ples in literature [6–9] on asymptotic methods. Sometimes EEP is presented
in a slightly more general model of unbalanced rotor [6–8], where the phase
shift between vertical and horizontal oscillations of the pivot can differ from
π/2. EEP is also a special case of generally excited pendulum in [10].
The usual assumption for approximate solution in the literature is the smallness
of dimensionless damping and pivot oscillation amplitudes in the EEP’s
equation of motion. The author could find only one paper [11], where oscillations
of EEP with high damping and yet small relative excitation were
studied.
In the present paper we study rotations of EEP with not small excitation
amplitudes and with both small and not small linear damping. Our analysis
uses the exact solutions for EEP with the absence of gravity and with
equal excitation amplitudes, when elliptical trajectory of the pivot becomes
circular. 1
The paper is organized as follows. In Section 2 the dimensionless equation
of EEP motion is derived. In Section 3 the exact rotational solutions and
their stability conditions are obtained in the case, with no gravity and the
circular trajectory of the pivot. In Section 4 first and second order approximate
solutions are obtained by multiple scale method [13] for the close to circle
trajectory of the pivot and high damping, where we assume that gravity is
small or the frequency of excitation is high. In Section 5 for the same excitation
and small damping second order approximate solutions are obtained with the
use of averaging method [3,14]. In Section 6 both solutions in Sections 4 and 5
are compared with the numerical solutions for different values of the damping
parameter.