Abstract

Prediction of vortex induced vibration (VIV) and estimation of fatigue damage for subsea multi planar structures exposed to significant current condition is an important topic for subsea engineering. Due to the multi-planar characteristics of structure, the VIV induced stress states of subsea jumper are normally with the combination of flexural and bending stresses. Consequently, the associated fatigue is a multi-axial fatigue problem. In this study a novel energy-critical plane method by Farahani [1][2] has been used for fatigue assessment instead of the traditional method with utilizing the stress range and SN curve, for example the 1st principle stress method as recommended by DNVGL-RP-F105 (2017) [3]. By using this method, the phase change of the stress from different modes is considered. A case study based on previous jumper experiments by ExxonMobil is included. Fatigue results have been compared with DNVGL-RP-F105 (2017) [3] approach. Advantages of energy-critical plane approach have been discussed. Phase change between flexural and torsional stresses has been successfully captured and its effect on fatigue damage has been presented. Additionally, some discussions have been performed with respect to the application of DNVGL-RP-F105 (2017) [3] to calculate the VIV fatigue to subsea rigid jumpers.

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