This paper presents a significant methodology advancement that addresses one of the industry's most challenging problems:the accurate prediction of detailed local stresses in unbonded flexible risers. Flexible risers exhibit highly nonlinear dynamicbehavior due to the stick/slip interaction between the pipe wall layers in compliant systems that undergo large threedimensionaltranslations/rotations. Practical, accurate prediction of critical flexible pipe component responses requires anefficient method capable of incorporating detailed flexible pipe models into a global nonlinear dynamic analysis. Currentindustry practice is a two-step global/local approach involving a global nonlinear analysis with 1D centerline models, whichmay include bending hysteresis effects, followed by local analysis of a detailed model segment to the global results to predictcritical response items such as armour wire stresses.A Nonlinear Dynamic Substructuring (NDS) framework is developed that expands the classical methods of dynamicsubstructuring and component-mode synthesis to geometrically and locally nonlinear problems. This evolution/integration ofcapabilities enables the computationally efficient inclusion of detailed flexible pipe models into, and recovery of detailedresponse/stress time-histories directly from, the global nonlinear analysis itself. The NDS methodology is benchmarkedagainst published work involving the large deformations static and dynamic global analysis of a flexible riser. The fullpotential of the method is then demonstrated by efficiently incorporating 3D detailed flexible pipe substructure models, withbending hysteresis, into a global system nonlinear analysis and recovering stress time-histories in tensile armour layers.
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