Hydroelastic effects on hydrodynamic loads on an LNG pump tower structure

Hydrodynamic loads acting on a pump tower inside a liquefied natural gas (LNG) tank were numerically investigated by considering the hydroelasticity of the tower's flexible structural components. Nine tank motion scenarios were considered, including regular motions of the tank in sway and roll and irregular motions likely to occur for an LNG carrier at zero speed in a long-crested beam seaway. The investigated filling level was 50% with water and air as fluids. Two-way fluid-structure interaction (FSI) simulations coupled the finite element method (FEM), idealizing the tower structure, with the finite volume method (FVM), modeling the flow of water inside the tank. Unsteady Reynolds-averaged Navier-Stokes equations (URANS), using the volume of fluid (VoF) method, modeled the sloshing-induced free surface flow. Hydrodynamic loads were calculated on the tower's emergency pipe and on its two discharge pipes with FSI simulations and compared to loads obtained from calculations with Morison's equation. Generally, forces based on Morison's equation compared favorably to URANS simulated forces acting on the tower's main members. The tower's response loads were filtered to quantify the influence of its hydroelasticity, which was notable for regular and minor for irregular tank motions. Prevailing hydroelastic effects demonstrated the necessity of FSI simulations.