Vortex Induced Vibration of the GAP Bundle: From Selection of Flow Lines Arrangement to VIV Fatigue Analysis

MURPHY Sabah Oil Co. Ltd. is developing the Kikeh Field located offshore Malaysia in the South China Sea in a water depth of 1325m. This field development is based on a Floating Production Storage and Offloading unit (FPSO) and a Spar Dry Tree Unit (DTU). Fluids will be transported in fluid transfer lines (FTL) using SBM’s newly developed and patented Gravity Actuated Pipe (GAP) system to support a horizontal neutrally buoyant bundle of flow lines between two moored floaters. A mid-water bundle, comprising a carrier pipe, four flow lines and an umbilical, in a transverse current may experience Vortex Induced Vibration (VIV). This is a well-known phenomenon for a circular cylinder. Much less is understood however for a bundle arrangement. The methodology put in place to assess risks of VIV will be presented. Computational Fluid Dynamics (CFD) has been instrumental in defining the bundle arrangement minimizing the VIV amplitude. Two-dimensional model tests have been performed at a scale of 1/5 at MARIN facilities with the selected bundle configuration. In these experiments, a rigid bundle was subjected to controlled motions (towing and/or forced vertical oscillations). The salient results will be presented. Finally, a VIV fatigue analysis was performed using Shear 7 based on the results derived from the 2D model tests.