PSI - Issue 57

Kashif Kamran Toor et al. / Procedia Structural Integrity 57 (2024) 772–784 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

782

11

Fig. 12. Global and sub-model mesh.

4. Analysis results The fatigue damage was calculated as described in section 2. Shell type weld models were analysed using the DNV D curve. Solid weld models including the horizontal weld were assigned S-N curve FAT225, which is the IIW or equivalent DNV Notch Stress S-N curve. The applied S-N curves were selected for sea water with cathodic protection. A summary of calculated fatigue lives using different modelling approaches is given in Table 4.

Table 4. Summary of fatigue results.

No Weld

Weld Shell

Weld Notch full

Weld modeling method Fatigue Life [Years] DNV-D 2.505

DNV-D

FAT225

200.6 A 1002.1 B

173.4 A 2506.5 B

5. Discussion of results Based on the calculated results in Table 4 the following comments are made: •

A complex welded joint has been analysed using different modelling approaches to predict the design fatigue life. The INF technique has been used to include the load effect from all elements of the joint which is considered as an accurate representation of load effect at the geometric singularity. Very conservative hot spot stress was calculated in the shell model excluding the local weld stiffness, and a very low fatigue life was predicted for the selected hot spot. • Local weld geometry and stiffness can be included in the FE model using different modelling approaches. The weld dimensions were included based on the as-built design documentation. The weld profile at the hot spot was also confirmed by inspection of photographs of similar locations in the substructure. Two modelling techniques were applied to include the weld stiffness into the FE model. The oblique shell element technique was applied to model the weld for the local geometry as well as the overall weld stiffness. A solid element methodology was used to model the local weld profile and the notch radius at the weld toe for calculation of notch stress. • The calculated fatigue life increased significantly when the local weld stiffness was added using the shell elements. This shows that the shell elements formulation without weld over-estimates the hot spot stress for the type ‘b’ hot spot