One of the many design challenges in offshore industry is the fatigue life estimation of risers due to the loading that is generated by vortex induced vibration (VIV). In deep waters, where the long risers are subjected to sever VIV-induced stresses and may encounter multi-modal vibration, the VIV-induced stresses could be the most significant contributor to the overall damage of the structure. The variable amplitude nature of the stress-time history often creates significant errors in the estimated fatigue life of the structure. The irregularities in the loading scenario could also create a considerable degree of plasticity at the crack tip, thus leading to. variability in material response. The uncertainties in the estimated fatigue damage under such a variable amplitude loading has resulted in the use of large safety factors by industry for establishing the fatigue life of the risers.

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