的Newton迭代法对非线性方程进行求解，成功地计算了Carreau流体在平板收缩流动中的速度、压力、粘度以及应力的分布，同时得到温度场的分布，计算的应力分布与实验的结果及Renardy的分析结构相符。     

有流动条件下双组分系统凝固过程的数值模拟

本文采用SIMPLE方法对有流动条件下双组分系统的凝固过程进行数值模拟，求解混合物参数的控制方程，混合物中两相的体积分数和溶质浓度利用平衡相图关系确定，控制方程用有限体积法离散，SIMPLE方法求解，对NH4Cl水溶液的流动凝固过程进行了数据模拟，给出数据求解的结果，分析了对流和输动现象对宏观相界面形态，相变速率和最终宏观的组分分凝现象的影响。     

粉末注射成形喂料充模层状二维流动的基本方程

将粉末注射成形喂料在薄壁模腔中的流动视为层状二维流动,以喂料流动的守恒方程组为基础,建立了描述粉末注射成形喂料充模流动的数学模型。推导了喂料熔体流导率的计算公式,得出压力场的控制方程是一非线性椭圆偏微分方程。使模型的计算成为可能,为进一步对粉末注射成形进行计算机模拟和数值分析奠定了数学基础。     

有限元网格对RTM充模模拟的影响

本工作基于有限元控制体积法编写了模拟程序,研究了节点数量、网格密度对模拟过程的影响.以带圆孔的长方形为例,模拟比较了不同网格密度和注入口位置对充模时间、流动前沿以及干点形成区域的影响.结果表明,节点数量增加到一定程度时,只延长计算时间,对充模时间影响很小;网格疏密分布影响流动前沿的位置,根据流动前沿的形状可以确定排气口的位置和数量.     

微-细双尺度单胞下织物预成型体渗透率预测

建立了描述双尺度单胞内树脂流动的数学模型,基于最小势能原理建立了织物单胞逼近真实的几何模型。研究了由纱线卷曲和相互挤压引起的微观渗透率分布的不均匀性及其在流动求解上的处理方法; 基于有限差分法建立了树脂流动控制方程数值求解方法,并开发了相应软件包,求得了单胞内树脂流动压力和速度场,进而获得了渗透率预测值; 通过与文献预测数据和实验值对比,证明了本文中预测模型和求解方法的正确性。     

挤出口模内幂律流体的罚有限元模拟

模拟了幂律型流体在圆形截面过渡为正方形截面的收缩口模内的三维非等温挤出流动。采用罚有限元法处理了流体的不可压缩条件,消去了动量方程中的压力项,并运用降阶积分方法确保了压力解的稳定性;采用SU PG方法构造能量方程的非对称权函数,克服了对流项占优时数值解的失真;考虑了聚合物在口模内流动时产生的剪切热,运用A rrhen ius模型计算了温度对黏度的影响。计算实例表明,可以获得合理的温度、压力、应力和温度分布。     

A structured/unstructured grid generation method and its application

Summary. A hybrid structured/unstructured grid is generated by using both the advanced layer method and the advanced front method. A domain decomposition method in this hybrid grid to simulate 2-D viscous flow is discussed. The Euler equations are solved on the unstructured grid in the flow field region far from the wall, and the RNS equations are solved on the structured grid in the flow field region near the wall. Two solutions are matched on the interface of these two regions. Based on this viscous flow solver the mono-objective/bi-objective optimization and the inverse design calculation are given. Numerical results show that calculated pressure distributions of given airfoils agree well with the corresponding experimental data and performances of optimal airfoils are much better than the initial airfoils. The agreement between designed and target pressure is fine in the inverse design calculation.     

弹性圆柱薄壳在流体中的变形与内力分析

应用薄壳弹性理论及流体力学基本方程,给出了圆柱壳在流体中流固耦合问题的基本关系式。阐述并应用相容拉格朗日-欧拉方法推导出流体绕壳横向流动时弹性圆柱薄壳的小弯曲变形问题的方程,并求解了流场的速度势和壳体的变形及内力分布。通过具体算例,绘出了流场分布图,讨论了有关参数变化对圆柱壳变形和表面压力系数的影响。     

Viscous-inviscid interaction schemes for external aerodynamics

For aerofoils a calculation, which involves the coupling of the external inviscid flow with the viscous flow in the boundary layer and the wake, still provides a worthwhile alternative to the solution of the ‘time-averaged’ Navier-Stokes equations. Classical viscous-inviscid interaction methods which can be extended to include flows with separations and significant pressure gradients across the boundary layer are described. Basic theoretical principles of interactive methods in two dimensions are discussed. The extension of the classical methods leads to generalisations of the concept of displacement thickness and the momentum integral equation. The boundary conditions for the equivalent inviscid flow (EIF) are also described and these also include the effect of normal pressure gradients. An integral method based on the lag-entrainment method for the calculation of the turbulent boundary layer is described. The correlations associated with the method are extended to include separated flow. Two methods of solving the boundary-layer equations through a separation region are described: the inverse method and the quasi-simultaneous method. Principles of techniques for coupling the flows are described and the properties of the direct, fully inverse, semi-inverse and quasi-simultaneous methods are discussed. Results from a method for incompressible flow about a stalled aerofoil, a method for compressible flow about a high-lift aerofoil and a method for compressible flow about a transonic aerofoil are compared with experimental results. The current situation regarding the development of viscous-inviscid interaction methods is briefly summarized and future possibilities are considered.     

对旋式轴流泵全流道三维非定常紊流场的数值模拟

基于非定常不可压牛顿流体的控制方程和标准e-k紊流模型,应用SIMPLEC算法,数值模拟了对旋式轴流泵联立全流道在一个完整的转动周期内的三维紊流流场。通过给出全流道中间周向截面的压力与速度等值线图,以及中间干涉面的压力等值线及分布云图,直观地显示了一个转动周期内前置叶轮、后置叶轮及全流道的流场特性变化和干涉情况,表明联立全流道非定常三维紊流场的数值模拟方法是人们认识对旋流场流动与干涉机理经济实用的理论手段。     

三维RIM充模模拟

采用混合数值方法对三维ＲＩＭ充模过程进行了数值模拟,即在模腔宽度上采用有限元法,而在厚度方向上采用有限差分方法,对三维问题进行求解。采用这种方法,避开了直接求取三维有限元所带来的困难,同时采用了任意拉格朗日－欧拉法处理流动前缘。文中对数值结果进行了讨论。     

RTM工艺树脂流动过程数值模拟及实验比较

树脂充模是RTM工艺成型过程中的重要一环。研究了RTM工艺树脂流动过程的特点,建立了树脂渗流控制方程。采用贴体坐标/有限差分法模拟了树脂渗流过程,给出了不同时刻树脂流动前沿曲线及终止时刻压力场分布,计算结果与试验结果吻合良好。     

Investigation of heat transfer during change in the state of aggregation of a system

New differential equations are derived to describe the boundary conditions at a front defining a change of state. A method based on these equations is suggested for numerical calculation of the temperature field in a system undergoing a change of state.     

The attenuation of shock waves in a nonequilibrium gas

The evolution of weak shock waves in nonequilibrium gas media with fluctuating parameters is investigated. Two-dimensional nonlinear, evolution equations are derived for the averaged parameters of an acoustic field induced by a body in a supersonic flow of active medium. A possible mechanism of reduction of the amplitude and broadening of the front of weak shock waves in nonequilibrium gas media is discussed.     

爆炸管道出口外流场的数值模拟

采用带化学反应的多组分Euler方程,数值模拟了爆炸管道出口形状对爆轰波泄出外流场结构的影响.采用高速阴影光学显示技术拍摄了外流场的照片,对数值计算方法进行了验证.在此基础上,考察了不同出口形状对爆轰波溢出后的外流场的动力学演变规律的影响,分析讨论了涡环与激波的相互作用过程.     

A survey of flow at low pressures

The theory of internal flows at such low pressures that the Navier-Stokes equations are not valid is reviewed. In the extreme low pressure range (free molecular flow), where the flow rate is independent of pressure, the basic theory is well developed. However, the influence of channel lenght, cross sectional shape, or surface characteristics have not been totally defined. Slip theory, which extends the low pressure range of the Navier-Stokes equation by modifying the wall boundary conditions, is discussed. The theory provides a good basis for experimental data correlation, but is not adequate to extend the viscous equations into the free molecular range. The empirical methods used to provide a smooth transition from slip to free molecular flow are reviewed, and a method of obtaining an equation for the total flow regime is illustrated. The extensive work in physical gas dynamic is discussed. Boltzmann's equation which has been solved numerically for small pressure gradients was found to be valid only in the viscous regime near the free molecular flow range.