Frictional effect on circular armour wire lateral buckling in umbilicals

The present paper addresses the frictional effect on the circular armour wire lateral buckling in an umbilical for wet annulus condition. A nonlinear static finite element model is developed where only one single circular armour wire is simulated and the contact interface with the neighboring layer is represented by a deformable rigid toroid surface. The isotropic Coulomb friction model regularized with an elastic domain is implemented to simulate the shear interaction. Case studies are carried out by applying different axial compression and cyclic bending curvatures between zero and a maximum value in one bending direction. The minimal axial compression that may cause the armour wire lateral buckling after numerous bending cycles is approximately estimated by fitting the numbers of bending cycles to initiate the buckling under different axial compression through an empirical model. The friction coefficient and the maximum elastic slip employed in the Coulomb friction model are varied for the parametric studies, and their effects on the armour wire sticking-slipping status, the end shortenings and deflections in cyclic bending, the critical lateral buckling limit, as well as the stress state at the onset of lateral buckling are extensively discussed.