A global-local fretting analysis methodology and design study for the pressure armour layer of dynamic flexible marine risers

In this paper, a global-local fretting design methodology for the pressure armour layer of flexible marine risers is outlined. This includes global dynamic riser analysis, geometrical and analytical sub-models and local nub-groove contact finite element analysis. Furthermore, a fretting test rig is developed and utilised to quantify coefficient of friction and wear coefficient under representative nub-groove loading conditions. The combination of the global-local computational methodology and experimental characterisation of pressure armour wire material allows for the development of running condition fretting maps. This identifies design criteria for critical riser global curvatures that are associated with minimum number of cycles to failure. The design methodology presented in this paper is applied to a realistic riser design study, using extreme sea-state loading conditions. In this case study, the predicted pressure armour fretting fatigue lives are found to be in the same range as the plain fatigue lives of the tensile armour layer.The authors would like to thank the Irish Research Council and Wood plc. for funding of this project through the Enterprise Partnership Scheme (EPSPG/2013/638), the National University of Ireland for funding through an NUI Travelling Scholarship. The authors also wish to acknowledge the support of the NUI Galway Engineering Building technical staff; particularly Mr. Bonaventure Kennedy and Mr. Patrick Kelly.2021-09-1