Theoretical and numerical methods to predict the behaviour of unbonded flexible riser with composite armour layers subjected to axial tension

摘要

Unbonded flexible risers are widely applied to deep-water oil and gas production field, and their complex cross-section mechanical properties have always been a challenging issue in ocean engineering. Over the recent years, the traditional steel tensile armour layers of unbonded flexible risers are replaced by composite materials, owing to their advantages of lightweight and high strength. In this paper, a theoretical deduction based on energy method and a numerical method in consideration of detailed geometric properties are proposed to analyze the behaviour of the unbonded flexible riser with composite armour layers. Both the theoretical and numerical methods take full consideration of the material orientation of composite, and for the numerical model, two local coordinate systems are established to define the material properties of composite armour layers. Based on a 2.5-inches unbonded flexible riser model with eight-layers, some cases from theoretical and numerical methods are presented for validation. Then the effect of the fiber volume fraction of composite on the axial tensile stiffness, as well as the weight of the unbonded flexible riser, is discussed. Furthermore, characteristics analysis of axial stiffness is carried out and the effect of the boundary condition is discussed as well.