Random vortex induced vibration response of suspended flexible cable to fluctuating wind

Abstract

A popular dynamical model for the vortex induced vibration (VIV) of a suspended flexible cable consists of two coupled equations. The first equation is a partial differential equation governing the cable vibration. The second equation is a wake oscillator that models the lift coefficient acting on the cable. The incoming wind acting on the cable is usually assumed as the uniform wind with a constant velocity, which makes the VIV model be a deterministic one. In the real world, however, the wind velocity is randomly fluctuant and makes the VIV of a suspended flexible cable be treated as a random vibration. In the present paper, the deterministic VIV model of a suspended flexible cable is modified to a random one by introducing the fluctuating wind. Using the normal mode approach, the random VIV system is transformed into an infinite-dimensional modal vibration system. Depending on whether a modal frequency is close to the aeolian frequency or not, the corresponding modal vibration is characterized as a resonant vibration or a non-resonant vibration. By applying the stochastic averaging method of quasi Hamiltonian systems, the response of modal vibrations in the case of resonance or non-resonance can be analytically predicted. Then, the random VIV response of the whole cable can be approximately calculated by superimposing the response of the most influential modal vibrations. Some numerical simulation results confirm the obtained analytical results. It is found that the intensity of the resonant modal vibration is much higher than that of the non-resonant modal vibration. Thus, the analytical results of the resonant modal vibration can be used as a rough estimation for the whole response of a cable.