The vibration of deep-sea mining riser excited by both internal and external flows

This paper reports the experimental results of the coupling response of a catenary flexible riser excited by both internal liquid-solid two-phase flow and the external shear current. The conveyed flow density ranges from 1000 to 1200 kg/m³, with velocity changing from 0 to 2.15 m/s. The vibration of the flexible riser was tested in the depth-averaged reduced velocity (U_r) range of 4.52-54.05. The experimental results indicate that only the in-plane response is excited by the internal liquid-solid flow when the riser is immersed in still water. As either the internal flow density (ρ_in) or velocity (u_in) grows, the in-plane response is enhanced, resulting in the augmented fluctuations of pressure difference and top tension. In the presence of external flow, the out-of-plane response is also excited. The critical reduced velocity for mode transition becomes larger as either u_in or ρ_in increases. Nonetheless, both the in-plane and out-of-plane responses are not sensitive to the internal flow when U_r is sufficiently high.