A Study on the Influence of Ship Roll Characteristics on the Risk of Cargo Shifting

摘要

In a previous work a methodology for assessing the risk of cargo shifting has been developed and used to study the influence of different parameters on the risk of cargo shifting. It has been found that ship rolling is one of the major contributing factors of cargo shifting. Linear theory of ship motions is presently used in the methodology because of computational efficiency and simplicity. Because the roll motion is complex and difficult to predict because of nonlinearities, the present study has been performed in order to study the influence of the roll motion on the risk of cargo shifting. This study may be seen as a sensitivity analysis of roll motion with respect to cargo shifting. The risk has been studied by the number of potentially dangerous conditions and how they depend on such parameters as wave height and period, and ship heading toward waves. The influence of roll amplitude and phase, as well as the influence of roll stabilizing devices, on the number of dangerous conditions Is studied for two vessels and two load cases each. Roll amplitude influence is analyzed by changing the amplitude of the transfer function, and the results show that the influence of roll amplitude is very large. This influence is especially marked when the roll amplitude is large and the vertical and horizontal accelerations are small to moderate. The influence of roll stabilizing devices is studied by cutting of the resonance peak in the transfer functions. The results show that roll stabilizing is often efficient but that it can be more important to choose load case in order to attain good seakeeping characteristics, especially with respect to roll motion.