CFD simulations of free running ship under course keeping control

The free running ONR Tumblehome ship model is numerically studied under course keeping control. 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 handle the free running ship motions with twin actual rotating propellers and moving rudders. Self-propulsion computation in calm water is first performed to achieve the approach speed (U=1.11 m/s, Fr=0.2) using a proportional-integral controller. The obtained self-propulsion model point is then used for the free running computation under course keeping control in waves, where three regular waves are considered: head wave, bow quartering wave and beam wave. To fulfil the course keeping demand, a new course keeping control module is developed using feedback controller based on the CFD solver naoe-FOAM-SJTU. The predicted results are compared with the benchmark data in Tokyo 2015 CFD Workshop in ship hydrodynamics. Good agreements are achieved for both self-propulsion and course keeping tests, which shows that free running ship simulations especially in waves using the CFD approach coupled with newly developed course keeping module is feasible and reliable. Furthermore, flow visualizations are also presented to explain the hydrodynamic performance of ship hull-propeller-rudder interaction in waves under course keeping conditions.