A weld-distortion analysis method of the shell structures using ultra structural FE model

Ha, Yunsok; Yi, Myungsu

doi:2015.33.3.62

J Weld Join > Volume 33(3); 2015 > Article

Research Paper

Journal of Welding and Joining 2015;33(3):62-67.
DOI: https://doi.org/10.5781/JWJ.2015.33.3.62 Published online June 30, 2015.

A weld-distortion analysis method of the shell structures using ultra structural FE model

Yunsok Ha^*, Myungsu Yi^*

Correspondence: Yunsok Ha,
Email: yunsok.ha@samsung.com

Abstract

A very large shell-structure built in shipyards like ship hulls or offshore structures are joined by welding through full process. As the welding contains a high thermal cycle at a local area, the welded structures should be distorted unavoidably. Because a distorted ship block should be revised to the designed value before the next stage, the ability to predict and to control the weld distortion is an accuracy level of the yard itself. Despite the ship block size, several present thermal distortion methodologies can deal those sizes, but it is a different story to deal full ship size model. Even a fully constructed ship hull not remaining any welding can have an accuracy issue like outfitting installation problems. Any present thermal distortion methodology cannot accept this size for its recommended element size and the number. The ordinary welding breadth at erection stage is about 20~40 mm. It can hardly be a good choice to make finite element model of these sizes considering human effort and computational environment.
The finite element model for structure analysis of a ship hull is prepared at front-end engineering design stage which is the first process of the project. The element size of the model is as fine as the longitudinal space, and it is not proper to obtain a weld distortion at the erection stage. In this study, a methodology is suggested that a weldment can be shrunk at original place instead of using structural finite element model. We cut the original shell elements at erection weld-line and put truss elements between the edges of cut elements for weld shrinkage. Additional truss elements are used to facsimile transverse weld shrinkage which cannot be from the weld-line truss element shrink. They attach to weld-line truss element like twigs from barks. The capacity of developed elements is verified through an accuracy check of erection process of a container vessel at the apt. hull. It can be a useful tool for verifying a centering accuracy after renew and for block-separating planning considering accuracy.

Key Words: Shell structure, Erection, Butt weld, Truss element, Poison ratio, Inherent strain