The Structural Behaviour of a Ship’s Sub-Block During Lifting Operation

Abstract

The process of lifting a ship’s block is one of the important process in shipbuilding. The purpose of lifting or transfering of the blocks is to relocate the block to a new position before joining with other blocks. Prior to the lifting operation of ship’s sub-block, some stress and deflection analysis shall be done, in order to assess the magnitude of the deformation and the stresses acting on the structural members of the block. Based on the assessment, some changes in lifting operation can be intiated for example changing the lifting eye pad location to minimize plate deformation and bucking of structural members. In this study, the structural behaviour of a block was investigated using basic finite element method in order to simulate the deflections and stresses during the lifting operation. The initial dimension of the sub-block that was being investigated are with its dimensions: 21 meters in length, 16 meters in width, 4 meters in height. The type of material of all the structural components used in the sub-block is High Tensile Steel DH36. The investigation used Multiframe software. There are four case studies conducted with varying padeye location and number of lifting eye pads used in a single lifting. The sub block is approximately at 160 tonnes. These results were assessed with the DNV-GL acceptance criteria which can be found in DNV-GL Rules for finite element analysis. The highest yield ulitilization factor was found in case study 3 at 0.864, where it did not comply with the permissible coarse mesh yield utilization factor which is limited to 0.80. The lowest yield utilization factor was found in case study 2 at 0.278. Using the DNV-GL acceptance criteria it is concluded that case study 2 is the best configuration in lifting the sub-block.