考虑非傅立叶效应的固液相变分子动力学模拟
Molecular dynamics simulation of solid-liquid phase change considering non-Fourier effect

采用耦合双温度模型的分子动力学方法对飞秒激光照射金箔的固液相变过程进行了模拟研究，利用序参数法对固液原子进行判定从而确定了金箔发生相变时的固液界面位置和温度，对基于傅立叶定律的抛物线模型和考虑非傅立叶效应的双曲线模型模拟得到的结果进行对比分析，在此基础上采用耦合双曲线模型的分子动力学方法研究了激光能量密度和脉冲宽度对金箔相变过程的影响.结果表明，当激光作用于金箔时，金箔上表面首先熔化，固液界面随时间不断向金箔底部移动，并且在相同条件下，双曲线模型下的金箔熔化深度和固液界面温度均大于抛物线模型的结果.当考虑非傅里叶效应时，激光能量密度越大，固液界面温度越高，金箔熔化时间越短；激光脉冲宽度越小，固液界面温度越大，金箔熔化速度越快.
The solid-liquid change of gold foils irradiated by a femtosecond laser pulse is simulated and studied by the molecular dynamics method combined with the two-temperature model. A local order parameter is adopted to distinguish the solid and liquid phase atoms, and then the changing laws of the location and temperature of solid-liquid interface versus time are obtained. Comparisons between numerical results with the parabolic model based on Fourier law and hyperbolic model considering non-Fourier effect are presented. On this basis, the effects of laser energy flux density and pulse width on the phase changing process are investigated by the molecular dynamics method combined with the hyperbolic model. Results show that when the laser is applied to the gold foil, the upper surface of the gold foil is first melted, and the solid-liquid interface continuously moves to the bottom of the gold foil versus time. The melting depth and temperature of solid-liquid interface of hyperbolic model are much bigger than the results of parabolic model in the same conditions. When considering the non-Fourier effect, the higher the laser energy flux density, the higher the interfacial temperature and the shorter the melting time. The smaller pulse width is, the interfacial temperature is higher and the melting is more rapidly.