Flat plate pressure impact on a still water surface: The effect of surrounding ambient pressure and plate size

Abstract

The study of the impact between a rigid structure and water has raised the interest of many researchers in these recent years. This problem is relevant to various engineering applications, and particularly in the nautical environment (renewable energy, marine applications...). The present paper details an experimental investigation of rigid circular plates impacts into pure water. The analyses are based on impact pressure temporal signals, pressure impulses and frequency analysis recorded while the plates were impinging the still water surface. The measurement campaigns were carried out at the University Le Havre Normandy’s LOMC laboratory, in a recently developed experimental facility. In the previous experimental and numerical studies, it was observed that the magnitude of the peak slamming pressure is reduced if compared to the theoretical model predicted by von Karman (1929). Similar observations were made here and the decrease was partly attributed to the cushion effect resulting from the presence of an entrapped air layer between the rigid plate and the water free surface. This work aims to study the influence of the cushion effect on the impact pressure by using four rigid circular plates with different diameters in order to modify the volume of the air layer. Initially, the measurements were carried out for an ambient pressure equal to the atmospheric pressure. In a second part of the study, the same measurements were performed for two lower ambient pressures (about 75% and 50% of the atmospheric pressure) in order to minimise the cushion effect. And finally, a frequency analysis is presented with comparisons to theoretical results of Minnaert (1933) in order to correlate the air layer size to the pressure oscillation characteristics. The obtained results were compared with previous experimental and theoretical studies for low impact velocities (V≤1.2 m/s).