Change in Wave Pressure at the Front and Rear Walls According to the Porosity of Perforated Caisson Breakwater

Abstract

This paper presents experimental results on wave pressures acting on the front and rear walls of a perforated caisson breakwater. Measurement of wave pressures was made first for a non-porous caisson in order to compare and verify the experimental results with the well-known Goda’s pressure formula. Then, the experiment was carried out for a porous caisson having wave chamber slab, by varying the front wall porosity. In general, higher pressures were measured along the both vertical walls with respect to the front wall porosity. Magnitudes of wave force based on integration of the measured wave pressures also showed similar trend, especially for steeper waves. The integrated wave forces were significantly greater than that based on Takahashi’s pressure formula, probably due to geometrical feature of the caisson having the wave chamber slab, which made favourable condition of gentle air compression and subsequent burst phenomenon inside the chamber. Further experimental verification by direct measurement of wave force is required before using the above finding in the practical design of perforated caisson breakwaters.imental results with the well-known Goda’s pressure formula. Then, the experiment was carried out for a porous caisson having wave chamber slab, by varying the front wall porosity. In general, higher pressures were measured along the both vertical walls with respect to the front wall porosity. Magnitudes of wave force based on integration of the measured wave pressures also showed similar trend, especially for steeper waves. The integrated wave forces were significantly greater than that based on Takahashi’s pressure formula, probably due to geometrical feature of the caisson having the wave chamber slab, which made favourable condition of gentle air compression and subsequent burst phenomenon inside the chamber. Further experimental verification by direct measurement of wave force is required before using the above finding in the practical design of perforated caisson breakwaters.