A Simplified Nonlinear Analysis Procedure for the Flexible Risers in Subjected to Combined Loading Effects

A dynamic analysis of flexible risers in large-scale domain remains the offshore industry’s most challenging problems. The cross section of flexible risers, consisting of multiple metallic and plastic layers, experiences inter-layer slippage during cyclic bending. This results in nonlinear and hysteretic bending behavior with rapid dissipation of energy. For the dynamic analysis for flexible risers in the large scale domain, this study replaces all layers of risers with simple beam elements with a nonlinear beam model. This simplified beam model traces the curvature to bending moment relation and captures the variation of stiffness due to the onset of slippage. The suggested methods formulate both the change of configuration due to large deflection and contact between risers and seabed, therefore more realistic and effective analysis can be achieved. In the current study, the details of the analysis method are described. Main formulation methods of the total Lagrangian framework and the interaction between risers and seabed are described as well as the nonlinear bending model for flexible risers. The validity of the developed method is examined through some case studies, and the results show how the bending nonlinearity of flexible risers affects the overall behavior of riser systems during its operation.