Study Of Large Hull Welding Deformation Simulation Technology And Its Application

Welding is the uppermost manufacturing method in ship building, and its quality has significant effect in quality and efficiency of ship building. The welding deformation control is the most difficult link in whole welding process. The existence of welding deformation has not only brought about the variation of structure shape, the declined precision and the bearing capacity reduction. Moreover, the additional bending moment and stress concentration under working load is the primary factor causing the early failure of ship structure, but also reduced the ship structure fatigue strength. The prediction and control of welding deformation has been an important and urgent problem in shipbuilding. In order to resolve the problem, exerting a reverse deformation amount (compensation quantity) is the best choice. The solution is providing prediction data for welding technology designing and determining the reservation deformation in production process so as to guarantee the welding precision and structure quality.For large-scale ship structure, based on three-dimensional solid element model, the current conventional thermal elastic-plastic FEM method is impossible to be used for simulating welding process because it acquires large capacity computer memory and is just only applicable to welding mechanics behavior analysis of welded joint or small structures. Introducing method based on inherent strain as a approximate method into the numerical simulation for prediction of welding deformation is relatively quick and effective, especially for the welding deformation prediction of large-scale complex structure, also, it can obtain the residual stress and deformation amount with high accuracy, which providers a powerful tool for computing the reverse deformation amount (compensation quantity), so it will get great practical value and application prospects. But one thing to be mentioned is that the method based on inherent strain depends on the inherent strain database which is the premise of predicting welding deformation accurately and has great importance on welding deformation prediction. Meanwhile the finite element method with 3D plate elements based on the theory of thermo elastic-plastic FEM has also been a approximate method of using more, and this method can also achieve high precise result on welding deformation prediction within a short period of time.This paper takes the 50000T multi-purpose ship as an object, and adopts the method based on inherent strain and 3D plate element T-E-P FEM method respectively to predict the welding deformation of its double bottom structure. Numerical results of the two methods and the site measurements will be compared. In the method based on inherent strain, a simplified inherent strain formula with a parameter of thickness of plates is obtained according to a large amount of computation and measurement, thus based on the inherent deformation calculated by the simplified formula and practical experience the inherent strain database of hull welding can be acquired. Then, using the inherent strain database, the deformations of the double bottom structure in NO.6 Cargo of 50000T multipurpose ship are predicted by special software WSDP. While the 3D plate element T-E-P FEM method is trying to established the FE model with 3D plate element, and applying the software ABAQUS to simulate welding process of the same section, which is based on the theory of thermo-mechanical.The study shows that the numerical results from the method based on inherent strain theory agree well with the experimental data, which will improve inherent deformation database and validate its practicability as well as the simplified formula. The special welding software WSDP based on inherent strain is well competent for the prediction of welding deformation of hull structure, which provides a powerful tool for acquiring welding compensation amount and achieving accuracy shipbuilding. Similarly, 3D T-E-P FEM method also has great feasibility within a shorter period of time and providers a new idea and method for predicting the welding deformation of large-scale complex structure.