Stress optimization of the weld zone of large thin-walled tank structures

While a large thin-walled tank structure is subjected to internal pressure, large local bending moment and stress gradient is formed in the weld zone between the cylinder shell and the semi-spherical shell. It is known that it is difficult to realize the constant strength design through the traditional method. Also, the topological optimization is relatively difficult due to the existence of internal pressure on the design region. In this paper, finite element analysis is conducted to analyze the stress field of the conventional design firstly. It is discovered that there is a change of stress transmission path from the inner wall to the outer wall, which produces a high stress gradient in the weld zone. Secondly, based on the concept of stress transmission path control, two weakened zones are constructed respectively in the transition ring and the thick section of cylinder shell. Then a parameter optimization model is formed. Finally, Non-dominated Sorting Genetic Algorithm (NSGA) is adopted for the parameter optimization, more uniform stress distribution of the weld zone can be obtained and the stress gradient is reduced by 80% and the maximum stress value is reduced by 40%.