Study on extreme roll event with capsizing induced by pure loss of stability for the free-running ONR Tumblehome

International Maritime Organization (IMO) has stated that the direct assessment for the pure loss of stability, one of the typical stability failure modes, is necessary for ship designers and under development currently. In this study, extreme roll motions with large amplitudes, induced by the pure loss of stability, are predicted for a benchmark combatant ONR Tumblehome running in stern quartering waves by the computational fluid dynamics (CFD) simulations. An unsteady Reynolds-averaged Navier–Stokes (RANS) solver coupled with a dynamic overset grid approach is used to predict six degree of freedom (DOF) motions. The discretized propeller model is applied to the free-running model, along with a course keeping controller. Different speed conditions are considered for the ship to investigate the instability zone where the pure loss of stability occurs and the CFD results for the roll amplitude are compared with the experimental data, with an average difference less than 3%. In addition, it is observed that ship capsizing occurs coupled with a rapid increase of yaw angle, which is consistent with the phenomenon in the existed model tests. Overall, it indicates that this viscous simulation model is capable for the prediction of the extreme roll as well as the capsizing.