The Effect of Boundary Conditions and Longitudinally Varying Stiffness on the Oblique Impact of a Flexible Plate on a Quiescent Water Surface

The oblique impact of rectangular aluminum plates (length 108 cm and width 41 cm) on a quiescent water surface are studied experimentally. The plates are mounted at a 10 degree pitch angle (leading edge up) via a 6-component dynamometer frame to a translational carriage capable of both horizontal and vertical motion. Previous experiments were performed with three uniform plates (thicknesses of 6.61, 8.27, and 13.22 mm) mounted via pinned supports at the leading and trailing edges. It was found that thinner (more flexible) plates experience a lower net force during most of the impact, but a larger, later, and sharper peak force at the end of the impact. These effects are attributed to the interaction between the plate’s deflection and the flow, which causes the local pitch angle at the instantaneous location of the spray root to be small. The spray root is a free surface feature that moves across the plate surface and is a large source of hydrodynamic pressure. In the present experiments, two approaches to prevent small local pitch angles and reduce the peak force are explored. In the first, the plate is clamped at the leading edge to maintain the local pitch angle at the prescribed value near the end of the impact and uses a thinner uniform plate (4.81 mm) to maintain flexibility. In the second, the pinned supports are maintained but the plate thickness varies (from 6.29 mm at the trailing edge to 12.72 mm at the leading edge).