Coupled vibration of composite riser under gas–liquid internal flow

In this paper, a dynamic prediction model for coupled vortex-induced vibration (VIV) of the composite marine riser in cross-flow (CF) and in-line (IL) directions under the action of gas–liquid two-phase internal flow is proposed. Then, numerical simulations are performed to discuss the influences of the ocean current velocity, internal flow velocity of gas–liquid mixed transportation, gas volume fraction, and fiber orientation angle on the dynamic characteristics of coupled VIV in CF and IL directions of a composite riser. Of particular interest in this process is the combined influence of multiple factors on coupled vibration characteristics of a composite riser. The results show that due to the influence of the gas–liquid two-phase internal flow and composite materials, when the current velocity is large, the vibration modes in the CF and IL directions are not approximately twice the relationship. When the fiber orientation angle and gas volume fraction are changed, the vibration of the riser in the CF direction will appear as traveling wave characteristics. At this time, the vibration amplitude in the CF direction will increase significantly, and the vibration periodicity will decrease. In addition, the CF bending stress of the riser is more sensitive to the change of parameters. There is the jump phenomenon, and the change of fiber orientation angle will aggravate this phenomenon.