Stability of the umbilical was initially assessed using traditional two‑dimensional stability analysis in accordance with DNV-RP-F109. The results of this analysis concluded that the umbilical was unstable when subject to 100 year return period cyclonic conditions, particularly in the shallower water near the platform. The 2D stability assessment indicated that 402 concrete mattresses would be required to ensure the absolute stability of the umbilical.
Given the cost associated with the installation of concrete mattresses, Atteris reassessed the stability using a combination of three-dimensional dynamic stability analysis – using Atteris’ in‑house and verified stability software CORUS 3D, and an analytical stability assessment, considering the following:
