Converting laser scans of tubular joints to finite element models

Jacket type substructures for offshore wind turbines gained prominence in the 2010s, especially in wind farms where monopiles became less feasible due to increasing water depths. As these turbines near the end of their design life, extending their operational lifetime or repowering offers significant economic and ecological advantages compared to decommissioning. However, these strategies both require an accurate assessment of the remaining fatigue life of the substructure. Previous studies showed that the actual weld geometry strongly affects local stress concentrations, influencing the fatigue life of offshore substructures. Current fatigue assessments in the design phase assume perfectly cylindrical tubular members with simplified welds, while also omitting surface degradation effects. This research aims to improve the fatigue assessment of offshore jackets by incorporating the as-built joint geometry, including ovality, out-of-roundness, surface irregularities, and the real weld geometry, to better estimate stress concentrations and fatigue damage accumulation. Four full-scale tubular joints were scanned. The joints originate from a decommissioned gas platform jacket that was installed in the North Sea in the 1980s and was decommissioned in 2023. A handheld 3D laser scanner was used to capture the real geometry of the joints. Since the scanning principle is based on the reflection of light, only the outer surface can be scanned. In this work, a framework was developed to automatically extend the tubular members and reconstruct the inner parts that could not be scanned.