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 (Ur) 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 (ρin) or velocity (uin) 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 uin or ρin increases. Nonetheless, both the in-plane and out-of-plane responses are not sensitive to the internal flow when Ur is sufficiently high. Generally, the out-of-plane response is predominately contributed from the external flow, while the internal liquid–solid flow is the main contributor to the in-plane response at lower Ur.