We demostrate the importance of general relativistic apsidal
precession in warped black hole accretion discs by comparing
three-dimensional smoothed particle hydrodynamic simulations in which
this effect is first neglected, and then included. If apsidal
precession is neglected, we confirm the results of an earlier
magnetohydrodynamic simulation by Krolik & Hawley (2015). We thus show
that at least in this case the alpha-viscosity model produces very
similar results to those of simulations where angular momentum
transport is due to the MRI. This is shown below, with the twist
(left) and tilt (right) shown in the same style as Krolik & Hawley
(2015).

We re-examine the Bardeen-Petterson effect in accretion discs
subject to Lense-Thirring precession in the bending wave regime (where
the disc viscosity is smaller than the disc aspect ratio) using three
dimensional smoothed particle hydrodynamics (SPH) simulations. Below
are some of our simulations, each using 10 million particles.