ORCA Offshore carried out lift dynamic motion analysis using the software tool MOSES from Ultramarine. One major challenge for this project was the limited bottom clearance of only 0.6 m. Furthermore, the seabed is formed from very soft mud which will have an unknown effect on the behavior of the vessel. The standard diffraction calculation as used in MOSES cannot take this into account.
To verify the effect of the small keel clearance and the soft mud layer, several CFD (Computational Fluid Dynamics) simulations have been carried out. With a CFD simulation it is possible to calculate the motions of a rigid body in a dynamic environment composed of air, water and mud. The CFD simulations have been executed for several regular wave periods and calculate the Heave and Pitch Motion Response of the vessel, as well as the pressure on the skeg. A CFD simulation has also been used to calculate the Pitch Free Decay Period of the vessel in this specific environment.
A CFD simulation provides insight in the spatial distribution of fluid flows and its interaction with its environment. The simulation takes into account the fundamental physical phenomena involved.