Study on the Nonlinear Tension—Torsion Coupled Stiffness of the High-Current Composite Umbilical Considering the Thermal Effect

The gradual advances of offshore oil and gas exploitation and the development tendency of equipment integration have prompted the design of a new type of the high-current composite umbilical to meet development needs. In order to study the mechanical behavior of the high-current composite umbilical (HCCU) and provide design suggestions, a theoretical analysis framework of the tension-torsion coupled behavior of the spirally wound structure is proposed, which focuses more on the radial mechanical behavior. Then, by considering the mechanical and thermal conditions during the operation of HCCU, a semi-analytical method of the tension and torsion stiffness of the high-current composite umbilical considering the temperature effect is established. Furthermore, a practical case of HCCU is given, and the thermal effect on the radial and axial mechanical behaviors are analyzed. It is found that the thermal effect has a significant influence on the radial stiffness, and shows non-linear variation characteristics. Finally, the sensitivity analysis is carried out to study the influence of the design parameter on the stiffness of tension and torsion. The results indicated that the equivalent radial stiffness and helical angle have obvious effect on the tension-torsion coupled stiffness, which can provide reasonable reference for the design of HCCU.