The motions and drift forces of side-by-side (SbS) moored FSRU and LNGC including sloshing effect are studied by experiments. FSRU and LNGC have LNG cargo tanks and sloshing of LNG can affect the motions and drift forces of structures due to the coupling between sloshing and floating body motion. The effect of coupling can vary by filling level of LNG and the effect of filling level is investigated. The coupling effect is most strong at low filling level in beam sea. The effect of gap flow and sloshing is also investigated in the present study as well. The horizontal motions and drift forces are analyzed and it is confirmed that the gap flow is affected by the sloshing. The sway motion, sway drift force and gap flow are influenced by the sloshing in head sea although the sloshing is weak.
Sloshing influences the motions and mooring loads of FSRU and LNGC. When FSRU and LNGC is moored side-by-side, the internal sloshing can also interact with the sloshing flow in the gap between FSRU and LNGC. The motions and drift forces in SbS moored vessels are important design factors and must be considered for heading control, mooring design, loading arm operation and berthing. The studies of the coupling effect of sloshing on the motions are well known. Representative studies are Gaillarde (2004), Kim (2007), Kim (2008), Lee (2008), and Lee (2009). The gap flow problem is difficult to predict, especially gap flow height and drift forces. Hong (2010) and Bunnik (2009) showed new methods for modeling of gap flow problem. But the study of SbS moored two bodies including the sloshing has not been reported yet. The gap flow and sloshing of LNG can interact of course and this interaction may affect the characteristics of motion and drift force.