Tension Based Mitigation of Drilling Riser VIV

Abstract

As offshore drilling reaches into greater and greater depths, risers are exposed to more and more current. As a result, vortex induced vibration (VIV) has become an important consideration for offshore drilling. VIV increases drag from the current, increasing flex joint angles and vessel offsets, and causes fatigue, with detrimental effect on usable life of the riser and connected equipment. Many VIV mitigation methods such as strakes and fairings are in use, but operational concerns such as time loss during installation/removal exist. This thesis investigates the possibility of VIV mitigation by controlling local tension of the riser. Special riser joints with weight modules have been proposed to create greater tension variance along the riser arc length. Based on ISO 13624-1, several riser stack-ups are numerically simulated for VIV response on drag and fatigue. Results show that limited improvement is possible over staggered stack-up shown in ISO 13624-1, although with trade off in increased tension requirement.