  The steady sliding state of periodic structures such as charge density waves
and flux line lattices is numerically studied based on two and three
dimensional driven random field XY models. We focus on the dynamical phase
transition between plastic flow and moving solid phases controlled by the
magnitude of the driving force. By analyzing the connectivity of co-moving
clusters, we find that they percolate the system within a finite observation
time under driving forces larger than a certain critical force. The critical
force, however, logarithmically diverges with the observation time, i.e. the
moving solid phase exhibits only within a certain finite time, which
exponentially grows with the driving force.
