Research on contact algorithm of unbonded flexible riser under axisymmetric load

Review of the Development of an Unbonded Flexible Riser: New Material, Types of Layers, and Cross-Sectional Mechanical Properties

“…Taking a class of eight-layer 2.5-inch unbonded flexible risers as an example, an equivalent simplified eight-layer numerical model and a fivelayer numerical model (the internal four-layer structure was equivalent to one layer) were established, and the effect of simulating the cylindrical shell layer using a shell element or a body element was taken into account to study the axial load carrying capacity of the unbonded flexible risers. Zhang et al [11] also developed a numerical model containing detailed geometries, and all the layer structures were also simulated using body elements and analyzed the structural response under external loads such as axial tension, torque, and internal and external pressures. In summary, the establishment of a three-dimensional numerical model of an unbonded flexible riser under axisymmetric loading has roughly gone through development from simplifying part of the layer structure to taking into account the detailed geometrical properties of each layer, and due to the existence of a large number of geometrical nonlinearities and contact nonlinearities within the numerical model, it is generally solved by explicit algorithms.…”

“…Taking a class of eight-layer 2.5-inch unbonded flexible risers as an example, an equivalent simplified eight-layer numerical model and a five-layer numerical model (the internal four-layer structure was equivalent to one layer) were established, and the effect of simulating the cylindrical shell layer using a shell element or a body element was taken into account to study the axial load carrying capacity of the unbonded flexible risers. Zhang et al [ 11 ] also developed a numerical model containing detailed geometries, and all the layer structures were also simulated using body elements and analyzed the structural response under external loads such as axial tension, torque, and internal and external pressures.…”

“…Furthermore, the test results were compared to the predictions provided by several research organizations; therefore, most of the subsequent theoretical and numerical method studies are based on this test as reference and validation, and the test results show that the experimental data of the structural response under axial tension and torque loading are in good agreement with the theoretical predictions. Ramos Jr. et al [ 11 , 93 ] investigated the relationship between axial force and axial elongation of unbonded flexible risers by loading cyclic axial force, and the results showed that unbonded flexible risers also suffer from some nonlinear hysteresis under cyclic axial force. Vargas-Londoño et al [ 94 ] found a similar phenomenon in a subsequent experimental study and found that the different spiral steel strips in the tensile armored layer did not have the same load-carrying capacity.…”

Nonlinear Slippage of Tensile Armor Layers of Unbonded Flexible Riser Subjected to Irregular Loads

“…On the contrary, the standard solving algorithm has a higher solving efficiency; however, the calculation is not easy to converge while considering the geometric and material nonlinearities as well as the nonlinearities of interlayer and intralayer mutual contact. With the improvement of computer computational performance, more and more scholars began to consider the establishment of numerical models containing the detailed geometric characteristics of unbonded flexible risers [20,[27][28][29][30][31][32][33][34]. Among them, Ren et al [35][36][37] numerically simulated the unbonded flexible riser model using its actual geometry, including the S-type carcass layer and the Z-type pressure armor layer.…”