Experimental investigation of slug flow-induced vibration of a flexible riser

Slug flow-induced vibration (SIV) of a curved flexible riser is experimentally investigated in this work using a nonintrusive measurement. Two high-speed cameras are employed to capture the vibration displacements of flexible riser as well as the characteristics of gas-liquid two-phase flow in the riser. The SIV mainly occurs in the curvature plane of the flexible riser. The fluctuation frequencies of the pressure of slug flow take part in the dynamic response of riser, and the oscillation frequencies are also observed in the pressure fluctuation, illustrating the fluid-structure interaction. The periodicity of vibration amplitude is associated with the periodic appearance of the longest liquid slug. Larger amplitude occurs when the longest liquid slug passes through the flexible riser. The response is enhanced as the gas-liquid ratio increases. Mode switching appears first in the trough of response envelope, where the distribution of frequency is more widely spread and the response energy is relatively low. Because of the multi-mode response, the contribution of travelling wave increases gradually. Nevertheless, due mainly to the limited gas-liquid ratio and riser length, the in-plane response is dominated by the first mode in the considered cases.