  We present results from a numerical study of rotating black hole formation in
3-dimensional asymptotically anti-de Sitter (AdS) spacetime, focusing on the
structure of the black hole interior. While black holes in $AdS_3$ are of
theoretical interest for a wide variety of reasons, we choose to study this
system primarily as a toy model for astrophysical (4-dimensional) black holes
formed from gravitational collapse. We investigate the effect of angular
momentum on the geometry inside the event horizon, and see qualitative changes
in the interior structure as a function of the spin parameter. For low spins,
we find that a central spacelike curvature singularity forms, connecting to a
singular, null Cauchy horizon. For spins above a threshold consistent with the
linear analysis of Dias, Reall and Santos, curvature on the Cauchy horizon
remains bounded, signaling a violation of the strong cosmic censorship
conjecture. Further increasing the spin leads to a decrease in the relative
size of the spacelike branch of the singularity, which vanishes completely
above a second threshold. In these high-spin cases, the interior evolution is
bounded by a regular Cauchy horizon, which extends all the way inward to a
regular, timelike origin. We further explore the geodesic focusing
("gravitational shock-wave") effect predicted to occur along the outgoing
branch of the inner horizon, first described by Marolf and Ori. Remarkably, we
observe the effect at late times in all of the black holes we form, even those
in which the inner apparent horizon collapses to zero radius early in their
evolution.
