This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm2 based on the two-temperature equation, and obtains the evolution of the free el...This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm2 based on the two-temperature equation, and obtains the evolution of the free electron temperature and lattice temperature over a large temporal and depth range, for the first time. By investigating the temporal evolution curves of the free electron temperature and lattice temperature at three representative depths of 0, 100 nm and 500 nm, it reveals different characteristics and mechanisms of the free electron temperature evolution at different depths. The results show that, in the intense femtosecond laser ablation of aluminum, the material ablation is mainly induced by the thermal conduction of free electrons, instead of the direct absorption of the laser energy; in addition, the thermal conduction of free electrons and the coupling effect between electrons and lattice will induce the temperature of free electrons deep inside the target to experience a process from increase to decrease and finally to increase again.展开更多
针对COB-LED(Chip on Board-Light Emitting Diode)散热问题,文中基于二维热传导方程建立了一个可快速计算COB-LED散热器表面热分布的数学模型。为了便于模型求解,采用有限差分法求解该数学模型并选择交替方向隐格式作为其差分格式。根...针对COB-LED(Chip on Board-Light Emitting Diode)散热问题,文中基于二维热传导方程建立了一个可快速计算COB-LED散热器表面热分布的数学模型。为了便于模型求解,采用有限差分法求解该数学模型并选择交替方向隐格式作为其差分格式。根据模型中的边界条件和初始条件设计COB-LED常温点亮实验,并基于ANSYS有限元分析软件进行仿真分析。通过比较求解结果、仿真结果和实验结果验证该数学模型的合理性。结果表明,求解结果与实验结果中最高温度相对误差约23.57%,且两者的温度变化趋势一致。求解结果与仿真结果中最高温度相对误差约34.84%,且温度分布较为接近,证明了该数学模型的合理性与正确性。展开更多
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 ...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.展开更多
The demands for profile and flatness of nonoriented electrical steels are becoming more and more severe. The temperature field and thermal contour of work rolls are the key factors that affect the profile and flatness...The demands for profile and flatness of nonoriented electrical steels are becoming more and more severe. The temperature field and thermal contour of work rolls are the key factors that affect the profile and flatness control in the finishing trains of the hot rolling. A theoretic mathematical model was built by a two-dimensional finite difference to calculate the temperature field and thermal contour at any time within the entire rolling campaign in the hot rolling process. To improve the calculating speed and precision, some special solutions were introduced, including the development of this model, the simplification of boundary conditions, the computation of heat transfer coefficient, and the narrower mesh along the edge of the strip. The effects of rolling pace and work roll shifting on the temperature field and thermal contour of work rolls in the hot rolling process were demonstrated. The calculated results of the prediction model are in good agreement with the measured ones and can be applied to guiding profile and flatness control of nonoriented electrical steel sheets in hot strip mills.展开更多
The effect of mesa size on th e thermal characteristics of etched mesa vertical-cavity surface-emitting lase rs(VCSELs) is studied. The numerical results show that the mesa size of the top mirror strongly influences t...The effect of mesa size on th e thermal characteristics of etched mesa vertical-cavity surface-emitting lase rs(VCSELs) is studied. The numerical results show that the mesa size of the top mirror strongly influences the temperature distribution inside the etched mesa V CSEL. Under a certain driving voltage, with decreasing mesa size, the location o f the maximal temperature moves towards the p-contact metal, the temperature in the core region of the active layer rises greatly, and the thermal characterist ics of the etched mesa VCSELs will deteriorate.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10904079 and 60838001)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20090031120041)the Natural Science Foundation of Tianjin (Grant No. 10JCYBJC01300)
文摘This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm2 based on the two-temperature equation, and obtains the evolution of the free electron temperature and lattice temperature over a large temporal and depth range, for the first time. By investigating the temporal evolution curves of the free electron temperature and lattice temperature at three representative depths of 0, 100 nm and 500 nm, it reveals different characteristics and mechanisms of the free electron temperature evolution at different depths. The results show that, in the intense femtosecond laser ablation of aluminum, the material ablation is mainly induced by the thermal conduction of free electrons, instead of the direct absorption of the laser energy; in addition, the thermal conduction of free electrons and the coupling effect between electrons and lattice will induce the temperature of free electrons deep inside the target to experience a process from increase to decrease and finally to increase again.
文摘针对COB-LED(Chip on Board-Light Emitting Diode)散热问题,文中基于二维热传导方程建立了一个可快速计算COB-LED散热器表面热分布的数学模型。为了便于模型求解,采用有限差分法求解该数学模型并选择交替方向隐格式作为其差分格式。根据模型中的边界条件和初始条件设计COB-LED常温点亮实验,并基于ANSYS有限元分析软件进行仿真分析。通过比较求解结果、仿真结果和实验结果验证该数学模型的合理性。结果表明,求解结果与实验结果中最高温度相对误差约23.57%,且两者的温度变化趋势一致。求解结果与仿真结果中最高温度相对误差约34.84%,且温度分布较为接近,证明了该数学模型的合理性与正确性。
文摘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.
文摘The demands for profile and flatness of nonoriented electrical steels are becoming more and more severe. The temperature field and thermal contour of work rolls are the key factors that affect the profile and flatness control in the finishing trains of the hot rolling. A theoretic mathematical model was built by a two-dimensional finite difference to calculate the temperature field and thermal contour at any time within the entire rolling campaign in the hot rolling process. To improve the calculating speed and precision, some special solutions were introduced, including the development of this model, the simplification of boundary conditions, the computation of heat transfer coefficient, and the narrower mesh along the edge of the strip. The effects of rolling pace and work roll shifting on the temperature field and thermal contour of work rolls in the hot rolling process were demonstrated. The calculated results of the prediction model are in good agreement with the measured ones and can be applied to guiding profile and flatness control of nonoriented electrical steel sheets in hot strip mills.
基金National High Technology Research and Development Programof China(2001AA312180)
文摘The effect of mesa size on th e thermal characteristics of etched mesa vertical-cavity surface-emitting lase rs(VCSELs) is studied. The numerical results show that the mesa size of the top mirror strongly influences the temperature distribution inside the etched mesa V CSEL. Under a certain driving voltage, with decreasing mesa size, the location o f the maximal temperature moves towards the p-contact metal, the temperature in the core region of the active layer rises greatly, and the thermal characterist ics of the etched mesa VCSELs will deteriorate.
