Experimental investigation on dynamic responses of FLNG connection system during side-by-side offloading operation

Abstract

This paper presents an experimental investigation on dynamic responses of the connection system in the FLNG (Floating Liquefied Natural Gas) system during side-by-side offloading operations. A typical side-by-side connection system for an FLNG and LNG (Liquefied Natural Gas) carrier that includes 16 hawsers and 6 fenders is adopted. Three typical irregular wave cases are used in the model test. Relationships between relative vessel motion and the load born by the connection system are obtained, and features of dynamic connection system responses are summarized based on the analysis results. The results show that hawsers and fenders at different locations are sensitive to different motion patterns; loads on connection systems have distinct dynamic properties, and snap loading crucial to the safety of offloading processes can be induced. Moreover, for partially filled conditions, sloshing effects on vessel motion and on the connection system are examined. FLNG and LNGC are subjected to large low frequency responses in side-by-side configurations due to hydrodynamic interactions and sloshing effects. Furthermore, sensitivity analyses of the connection system relative to wave amplitudes and directions are conducted. According to our sensitivity studies, high wave amplitudes can excite pronounced relative motions and large loads on the connection system; heading and oblique waves significantly affect spring hawsers in mid-ship areas and breast hawsers in bow and stern areas; and positive sheltering effects can be obtained when FLNG occupies the weather side.