Hydroplastic response of a square plate due to impact on calm water

This paper investigates large, plastic deflections of a square plate due to impact on calm water. Most research in the area has examined linear elastic structural responses to such impact, but hydrodynamic responses during large, plastic deformations of engineering structures remain under-explored. A setup for an experimental drop test was designed for this purpose with equal emphasis on the hydrodynamical and structural mechanical aspects. Dual cameras were used to monitor the deforming plate from above during impact, and its deformation was tracked using a three-dimensional digital image correlation technique. The complex hydrodynamics of the impact were captured using a high-speed camera from below. The experimental results for flat impact showed a large air pocket under the deforming plate. The material properties of the plate were documented through separate tests. Hydroelastic theories were offered to account for large deformations and validated against the experimental results. Analytical hydroplastic theory shows that the maximum deflection is approximately equal to the velocity of impact times the square root of the ratio of the added mass to the plastic membrane capacity of the plate. An important source of error between the theory and the experiments was the effect of deceleration of the drop rig on deflection of the plate. This error was estimated using direct force integration and Wagner’s theory.