In general, LNG carriers for ocean going ship with membrane cargo containment system have acceptable tank filling level in the cargo tanks of below 10% and over 70% of tank height. The main reason of the filling restrictions is due to high sloshing impact pressures at low filling levels, which is around 30% filling level. In the case of LNG-FPSOs at specific site operation condition, it is not possible to restrict filling levels of the LNG cargo tank due to production and offloading with LNG carrier. The practical application for partial filling operation of LNG-FPSOs is to suggest the operational envelop. The method restricts the wave heights and headings during the partial filling operation. The other way is to increase LNG cargo tank numbers or change the shape and dimension of cargo tank to reduce the sloshing impact pressures at low filling levels. In the present study, the numerical sloshing assessments for LNGFPSOs are carried out to find the possibility of partial filling operation of LNG cargo tank. The various cargo filling levels and coupled ship motion interaction effects due to sloshing are also considered.
This report is concerned with a practical sloshing load assessment of LNG-FPSOs for partial filling operations. The procedure of the sloshing load assessment consists of two stages. The first stage is the estimation of global ship motions in wave considering partial filling tank liquid motion. The second stage is the sloshing calculation using SHI-SLOSH CFD code (Ha et al, 2002 and Park et al, 2006) under a selected sea states. In general, sloshing motions inside tanks have not been included in the conventional seakeeping analysis due to their complexity. In most seakeeping computations, the liquid inside the tanks has been generally treated as a rigid mass.
