  A shock-like structure appears in a time-averaged pattern produced by the
Kuramoto-Sivashinsky equation and the noisy Burgers equation with fixed
boundary conditions. We show that the effective viscosity computed from the
width of the time-averaged shock structure is consistent with that computed
from the time correlation of the fluctuations. The effective viscosity depends
on the lengthscale, although our system size is not sufficiently large to
satisfy the asymptotic dynamic scaling law. We attempt to determine the
effective viscosity in a finite size system with the projection operator
method.
