| Unbonded flexible pipes have been widely used in deep waters due to their ability to withstand harsh environmental loads and comply with the movements of the production units.However,determination of various mechanical characteristics of flexible pipes has never been an easy task due to their complex structure.In the end fitting region,the anchoring mechanism constrains the movements of tensile armours,which results in a higher bending stiffness and severe stress concentrations.For dynamic applications,such as a flexible riser,accelerated fatigue may also occur.Therefore,the end fitting region is always the crital area of integrity concerns,particularly of fatigue assessment.The main work of this thesis is as follows:(1)The analytical model related to end fitting effect on stress evaluation of tensile armours is reviewed.This model uses the Euler equation to find the path adopted by the armour as loaded,and covers the shortage of current models which do not consider the effect of the rigid boundary condition.An independent derivation is performed based on a thorough understanding of this model.The numerial verification in the literature is reproduced,and some improvements are made on the finite element model.(2)The stress calculation is conducted for the tensile armours in a 12-inch flexible riser operated in the South China Sea.Specifically,the AQWA package is firstly used to determine the hydrodynamic response of the FPSO;the OrcaFlex software is then employed to perform the global analysis to get the axial tensions at the top end;the armour stresses are finally calculated using the analytical model.The results show that the obtained tensions are relatively small due to the shallow water depth and riser configuration,yielding small axial stress and transverse bending stress in the wire.However,the ratios of bending stress over axial stress are high,which highlights the importance to take end fitting effect into account. |
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