  The time dependent evolution of the accretion disk around black hole is
computed. The classical description of the $\alpha$-viscosity is adopted so the
evolution is driven by the instability operating in the innermost
radiation-pressure dominated part of the accretion disk. We assume that the
optically thick disk always extends down to the marginally stable orbit so it
is never evacuated completely. We include the effect of the advection, coronal
dissipation and vertical outflow. We show that the presence of the corona
and/or the outflow reduce the amplitude of the outburst. If only about half of
the energy is dissipated in the disk (with the other half dissipated in the
corona and carried away by the outflow) the outburst amplitude and duration are
consistent with observations of the microquasar GRS 1915+105. Viscous evolution
explains in a natural way the lack of direct transitions from the state C to
the state B in color-color diagram of this source. Further reduction of the
fraction of energy dissipated in the optically thick disk switches off the
outbursts which may explain why they are not seen in all high accretion rate
sources being in the Very High State.
