Numerical Simulation of Vortex-induced Vibration Characteristics of Rough Riser

Marine riser is key equipment connecting the floating platform and the seabed wellhead, and vortex-induced vibration (VIV) is the main cause of its fatigue damage. Roughness of the marine riser surfaces is significantly affected by attached marine organisms, and makes dynamic characteristics of the riser VIV more abundant and complex. In this study, based on the bidirectional fluid-structure coupling method of CFD (computational fluid dynamics) and CSD (computational structure dynamics), a modified model of velocity gradient on the rough wall is introduced to construct numerical calculation program of VIV of a rough riser. Effects of roughness, inlet velocity and other parameters on VIV characteristics of the riser were studied, and influence of surface roughness on characteristics of the riser VIV was explored. The results show that, with the increase of the inflow velocity and surface roughness, increase of the stream-wise and transverse vibration frequency of the riser is significant. Larger surface roughness will strengthen the multi-frequency and broadband vibration of the riser, but smaller surface roughness will restrain the multi-frequency and broadband vibration. With the increase of the surface roughness, frequencies twice and three times of the main frequency of the riser in the transverse direction decrease, and multi-frequency vibration characteristics decrease, but broadband vibration characteristics will increase. © 2021, Editorial Office of Ship Building of China. All right reserved.