Optimum Design of Lug Arrangement Based on Static and Dynamic Analyses for Block Lifting

In a shipyard, special equipment called lugs are used for lifting blocks by using a crane. During lifting, the motions of the crane and the block are determined by the lug arrangement. In this study, a method for the lug arrangement is proposed to achieve safe block lifting. For this, an optimization problem for the lug arrangement is mathematically formulated and solved by using the multiobjective genetic algorithm. Static and dynamic motion analyses are then introduced to calculate the block motion. To check the applicability of the proposed method, it is applied to examples of the lug arrangement in a shipyard. 1. Introduction When constructing a ship or an offshore structure, many blocks or modules are routinely transported and lifted to be assembled in the shipyard. Recently, these blocks have become more complicated and larger than in the past, in order to improve productivity. For this reason, shipyards are now equipped with lifting processes that operate more sophisticated and heavier blocks. Figure 1 shows the procedure of the lifting process. This process is executed in the order of hoisting, moving, and lowering. To perform the lifting process for heavy blocks, a range of equipment is used. Among them, a gantry crane (or Goliath crane) is one of the main types of equipment used for lifting the blocks from the preerection area to the dock or to a specific position. The gantry crane consists of several types of subequipment (Roh & Lee 2010). Figure 2 shows the lifting system including a gantry crane, its subequipment, and a block. special subequipment called lugs are attached to the block and the lugs act as an interaction point between the block and the crane. A hook is connected to the lug with a sling wire, and the sling wire transmits tension acting on a block loader. The block loader distributes the tension evenly on sling wires and moving sheaves (simply and sheaves). The main wire transmits tension acting on a trolley. The trolley holds the block loader and moves along the crane. in general, the gantry crane has three block loaders and each block loader has 14 sheaves.