The impact of a flexible plate on a calm water surface: the effect of pitch and submergence time*

The oblique impact of an elastic rectangular plate (length 108 cm, width 41 cm and thickness 0.66 cm) on a quiescent water surface is studied experimentally. The plate is installed via pinned supports to a dynamometer system, which is connected to a carriage capable of combined horizontal and vertical velocity components, U and V, respectively. The two short edges of the plate are held horizontal, while the angle between the plate's two long edges and the still water surface (called the pitch angle, alpha), U and V are varied. These variables are chosen to create a set of experimental conditions that maintain a constant plate stiffness ratio in the regime of strong fluid-structure interaction while varying alpha and the submergence time ratio (the time of the plate's water entry divided by the plate's first order natural period). As alpha is decreased, the submergence time ratio has a larger effect on the dimensionless force, moment and deflection. At small alpha, the spray root breaks up before reaching the plate's leading edge. The kinetic energy of the plate in the pinned support reference frame provides further insights into the strength of the fluid-structure interaction.