Water entry of compliant slender bodies: Theory and experiments

Hydroelastic phenomena play a critical role on the dynamics of lightweight marine vessels, but a comprehensive understanding of their potential benefits and drawbacks in water impact remains elusive. In contrast with the literature on hydroelastic impact that focuses on plane strain deformations and two-dimensional fluid flows, we address the water entry of compliant slender bodies. We propose a mathematically-tractable framework to predict the rigid body motion and elastic deformation of a beam impacting the water surface in free fall. At each location on the beam, the hydrodynamic loading is determined from the level of submersion of the cross-section and its local velocity and acceleration. Slamming, added mass, and drag are all included in the model and cogently weighted based on the level of submersion of the cross-section. Edge effects are incorporated in the model through a shape function that modulates the hydrodynamic loading as a function of the distance from the edges. Model predictions are validated through experiments on compliant beams of circular cross-section, which detail both the structural response and the resulting flow physics, through the integration of high-speed imaging, direct acceleration measurement, and particle image velocimetry. Results of this study are expected to aid in the design of lightweight ship hulls, experiencing dynamic bending deformations during sailing and maneuvering.