Dynamic Ship Simulations

The simulation of floating vessels exposed to seaway is based on an implicit coupling between the dynamic rigid body motion (6-DOF) and the RANS-based fluid solver FreSCo+.

The approach becomes challenging when the vessel is exposed to (unsteady) propagating wave fields due to the non-linear interaction between the propagating wave field of the approach flow and the diffraction field. The interacting waves travel towards the domain boundaries and are usually incompatible with the imposed boundary condition. The challenges are associated to cumbersome grid requirements (aka. as "numerical beach"), which restrain the flexibility and enhance the computational costs. The requirements follow from the aim to accurately predict the wave propagation towards the floating object and concurrently supress wave reflections at the outlet boundary. The situation becomes more difficult when the direction of the propagating wave field dynamically changes.



To overcome these difficulties, a viscous/inviscid-coupling approach is applied. Therin, the viscous RANS method is implicitly forced to comply with a prescribed inviscid solution towards the far-field boundaries. Employing consistent boundary conditions at all far-field boundaries, the method facilitates the use of small domains and allows to investigate the behaviour of floating objects exposed to time-variable wave-field directions.


The example included refers to the Kriso container ship in head waves (Re = 6.5 106, Fn = 0.26). The compact domain length spans about 2 ship lengths and agrees with the wave length of the approach flow. The width of the doamain is about one ship length. It is seen that the wave field develops correct in conjunction with the employed coupling strategy and no significant disturbances are observed along the boundaries.