Laboratory Investigation on the In-Line Dynamic Characteristic of Long Flexible Riser Under Vortex-Induced Vibration

摘要

This work presents the experimental results focused on the dynamicrncharacteristics of in-line response of a long flexible riser. The riserrnmodel is 28.04 m in length and 0.016 m in diameter, giving an aspectrnratio (length to diameter) of around 1750. The mass ratio (structuralrnmass over displaced fluid mass per unit) of the riser modelrnapproximates 1.0. By means of towing the riser model in a wave basin,rnthe uniform current was generated. The time series of strains of thernriser model under various current speeds (ranging from 0.15 m/s to 0.60rnm/s) were monitored using the Fiber Bragg Grating (FBG) sensors. Thernmode decomposition method was employed to analyze the measuredrnstrain signals. The dominant frequency, displacement traces, standardrndeviation of displacements and fatigue life associated with the in-linernvibration were obtained. The experimental results indicted that thernhigher order response mode from the in-line vibration together with thernlarge deflection may reduce the fatigue life of risers as severely as thatrnfrom the cross-flow vibration, which should be paid much morernattentions to the practical engineering applications.