Molecular Dynamic Simulation Of Converging Shock Wave

Converging shock is a kind of shock that converges to a spherical or cylindrical convergence center.Unlike propagation of the planar shock,the surface of converging shock continuously decreases during the process of convergence,and the intensity of shock continues to increase.The central area will become a region of extremely high temperature and pressure.So the converging shock is usually used as a means of effi-ciently collecting energy in a small area.Convergence shock is widely existed in the phenomena of various scales from the collapse of supernovae on the astronomical scale to the collapse of light bubbles on the microscale.It' s significant not only in scientif-ic research,but also in engineering applications,such as Inertial Confinement Fusion.At the same time,during the propagation of converging shock,the stability of the con-verging shock has a great influence on the efficiency of the final collecting energy.The current research on the converging shock is usually focusing on the macroscopic scale,but the propagation of converging shock and the instability of interface impeded by converging shock are multi-scale problems.So this paper will study propagation of converging shock and instability of interface impeded by converging shock at the mi-croscopic scale by the classical molecular dynamics simulation,the main conclusions are follows:Firstly,the generation of converging shock waves in molecular dynamics is real-ized in this paper.The validity of the potential function is verified,and the propagation and characteristics of converging shock on the microscopic surface are studied.In this paper,classical molecular dynamics is used for the first time to study the propagation of cylindrical shock,and the change of parameters such as density,radial velocity,and temperature at different times during the propagation is analyzed.At the same time,different intensities of shock are analyzed.The rule of self-similarity of different inten-sities of shock after dimensionless has little difference.Then,the evolution of the Cu-He unperturbed interface under the impact of con-verging shocks at the microscale is studied.It is found that there is no obvious decel-eration stage before the reshock of the secondary shock reflected from the convergence center,and the effect of Rayleigh-Taylor is not obvious;After impact of converging shock,some tiny perturbations appeared in the unperturbed interface due to the random thermal motion of atoms.After reshock,the amplitudes of these tiny perturbations in-crease rapidly.Therefore,on the micro-scale,the micro-perturbations caused by the thermal motion will produce non-negligible growth due to the multiple impact of con-verging shock.Finally,this paper simulates the evolution of the Cu-He interface with single-mode perturbation under the impact of converging shock,studying the development and evo-lution characteristics of interface at the microscale,and systematically studying the ef-fects of amplitude,wavenumber,and Atwood number on the development of the in-stability of interface.Firstly,the evolution process of perturbation under the impact of converging shock is analyzed,and it is found that the disordered shock formed after the initial convergent shock passing through the perturbed interface gradually recover-s into a cylindrical converging shock during the inward process.Then,based on the analysis of the evolution of interface with different initial amplitudes,it is found that after reshock,for large amplitude,growth rate of the perturbation tends to be consistent;based on the analysis of the evolution of interface with different initial wavenumbers,it is found that the growth rate of the perturbation at large wave numbers slows down and the saturation occurs earlier;based on the analysis of the evolution of interface with different Atwood numbers,it is found that at different Atwood numbers,the growth rate of the perturbation is almost the same under the initial shock,but after reshock,the growth of the perturbation amplitude appears obvious differences.Finally,the change of pressure of the convergent center is analyzed.It is found that the initial pressure peak of the convergent center is not related to the initial disturbance amplitude,but the sub-sequent pressure peak is affected by the development of the instability of the interface.And he perturbation of interface will weaken the pressure in the convergent center.