  We investigate the dynamical behavior of a non-ideal Duffing oscillator, a
system composed of a mass-spring-pendulum driven by a DC motor with limited
power supply. To identify new features on Duffing oscillator parameter space
due to the limited power supply, we provide an extensive numerical
characterization in the bi-parameter space by using Lyapunov exponents.
Following this procedure, we identify remarkable new periodic windows, the ones
known as Arnold tongues and also shrimp-shaped structures. Such windows appear
in highly organized distribution with typical self-similar structures for the
shrimps, and, surprisingly, codimension-2 bifurcation as a point of
accumulations for the tongues.
