The controlled impact of elastic plates on a quiescent water surface

Abstract

The impact of flexible rectangular aluminum plates on a quiescent water surface is studied experimentally. The plates are mounted via pinned supports at the leading and trailing edges to an instrument carriage that drives the plates at constant velocity and various angles relative to horizontal into the water surface. Time-resolved measurements of the hydrodynamic normal force (Fn) and transverse moment (Mto), the spray root position (ξr) and the plate deflection (δ) are collected during plate impacts at 25 experimental conditions for each plate. These conditions comprise a matrix of impact Froude numbers Fr = Vn(gL)−0.5, plate stiffness ratios RD = ρwV2 nL3D−1 and submergence time ratios RT = TsT−1 1w . It is found that RD is the primary dimensionless ratio controlling the role of flexibility during the impact. At conditions with low RD, maximum plate deflections on the order of 1 mm occur and the records of the dimensionless form of Fn, Mto, ξr and δc are nearly identical when plotted vs tT−1 s . In these cases, the impact occurs over time scales substantially greater than the plate’s natural period, and a quasi-static response ensues with the maximum deflection occurring approximately midway through the impact. For conditions with higher RD ( 1.0), the above-mentioned dimensionless quantities depend strongly on RD. These response features indicate a dynamic plate response and a two-way fluid–structure interaction in which the deformation of the plate causes significant changes in the hydrodynamic force and moment.