Preliminary Instability-Analysis of Deepwater Riser With Fairings

Instability of deepwater riser with fairings is investigated in this study. Despite the advantages over other devices for suppressing vortex-induced-vibration (VIV), fairings may be susceptible to flutter type instability. A two-body mathematical model is established for the coupled transverse-torsion motion of a top tensioned riser with fairings. The inner part (riser) can only move transversely while the outer part (fairing) has transverse-torsion motion. The effect of the transverse velocity on the angle of attack is taken into account and damping is considered for both degrees of freedom. An eigenvalue analysis is employed to examine the issue of stability. The emphasis is on identifying the critical current speed for a given riser and fairing configuration. The effects of key parameters are investigated and the results indicate that the section hydrodynamic characteristics of the fairings have a significant impact on the instability.