  We extend our previous numerical simulation of accretion disks with shock
waves when cooling effects are also included. We consider bremsstrahlung and
other power law processes: $\Lambda \propto T^{\alpha} \rho^2$ to mimic cooling
in our simulation. We employ {\it Smoothed Particle Hydrodynamics} technique as
in the past. We observe that for a given angular momentum of the flow, the
shock wave undergoes a steady, radial oscillation with the period is roughly
equal to the cooling time. Oscillations seem to take place when the disk and
cooling parameters (i.e., accretion rate, cooling process) are such that the
infall time from shock is of the same order as the post-shock cooling time. The
amplitude of oscillation could be up to ten percent of the distance of the
shock wave from the black hole when the black hole is accreting. When the
accretion is impossible due to the centrifugal barrier, the amplitude variation
could be much larger. Due to the oscillation, the energy output from the disk
is also seen to vary quasi-periodically. We believe that these oscillations
might be responsible for the quasi periodic oscillation (QPO) behaviors seen in
several black hole candidates, in neutron star systems as well as dwarf novae
outbursts such as SS Cygni and VW Hyi.
