Accelerating Time-Domain Fatigue Screening of Offshore Structures with an Integrated Unit Load Response and Submodelling Workflow
Date Issued
2025
Author(s)
Abstract
Time-domain fatigue analysis of floating offshore wind turbines (FOWTs) is accurate
but often prohibitive for early-stage design. The Unit Load Response (ULR) method,
based on linear superposition, offers an efficient alternative, but its application to
large, shell-based structures with complex distributed loads remains a challenge. We
propose a workflow that integrates ULRs with force-based submodelling to enable
whole-structure fatigue screening at design cost. Two key innovations make it
practical: (i) A "Virtual Test Rig" is used to create a computationally fast, stiffnessequivalent simplified global model for extracting boundary loads. (ii) A ULR catalogue
is generated for a detailed local submodel, which includes a trilinear interpolation
scheme (with water height, pitch, roll) to efficiently handle complex, wave pressure
fields. The workflow is first verified on a canonical portal frame and then applied to a
full-scale semisubmersible FOWT. Across 14 critical locations, the reconstructed stress
time histories match the submodel with a median bias ≈ of approximately −3.8% to−4.9%, and the stress and fatigue rankings are preserved, with Kendall’s τ-a ≥ 0.7 at
stress concentrations and τ-a ≥ 0.8 overall. Compared to classic step-by-step
submodelling, the method achieves ~13-29 times lower wall-clock effort and produces
outputs that are otherwise impractical at scale (e.g., full-hull damage maps), enabling
earlier, more informed fatigue-driven design decisions
Subjects
Fatigue Analysis
Unit Load Response (ULR)
Floating Offshore Wind Turbine (FOWT)
Submodelling
Time-Domain Analysis
Fatigue Screening
Publisher
Elsevier BV
Type
preprint
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