International Shipbuilding Progress - Volume 49, issue 4

Authors: Varyani, K.S. | McGregor, R.C. | Krishnankutty, P. | Thavalingam, A.

Article Type: Research Article

Abstract: In order to improve the formulation of ship-ship interaction forces and moments in the mathematical model of a ship manoeuvring simulator, new empirical models are developed in a three stage process. The first process involves the use of a discrete vortex distribution numerical technique and slender body theory to obtain sway and yaw moment coefficients. The second process involves using these numerical results to predict new empirical models for maximum peak of sway forces and yaw …moments. The third process involves development of new generic models using the numerical results. The research shows that the generic model is as accurate as the numerical model and is also more accessible to a navigator, Master or pilot. Show more

Citation: International Shipbuilding Progress, vol. 49, no. 4, pp. 237-262, 2002

Authors: Liu, Pengfei | Bose, Neil | Colbourne, Bruce

Article Type: Research Article

Abstract: In panel methods, numerical Kutta conditions are applied in order to ensure that pressure differences between the surfaces at the trailing edges of lifting surface elements are close to zero. Previous numerical Kutta conditions for 3-D panel methods have focused on use of the Newton-Raphson iterative procedure. For extreme unsteady motions, such as for oscillating hydrofoils or for a propeller behind a blockage, the Newton-Raphson procedure can have severe convergence difficulties. The Broyden iteration, a modified …Newton-Raphson iteration procedure, is applied here to obtain improved convergence behavior. Using the Broyden iteration increases the reliability, robustness and in many cases computing efficiency for unsteady, multi-body interactive flows. This method was tested in a time domain code for an ice class propeller in both open water flow and during interaction with a nearby ice blockage. Predictions showed that the method was effective in these extreme flows. Show more

Citation: International Shipbuilding Progress, vol. 49, no. 4, pp. 263-273, 2002

Authors: Santos, Tiago A. | Soares, C. Guedes

Article Type: Research Article

Abstract: This paper presents a probabilistic methodology for assessing the survivability of damaged passenger Ro-Ro ships through the identification of critical damage scenarios. The Static Equivalent Method is used to calculate the critical sea state the ship can survive in a given damage scenario and Monte-Carlo simulation is used to take into account the uncertainties in the ship's loading condition at the time of the accident: intact draught, vertical and longitudinal position of the centre of gravity …and permeability of the Ro-Ro decks. The application of these methods to the ranking of damage scenarios according to the critical sea state the ship can survive is presented for two different passenger Ro-Ro ships. The critical damage scenarios for each ship are then identified. A sensitivity analysis is carried out to identify the most important random variables affecting the ship's survivability. The number of Monte Carlo runs necessary for stabilising the results is also investigated. Show more

Citation: International Shipbuilding Progress, vol. 49, no. 4, pp. 275-300, 2002

Authors: Surendran, S. | Reddy, J. Venkata Ramana

Article Type: Research Article

Abstract: The prediction of ship stability during the early stages of design is very important from the point of safety. Ships experience six modes of rigid body motions in a seaway, which can be split into two groups as translatory and oscillatory motions. Out of the six motions of a ship, the critical motion leading to capsize of a vessel is the rolling. In the present study, particular attention is paid to the performance of a ship in beam sea. The …rolling motion of a ship has been described by a nonlinear differential equation taking into account the nonlinearities in both the restoring moment and the damping moment. Solution of differential equation of roll motion is sought using MATLAB. The effect of different representation of restoring moment on roll motion is investigated. It is seen that, the effect of different representation of restoring moment on roll motion depends on the characteristics of the GZ curve. A parametric investigation is undertaken to identify the effect of different parameters viz., wave steepness, encountering frequency etc., on the capsizing conditions of a ship. The rolling response of ship is determined in the frequency domain. The analysis has been carried out by varying both the wave steepness and the wave frequency. The approach has been demonstrated considering a Ro-Ro ship as test vessel. Show more

Keywords: ship safety, stability, capsizing, beam sea, nonlinear damping, nonlinear restoring, roll response

Citation: International Shipbuilding Progress, vol. 49, no. 4, pp. 301-320, 2002