  We include feedback in global hydrodynamic simulations in order to study the
star formation properties, and gas structure and dynamics, in models of
galactic disks. We extend previous models by implementing feedback in
gravitationally bound clouds: momentum is injected at a rate proportional to
the star formation rate. This mechanical energy disperses cloud gas back into
the surrounding ISM, truncating star formation in a given cloud, and raising
the overall level of ambient turbulence. Propagating star formation can however
occur as expanding shells collide, enhancing the density and triggering new
cloud and star formation. By controlling the momentum injection per massive
star and the specific star formation rate in dense gas, we find that the
negative effects of high turbulence outweigh the positive ones, and in net
feedback reduces the fraction of dense gas and thus the overall star formation
rate. The properties of the large clouds that form are not, however, very
sensitive to feedback, with cutoff masses of a few million solar masses,
similar to observations. We find a relationship between the star formation rate
surface density and the gas surface density with a power law index ~2 for our
models with the largest dynamic range, consistent with theoretical expectations
for our model of disk flaring. We point out that the value of the
"Kennicutt-Schmidt" index depends on the thickness of the disk. With our simple
feedback prescription (a single combined star formation event per cloud), we
find that global spiral patterns are not sustained; less correlated feedback
and smaller scale turbulence appear to be necessary for spiral patterns to
persist.
