Effective Mass of Fluid for Rocking Motion of Flat-Bottom Cylindrical Tanks

In analyzing the rocking motion of the flat-bottom cylindrical tanks subjected to severe earthquakes, the effective mass of fluid for the rocking motion and its moment inertia around the pivoting bottom edge of the tank would be indispensable dynamical properties, because they couples the fluid-shell interaction motion, the so-called bulging motion, with the rocking motion. This paper quantifies them based on the equilibrium of the fluid pressure and inertia force accompanying the angular acceleration acting on the pivoting bottom edge of the tank. Employing a general mathematical solution for the fluid pressure that can calculate either fully or partially uplifted tank bottom, this paper presents mathematical formulae of the effective mass of fluid for the rocking motion and its moment inertia. These quantities are given by an explicit function of dimensional variables of the tank but with Fourier series. For designer’s convenience, the effective moment inertia and effective mass of fluid for the rocking motion and its center of gravity from the pivoting bottom edge are normalized accordingly and are depicted on diagrams.