The Evolution Of Interstellar Dust

In recent years,the update of the existing(sub-)millimeter arrays,The At-acama Large Millimeter/Submillimeter Array and The Very Large Array have significantly improved the observations about dust evolution in protoplanetary disks.According to the opacity of the dust grains,we can model the size of the dust grains and their distribution in protoplanetary disks.A number of works indicate that the dust dynamic is very important to planet and star for-mation,before ordinary gravitation accretion could start.However,there are still important parts of the physics involved that are poorly understood and the observational evidence are limited due to large time scale of the phenomenon.Simulation based on reasonable models may shed lights on these problems.In our work,we consider sub-millimeter grains which are proved to exist in nebular medium,or protoplanetary disks.These dust grains are considered as exclusively spherical particles,and each grain has a three-dimensional initial position,velocity,and angular velocity degrees of freedom.They are the basic components of the dust clusters in our model.The collision of these units can produce a variety of forces,including friction forces,elastic forces,attraction forces,inelastic forces and frictional torques.After these quantities are deter-mined,we use molecular dynamics to integrate the trajectory of the system.This method is known as granular mechanics.Also,we introduced periodic boundary conditions to mimic the effect of large system.Finally,we implemented our granular mechanics model and tested it by considering two-dimensional systems.The test results show that our model can correctly describe the dynamic of interacting submillimeter grains,behavior of fluid and the formation of large clusters were observed in our numerical experi-ments.Further more,reasonable structure of cluster can be build by our model.We are looking forward to apply this model to study the dynamic of formation of gravitation accretion kernels in near future.