Numerical simulation of solidification morphologies of Cu-0.6Cr casting alloy using modified cellular automaton model

The purpose of this study is to predict the morphologies in the solidification process for Cu-0.6Cr(mass fraction,%)alloy by vacuum continuous casting(VCC)and verify its accuracy by the observed experimental results.In numerical simulation aspect, finite difference(FD)method and modified cellular automaton(MCA)model were used to simulate the macro-temperature field, micro-concentration field,nucleation and grain growth of Cu-0.6Cr alloy using real data from actual casting operations.From the observed casting experiment,the preliminary grain morphologies are the directional columnar grains by the VCC process.The solidification morphologies by MCAFD model are in agreement with the result of actual casting experiment well.

Inconel625合金激光熔覆过程中显微组织演变的数值模拟

基于MATLAB模拟平台并结合晶粒的形核与生长理论,采用元胞自动机-有限差分方法构建了Inconel625合金激光熔覆层显微组织演变的数值计算模型,利用该模型对单道激光熔覆过程中合金的显微组织演变进行了模拟,并进行了试验验证,同时研究了激光热输入和异质形核数量对熔覆层晶粒形貌的影响。结果表明:采用建立的模型模拟得到熔覆层内部由柱状晶以及分布在柱状晶之间的亚晶粒组成,靠近熔合线区域由胞状晶组成,与试验结果相吻合;模拟和试验得到柱状晶的平均宽度分别为2.817,2.743μm,相对误差仅为2.69%,验证了计算模型的可靠性;随着激光热输入的减小或异质形核数量的增大,熔覆层组织逐渐细化,晶粒数量增多,柱状晶宽度减小。

Fe-0.04%C合金焊缝熔池凝固过程中枝晶生长及溶质浓度分布模拟

基于枝晶生长的扩散界面模型,改进元胞自动机法,并结合有限差分法,综合考虑浓度场、温度场以及熔池形状,建立Fe-0.04%C(质量分数)合金枝晶生长和溶质浓度分布模型。模拟单个等轴晶的生长形貌及枝晶尖端生长速度随时间的变化关系、多个等轴晶的生长形貌和溶质浓度分布、柱状晶的生长形貌和耦合温度场后的柱状晶-等轴晶转变过程,并与实验进行对比。结果表明:取向角对枝晶形貌有一定的影响;枝晶尖端生长速度随时间的延长最后趋于稳定;熔池形状影响柱状晶生长形貌;溶质主要富集在枝晶根部及晶界处。模拟结果与实验结果吻合较好。

毫米波辐射下培皿内细胞的比吸收率分析

采用电磁场时域有限差分法和二阶吸收边界条件 ,计算了 8毫米的毫米波辐射下培皿内细胞单层上细胞对毫米波的比吸收率 (SAR) ,从多个角度给出了SAR在培皿内细胞单层上的分布规律 ,分析了造成SAR不均匀分布的原因 ,提出了提高SAR分布均匀性的建议 。

电阻点焊熔核微观组织模拟

基于有限差分思想建立了电阻点焊的三维宏观传热模型,并在此模型基础上通过进一步细化网格差分得到枝晶形核和生长所需的温度信息.基于元胞自动机方法建立枝晶形核和生长的微观模型,将已建立的宏观温度场模型和微观元胞自动机模型互相耦合起来,建立了电阻点焊熔核微观组织模拟的宏微观耦合模型.利用耦合模型模拟了5754铝合金电阻点焊一定参数下熔核的微观组织形成过程,所得的模拟结果为"柱状+等轴"晶组织,与试验结果吻合较好.

A Two-Dimensional Computational Model for the Simulation of Dendritic Microstructure and Solute Distribution of Fe-0.04%C Alloys

A new model of dendritic growth and solute distribution of Fe-0.04%C binary alloys was developed, which is based on the sharp interface model of dendritic growth. This innovative model improved the cellular automaton method, combined with the finite difference method, considered concentration field, temperature field and the shape of molten pool. This model simulated the growth morphologies of single equiaxial crystal, the relationship between tip growth velocity and time, multi-equiaxed crystals’ growth morphologies and solute distribution, the growth of columnar crystals, columnar-to-equiaxed transition after coupling temperature field, and compared with experimental results. The results indicate that crystallographic orientation has certain influence on dendritic morphologies, that the tip growth velocity tends to be stable with the extension of time in the end, that the shape of molten pool influences the growth morphologies of columnar crystals and that the solute mainly concentrates in dendritic roots and among grain boundaries. The simulated results are in accord with experimental results.

基于CDMA蜂窝网的飞行器三维定位算法

针对中低空飞行器提出了一种将码分多址(CDMA)蜂窝网导频信号被动定位与惯性导航系统进行组合的导航定位方法。该定位方法是根据CDMA蜂窝网导频信号的到达时差(TDOA)进行两次加权最小二乘解算,并利用飞行器惯性组合的原始信息进行解模糊,从而实现中低空飞行器的三维实时定位。蒙特卡罗仿真证明:在高斯白噪声条件下,该算法运算速度快,精度高,其均方误差逼近克拉美罗下界(CRLB),为组合导航实时性要求提供了理论参考。