ON THE FRICTIONAL DAMPING IN ROLL OF SHIP SECTIONS

Article type: Research Article

Authors: Molin, Bernard

Affiliations: Ecole Supérieure d'Ingénieurs de Marseille, Marseille, France

Abstract: The viscous force and moment acting upon two-dimensional bodies, undergoing forced oscillations in a fluid at rest, are studied, under the assumptions of laminar, unseparated flow, small Keulegan-Carpenter number (K_c) and large Stokes parameter (β). Unbounded fluid conditions are considered first. Previous results by Stokes (1851), for circular cylinders, and by Molin & Etienne (2000), for non-circular cylinders in translatory motion, are extended to rotational motion. A complete viscous damping matrix is derived. Numerical results are given for elliptical and rectangular shapes. Fluid bounded by a free surface is considered next. The simple case of a piston wavemaker is first analyzed, with the remarkable result that the viscous correction to the damping force (due to wave generation) can be negative. The viscous force is finally derived for ship sections in sway or roll motion. Numerical results are given for rectangular shapes of different beam over draft ratios. The practical implications of these results, for the damping of roll resonance, are discussed.

Journal: International Shipbuilding Progress, vol. 51, no. 1, pp. 59-85, 2004