Bending Properties of Unbonded Flexible Risers with Composite Materials

Abstract

Unbonded flexible risers are widely applied to transport oil and gas resources from seabed to platform, and composite cylindrical layers are sometimes contained due to design requirements. Based on an 8-layer unbonded flexible riser model, the bending properties of the unbonded flexible risers with composite cylindrical layers are studied. A theoretical method of combining axisymmetric and bending loads acting on unbonded flexible risers is proposed, and a numerical method with detailed geometric characteristics taken into account is established for verification. The influence of two typical composite materials as well as the fibre volume fraction on the bending properties of the unbonded flexible risers is analyzed. The theoretical and the numerical results are in good agreement, which shows that the bending properties of the unbonded flexible risers are greatly affected by the axial Young’s modulus of the composite cylindrical layers, and composite material with larger axial Young’s modulus would greatly enhance the bending stiffness of the unbonded flexible risers, expecially in the full-slipping stage. In addition, the axial tensile stiffness and bending stiffness of full-slipping stage are proportional to the fibre volume fraction of the composite cylindrical layers.

Keywords

• unbonded flexible risers
• composite materials
• cylindrical layers
• bending stiffness
• fibre volume fraction