Aeration effects on water-structure impacts: Part 1. drop plate impacts

Current offshore engineering design codes for wave loading are based on pure water, but wave impacts often involve aerated flow, either as a result of air entrapment as the wave overturns or due to impact with a wave that is already broken. Therefore, it is necessary to develop a new understanding of how design codes should incorporate water-air mixture for wave impact. This experimental study investigates aeration effects on wave impacts by means of slamming impacts of a square flat plate onto a pure and aerated water surface, with zero degree dead-rise angle. The (low) aeration level between 0% and 1.6% was applied and the drop velocity varied from about 1 m/s to 7 m/s. There was a significant reduction in the peak impact loads (both pressure and force) for impact in aerated water compared to that in pure water. There was also a significant reduction in the first phase of the pressure and force impulse for aerated water. The variation in impulsive loadings is less sensitive than peak loadings for impacts. The implication for design is that maximum instantaneous loads may be conservative in the presence of aerated water. •Aeration effects on wave impacts have been experimentally investigated by means of slamming impacts of a square flat rigid plate onto a pure and aerated water surface with zero degree deadrise angle.•Spatial distributions of impact pressure on the square plate have been characterised under different impact velocities.•Significant reduction in the peak impact loads (both pressure and force) were found for slamming impact in aerated water compared to that in pure water.•Significant reduction was observed in the first phase of the pressure and force impulse for aerated water.•Variation of impulsive loadings is less sensitive than the peak loadings for slamming impacts.•Implications for design are that maximum instantaneous loads may be conservative in the presence of aerated water for offshore structure design.