基于Schwarz混乱松弛法的压铸充型模拟并行分区算法

压力铸造充型过程数值模拟是压铸计算机辅助工程应用的一个重要方面,而计算规模和效率一直是这一模拟过程中的关键问题.为扩大求解规模,该文应用Schwarz混乱松弛的思想,设计了一种异步并行算法,并在并行机群计算系统实现.该算法将整体的求解域分解为多个子域,每个子域的计算作为子任务分配给并行计算系统内的节点,每个节点可异步求解.采用通信机制进行数据交换,实现全局收敛.这种算法能够有效利用多节点优势,计算规模随节点数呈线性增加.对气缸盖罩盖零件进行了充型模拟验证,获得了满意结果.     

Simulation of Magnesium Alloy AZ91D Microstructure Using Modified Cellular Automaton Method

A two-dimensional modified cellular automaton model was developed to simulate the solidification process of magnesium alloy. The stochastic nucleation, solute redistribution, and growth anisotropy effects were taken into account in the present model. The model was used to simulate the grain size of magnesium alloy AZ91D for various cooling rates during the solidification process. To quantitatively validate the current model, metallographic experiments were carried out on specimens obtained from sand mold AZ...     

Mathematical Model of Fluid Flow and Solidification in Mold Region of Continuous Slab Casting

To simulate the phenomena in the mold region of continuous casting by coupling fluid flow and solidification, a three-dimensional mathematical model has been developed based on the K-ε turbulence equations and the SIMPLER algorithm. A pseudo source term was introduced into the energy equation to account for the latent heat and kinetic energy. The fluid flow in the mushy zone was calculated by defining the fluid viscosity as a function of the solid fraction in the mushy zone. Fine meshes in the solid region improve convergence and reduce iteration time. Comparison of the fluid flow and temperature distribution with and without solidification shows that although the solid shell in the mold is thin, it still greatly affects the flow pattern. The numerical results obtained provide details of the fluid flow and solidification phenomena which can be used to optimize the nozzle structure and other process parameters in continuous casting.     

铝合金微观组织模拟及并行计算

微观组织模拟计算规模庞大,对宏观铸件进行整体微观组织模拟存在极大困难,为此该文将CA(cellularau-tomaton)模型与宏观的传热计算相结合,模拟砂型和金属型铝合金铸件的凝固组织形成过程,提出了改进的CA模型,用更接近实际晶粒轮廓的方法对微观组织进行模拟。在串行算法的基础上开发了相应的并行算法,该算法在保证原有计算精度的前提下,极大地提高了计算规模和效率。对试验结果和模拟结果进行了对照分析,二者基本一致。     

Static and Metadynamic Recrystallization of Low Carbon Steels During Mechanical Deformation

Static and metadynamic recrystallization models were developed with the coefficients determined by multiple nonlinear regression analyses to describe microstructure evolution in low carbon steels.The effects of initial grain size, deformation temperature, strain, and strain rate on the austenitic recrystallized volume fraction and grain size were studied using a Gleeble machine. The results show that deformation reduces the grain size when the recrystallized volume fraction is large. The static recrystallized volume fraction increases with increasing deformation temperature, strain, and strain rate, and decreasing initial grain size. The grain size during metadynamic recrystallization is independent of the deformation strain and the initial grain size. The recrystallized volume fraction, the grain size, and the grown grain size calculated by the correlations are consistent with the measured values.     

压力铸造充型过程流动与传热数值模拟的研究

为了解压力铸造的充型特点 ,基于有限差分法建立了液态金属充填型腔过程的流动及耦合传热计算的数学模型 ,使用 SOL A - VOF数值模拟技术开发了压铸充型过程流动与传热的数值模拟分析软件。分别用层流假设和 K- ε紊流模型对“弓”形型腔的充型过程的流场进行了模拟计算 ,并与压铸水模拟实验的高速摄像进行比较 ,结果表明 ,采用紊流模型能更精确地模拟压铸充型过程。最后使用所开发的模拟分析软件 ,对具有三维复杂形状的实际压铸件的充型过程的流场、温度场进行了模拟 ,并分析了充型过程中模具在型腔表面的温度变化规律 ,提出“瞬态层”的概念 ,大大缩小了计算区域 ,提高了计算效率     

Dendritic Morphology Simulation Using the Phase Field Method

Dendritic morphology was simulated using a macro- and micro-coupled method. Since the microstructure of a whole casting cannot be easily analyzed, a scheme was developed to calculate the temperature of the whole casting with the microstructure analyzed by selecting one cell in the central region of the casting. The heterogeneous nucleation was described using a Gaussian distribution with the dendritic growth controlled by the solution of the phase field equation. The initial temperature distribution in the microdomain was obtained by interpolating the cell temperatures near the selected cell with the interface undercooling assumed to be the sum of thermal, solute, and curvature effects. The solute distribution was calculated from the mixed solute conservation equation with noise introduced to produce the side branches. The simulation results agree well with experimental results.     

用改进的 SOLA-VOF 法模拟铸造充型过程

铸造充型过程对铸件质量的影响很大，文中对流体充型过程的数值模拟做了研究。以ＳＯＬＡ－ＶＯＦ法为基础提出了改进算法。在三维自由表面处理上，提出一种简单而实用的方法，对原算法的累积流量误差做了修正，方程求解改用预处理共轭梯度法，保证了解的收敛性。为了模拟紊流现象，引入了Ｋ－ε双方程模型，用实验验证这些改进的效果，又用国际会议的标准检验实验进行了验证，着重于紊流现象的分析，模拟结果与验证实验吻合较好。     

大断面球墨铸铁曲轴的热分析试验

本文报导了在生产大断面球墨铸铁柴油机曲轴现场实测的热分析试验。对６３００和 ６３２０型大功率球墨铸铁曲轴所测的冷却曲线表明，在共晶平台温度和石墨球的大小之间 有更密切的对应关系。共晶平台温度越高，则最后得到的石墨球越少。并且，过冷度 （ＴＥＮ－ＴＥＵ）越大，则产生石墨畸变和晶间碳化物的程度也越严重。 热分析法是检验大断面球墨铸铁曲轴工艺合理性的有效方法。 扫描电子显微镜研究表明，晶间碳化物的沉淀析出，是与银、磷等元素的偏析有 关。