  We study the oscillations of an axisymmetric, viscous, radiative, general
relativistic hydrodynamical simulation of a geometrically thin disk around a
non-rotating, $6.62\,M_\odot$ black hole. The numerical setup is initialized
with a Novikov-Thorne, gas-pressure-dominated accretion disk, with an initial
mass accretion rate of $\dot{m} = 0.01\,L_\mathrm{Edd}/c^2$ (where
$L_\mathrm{Edd}$ is the Eddington luminosity and $c$ is the speed of light).
Viscosity is treated with the $\alpha$-prescription. The simulation was evolved
for about $1000$ Keplerian orbital periods at three Schwarzschild radii (ISCO
radius). Power density spectra of the radial and vertical fluid velocity
components, the total (gas $+$ radiation) midplane pressure, and the vertical
component of radiative flux from the photosphere, all reveal strong power at
the local breathing oscillation frequency. The first, second and third
harmonics of the breathing oscillation are also clearly seen in the data. We
quantify the properties of these oscillations by extracting eigenfunctions of
the radial and vertical velocity components and total pressure. This confirms
that these oscillations are associated with breathing motion.
