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A 2D forced roll oscillation experiment was performed to examine and characterize the physics of vortex generation from ship bilge keels. Measurements included ship model motions, normal force on the bilge keels, and flow field visualizations using Particle Image Velocimetry (PIV). Data was collected for a range of roll oscillation amplitudes, including large amplitudes where the bilge keels interacted with the free surface and for three roll oscillation frequencies. This paper presents analysis and description of the observed phenomena, and examines whether a functional relationship can be established between the force measured on the bilge keel and the flow field generated by the bilge keel. A qualitative discussion of the observed flow characteristics, including the vortex generation at the tip of the bilge keel, detachment, and interaction with the free-surface, is presented. In addition, the circulation in front and behind the bilge keel was calculated, analyzed, and compared to the measured bilge keel force. The analysis conducted was intended to provide improved understanding of the phenomena which occur during bilge keel vortex generation and aid in the development of improved roll damping and bilge keel force models for the prediction of ship motions. |
