On Simulating Variability of Sloshing Loads in LNG Tanks

Local pressure measurements during liquid impacts in LNG tanks show a large variability, due to the free-surface roughness and the liquid fragmentation resulting from free-surface instabilities initiated by the gas escaping redfrom the closing gas pocket. It also makes the experimental discrimination of the effect of any multiphase parameter (density ratio, compressibility, phase transition) on impact loads more complex. The main challenges are (i) to capture both experimentally and numerically the development of the free surface instabilities; and (ii) to quantify their effect on the variability of local pressures. Numerical modeling of the initiation of the free surface instabilities requires an accurate VOF-variant. Surface tension forces are modelled via a Young-Laplace jump condition, where the interface curvature is computed using a local height function. A parabolic interface reconstruction is required to ensure convergence of the curvature in space and time. Advection is performed with a modified EMPFA method. Spurious velocities are avoided by careful treatment of the (almost) discontinuities of the flow field. The model will be demonstrated on various simulations of breaking waves.