  The effects of binary tidal forces on transport within an accretion disk are
studied with a time-dependent hydrodynamical model of a two-dimensional
isothermal accretion disk. Tidal forces quickly truncate the accretion disk to
radii of order half the average radius of the Roche lobe, and excite a
two-armed spiral wave that remains stationary in the rotating reference frame
of the binary system. We measure an effective alpha of order 0.1 near the outer
edge of the disk in all of our models, independent of the mass ratio, Mach
number, and radial density profile. However, in cold disks with high Mach
number, the effective alpha drops rapidly with decreasing radius such that it
falls below our threshold of measurement (roughly .001) at a radius of only one
third the tidal radius. In warmer disks where the Mach numbers remain below 20,
we can measure an effective alpha down to radii 10 times smaller than the
maximum size of the disk.
