  In this work we study the power spectrum of the Stochastic Gravitational Wave
Background produced by standard and biased domain wall networks, using the
Velocity-dependent One-Scale model to compute the cosmological evolution of
their characteristic scale and root-mean-squared velocity. We consider a
standard radiation + $\Lambda \rm CDM$ background and assume that a constant
fraction of the energy of collapsing domain walls is emitted in the form of
gravitational waves. We show that, in an expanding background, the total energy
density in gravitational radiation decreases with cosmic time (after a short
initial period of quick growth). We also propose a two parameter model for the
scale-dependence of the frequency distribution of the gravitational waves
emitted by collapsing domain walls. We determine the corresponding power
spectrum of the Stochastic Gravitational Wave Background generated by domain
walls, showing that it is a monotonic decreasing function of the frequency for
frequencies larger than that of the peak generated by the walls that have
decayed most recently. We also develop an analytical approximation to this
spectrum, assuming perfect linear scaling during both the radiation and matter
eras, in order to characterize the dependence of the amplitude, peak frequency
and slope of the power spectrum on the model parameters.
