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Theoretical and finite-element study of mechanical behaviour of central, large-diameter umbilical cables under tension and torsion

In recent years, mechanical behaviour of umbilical cables subjected to combined actions of tension and torsion during deep water installation and operation has become a more relevant matter. Extended from the model initially proposed by Knapp, a modified theoretical model has been developed to account for a number of features, such as different materials and geometries of helixes in the same layer, Poisson effects in helixes and a central, large-diameter, thin-walled tube with a double layer. A three-dimensional finite-element model using ABAQUS under tension–torsion load is used. Accordance of mechanical behaviour between the results validates the applicability of the theoretical model. The theoretical model and finite-element model are used for a better assessment of the effect of various important parameters such as helical pitch, Poisson effect, boundary conditions, friction, etc., on the mechanical behaviour of umbilical cables. Based on the parametric studies, a few conclusions are drawn which aim to assist with the design process of umbilical cables.