Experimental Investigation of Dynamics and Bifurcations of an Impacting Spherical Pendulum

Since Newton first considered the motion of a spherical pendulum over 200 years ago, many researchers have studied its dynamic response under a variety of conditions. The characteristic of the problem that has invited so much investigation was that a spherical pendulum paradigms much more complex phenomena. Understanding the response of a paradigm gives an almost multiplicative effect in the understanding of other phenomena that can be modeled as a variant of the paradigm. The spherical pendulum has been used to damp irregular motion in helicopters and on space stations as well as for many other applications. In this study an inverted impacting spherical pendulum with large deflection was investigated. The model was designed to approximate an ideal pendulum, with the pendulum bob contributing the vast majority of the mass moment of inertia of the system. Two types of bearing mechanisms and tracking devices were designed for the system, one of which had low damping coefficient and the other with a relatively high damping coefficient. An experimental investigation was performed to determine the dynamics of an inverted, impacting spherical pendulum with large deflection and vertical parametric forcing. The pendulum system was studied with nine different bobs and two different base configurations. During the experiments, the frequency of the excitation remained between 24.6 and 24.9 Hz. It was found that sustained conical motions did not naturally occur. The spherical pendulum system was analyzed to determine under what conditions the onset of Type I response (a repetitive motion in which the pendulum bob does not traverse through the apex. The bob strikes the same general area of the restraint without striking the opposite side of the restraint.), sustainable Type II response (this is the repetitive motion in which the pendulum bob traverses through the apex. The bob strikes opposite sides of the restraint.), and mixed mode response (motion in which the pendulum bob randomly strikes either the same area of the restrain or the opposite side of the restraint) occurred.