SELF-OSCILLATIONS DESCRIBED BY THE GENERALIZED VAN DER POL EQUATION

Abstract

Quasilinear self-oscillations, represented by the generalized Van der Pol equation, are considered. The generalization of the equation is carried out by replacing the second degree of the velocity by its arbitrary non-negative degree. An approximate analytical solution, describing the transition of the oscillatory system to the regime of steady-state self-oscillations, is constructed using the energy balance method. A compact formula is obtained for calculating the amplitude of this regime and it is proved that it does not depend on the initial conditions. The calculation of the indicated amplitude involves using the table of gamma functions. It is shown that in some cases the obtained approximate analytical solution generalizes the known results of the theory of oscillations. To identify the errors of this solution, we integrated the generalized differential equation numerically using a computer for specific numerical data. The satisfactory consistency of the numerical results obtained by applying two different methods confirmed the adequacy of the approximate formulas for engineering calculations. The oscillations described by the generalized equation with the dissipative force of opposite sign are also studied. In this case the motion of the oscillatory system depends on the initial conditions. For the deviations of the oscillator from the position of static equilibrium smaller than a threshold value, free damped oscillations occur. In the case of large initial deviations beyond the threshold, free oscillations build up and over time the oscillator sweeps tend to the infinity for a limited period of time. The threshold deviation formula is derived which makes it possible to draw a conclusion about the stability of a dynamic system for various nonlinearity indices in the equation of motion and various initial perturbations.