Numerical simulation of dust aggregate collisions. I. Compression and disruption of two-dimensional aggregates

We carry out numerical simulations of dust aggregate collisions to study the compression and disruption processes of aggregates in their growth. To compare with the pioneering studies of Dominik & Helens, we focus on twodimensional head-on collisions, in which we obtain similar results for compression and disruption to theirs. In addition to the similarities, we examine the dependence of the collisional outcomes on the aggregate size and the parameters relevant to the particle interaction in detail by treating large aggregates that consist of up to 2000 particles. Compression of aggregates by collisions reduces the radius of gyration and increases the number of contacts between the constituent particles. Our results show that the changes in the gyration radius and the number of contacts after impact depend on the impact energy and that the dependence is scaled by the energy necessary to roll all contacts. We provide empirical formulae for the changes in the gyration radius and the number of contacts. Furthermore, we find that the degree of maximum compression is determined by the ratio of rolling energy to breaking energy. This indicates that ice aggregates become more compact than quartz aggregates in the same impact conditions. Any aggregates are catastrophically disrupted when the impact energy exceeds approximately 10 times the energy necessary to break all contacts. Our results, however, suggest that it becomes harder to disrupt the aggregates with an increasing number of oarticles.