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SUBSEA CABLES

stresses at every point of contact. (see   multiphysics analysis is the option to             a.
Figure 1).”                                explore many loading conditions on                 b.
                                           various cable designs and compare the
   Continuum Blue’s answer was to build    results in a very short space of time.
a bespoke, or customized program,
so that JDR could quickly and easily          “It now takes two days to build a full
generate the 3D cable structure using      3D cable model ready to solve from an
COMSOL Multiphysics® software and its      initial design and 2D drawing, and from
Livelink™ for MATLAB® to build the cable   there it is left to COMSOL® software to
model (see Figure 2). The MATLAB® code     solve the various load conditions needed
added advanced material properties         to be assessed. We can conduct seven
and relations from Continuum Blue’s        or eight different types of analyses. For
extensive materials database, and          example, we test different axial load
utilized these properties to help define   conditions and various bend radiuses.
the bespoke contact expressions and        This allows JDR to assess many design
parameters that were necessary to solve    scenarios, where comprehensive stress,
the contact analysis. Everything was then  strains, and contact analysis plots can be
imported into COMSOL Multiphysics          analyzed, ensuring cable survival during
so that it could be solved. Wires were     laying and use. This improves the life
modeled as contact pairs moving            of the cable while reducing the costs
between a sliding surface and analyzed     involved in testing and manufacturing
for pure bending, pure tension, and a      (see Figure 3).”
combination of both.

   According to Yeoman, the beauty of

                                                                                              FIGURE 3. a.) Stress analysis of subsea
                                                                                              cable components under combined bend
                                                                                              and axial load conditions (isometric & front
                                                                                              view). b.) Detailed stress analysis of armor
                                                                                              layered structures only.

FIGURE 2. Screenshot of the bespoke cable building code developed by Continuum Blue.          èMORE INFORMATION, LESS
Top left: Cable cross section. Bottom left: Input parameters. Right: Sectional 3D Structure.  COST
The colored regions indicate various components within a subsea cable that include armor
layers (red), various hose types (large high pressure (magenta), medium pressure (yellow),    “The first time we adopted this approach
and low pressure (green)), quad core structures for power and data transmission (cyan),       it worked really well,” comments Poole.
and various filler elements (blue).                                                           “The models were clear, the local stress
                                                                                              analysis was reliable and we were able
                                                                                              to feed the values obtained into our
                                                                                              OrcaFlex models.” JDR has now worked
                                                                                              with Continuum Blue on developing
                                                                                              its capabilities, and JDR can now easily
                                                                                              analyze subsea cable structures with
                                                                                              multiple internal counter-rotating
                                                                                              structures and up to six protective armor
                                                                                              layers. From ten weeks on the original
                                                                                              project, turn-around time is now down
                                                                                              to two weeks and the amount of data
                                                                                              produced has risen fivefold. Additionally,
                                                                                              analysis can be half the cost of physical
                                                                                              testing.

                                                                                                 While some of JDR’s customers still
                                                                                              choose physical testing, others are opting
                                                                                              for a combination of global and local
                                                                                              analysis. “We are simply providing our
                                                                                              customers with a choice and we plan to
                                                                                              extend our use of COMSOL so that we can
                                                                                              continue to give them more information,”
                                                                                              concludes Poole. v

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