Tension-bending analysis of flexible pipe by a repeated unit cell finite element model

Unbonded flexible pipes consist of multiple subcomponents which interact through frictional contact. A full 3-D finite element analysis of unbonded flexible pipes is computationally expensive, and a more efficient approach for practical engineering purposes is required. This work presents a repeated unit cell (RUC) finite element model for analyzing flexible pipes subjected to combined constant tension and curvature. Periodic boundary conditions reduce the model size by taking advantage of the structural and loading periodicities, and by assuming uniform wire behavior in the armor layer. The RUC model is suitable for resolving the local tensile armor stress distribution and the global pipe response. A flexible pipe is studied with the RUC model for various tension-bending load configurations and the results have been compared with existing analytical models for validation. The study showed strong correlation between the RUC model and the analytical models, with some difference in the wire bending stresses. This difference can to some degree be explained by the difference in the wire kinematics assumptions. It is found that the proposed RUC model is a robust and computationally efficient approach for analyzing flexible pipes.