In an analysis of floating body's motion for ocean engineering, potential theory is known as a conservative method. However, This holds that viscous effects are neglected, which can deliver serious problems when predicting vessel's roll motions as well as complicated configurations such as the structures with moon pool, side-by-side moored vessels, 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.

In this study, CFD simulation for a single vessel is performed as an initial study for motion analysis of side by side vessels.


In this study, we performed a FVM numerical analysis with respect to a six-degree of freedom motion of a floating body by solving the non-steady state Navier-Stokes equation. For this, we employed the open source codes, OpenFOAM C++ libraries. Taking advantages of viscous damping and vortex shedding, three-dimensional numerical simulations for 6 DOF motions of a single vessel are carried out. Two wave directions, head sea and beam sea, are considered for the simulation with external linear stiffness to prevent drift away of the vessel. The results from developed analysis method were compared with linear potential theory and model test results for validation.

Numerical Method
Coordinate systems

Euler's angle is generally used to describe the dynamic behavior of a solid body. The Euler's angle with a single rotational axis shows a "gimbal lock" where two axes are overlapped to be viewed as one single axis, and thus the rotation of two axes appears as the same rotation. In this study, to prevent gimbal lock and to avoid the effect of the order of the coordinate system rotation, quaternion was used as a technique of expressing the coordinate systems.

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