This paper presents a numerical study on the structure optimization of a full-sized floating liquefied natural gas (FLNG) membrane tank. When floating with partially filled liquid, impact pressure on boundaries plays an important role in the sloshing membrane tank. Modification of bottom structure can lead to various pressure distributions on the tank bottom and sidewalls. The optimization is studied by carrying out the numerical simulations and particularly focusing on the structure of sloped-bottom. The applied CFD package, FLOW-3D 10.1, solves the Navier-Stokes equations with the standard k-ε turbulence model and Volume-of-Fluid method to describe the free surface movement. The numerical result is validated against the experimental data and numerical result from the Smoothed Particle Hydrodynamics method. Liquid behavior is investigated in four different tanks. A modified method using average value of fluid peak depth is applied to locate the natural sloshing frequency. The greatest local pressure was approximately 65 KPa near the intersection of slope and bottom. The comparison of peak pressure indicates that tank with 15% width sloped-bottom has smaller affected area of high pressure and lowest value of peak pressures, which is the optimized sloped-bottom tank in pressure performance. The outcomes from the numerical simulation are expected to be a reference data for the design of FLNG cargo containment system.

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