Page No. 1 - 19: An efficient nonlinear numerical scheme to predict ship roll responses in heavy seas

Abstract

Estimation of the roll motion of a vessel plays a vital role in the safe and efficient operation of a ship. It gives the designer prior knowledge of the limiting characteristics for transportation of cargo or passengers in a given sea-way. It is also crucial for the design of efficient, onboard roll control devices such as active fin stabilizer systems for both passenger and defense vessel applications. Traditionally, classification society based rules and empirical methods have been used to estimate the motion characteristics at the design stage. Although useful for the early phases of design, they tend to be inaccurate and conservative for more advanced design applications. Over the past couple of decades, computer based simulations have proven to be a more useful, efficient and robust tool for the designer. Typically based on linear theory, although they tend to be fairly accurate for moderate waves, the accuracy can quickly diminish for more realistic or severe sea states. This paper demonstrates the application of an efficient nonlinear computer program to predict the rolling of a ship. The computational model has been developed based on the direct time-domain body-nonlinear strip theory. The nonlinear theory is important to estimate ship motions in a severe sea-state. To model the viscous damping, the fully nonlinear form of the semi-empirical Ikeda-Kawahara method is employed.