The offshore exploration of gas requires the use of new platforms design called FLNG (Floating Liquefied Natural Gas). Nowadays just a few number of FLNG are in advanced stages of design or under construction. This type of vessel requires large tanks to storage the liquefied gas and in some cases the movement of the liquid inside the tanks can modify the vessel behavior in waves. The work objective is to obtain the influence of liquid cargo in the floating vessels motions.

An experimental setup was proposed to investigate this influence. A FLNG model was tested for two configurations: with fixed dry cargo and with liquid cargo. For the latter, the model was equipped with tanks which were filled with water in three different levels. In total six different tests were carried out in the Hydrodynamic Calibrator from University of Sao Paulo, a tank with 14 m long, 14 m wide and 4 m depth equipped with 144 flaps capable of generating waves with different angles of incidence. The vessel motion was obtained for the six degree of freedom using an optical system. Furthermore, numerical models were made in WAMIT for both configurations with and without free surface effect due the liquid inside tanks.

Results presented significant differences in the RAO curves. Basically, amplification in surge and sway motions was observed and changes in the roll natural period were obtained, both due the presence of liquid cargo. Furthermore, some limitations were obtained for numerical model mainly in cases with tanks filled at low levels. In these cases, the viscous forces presented significant influence and some effects as breaking waves (sloshing) inside tanks were observed. Both breaking waves and viscous forces are not considered in WAMIT model, once it uses the potential linear wave theory. Discussions are concerned in the comparison of motions obtained for the two tested configurations and in the limitations and applications of numerical model.

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