Wave impact load occurring in a liquid storage tank during a sloshing motion is numerically simulated. Due to a violent sloshing, an excessive impact load can cause a critical damage to the tank structure. Recently this type of the accidents are reported and the problem becomes an important research topic in LNG (Liquefied Natural Gas) Tanker and FPSO (Floating Production Storage Offloading) design. To predict the sloshing impact load, Morison’s formula could be used for a practical reason. But using the Morison formula may provide directly an inaccurate estimation for the impact load because this formula is based on the linear model in the present nonlinear dominating phenomena. In this study, the wave impact load on the structure is obtained by imposing the exact nonlinear free surface conditions numerically and compared with that predicted by Morison’s formula. As a numerical method, a three-dimensional free surface flow in a tank is formulated in the scope of potential flow theory with the nonlinear free-surface conditions. A finite-element method based on Hamilton’s principle is employed as a numerical scheme. The problem is treated as an initial-value problem. The nonlinear problem is numerically solved through an iterative method at each time step.

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