The impact of a deep-water plunging breaker on a finite height two-dimensional structure with a vertical front face is studied experimentally. The structure is located at a fixed horizontal position relative to a wave maker and the structure’s bottom surface is located at a range of vertical positions close to the undisturbed water surface. Measurements of the water surface profile history and the pressure distribution on the front surface of the structure are performed. As the vertical position, $z_{b}$ (the $z$ axis is positive up and $z=0$ is the mean water level), of the structure’s bottom surface is varied from one experimental run to another, the water surface evolution during impact can be categorized into three classes of behaviour. In class I, with $z_{b}$ in a range of values near $-0.1\unicode[STIX]{x1D706}_{0}$, where $\unicode[STIX]{x1D706}_{0}$ is the nominal wavelength of the breaker, the behaviour of the water surface is similar to the flip-through phenomena first described in studies with shallow water and a structure mounted on the sea bed. In the present work, it is found that the water surface between the front face of the structure and the wave crest is well fitted by arcs of circles with a decreasing radius and downward moving centre as the impact proceeds. A spatially and temporally localized high-pressure region was found on the impact surface of the structure and existing theory is used to explore the physics of this phenomenon. In class II, with $z_{b}$ in a range of values near the mean water level, the bottom of the structure exits and re-enters the water phase at least once during the impact process. These air–water transitions generate large-amplitude ripple packets that propagate to the wave crest and modify its behaviour significantly. At $z_{b}=0$, all sensors submerged during the impact record a nearly in-phase high-frequency pressure oscillation indicating possible air entrainment. In class III, with $z_{b}$ in a range of values near $0.03\unicode[STIX]{x1D706}_{0}$, the bottom of the structure remains in air before the main crest hits the bottom corner of the structure. The subsequent free surface behaviour is strongly influenced by the instantaneous momentum of the local flow just before impact and the highest wall pressures of all experimental conditions are found.
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.
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