Nonstationary nonplanar free motions of an orbiting string with multiple internal resonances

The paper discusses the nonlinear free dynamics of an orbiting string satellite system. The focus is on the transversal oscillations, which are governed by two partial integro-differential equations in two transversal displacement components with quadratic nonlinearities. The system is weakly nonlinear but in practice works in conditions of simultaneous internal resonance. The investigation focuses on nonstationary motions arising from perturbed steady-state nonplanar oscillations. A four-mode model is used to study the problem: two modes are necessary to describe the basic oscillation and at least two other modes are involved in the resonance phenomena when the motion is perturbed. The multiple time scales method is used to obtain the equations that govern the amplitude and phase modulations. For increasing levels of system energy, fundamental and bifurcated paths of fixed points of the seven first-order differential equations are determined and their stability is investigated. The trajectories of motion of periodically modulated amplitude solutions and their stability are also studied. A model with a higher number of modes is used to evaluate the accuracy of the stability analysis of two-mode nonplanar oscillations perturbed by a two-mode disturbance.