International Shipbuilding Progress - Volume 48, issue 1

Authors: Cotton, B. | Spyrou, K.J.

Article Type: Research Article

Abstract: In this paper we present the results of a series of capsize tests based on a prismatic model ship. The aim of the experiments was to study the significance of some nonlinear phenomena predicted in theoretical studies of roll motion. Regions of bistability are observed near linear resonance. It is verified that, near resonance, the freqency-response curve is skewed towards lower frequencies due to the softening nature of the GZ curve. The experimentally derived capsize boundary …is then compared with the theoretical one. Finally we present some evidence for the sensitivity of capsize to initial conditions and discuss the importance of applying this to a testing procedure. Show more

Citation: International Shipbuilding Progress, vol. 48, no. 1, pp. 5-18, 2001

Authors: Liut, D. | Mook, D. | Weems, K. | Nayfeh, A.

Article Type: Research Article

Abstract: A general unsteady vortex-lattice technique, called FINS, is developed to model the flowfield around a fin attached to the hull of a moving ship. The fins can have any shape and movable flaps and be at any angle of attack below those where stall and/or cavitation occur. Then a method to combine this model with such existing motion-predicting programs as LAMP or FREDYN is developed. The combined programs, working in concert, can be used to predict …the motion of ships with fins attached to the hull in the time domain. Because of the great disparity in the dimensions of the hull and fins, different grid sizes and different time steps are required to produce the same accuracy. Moreover, LAMP and FREDYN are based on surface distributions of sources, whereas FINS is based on a lattice of discrete vortex lines. Consequently, the final combination of the two programs (LAMP and FINS in the present work) is a single program that simultaneously uses distributions of sources and vorticity over grids of vastly differing sizes while using different time steps for the different grids. To provide confidence in the new model of flow over the fins, it is shown in several examples that the numerical and experimental results are in close agreement. In a final example, the program with the combined models is used to predict the motion of a ship in a seaway. The results show a 50% reduction in the computed peak amplitudes of the roll motion of a CG47 cruiser in a random beam sea; the sea state is five. Show more

Citation: International Shipbuilding Progress, vol. 48, no. 1, pp. 19-50, 2001

Authors: Pavazza, Radoslav | Plazibat, Bože | Matoković, Ado

Article Type: Research Article

Abstract: An approximate analytical method of estimating effective breadth of deck plating is presented. The deck plating in the region of 0.4L amidships is considered, as subjected to linearly distributed line loads along the edges of the deck plating and in way of the longitudinal bulkheads, together with longitudinal normal forces at the ends of 0.4L region. It is assumed that the contraction of the deck plating is small (not neglected). Analytical solutions are obtained for the …stress distribution in the deck plating of ships without longitudinal bulkheads, for ships with a central longitudinal bulkhead and also for two symmetrically located longitudinal bulkheads. The method is applicable for ships without cargo hatch openings only, as tankers. The results are checked by the finite element method. Show more

Citation: International Shipbuilding Progress, vol. 48, no. 1, pp. 51-58, 2001