CFD Analysis of an Observed Mooring Line Trench to Assess the Potential for Further Trench Development-Paper

Paper

Pdf Summary

The study investigates whether seabed trenches around mooring chains at suction-pile anchors off West Africa are likely to deepen or expand. Such trenches can reduce soil resistance and threaten anchor capacity; repeated field surveys suggest they often approach a stable, equilibrium shape.<br /><br />Researchers used two- and three-dimensional computational fluid dynamics (CFD) to model an oscillating chain within a fixed trench based on observed field geometry. The simulations estimated shear stresses on the trench walls and bottom. These stresses were compared with seabed erosion thresholds drawn from published prediction methods and laboratory tests on representative Gulf of Guinea clay.<br /><br />The 3D simulations produced higher shear stresses than the 2D models, largely because of the chain’s complex geometry, rather than strong flow along the trench. Peak stresses were concentrated on the lower trench walls, while stresses at the bottom were low. Bottom stresses were well below estimated erosion thresholds, indicating that significant deepening is unlikely. Localized wall stresses overlapped with the lower range of estimated thresholds, so some widening may occur, but is expected to be slow. These findings are consistent with field observations of trenches that have changed little over time.<br /><br />The conclusions apply to operational chain motions and assume no chain–soil contact. The study did not assess storm loading or soil–structure interaction, which could affect erosion resistance. The authors recommend using 3D CFD where practical and investigating these omitted effects in future work.

Keywords

seabed trenches

mooring chains

suction-pile anchors

West Africa

computational fluid dynamics

shear stress

seabed erosion

anchor capacity

Gulf of Guinea clay

trench equilibrium