In seismic wave that includes long wave length, oil storage tanks have been badly damaged to floating roof unit at rare intervals. We consider fluid structure interaction problem (FSI) in which content liquid of the tank have sloshing vibration with the floating roof during the ground motion. Content liquid is followed by Navier-Stokes Fluid in general points of view. However the sloshing problem can be efficiently and practically solved using linear potential-based formulation with finite element method. This paper shows the efficiency of this formulation in comparison with experiment test result and at same time, is raising some points that are not adapted with the real phenomenon.
