Analysis of vortex-induced vibration in flexible risers using a physically-meaningful wake-oscillator model

Abstract

Flexible riser is prone to vortex-induced vibration (VIV), which can cause fatigue problems, making it essential to accurately estimate the VIV of the riser. The empirical wake-oscillator model is frequently used for VIV analysis, while the accuracy of the predicted response is not satisfactory in some cases, mainly due to its reliance on empirical parameters. To address these limitations, this study employs the wake-oscillator model developed by Tamura and Matsui, which provides a more explicit physical interpretation. Firstly, a set of interrelated partial differential equation is derived by integrating the wake-oscillator equations that characterize the flow with the structural motion equation that represent the riser’s movement. The effectiveness of the proposed method is validated by comparing the predicted outcomes (the displacement, dominant mode, and dominant frequency) with field and tank experiments. Additionally, space-time evolutions and spectral analysis were performed, and the energy conversion between the riser and the flow was examined to comprehend the physical mechanism of VIV of riser. Based on this, it was found that VIV of riser simultaneously exhibits traveling wave and standing wave characteristics. And there were also both mono-frequency and multi-frequency phenomena. Overall, the physically-meaningful model can accurately simulate the CF response of flexible riser, providing essential references for estimating its fatigue life, design, and operation of flexible risers.