Low-speed impacts between rubble piles modeled as collections of polyhedra, 2

We present the results of additional calculations involving the collisions of km-scale rubble piles. In new work, we used the Open Dynamics Engine (ODE). an open-source library for the simulation of rigid-body dynamics that incorporates a sophisticated coil is ion-detection and resolution routine. We found that using ODE resulted in a speed-up of approximately a factor of 30 compared with previous code. In this paper we report on the results of almost 1200 separate runs, the bulk of which were carried out with 1000-2000 elements. We carried out calculations with three different combinations of the coefficients of friction eta and (normal) restitution epsilon: low (eta = 0: epsilon = 0.8), medium (eta = 0, epsilon = 0.5), and high (eta = 0.5, epsilon = 0.5) dissipation. For target objects of similar to 1 km in radius, we found reduced critical disruption energy values Q*(RD) in head-on collisions from 2 to 100 J kg(-1) depending on dissipation and impactor/target mass ratio. Monodisperse objects disrupted somewhat more easily than power-law objects in general. For oblique collisions of equal-mass objects, mildly off-center collisions (b/b(0) = 0.5) seemed to be as efficient or possibly more efficient at collisional disruption as head-on collisions. More oblique collisions were less efficient and the most oblique collisions we tried (b/b(0) = 0.866) required up to similar to 200 J kg(-1) for high-dissipation power-law objects. For calculations with smaller numbers of elements (total impactor n(i) + target n(T) = 20 or 200 elements, we found that collisions were more efficient for smaller numbers of more massive elements, with Q*(RD) values as low as 0.4 J kg(-1) for low-dissipation cases. We also analyzed our results in terms of the relations proposed by Stewart and Leinhardt [Stewart, S.T., Leinhardt, Z.M., 2009. Astrophys. J. 691, L133-L137] where m(1)/m(i) + m(T)) = 1 - Q(R)/2Q*(RD) where Q(R) is the impact kinetic energy per unit total mass m(i) + m(T). Although there is a significant amount of scatter, our results generally bear out the suggested relation. (C) 2009 Elsevier Inc. All rights reserved.