On Air-Cavity Formation during Water Entry of Flexible Wedges

Riccardo Panciroli,Tiziano Pagliaroli,Giangiacomo Minak

doi:10.3390/jmse6040155

Riccardo Panciroli, Tiziano Pagliaroli + Show 1 more

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https://doi.org/10.3390/jmse6040155

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Abstract

Elastic bodies entering water might experience fluid–structure interaction phenomena introduced by the mutual interaction between structural deformation and fluid motion. Cavity formation, often misleadingly named cavitation, is one of these. This work presents the results of an experimental investigation on the water entry of deformable wedges impacting a quiescent water surface with pure vertical velocity in free fall. The experimental campaign is conducted on flexible wedges parametrically varying the flexural stiffness, deadrise angle, and drop height. It is found that, under given experimental conditions, cavity pockets form beneath the wedge. Their generation mechanism might be ascribed to a differential between structural and fluid velocities, which is introduced by structural vibrations. Results show that the impact force during water entry of stiff wedges are always opposing gravity, while, in case flexible wedges temporarily reverse their direction, with the body that is being sucked into the water within the time frame between the cavity formation and its collapse. Severe impact might also generate a series of cavity generation and collapses.

Highlights

The impulsive nature of the hydrodynamic loading experienced by structures impacting the water might induce mechanical vibrations [1,2,3]
Results show that the impact force during water entry of stiff wedges are always opposing gravity, while, in case flexible wedges temporarily reverse their direction, with the body that is being sucked into the water within the time frame between the cavity formation and its collapse
Most of the analytical and numerical works found in the literature [18,19,20,21] do not account for such fluid–structure interaction (FSI) phenomena, since these can be neglected in cases where structural deformations are small, and hydrodynamic pressure is similar to the one experienced by a rigid body

Summary

Introduction

The impulsive nature of the hydrodynamic loading experienced by structures impacting the water might induce mechanical vibrations [1,2,3] These introduce a series of so-called fluid–structure interaction (FSI) phenomena, such as air inclusions [4], ventilation, and cavitation [5], which are encountered in a wide range of water-entry problems, from naval [6,7,8,9] to aerospace applications [10,11,12]. The evolution of the wetted body area in time is an important characteristic of the impact, and variations of the structural shape due to its flexibility might affect the loads [17]. Such problems are still difficult to analyze and compute. Most of the analytical and numerical works found in the literature [18,19,20,21] do not account for such FSI phenomena, since these can be neglected in cases where structural deformations are small, and hydrodynamic pressure is similar to the one experienced by a rigid body (see, e.g., References [22,23,24,25,26,27])

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