It was analyzed that the finite element-cellular automaton （CAFE） method was used to simulate 3D-microstructures in solidification processes. Based on this method, the 3D-microstructure of 9SMn28 free-cutting steel ...It was analyzed that the finite element-cellular automaton （CAFE） method was used to simulate 3D-microstructures in solidification processes. Based on this method, the 3D-microstructure of 9SMn28 free-cutting steel was simulated in solidification processes and the simulation results are consistent with the experimental ones. In addition, the effects of Gaussian distribution parameters were also studied. The simulation results show that the higher the mean undercooling, the larger the columnar dendrite zones, and the larger the maximum nucleation density, the smaller the size of grains. The larger the standard deviation, the less the number of minimum grains is. However, the uniformity degree decreases first, and then increases gradually.展开更多
3D microstructures of Fe–6.5%Si(mass fraction) alloys prepared under different cooling conditions were simulated via finite element-cellular automaton(CAFE) method. The simulated results were compared to experimental...3D microstructures of Fe–6.5%Si(mass fraction) alloys prepared under different cooling conditions were simulated via finite element-cellular automaton(CAFE) method. The simulated results were compared to experimental results and found to be in accordance. Variations in the temperature field and solid-liquid region, which plays important roles in determining solidification structures, were also examined under various cooling conditions. The proposed model was utilized to determine the effects of Gaussian distribution parameters to find that the lower the mean undercooling, the higher the equiaxed crystal zone ratio; also, the larger the maximum nucleation density, the smaller the grain size. The influence of superheat on solidification structure and columnar to equiaxed transition(CET) in the cast ingot was also investigated to find that decrease in superheat from 52 K to 20 K causes the equiaxed crystal zone ratio to increase from 58.13% to 65.6%, the mean gain radius to decrease from 2.102 mm to 1.871 mm, and the CET to occur ahead of schedule. To this effect, low superheat casting is beneficial to obtain finer equiaxed gains and higher equiaxed dendrite zone ratio in Fe–6.5%Si alloy cast ingots.展开更多
针对高升阻比风力机翼型前缘曲率半径较大的问题,传统的翼型参数化方法前缘控制能力不足,且基于面元法XFOIL预测精度差的问题,利用增强类函数/形函数转换(CST)参数化方法控制翼型的形状变化、拉丁超立方实验设计、计算流体力学(CFD)流...针对高升阻比风力机翼型前缘曲率半径较大的问题,传统的翼型参数化方法前缘控制能力不足,且基于面元法XFOIL预测精度差的问题,利用增强类函数/形函数转换(CST)参数化方法控制翼型的形状变化、拉丁超立方实验设计、计算流体力学(CFD)流场计算模块、高斯过程回归模型和遗传算法,提出了基于高可信度Reynolds average Navier-Stocks(RANS)和高斯回归模型辅助遗传算法的翼型优化设计方法。结果表明:基于高斯回归模型的翼型优化方法,可以将优化所用CFD计算次数降低一阶,从而大幅度提升优化设计效率。由标准算例超临界翼型RAE2822的降阻设计表明,在百次量级的CFD次数阻力降低43.16%,激波被削弱且升力、力矩和面积严格满足约束。由风力机翼型NACA64618的最大化升阻比优化设计表明,所设计翼型不仅在设计攻角和副设计攻角处升阻比大大增加,在整个小攻角范围内其气动性能都得到了提升,且两个主设计点,无不良阻力的产生。展开更多
基金supported by the National Natural Science Foundation of China (No.50874007, 50774109)
文摘It was analyzed that the finite element-cellular automaton （CAFE） method was used to simulate 3D-microstructures in solidification processes. Based on this method, the 3D-microstructure of 9SMn28 free-cutting steel was simulated in solidification processes and the simulation results are consistent with the experimental ones. In addition, the effects of Gaussian distribution parameters were also studied. The simulation results show that the higher the mean undercooling, the larger the columnar dendrite zones, and the larger the maximum nucleation density, the smaller the size of grains. The larger the standard deviation, the less the number of minimum grains is. However, the uniformity degree decreases first, and then increases gradually.
基金Project(2012AA03A505)supported by the High-Tech Research and Development Program of ChinaProject(51474023)supported by the National Natural Science Foundation of China
文摘3D microstructures of Fe–6.5%Si(mass fraction) alloys prepared under different cooling conditions were simulated via finite element-cellular automaton(CAFE) method. The simulated results were compared to experimental results and found to be in accordance. Variations in the temperature field and solid-liquid region, which plays important roles in determining solidification structures, were also examined under various cooling conditions. The proposed model was utilized to determine the effects of Gaussian distribution parameters to find that the lower the mean undercooling, the higher the equiaxed crystal zone ratio; also, the larger the maximum nucleation density, the smaller the grain size. The influence of superheat on solidification structure and columnar to equiaxed transition(CET) in the cast ingot was also investigated to find that decrease in superheat from 52 K to 20 K causes the equiaxed crystal zone ratio to increase from 58.13% to 65.6%, the mean gain radius to decrease from 2.102 mm to 1.871 mm, and the CET to occur ahead of schedule. To this effect, low superheat casting is beneficial to obtain finer equiaxed gains and higher equiaxed dendrite zone ratio in Fe–6.5%Si alloy cast ingots.
文摘针对高升阻比风力机翼型前缘曲率半径较大的问题,传统的翼型参数化方法前缘控制能力不足,且基于面元法XFOIL预测精度差的问题,利用增强类函数/形函数转换(CST)参数化方法控制翼型的形状变化、拉丁超立方实验设计、计算流体力学(CFD)流场计算模块、高斯过程回归模型和遗传算法,提出了基于高可信度Reynolds average Navier-Stocks(RANS)和高斯回归模型辅助遗传算法的翼型优化设计方法。结果表明:基于高斯回归模型的翼型优化方法,可以将优化所用CFD计算次数降低一阶,从而大幅度提升优化设计效率。由标准算例超临界翼型RAE2822的降阻设计表明,在百次量级的CFD次数阻力降低43.16%,激波被削弱且升力、力矩和面积严格满足约束。由风力机翼型NACA64618的最大化升阻比优化设计表明,所设计翼型不仅在设计攻角和副设计攻角处升阻比大大增加,在整个小攻角范围内其气动性能都得到了提升,且两个主设计点,无不良阻力的产生。
