# Numerical Simulation Study on Welding Process of Upper Frame of Hydropower Unit
## 5 Results and Discussion
During the welding of the outer T-shaped welds, the outer side of the upper ring was constrained by the inner T-shaped welds, resulting in less deformation. In Scheme 2, the constraint is more significant at the middle position between the two arms of the outer side of the upper ring due to the combined effect of the inner T-shaped welds and the arms, leading to a reduction in deformation four times. In Schemes 1 and 3, the outer side of the upper ring was welded first, and there is no constraint from the inner T-shaped welds. As a result, the constraint at the middle position between the two arms of the outer side is minimal, leading to larger deformation, and the deformation curves of both schemes almost overlap. Figure 26b shows the Z-direction deformation on the inner side of the upper ring. Based on the previous analysis of deformation, it is observed that larger deformations occur on the side welded first, while smaller deformations occur on the side welded later. Therefore, in this case, the deformation in Scheme 2 on the inner side of the upper ring is larger compared to the deformations generated by welding the outer side first in the other two schemes, increasing by 0.832 mm. Although the deformation in Scheme 2 on the inner side of the upper ring is slightly larger than in Schemes 1 and 3, the distribution of deformation between the inner and outer sides of the upper ring is more uniform at this point. This is beneficial for the overall balance and stability of the structure, and the overall maximum deformation is smaller. Therefore, when welding the upper ring, it is  
Figure 25: Path schematic diagram. (**a**) upper ring path; and (**b**) lower ring path. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Scheme** & **Overall Deformation** & **X-Direction** & **Y-Direction** & **Z-Direction** \\ \hline
1 & 3.153 & 2.028 & 1.990 & \(-\)3.149\(-\)1.779 \\
2 & 2.186 & 2.025 & 1.989 & \(-\)2.181\(-\)1.777 \\
3 & 3.162 & 2.026 & 1.988 & \(-\)3.158\(-\)1.791 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Maximum deformation value in each direction for different welding sequences (mm). more reasonable to weld the outer T-shaped welds first and then the inner T-shaped welds, indicating that the welding sequence of Scheme 2 is more reasonable. Figure 26c shows the Z-direction deformation on the outer side of the lower ring. It can be observed that the deformation trends produced by the three welding sequences on the outer side of the lower ring are quite similar, with the lower edges between the two rib plates showing an upward curling trend. The Z-direction deformation of the lower ring in Scheme 2 is the smallest, decreasing by 4.2% compared to Scheme 1, and the difference in deformation compared to Scheme 3 is not significant. Therefore, when welding the rib plates to the lower ring, welding the T-shaped welds of the small rib plates first to form a certain rigidity, and then welding the large rib plates, can effectively reduce the degree of curling at the lower ring edges. Thus, the welding sequence of Scheme 2 is more reasonable. Figure 26d shows the Z-direction deformation on the inner side of the lower ring. It can be seen from the figure that the deformation trends on the inner side of the lower ring caused by the three welding sequences are similar. Both Scheme 2 and Scheme 3 result in smaller maximum Z-direction deformation values than Scheme 1. Therefore, when welding the brace ring, it is more reasonable to weld the outer T-shaped welds first, followed by the inner T-shaped welds. Thus, the welding sequences of Scheme 2 and Scheme 3 are more reasonable. Comparing the deformation caused by the three different welding sequences, Scheme 2's welding sequence is more favorable. That is, during welding, the small rib plates should be welded first, followed by the large rib plates; the brace ring should be welded with the outer T-shaped welds first, followed by the inner T-shaped welds; and the upper ring should be welded with the inner T-shaped welds first, followed by the outer T-shaped welds.