A two-phase incompressible-compressible (water-Air) smoothed particle hydrodynamics (ICSPH) method applied to focused wave slam on decks

The accurate prediction of extreme wave forces and slam on offshore decks and platforms remains an important practical problem in offshore engineering. A particular challenge is the accurate prediction of local impact pressures. These pressures are particularly sensitive to local flow conditions and are characteristically high in magnitude and of very short duration. The two phase incompressible-compressible smoothed particle hydrodynamics (ICSPH) method (Lind et al., Applied Ocean Research, 49:57-71, 2015) has demonstrated capability in this area in offering favourable predictions to the extremely large and highly transient slam pressures observed during high-speed free-falling plate impacts on wave crests. In this paper, ICSPH is compared to new experimental data measuring impact pressures due to focused wave slam on a fixed horizontal deck. Complex flow behaviour is observed on the deck underside with wave breaking and air-trapping playing a role. For the studied wave profile, ICSPH pressure predictions are in good agreement with experimental measurements with near-independence in particle resolution demonstrated at key pressure transducers. Numerical studies undertaken with and without the presence of the air phase highlight its role in providing physical impact pressure predictions. Importantly, it is demonstrated that air does not necessarily reduce but can, in fact, increase impact pressures through modification of the local wave profile. With further model refinement and computational acceleration, ICSPH may soon be used to provide reliable quantitative predictions for the design of realistic 3-D offshore structures with air-trapping.