In an analysis of floating body’s motion for ocean engineering, potential theory is known as a conservative method. This can be a relatively right approach since viscous effect of a single body is insignificant so that the results yield accuracy in global motion analysis. Moreover, the potential theory also requires less computing time compared to other methods such as model experiments and CFD (Computational Fluid Dynamics). However, complicated situations such as the structures with moonpool, side-by-side moored vessels, TLP, and semi-submersible with deep draft need to be evaluated by more accurate methods other than potential theory in order to overcome inaccurate solutions which can be occurred by viscous effects.
For side-by-side moored vessels, it clearly needs to be evaluated with accurate analysis because of viscous effect in areas of the gap between two vessels. A complex hydrodynamic interaction between two vessels can cause shielding effects which represents different motion aspects for both weather side vessel and shield side vessel. Another hydrodynamic effects caused by the gap is a gap-resonance problem that is an exaggerated motion when solved with linear potential theory.
In this study, CFD simulations for a single vessel and side-by-side vessels analysis are performed. The CFD codes are formulated for solving a Navier-Stokes using Finite Volume Method (FVM) using open source CFD code, OpenFOAM. Taking advantages of viscous damping and vortex shedding, three-dimensional numerical simulations for 6 DOF motions of a single vessel and side-by-side vessels are carried out. These conditions are considered for the simulation with external linear stiffness to prevent drift away of the vessels. The simulation results for a single vessel are compared with linear potential theory and model test results in order to validate the results. And the simulation results for side-by-side vessels are compared with linear potential theory in order to show that CFD code can be used effectively to predict the motions of side-by-side vessels in regular waves.