Here, the performance of a steel lazy-wave riser (SLWR) was numerically investigated and compared to a conventional steel catenary riser (SCR) for an internal turret and spread-moored FPSO in extreme 100-yr return and ambient metocean conditions. As expected, the SLWR demonstrated favourable characteristics by the elimination of local dynamic buckling in the touch down zone (TDZ) via a wave configuration that decouples surface-motion, hence significantly reducing the maximum stress and fatigue damage. Non-collinear waves and current in the oblique direction relative to the vessel heading showed amplified stress concentrations in the sag and hog sections as a response to the increased compressive (heave and pitch) vessel motions. Correspondingly, in the ultimate limit state, a SLWR showed similar stresses for both turret and spread-moored FPSOs. However, the turret-mounted SLWR demonstrated a less superior fatigue life compared to its midship-mounted, spread-moored counterpart, owing to riser hangoff location differences and correspondingly varied motions experienced by the riser.
A Steel Lazy Wave Riser for Turret vs. Spread-Moored FPSO in Extreme and Wave-Induced Fatigue Conditions
Szczepanski, D, Balash, C, & Martens, M. "A Steel Lazy Wave Riser for Turret vs. Spread-Moored FPSO in Extreme and Wave-Induced Fatigue Conditions." Proceedings of the ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. Volume 5: Pipelines, Risers, and Subsea Systems. Madrid, Spain. June 17–22, 2018. V005T04A078. ASME. https://doi.org/10.1115/OMAE2018-78736
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