Resonant frequencies in an elevated spherical container partially filled with water: FEM and measurement

Abstract

In this paper, a numerical-experimental study of the overall dynamical response of elevated spherical tanks subjectedto horizontal base motion is presented. The main objective is to gain insight in the physical response of this particularstructural typology widely used in the petrochemical industry as liquefied petroleum gas (LPG) containers. In order toidentify the natural frequencies of the modes that mainly contribute to the response, experimental free vibration tests onan elevated spherical tank model for different liquid levels were carried out. Next, a numerical model that takes intoaccount the coupling between fluid and structure was developed and validated against the experimental results. A verygood agreement between experimental and numerical results was obtained. The results obtained show the influence ofliquid levels on natural frequencies and indicate that the sloshing has a significant effect on the dynamical characteristicsof the analyzed system. In order to obtain a good representation of the overall dynamical behaviour of the system bymeans of a simplified lumped mass model, a minimum of three masses is suggested. Finally, appropriate names of thesethree masses are proposed in the present paper.