When matter orbits around a black hole obliquely with respect to the holes spin axis, a relativistic torque causes the orbits to precess. Forty years ago, astrophysicists proposed that the orbital angular momentum in accreting gas should align with the mass's spin near the hole. The location of the alignment front is determined by a balance between the torque, the resulting differential precession, and warp-induced inward mixing of misaligned angular momentum from the outer to the inner disk. Analytic approaches are restricted to linear one-dimensional analysis, using viscosity for dissipation, despite the fact that accretion disks are not viscous systems, but MHD turbulent. Numerical simulations are required, but three-dimensional high-resolution simulations required have only recently become possible. We are investigating alignment through MHD and hydrodynamic simulations of mis-aligned disks. Our approach has been to use a semi-Newtonian method, using idealized disks that can probe the physical process in detail.
