Investigation on Vortex-induced Vibration of the Staggered Riser Group Coupling Interference Effect

An experiment on vortex-induced vibration of the three-riser group in the 60°-staggered arrangement coupling interference effect is carried out to provide a theoretical reference and analysis basis for the design of riser groups. Based on the strains obtained by the fiber brag grating sensors and the modal decomposition theory, the concept of "interference efficiency" is introduced to analyze the dynamic characteristics and responses of the 60°-riser group. The riser model has an effective length of 2.0 m with an aspect ratio of 111.11. The adjacent risers are arranged at the spacing of 4 times the diameter. The results show that the 60°-riser group enters the "lock-in" region and the displacements reach "galloping" earlier than that of the isolated riser. High-order harmonic components appear in the in-line direction and the mode conversions are significant. Multi-frequency causes fatigue damage to be greatly aggravated. Therefore, the wake feedback effect and the interference of the gap flow can not be ignored.