This paper deals with the estimation of hydrodynamic forces acting on tube bundles in a circular tank by sloshing. The sloshing phenomena are calculated by the Boundary Element Method (BEM). The hydrodynamic forces acting on the tubes are integrated dynamic fluid pressures around the tubes. When there is one and four tubes in the tank, the displacements of the fluid surface by this analysis agree with the experimental results. This analysis is a vary effective method. By analysis, as the tubes increase, the hydrodynamic force acting on the tubes derease. The hydrodynamic force is the greatest on the fluid surface and decreases suddenly at the bottom of the tank.
