In principle, the generalized Eq. (4) represent the equation of the pendulum without dissipation and for any possible
motion of the pivot on a plane. When dissipation is taken into account, traditionally dissipative forces are introduced
ad hoc in the equations of motion, although a Lagrangian and Hamiltonian formalism for the case of linear damping is
known [35]. The Lagrangian and Hamiltonian functions when linear dissipation is considered are, of course, timedependent,
and obviously do not have the same meaning as for conservative systems. The phenomenological model of
the dissipative forces mostly appearing in the literature is assumed to be linear. However, and in order to offer a more
general view of the equations of the pendulum, we will introduce here nonlinear damping terms. These terms have been
used for several engineering applications, such as ship dynamics and vibration engineering (see for instance [36–38] and
other references therein). One of the reasons why nonlinear damping in engineering and other applied sciences is important
stems from the fact that it can be used as an effective passive control strategy to suppress various instabilities.
Moreover, different effects of nonlinear damping on the dynamics of some nonlinear oscillators, including erosion of
fractal basins and how they affect the routes to chaos, among others, have been shown recently. The nonlinear dissipative
forces we consider are strictly proportional to the Nth power of the velocity, and consequently we use a general
polynomial function of Nth degree of the form