Stability and response of a vertically-excited hanging articulated pipe in water (Stability and response of a system with parametric excitation and nonlinear damping)

Abstract

When a hanging articulated pipe is vertically excited in water, the dynamic behavior of the pipe is analysed as a dynamic problem of a system with parametric excitation and nonlinear damping. Though this system may become unstable under certain input conditions, a response may not diverge due to the fluid drag force being proportional to the squared velocity. In this study, the stability condition and responcse under an instability condition are analysed. A model experiment is also carried out to confirm the theoretical results, a simple equation between the response and the input is derived, and it is confirmed by the model experiment. A model experiment is also carried out t confirm the theoretical results. As a result, a simple equation between the response and the input is derived, and it is confirmed by the model experiment. It is seen that this simple equation if valid for small input nuder the conditions assumed in this study, and the response amplitude is proportional to the input amplitude in the case of the input frequency being twice the natural frequency of the system. In addition, the response amplitude decrease when the input frequency differs from twice the natural frequency.