Water Exit of a Floating Sphere with Low Constant Accelerations

Abstract

The water exit of a floating sphere with low constant accelerations is discussed in this study. Experiments are conducted to investigate the evolution of the free surface and the hydrodynamic loads during the water exit process. Once the sphere’s bottom lifts off the mean free surface, a layer of water adheres to the sphere and is carried upward due to inertia, forming a water column beneath it. Under the influence of gravity, this water column elongates and narrows, ultimately collapsing. The qualitative influence of the vertical acceleration on the water column is discussed. To verify and validate the experimental hydrodynamic loads, the Computational Fluid Dynamics (CFD) method is utilized. The numerical results obtained from CFD are in good agreement with the experimental results, and show the viscous effect has a negligible influence on the hydrodynamic loads during the water exit of the floating sphere. Assuming potential flow, a theoretical model is proposed for the analysis of the hydrodynamic loads. This model shows that the vertical hydrodynamic loads can be approximated by the buoyancy force and the added mass force. The added mass force is related to the acceleration of the body. When the acceleration is significantly less than gravitational acceleration, the buoyancy force dominates during the early stages of the water exit process. Furthermore, in the presence of ambient waves, the wave excitation loads must also be taken into account.

Keywords

Water exit / Sphere / Constant acceleration / Free surface / Hydrodynamic loads

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