Complementary URANS CFD and EFD for Validation Extreme Motions Predictions

Results are presented from a complementary URANS CFD and towing tank EFD study of extreme ship motions for the ONR Tumblehome. Experimental and CFD conditions include initial with bilge keels (beam and head waves) and subsequent without bilge keels (head waves) investigations. Head waves parametric roll conditions are for 3DOF motions (coupled heave-roll-pitch) and beam waves resonant excitation conditions are for 2DOF motions (coupled heave-roll). CFD shows good agreement with EFD for the ship with bilge keels in both beam and head waves. EFD tests and CFD simulations for head wave do not exhibit parametric roll for the model with bilge keels due to excessive roll damping. Based on Mathieu equation theory, appropriate conditions for head wave CFD simulations without bilge keels are carried out. Parametric roll is predicted for a range of Froude numbers; and the effects of increased wave steepness, drift angle, and smaller/larger GM are studied. Head waves towing tank EFD tests without bilge keels are ongoing and preliminary results are shown.