An analytical model is given to investigate the behavior of
unbonded flexible pipes under biaxial dynamic bending. The stickslip
conditions of each wire are studied in the framework of incremental
analysis by an operator splitting of the time step into a
stick-state prediction and a slip-state correction step. The tension
gradient is calculated using the classical return-mapping algorithm
and the obtained tension gradients are integrated numerically to
find the axial tension by imposing appropriate boundary conditions.
From the axial tension the bending moments with respect to
the principal bending axes of the pipe are obtained. Poisson's effect,
bending induced tension in the wire, shear deformations of
the supporting plastic layer and the changes of the effective torsion
and curvature increments of the wire after slip occurs are
taken into account in the model. The results of bending moment
ecurvature relationship from this model are compared with the
test data from simple bending and good correlations are found.
The comparison of the biaxial bending moment results between
this model and the available model also shows good agreement.