Four different breaking wave impacts against a flat rigid wall have been numerically simulated in 2D at two different scales, scale 1 and scale 1:6, with Froude-similar inflow conditions but keeping the same fluids (water and air) at both scales. Sufficiently refined discretizations have been used in order to adequately capture the impulsive loads at wall. The simulations have been performed with SPH-Flow, a CFD software, developed by HydrOcean and Ecole Centrale Nantes (ECN), which solves the compressible Euler equations for liquid and gas thanks to a Smoothed Particle Hydrodynamics (SPH) method. The four waves have been selected in order to generate wave shapes just before impact representative of those leading to the largest loads during 2D sloshing model tests for low filling levels or during wave impact tests in flumes. A flip-through impact and three gas-pocket impacts with different sizes of the gas cavity have been chosen.
Results obtained at scale 1 have been presented in Part 1 of this work (Guilcher et al., 2014). Results at scale 1:6 are presented in this Part 2, mainly by pressure maps P(y, t), where y is the vertical location of any point at wall and t is the time, and by time-traces of the different components of the energy, in the same way as for results at scale 1 in order to enable an easy comparison. Results at both scales are compared after scaling the results from scale 1:6 as though the flows were in complete similarity. Inconsistencies are shown and explained by unscaled gas and liquid compressibility.
Context
The context of this study is the sloshing assessment of LNG membrane tanks on floating structures based on sloshing model tests. Those tests are usually performed with model tanks at scale 1:λ (λ = 40) filled with water and a mixture of gases chosen in order to have the same gas-to-liquid density ratio as on board ships with Natural Gas (NG) and Liquefied Natural Gas (LNG). Irregular tank motions, calculated at full scale by a sea-keeping software, are imposed to the model tank by a six-degree-of-freedom hexapod after having been down-scaled according to Froude similarity. This down-scaling simply means that amplitudes are divided by λ and times are divided by (equation).
