RIASSUNTO
ABSTRACT:
Distortion is unavoidable in all stage of ship building starting from the thermal cutting process followed by the sub-assembly, the assembly of blocks and the block final assembly. In this report, the longitudinal bending deformation of a ship during the block assembly is investigated using a finite element method. For the theoretical prediction, elastic shell FEM employing the concept of the inherent deformation and the interface element is used. The local shrinkage due to welding is represented by the inherent deformation and the inherent force. The gap and the misalignment accumulating during the assembly are represented by the interface element. The versatility of the proposed method is demonstrated through examples.
INTRODUCTION
In ship structures, welding is extensively used during all stages of assembly. In block assembly to form a ship's hull, depending on assembly and welding sequences, the ship hull may longitudinally bend usually in a sagging mode. Controlling welding distortion during block assembly is essential to achieve overall dimensional accuracy of the ship. Experienced workers who could control welding distortion based on their experience are not easily available in recent years. Numerical tools that predict welding distortion are required to assist less experienced workers and production planning engineers to control welding distortion. Several tools are developed at Osaka University for this purpose. One of these tools performs elastic analysis based on the concept of the inherent deformation, and is suitable to predict welding distortion of large structures (Murakawa, 1998; Deng, 2007; Murakawa, 2007). To reproduce the distortion observed in the ship's hull after block assembly, it may be necessary to simulate all stages of the ship building and sum up the distortion accumulating during building subassemblies, assemblies, blocks and during the assembly of blocks to form the ship hull.