  We present simulations, without electrodynamical assumptions, of
$B(x,y,H(t)), M(H(t))$, and $J_c(H(t))$, in hard superconductors, for a variety
of twin-boundary pinning potential parameters, and for a range of values of the
density and strength of the pinning sites. We numerically solve the overdamped
equations of motion of up to 10^4 flux-gradient-driven vortices which can be
temporarily trapped at $\sim 10^6$ pinning centers. These simulations relate
macroscopic measurements (e.g., M(H), ``flame'' shaped $B(x,y)$ profiles) with
the underlying microscopic pinning landscape and the plastic dynamics of
individual vortices.
