Application of Immersed Boundary Method in Naval Hydrodynamics in foam-extend

The Immersed Boundary Method (IBM) recently developed in foam-extend is applied to various problems in the field of naval hydrodynamics. The IBM has recently been re-written in the foam-extend, becoming more robust and accurate.

The method is first validated on calm water resistance of a ONR vessel, where good comparison is achieved with the body fitted approach. It is demonstrated that intricate features of the geometry can be represented such as bilge keels. Comparison of the wave field and force shows that reasonable accuracy can be expected.

Even though the method is validation on calm water resistance, the actual purpose of the method is to provide an efficient tool for modelling dynamic appendages such as rudders, propellers or stabilizer fins. In this scenario, the hull of the vessel is modeled using a body fitted approach, since high accuracy of viscous effects and forces is required. For pressure-dominated devices such as rudders, the method provides sufficient accuracy, while at the same time allowing efficient and easy modelling of relative motion of appendages with respect to the vessel.

The capability of the method to model such appendages is demonstrated on two cases. In both cases the IBM is used to model two rudders located behind the vessel behind propellers modeled using the actuator disc approach. The first simulation is in calm water, which is used to demonstrate the effectiveness of the PID rudder controller, by initializing a simulation with a ship sailing with a side-ways distance to the prescribed straight trajectory. The PID controllers needs to bring the ship to sail along the straight trajectory. In the second simulation, vessel sails in irregular, stern-quartering waves where the rudders need to keep a steady coarse.