An experimental study on three types of roll damping devices—bilge keels, passive bilge fins, and paravanes—is described. These tests were conducted in the MIT Ship Model Towing Tank using scale models of a 76-ft single-chine trawler and a 119-ft double-chine trawler. The models were fitted with each damping device and excited in roll by a hull-mounted moment generator. Roll motions were measured at zero speed and at trawling and steaming speeds. Nondimensional damping ratios have been calculated and the effects on roll damping of each device are compared. The relationship of bilge keel and bilge fin area and aspect ratio to damping ratio are studied and some design considerations are presented. Practical aspects of each device type are also discussed.
An application of a toroidal hydrodynamic absorber is suggested for reducing low-frequency bending vibrations of fixed offshore platforms and planar oscillations of tethered platforms. A design methodology for such an absorber is presented. Results of an experiment intended to illustrate the effect of the absorber are presented.
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