International Shipbuilding Progress - Volume 51, issue 1

Authors: Bulian, Gabriele

Article Type: Research Article

Abstract: In this paper an approximate solution for the 1-DOF nonlinear roll decay is proposed. The solution is obtained by means of the averaging technique. The obtained expression is used in a fitting procedure in order to evaluate the parameters of the analytical model. Fitting is based on experimental free decay data for a Ro-Ro hull and a check of the method is performed on simulated roll decay time histories. In order to assess the reliability of …the analytical method, a comparison is performed between the results obtained using the analytical approximation and those obtained by direct integration of the differential equation. Show more

Citation: International Shipbuilding Progress, vol. 51, no. 1, pp. 5-32, 2004

Authors: Krishnankutty, P. | Varyani, K.S.

Article Type: Research Article

Abstract: The hydrodynamic interaction forces acting on a moored ship due to the passage of another ship is estimated using slender body assumptions. The computations are performed for an assumed parabolic sectional area distribution for the ship and also using the real ship form. Subsequently the equations of motion of the moored ship are solved to study the forces on the mooring ropes for different rope constants. The obtained hydrodynamic interaction and mooring rope forces are compared …with known experimental/ theoretical values. Show more

Citation: International Shipbuilding Progress, vol. 51, no. 1, pp. 33-57, 2004

Authors: Molin, Bernard

Article Type: Research Article

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. Show more

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