Partial cargo shift-induced instantaneous impact loads to ships with highly-viscous liquefied cargoes

Abstract

Prior studies have revealed that capsizing and sinking of bulk carriers with highly-viscous liquefied cargoes is primarily caused by a collapse of viscous shear forces as the inertial forces of the liquefied cargoes are greater than the viscous shear forces during rolling induced by oblique waves, specifically, as vessels sailing along the north-south oriented coasts (experiencing NE or NW winds) in wintertime. Post investigations show that this occurs only when a cargo shift takes place in all cargo holds for a typical nickel ore bulk carrier with five cargo holds. Nevertheless, the studies on partial cargo shifts remain poorly understood. Although the partial cargo shifts are not likely to lead to a catastrophic consequence, it can result in a dangerous list of a few degrees for bulk carriers. Many marine accidents with the partial cargo shifts have been reported over the past decade. The instantaneous impact loads, including the horizontal sectional loads and torsional moments, previously ignored by many marine engineers, but subsequently identified by us, are actually enormous, usually resulting in not only a list of ships but also obvious or potential damage to ship's structures and deck fittings. Traditional methods are difficult to predict and calculate these exceptional loads. Here we address the horizontal sectional loads and torsional moments in oblique waves at a variety of cargo shift situations using improved Arbitrary Lagrange Euler method and Finite Volume method. The results obtained from the numerical methods are well in agreement with those acquired from the model tests, implying that the numerical simulations are more suitable for capturing and tracking the complex surface of fluid sloshing with high viscosity.