Vanishing atoms in low-gravity granular impact simulation


I am attempting to model the impact of a projectile into a granular bed in microgravity. The simulation is ‘two-dimensional’, composed of one sheet of spherical grains constrained against out-of-plane movement. The impactor is a larger diameter grain that has an assigned velocity of around 2cm/s and hits the surface of the granular bed at an angle.

This simulation works fine for higher gravitational accelerations (Earth and Moon gravity), but when I reduce to microgravity I suddenly have atoms vanishing from the simulation space immediately after the impactor makes contact. The initial simulation has about 8600 grains and suddenly most of the grains, including the impactor, disappear and leave around 20 in the simulation box. I am mystified as to why this is happening.

Does anyone have suggestions for what could cause atoms/grains to vanish like this under these types of dynamic circumstances? I am happy to share more details about my model and results if needed.

Thank you,


If there is little gravity, what is there that should retain particles or force them to stick together?