The Response of a Hanging Articulated Pipe under Vertical Random Excitation in Water : The Response of a System with Random Parametric Excitation and Nonlinear Damping

Abstract

When a hanging articulated pipe is vertically excited at random in water, the dynamic behavior of the pipe is analysed as a dynamic problem of a system with random parametric excitation and nonlinear damping. Though this system may become unstable under certain input conditions, the response will not diverge due to the fluid drag force being proportional to the squared velocity. In this study, the response under the instability condition is analysed. A model experiment is also carried out to confirm the analytical model. 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 is valid for small input, and the root mean square of the response velocity is proportional to the power spectral density of the parametric excitation at twice the natural frequency of the excelling mode of the system.