Vertical Water Entry of a Flexible Wedge into Calm Water: A Fluid-Structure Interaction Experiment

Abstract

Slamming water impact occurs frequently on high-speed craft and restricts the operating envelope of a vessel. One approach to understanding the hydroelastic nature of this phenomenon is to study the vertical impact of a V-shaped wedge on calm water, which models a single slamming event after a vessel has become partially airborne. The dynamic structural response of the bottom plate of a wedge dropped vertically (drop height = 7.9 cm) is investigated both experimentally and computationally. The experiments were conducted with a flexible bottom model at Virginia Tech. Pressure on the wedge bottom, rigid body motion (vertical acceleration and vertical position), and full-field out-of-plane deflection were measured. The out-of-plane deflection was measured using stereoscopic digital image correlation. Predictions on the hydrodynamic pressure field were made using Wagner's method, Vorus's method, and an unsteady Reynolds-averaged Navier-Stokes solver, all assuming a rigid plate. In the present work, the reconstructed pressure distribution from the experiment was used as the loading condition in a dynamic, linear finite element plate model (one-way coupled approach). Both the predicted pressure and predicted deflection were compared with the experiment. It was found that in the experiment, there is a slight reduction in the measured hydrodynamic pressure compared with predictions. This reduction in pressure leads to a reduction in the reactions at the plate edges, which get transmitted to the frames of the vessel. This slight reduction at small loading cases has the potential to be more noticeable when more severe slamming loads are encountered. 1. Introduction Slamming water impacts occur when a vessel impacts the water surface at high speed relative to the free surface. Water impact was first studied by von Karman (1929) with the application of seaplane landing. Water impact, as it pertains to slamming, gradually attracted increasing attention in the application of high-speed craft. The understanding of this phenomenon has been applied to the structural design and evaluation of the operational envelope of high-speed planing craft. Sailors also consider slamming a serious risk because it contributes to major injuries in addition to mission-related setbacks such as speed reduction or heading change. The present investigation of slamming can lead to the development of better design criteria for small craft.