Experimental Study on Vortex-Induced Vibration of Rough Risers Coupling with Interference Effect in Tandem Arrangement

In order to study the response law of vortex-induced vibration(VIV) of marine risers under the combined action of roughness and interference effects, and to reveal the coupling mechanism of roughness and interference effects on the riser, a VIV experiment of rough risers in tandem arrangement was conducted in a wave-current combined flume.The experiment characterized the risers' roughness by arranging different specifications of attachments on the surface of the risers. Three rough risers with different roughness and smooth risers were arranged in tandem arrangement,with the rough risers arranged downstream. The experimental results indicate that the suppression of the attachments on the downstream risers' vibration are more significant both in the CF and IL directions as the reduced velocity increases. For the downstream riser, the amplitude response of rough riser is more significantly weakened compared with the smooth one at high reduced velocity. For the upstream risers, changes in the roughness and spacing ratio have an impact on their ‘lock-in’ region. When the roughness of downstream risers is relatively large(0.1300) and the spacing between risers is small(S/D=4.0), the reduced velocity range of ‘lock-in’ region in the CF direction of upstream risers is obviously expanded, and the displacement in the ‘lock-in’ region is severer.