Spectral fatigue analysis for legs of wind turbine units

Abstract

The analysis of spectral fatigue for wind turbine unit legs in this paper is grounded in dynamic analysis. The influence of weight in key areas, including the main hull, main deck, superstructure, cantilever, drilling floor, and others, is meticulously considered through the incorporation of mass elements. The calculation of Response Amplitude Operators (RAOs) for the legs is carried out using a frequency domain spectral analysis method. Critical fatigue locations are discerned by scrutinizing stress responses under design operating conditions, revealing vulnerabilities near the lower guides, spudcans, waterline, and specific chord and brace positions. The selected chords and braces, along with their respective locations, are visually depicted. Given that fatigue damage primarily results from cyclic load actions, this analysis excludes consideration of non-cyclic loads such as buoyancy and gravity. Additionally, the impact of wind load is not factored in; only fatigue resulting from wave and current loads is computed.