Internal flow effect on the cross-flow vortex-induced vibration of a cantilevered pipe discharging fluid

Motivated by the application of ocean CCS (Carbon dioxide Capture and Storage) proposal and the fact that a cantilevered pipe can gain or lose energy due to the discharging flow, this study devotes efforts to investigate the IFE (Internal Flow Effect) on the CF (Cross-Flow) VIV (Vortex-Induced Vibration) of a cantilevered pipe discharging fluid. In this study, a simple fluid-structure interaction model is proposed which employs a linear structural equation to describe the transverse vibrations and utilizes a distributed wake oscillator to create the VIV effect. The simulations are justified by comparing with experiments for VIV effect and the non-conservative IFE of flexible risers. Then simulations of a flexible riser are performed by varying incoming currents and internal flow rates. The IFE on VIVs are examined by the space-time modifications of riser responses and dominant vibration frequency for which the mode switching and sharing can be identified. When the internal flow velocity is small, the pipe is losing energy to the inner flow and the VIVs can be depressed significantly. However, the pipe would lose the stability when the internal flow exceeds a critical value. The critical internal flow velocity depends on the current velocity and VIV dominant mode.