Numerical Study on Mechanism of Twisting Deformation Observed in Bilge Block during Welding Assembly and Its Control

It is generally experienced by engineers in shipyards that it is difficult to predict and control distortions of curved 3D blocks during assembly. Even in case of bilge blocks in the parallel part, twisting of the block is often observed. So far, there is no theoretical explanation why it happens. According to the Authors' understanding, the distortion of the welded structure is produced by two causes. One is the local shrinkage introduced by welding, such as transverse shrinkage and angular distortion. The other is the gap and misalignment introduced during sequential welding process. In this study, the mechanism of the twisting deformation is investigated from these points of views. For this, elastic shell FEM developed by authors based on the concept of inherent deformation and interface element is employed. Further, the method to straighten the twisting distortion by line heating is proposed based on the numerical study.