Head-waves parametric rolling of surface combatant

Complementary CFD, towing tank EFD, and nonlinear dynamics approach study of parametric roll for
the ONR Tumblehome surface combatant both with and without bilge keels is presented. The
investigations without bilge keels include a wide range of conditions. CFD closely agrees with EFD for
resistance, sinkage, and trim except for Fr40.5 which may be due to free surface and/or turbulence
modeling. CFD shows fairly close agreement with EFD for forward-speed roll decay in calm water,
although damping is over/under predicted for largest/smaller GM. Most importantly CFD shows
remarkably close agreement with EFD for forward-speed parametric roll in head waves for GM¼0.038
and 0.033m, although CFD predicts larger instability zones at high and low Fr, respectively. The CFD and
EFD results are analyzed with consideration ship motion theory and compared with Mathieu equation
and nonlinear dynamics approaches. Nonlinear dynamics approaches are in qualitative agreement with
CFD and EFD. The CFD and nonlinear dynamics approach results were blind in that the actual EFD radius
of gyration kxx was not known a priori.