  We present a two-dimensional grid-based hydrodynamic simulation of a thin,
viscous, locally-isothermal corotating disk orbiting an equal-mass Newtonian
binary point mass on a fixed circular orbit. We study the structure of the disk
after multiple viscous times. The binary maintains a central hole in the
viscously-relaxed disk with radius equal to about twice the binary semimajor
axis. Disk surface density within the hole is reduced by orders of magnitude
relative to the density in the disk bulk. The inner truncation of the disk
resembles the clearing of a gap in a protoplanetary disk. An initially circular
disk becomes elliptical and then eccentric. Disturbances in the disk contain a
component that is stationary in the rotating frame in which the binary is at
rest; this component is a two-armed spiral density wave. We measure the
distribution of the binary torque in the disk and find that the strongest
positive torque is exerted inside the central low-density hole. We make
connection with the linear theory of disk forcing at outer Lindblad resonances
(OLRs) and find that the measured torque density distribution is consistent
with forcing at the 3:2 (m=2) OLR, well within the central hole. We also
measure the time dependence of the rate at which gas accretes across the hole
and find quasi-periodic structure. We discuss implications for variability and
detection of active galactic nuclei containing a binary massive black hole.
