Collisional compaction of dust aggregates influences the fate of dust clouds and protoplanetary disks. The influence of rolling motion, which is among the parameters describing grain motion in an aggregate collision, has been poorly investigated thus far. We used granular-mechanics simulations of aggregate collisions to study the influence of rolling friction mur on the compaction achieved. Compaction was quantified by the filling factor and the average grain coordination, whose initial value was 2. By varying mur by a factor of 8 around the often assumed value of mur=0.1, the final average coordination increased to 2.9 (mur=0.4) and up to 3.5 (mur=0.05). Even more substantial changes occur for the filling factor of the collided aggregate. Low rolling friction values lead to high compaction, accompanied by more abundant grain ejection. Other force parameters describing rolling (i.e. rolling stiffness and viscous dissipation) showed no discernible influence in the parameter range investigated here. This study underlines that the value of the rolling friction adopted in simulations of aggregate collisions must be chosen with care.
Planes et al. (Tue,) studied this question.