Numerical simulations of zigzag maneuver of free running ship in waves by RANS-Overset grid method

The twin-screw fully appended ONR Tumblehome ship model is numerically studied for the standard 10/10 zigzag maneuver. Simulations are carried out using naoe-FOAM-SJTU, a CFD solver developed on open source platform, OpenFOAM. Overset grid technique and 6DoF module with a hierarchy of bodies are applied to solve the motions of the free-running ship with twin rotating propellers and turning rudders. The self-propulsion point is using the constant value obtained by the previous CFD simulation of the twin-screw self-propelled ship in calm water. Simulations of the standard zigzag maneuver in both calm water and different incident waves are considered. The present CFD results agree well with the available experimental measurement for both ship motions and the main parameters of zigzag maneuver. This indicates that the direct simulations for ship zigzag maneuver in waves utilizing present methods are feasible and reliable. In addition, it is found that unsteady effects of the hydrodynamic loads on the free-running ship during zigzag maneuver in waves is noticeable. Furthermore, flow visualizations in different incident waves are presented so as to give a better understanding of the wave influences on free-running ship maneuver.