Evaluation of Forces on Bilge Keels in Oscillating Flow using CFD

The roll motion of a ship or a FPSO can be effectively mitigated by attaching keels along the bilges. Proper structural design of the bilge keels requires good estimates of the hydrodynamic loads acting on them. However, in simplified applications, Morison's equation may be adopted with constant hydrodynamic coefficients for the force evaluation. Reported bilge keel failures suggest that the understanding of the total loading on the bilge keel is incomplete. In this paper, direct CFD simulations are carried out for bilge keels with added structural members in regular oscillating, prismatic flows. The hydrodynamic loads from CFD are shown to be significantly larger than those used in conventional design approaches. Sensitivity studies are also conducted here to investigate the dependence of the hydrodynamic loads on different factors including bilge keel configurations and FPSO roll velocities.