Posters

Abstract

Wind turbines, like other offshore structures, experience severe fatigue damage as a result of the constant wave and wind loads. The magnitude and direction of wave and wind forces can have a significant influence on these structures. Previous research failed to account for wind and wave misalignment, as well as various wave theories. In this work, structural responses were evaluated using the three wave theories: airy, 5th-order Stokes, and the stream function. Also, the misalignment of the wind load in the range of -50 to +50 relative to the wave direction is considered. The 5-MW monopile wind turbine recommended by NREL in the Arabian Sea, at a depth of 23 meters, was numerically simulated over 10 years of existing wind and wave data. The frequency domain approach was used to analyze the structure by examining stress spectra. Three strategies were used to decide on important wave frequencies, considering the fatigue index.: 1: Probability of wave occurrence, including pair wave height period in eight different directions; 2: Static transfer function, including sensitivity of stress magnitude and direction to the specific frequencies; 3: Analysis of mode shapes and selection of frequencies inducing resonance; and 188 essential frequencies were extracted, then used for fatigue calculation in SACS software. Two wave spectra, P-M and Johnswap, are employed to provide a complete picture of wave circumstances. Fatigue is calculated using Miner's law and the Rayleigh distribution for long-term stress distribution. The finite element model uses Timoshenko beam elements, lumped mass, and springs. The study provides insights into fatigue damage under various wave load conditions, considering the unique characteristics of Chabahar Bay. The findings confirmed that the maximum effect on fatigue damage is attributed to the 5th-order Stokes theory, the stream function, and the Airy theory, respectively. Moreover, this evaluation confirmed that wind-wave misalignment decreased fatigue damage, which highlights the importance of wave-wind misalignment in mitigating fatigue damage. Also, the P-M spectrum exhibited a higher fatigue index in comparison with JONSWAP.