  We explore Implicit Monte Carlo (IMC) and Discrete Diffusion Monte Carlo
(DDMC) for radiation transport in high-velocity outflows with structured
opacity. The IMC method is a stochastic computational technique for nonlinear
radiation transport. IMC is partially implicit in time and may suffer in
efficiency when tracking Monte Carlo particles through optically thick
materials. DDMC accelerates IMC in diffusive domains. Abdikamalov extended IMC
and DDMC to multigroup, velocity-dependent transport with the intent of
modeling neutrino dynamics in core-collapse supernovae. Densmore has also
formulated a multifrequency extension to the originally grey DDMC method. We
rigorously formulate IMC and DDMC over a high-velocity Lagrangian grid for
possible application to photon transport in the post-explosion phase of Type Ia
supernovae. This formulation includes an analysis that yields an additional
factor in the standard IMC-to-DDMC spatial interface condition. To our
knowledge the new boundary condition is distinct from others presented in prior
DDMC literature. The method is suitable for a variety of opacity distributions
and may be applied to semi-relativistic radiation transport in simple fluids
and geometries. Additionally, we test the code, called SuperNu, using an
analytic solution having static material, as well as with a manufactured
solution for moving material with structured opacities. Finally, we demonstrate
with a simple source and 10 group logarithmic wavelength grid that IMC-DDMC
performs better than pure IMC in terms of accuracy and speed when there are
large disparities between the magnitudes of opacities in adjacent groups. We
also present and test our implementation of the new boundary condition.
