  We consider a lumped circuit model of an augmented electromagnetic railgun
that consists of a gun circuit and an augmentation circuit that is inductively
coupled to the gun circuit. The gun circuit is driven by a d.c. voltage
generator, and the augmentation circuit is driven by an a.c. voltage generator.
Using sample parameters, we numerically solve the three non-linear dynamical
equations that describe this system. We find that there is a resonant behavior
in the armature kinetic energy as a function of the frequency of the voltage
generator in the augmentation circuit. This resonant behavior may be exploited
to increase armature kinetic energy. Alternatively, if the presence of the
kinetic energy resonance is not taken into account, parameters may be chosen
that result in less than optimal kinetic energy and efficiency.
