Subsea cables and umbilicals are installed in areas with harsher environments, with increasing physical impacts, and with lower temperatures. This calls for an increasing demand of optimal cable designs, requiring increased analysis accuracy followed by verification through physical testing. The cable's bending stiffness and the cable elements' bending stresses are among the most important parameters established through cable analyses. The bending stiffness is essential for subsequent analyses as it determines how the cables behave during handling, installation, and operation. This paper presents the development of a dynamic bending stiffness test rig that Nexans Norway AS has built in order to verify the bending stiffness models developed through an internal R&D study. The rig is located inside a refrigeration chamber which controls the cable's temperature in order to study its temperature sensitivity. The verification of the rig was performed by comparing calculated bending stiffness values based on test data compared to a known bending stiffness value of an accurately produced super duplex steel tube.
As the offshore industry is operating in ever deeper waters, subsea cables and umbilicals are exposed to harsher environments with increasing physical impacts and with lower temperatures. In the subsea cable and umbilical industry, this calls for an increasing demand of optimal cable designs, requiring increased analysis accuracy followed by verification through physical testing.
The cable's bending stiffness and the cable elements' bending stresses are among the most important parameters established through cable analyses. The bending stiffness is essential for subsequent analyses as it determines how the cables behave during handling, installation, and operation. The bending stresses relate the cable's bending curvature to the corresponding element stresses which are decisive for analyzing the cable's fatigue properties and capacity (allowed combinations of axial cable tension and cable bending curvature).
Bending stiffness and bending stresses are a complex topic from an analysis perspective, in particular due to the complex shear interactions between the cable elements at cable bending. The scientific literature provides a large number of publications on bending stiffness and bending stresses. Lutchansky (1969) calculates bending stresses of helical cable elements based on the assumption that the shear forces are proportional to the shear displacements between the helical cable element and the beneath sheath. The excellent PhD thesis of Kebadze (2000) provides a comprehensive introduction to cable analyses including bending stiffness and bending stresses. Kebadze uses Coulomb friction to model the shear forces between the cable elements at cable bending.
