Sloshing effects accounting for dynamic coupling between vessel and tank liquid motion

Sloshing, a violent behaviour of liquid contents in tanks submitted to the forced vessels' motion on the sea represents one of the major considerations in LNG vessels design over several past decades. State of the art of sloshing analysis relies on small-scale sloshing model tests supported by extensive developments of CFD computation techniques, commonly studying one isolated tank submitted to the forced motion without their mutual interaction. In reality, wave-induced response of the vessel carrying liquid cargo is affected by internal liquid motion, and consequently, tank liquid flow is altered by the vessel motion in return. An efficient numerical model for dynamic coupling between motions exerted by tank liquid (sloshing) and rigid body motions of the vessel (seakeeping) was developed in Bureau Veritas, formulated under the assumptions of linear potential theory in frequency domain. As already experienced with anti-rolling tanks, strong coupling effect is perceived on the first order transverse motions. However, consequences of coupled motions on sloshing loads have not been explored yet. This paper presents comparative analysis of sloshing effects induced by coupled and non-coupled vessel motion, introduced as the excitation to 6 d.o.f. small-scale model test rig. Possible risk of coupled effects is demonstrated on the example of standard size of LNG carrier operating with partly filled cargo tanks.