集中系モデルによるスロッシング現象の解析

Abstract

Sloshing phenomena in containers under earthquakes often cause serious accidents. In case of an oil tank with floating roof, the sloshing phenomenon and the structural vibration should be treated as the coupled problem. Lagrangian fluid finite element model has been used for the analysis of the coupled problem because the compatibility and the equilibrium condition are automatically satisfied at the boundary between the fluid and the structure. However, the degree of freedom of the Lagrangian model becomes large because the fluid particles in the Lagrangian model move vertically and horizontally. In addition, the Lagrangian model has physically-meaningless spurious modes caused by the redundancy of the degree of freedom. In this paper, to establish the efficient and accurate analytical model for the coupled problem, liquid in a rectangular container is modeled as the nonlinear concentrated mass model. The model consists of masses, non-linear connecting springs and connecting dumpers. Some masses move horizontally, the others move vertically. The horizontally movable masses are governed by the equations of motion. The vertical displacements of masses are determined from the displacements of the horizontally movable masses based on the incompressibility of the liquid. The characteristics of the connecting springs are derived from the static and dynamic pressures of the liquid. The degree of freedom of the proposed model is smaller than that of Lagrangian model and the spurious modes does not occur in the proposed model. To confirm the validity of the proposed model, the time history response of the model is compared with experimental result.