Umbilical cable is one of the key equipment for deep sea oil and gas exploration. To ensure structural safety and normal functioning, the umbilical cable is often presented with a specific global configuration for compensating for the floating body motion due to the harsh environmental load during operation. Considering the reciprocating periodicity of the dynamic response of the umbilical cable under ocean wave loads, the fatigue analysis is required to ensure the safe operation. However, the numerous sea conditions lead to a huge amount of calculation. Aiming at the global configuration design of the lazy-wave umbilical cable, this study carried out a global configuration optimization design method based on a few representative fatigue conditions. The design variables were the control parameters of the global configuration, and the total length and the cumulative fatigue damage were the two objective functions. By resolving the optimization formulation, an optimal global configuration design for a dynamic umbilical cable with antifatigue performance and economic cost was obtained.

Marine flexible pipe/cables, such as umbilicals, flexible pipes and cryogenic hoses, are widely adopted in ocean engineering. The reinforcing armor layer in these pipe/cables is the main component for bearing loads, which is a typical multi-layer helically wound slender structure with different winding angles for different devices. There has been no general theoretical methodology to describe the tensile performance of these flexible pipe/cables. This paper first introduces a theory to solve the tensile mechanical behavior of a helically wound structure. Based on the curved beam theory, a solution of the tensile stress of a helically wound slender is derived. Then, the deformation mechanism of the marine flexible pipe/cables structure with different winding angles is studied. Through comparing theoretical and numerical results, the deformation characteristic of the helically wound slender structure is further explained. It is found that a sectional torsional deformation generates when the structure with a larger winding angle is under tension condition, while the sectional deformation of the structure with a smaller winding angle is mainly tension. Finally, a couple types of marine flexible pipe/cables under the tension condition are provided to analyze the mechanical performance and compare the difference between different theoretical models. The research conclusion from this paper provides a useful reference for the structural analysis and design of marine flexible pipe/cables.