Abstract：Under the top vessel motions, dynamic responses of the catenary risers would generate relatively oscillatory flow around themselves. Such oscillatory flow would easily trigger the ‘intermittent VIV’ at sag-bend part of the riser. This paper mainly focuses on the experimental investigations on the behaviors of a flexible cylinder in oscillatory flow with different combinations of both maximum reduced velocity and number. Fiber Brag Grating (FBG) strain sensors were used to measure the VIV response of the model cylinder. Then, modal analysis and wavelet analysis were adopted to deal with the experimental data, and VIV response featured of “time sharing” including “amplitude modulation” and “mode transition” was observed which is distinguished from that in steady flow. Finally, the effects on “time sharing” of VIV in oscillatory flow from both reduced velocity and number were discussed and summarized.
2014, Vol. 33 
