Minimizing Interference Between Top Tension Risers for Tension Leg Platforms

Interference between TTRs is a key design challenge. For spars, this is typically mitigated by having a large spacing between wellheads, thus increasing the distance between risers along the water depth. However, due to lower TTR tensioner stroke limits combined with larger vessel offsets, the feasibility of spacing out the wellheads for TTRs on a TLP is limited. The result is TTRs that are closer together through depth and therefore more likely to contact each other in extreme current conditions.

This paper presents the approach used to minimize the interference between the top tension risers on TLPs. Specific topics include considering current profiles with varying directions through the water depth, adjusting the top tension of the risers, and utilizing low-drag vortex-induced vibration (VIV) suppression strakes. The relative effect of each of these topics is also discussed.