Theoretical and numerical analysis of bending behavior of unbonded flexible risers

• In the analytical model, heat consuming caused by tendons sliding is used in the derivation of bending stiffness.
• The axisymmetric loads have great impacts on bending moment–curvature relationship and tendons' axial stress ranges.
• Under bonded state, the axial stress of tendon armors is more sensitive to bending moment than that after sliding.

This paper presents theoretical and numerical study on bending properties of unbonded flexible risers. To capture nonlinearities in layer's sliding, the stress component due to slip-stick behavior is considered and energy conservation principle considering sliding-caused heat consumption is employed in the analytical model. Besides, a finite element model estimating mechanics of unbonded flexible risers' bending is proposed. In the finite element model, couplings between bending moment–curvature and axial stress as well as contact interaction among layers and tendons have been considered. The theoretical and numerical results were validated against the corresponding experimental data in literature and mutually compared in analyzing nonlinear bending behavior of flexible risers. Moreover, the impacts of axisymmetric loads on riser's bending behavior have been further investigated.