Artificial viscosity and the simulation of fragmentation

The results of experiments to clarify the effects of spurious angular momentum transport on the axisymmetric collapse of a rotating, self-gravitating cloud are described. The calculations used the SPH method with a new form of artificial viscosity which conserves total linear and angular momentum. The artificial viscosity acting on all three components of linear momentum and acting on the z component of linear momentum was examined. The results are compared with those previously obtained, and it is inferred that the donor cell scheme is probably affected by spurious angular momentum transport. The effect of artificial viscosity on the evolution of initially uniformly rotating clouds and clouds which rotate differentially was also studied. For the former case, it was found that the evolution is toward a barred spiral, while in the latter case a disk is produced with some hint of a ring.