Shock Pressures Caused by Waves Breaking Against Coastal Structures

摘要

Shock pressures of high intensity and short duration may occur during breaking of waves on coastal structures, slamming of ships, landing of seaplanes, and water entry of naval projectiles with flat nose. The phenomenon of shock pressures resulting from the impact between a solid and a liquid can better be described as a water hammer phenomenon wherein elasticity of the solid and compressibility of the liquid are the governing factors. The water hammer theory predicts the extreme values of shock pressures since it neglects the effect of air that might be entrapped between the solid and the liquid at moment of impact. Analytical formulations of shock pressures as a water hammer phenomenon and as the compression of a thin layer of air entrapped between the solid and the liquid at moment of impact are presented herein. Tests were conducted by dropping a steel, aluminum, or plastic plate whose edge was hinged at the water surface into a steel tank that was partially filled with water. Shock pressures were measured at two locations by means of strain gage and piezoelectric type pressure cells mounted in the plate with special adaptors. The ratio between recorded and theoretical pressures when treated statistically was found to fit the Poisson distribution well. (Author)