Strength Analysis For The Inner Bottom Of Bulk Carriers By Grab Impact

Bulk carriers are ships especially designed to carry loose cargo in bulk. Along with thedevelopment of integration of global trade, the size of bulk carriers increases rapidly. In orderto improve the economy of the ships, it needs to improve the cargo handling speed and usebig grab by loading and unloading bulk cargo. Generally, the light weight of empty grab islarge. If a heavy grab hit on the inner bottom in cargo hold, it may result in permanentdeformation of the inner bottom plate, damage of the metal coating, even structure failure, andmay reduce the ship service life. This paper aims to explore the strength of the structure ofinner bottom under the grab impact loads during the bulk cargo unloading process.This paper compared different additional class notation GRAB in Common StructureRules (CSR) and from different classification societies. By applying finite element softwareANSYS/LS-DYNA during unloading process, the impact process of double bottom hitting bygrab and bulk cargo ship bottom are analyzed. The structural deformations, the impact forceand energy absorptions of inner bottom structure impacted by grab at different positions werestudied. The calculation results revealed that it is necessary to consider the influence of lightweight of grabs (as a function) for determination of plate thickness of inner bottom in cargoholds. Under assumption that inner bottom is simplified as a stiffened plate, parametricinvestigation were performed for different cases. Comparing the results of calculations withthe simplified formula for stiffened plates resulted from impact tests, the FE results have beenhas verified their accuracy and repeatability. Finally, with a large number of parameters ofdeformation calculations, the linear correlation between permanent deformation of innerbottom plating thickness and important influence factors such as the inner bottom platingthickness, the grab mass, grab drop speed as well as material yield stress. This proportionalrelationship between the dimensionless parameter and permanent deformation of inner bottomplate, provided efficient and simplified tools for the improvement of CSR rule and could bereferred by classification societies.