Investigation of impact of rigid and elastic bodies with water

Abstract : Impact tests of rigid flat-bottom models indicated that the maximum impact pressure is nowhere near the theoretical infinitely large hydrodynamic pressure nor near the theoretical acoustic pressure. The cushioning effect of the compressible air trapped between the impact body and the water surface reduces the maximum impact pressure to about one-tenth of the acoustic pressure. However, the nature of the trapped air phenomenon is not very stable. Much more air was trapped for the impact of a flat bottom and a 1-deg wedge than for a wedge with dead rise angles of 3 deg or higher. Tests of elastic models verified the fact that the pressure generated by the impact is affected by the vibratory movement of the impact surface and that it can be separated into rigid body impact pressure and interacting pressure. This dynamic interaction is closely related to the hydrodynamic phenomenon rather than to the acoustic phenomenon. In summary, the present study demonstrates that for the impact of rigid and elastic bodies, water can be treated as an incompressible fluid regardless of the size of the dead rise angle, trapped air must be taken into consideration for small dead rise angles, and the structural response to impact can be treated as the impact of a deformable body on an incompressible fluid, with or without trapped air.