Horizontal impact loads and torsional moment induced by partial cargo shifts

Abstract

Previous studies demonstrate that significant cargo shifts occurred in all cargo holds of vessels in carriage of nickel ores may lead to catastrophic consequences of ship capsizing and sinking. Nevertheless, partial cargo shifts, despite its seldom occurrence in other types of vessels, are not unusual in bulk carriers, specifically for those with nickel ores which tend to liquefy as vessels experience long-time engine vibrations or unfavorable oblique waves. Regrettably, it has not been well described in previous literatures, therefore overlooked by ship operators and naval architects in ship structural design. The instantaneous impact loads to vessel's structures induced by partial cargo shifts, thus, remain unclear. Despite partial cargo shifts being unlikely to lead to life lost or ship capsizing, critical damage to cargo holds, shell plates and precise apparatuses in the wheelhouse can be identified frequently, sometimes even causing ship a hazardous list of 6–15°. Unfortunately, a number of similar accidents occurred in S.E. Asia waters have been found without reporting these accidents to IMO due to various reasons. The instantaneous impact loads, involving the torsional moments and horizontal sectional loads, initially overlooked by plenty of naval architects but subsequently estimated by our research team, are really huge, usually giving rise to a dangerous list of vessels as well as apparent or underlying damage to vessel's configurations. Conventional approaches, such as potential flow theory, volume of fluid method, moving particle semi-implicit method, smoothed particle hydrodynamics, etc., are significantly limited by their unsatisfactory precision in predicting and calculating those extraordinary loads. Here we estimate the torsional moments and horizontal sectional loads in oblique waves at various exciting rolling frequencies using improved Finite Element approach. The final results yielded from the model tests are strikingly in line with that from the numerical approach, manifesting that the modified numerical method behaves in a reasonable manner in tracking and capturing the complicated surface of large viscous fluid.