Page 26 - Oil and Gas Simulations
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JDR CABLES, UNITED KINGDOM

Analysis of Subsea
Umbilicals and Cables

Simulation has enabled JDR to provide its customers with
full stress analysis in addition to physical testing. At half the
cost for five times the amount of data, this option is now a
popular choice.

by JENNIFER HAND                             Automation Engineer, is responsible for         An umbilical cable on a drum ready to be
                                             testing and analyzing products at JDR,          placed on a ship for laying.
Deep water pressure, wind and wave           which custom-designs and manufactures
forces, and the rough ocean bed—these        subsea power cables, umbilical systems,         from the time and cost factors, we cannot
all have to be anticipated in the design of  and reeler packages for a broad range           replicate conditions 100%.”
underwater cables for the offshore oil and   of applications in the oil and gas and
gas industry. Known as umbilical systems,    renewable sectors.                                 JDR was already using OrcaFlex, a
these cables house power, hydraulic                                                          specialized package designed for the
control, electric signal, fiber optic, and      “In order to understand fatigue              offshore marine industry, to analyze
chemical injection links, and therefore      properties and performance, a typical           the whole system formed by ship, cable,
must be extremely durable—particularly       fatigue regime for an umbilical is to           seabed, weather, water, and wellhead.
under severe coupled bending, torsional,     undergo 100,000 usage cycles around a           After ISO standards were updated in 2009
and axial loads. In addition to these harsh  sheave wheel on a large fatigue rig,” says      with new specifications for the analysis
conditions, umbilicals have to withstand     Poole. “At approximately 6,000 cycles per       of umbilicals, JDR began conducting local
handling under tension as they are           day, plus all the other required testing,       stress and thermal analysis of their cables
reeled out and back numerous times by a      it takes at least a month to complete the       using simulation.
winch designed to have a tight radius to     process and costs between $30,000 and
minimize its footprint on a ship’s deck.     $50,000 for all the resources involved. It is      Umbilicals, however, pose a particularly
                                             critical that we can predict the behavior       complex analysis challenge, as Poole
   Because umbilicals are long, they need    of our products to ensure they meet the         explains: “Typically, they incorporate
to be strong and are generally very heavy    requirements, so while physical testing is      multiple layers of wire with helical
and difficult to handle. Thus, the physical  very important, it has its limitations. Apart   geometries and multiple contact points,
testing of these cables is cumbersome                                                        or they contain aramid (Kevlar® fiber)
and expensive. Tim Poole, Design                                                             braid, a synthetic material that is very
                                                                                             difficult to analyze because of its braided
                                                                                             construction.” JDR therefore turned to
                                                                                             COMSOL Certified Consultant Continuum
                                                                                             Blue for some specialist assistance.

FIGURE 1. Illustration of the counter-rotating armor layered that includes multiple contact  èHELICAL WIRES WITH
points of individual armor wires.                                                            MULTIPLE CONTACT POINTS

                                                                                             Dr. Mark Yeoman of Continuum Blue
                                                                                             picks up the story. “Our starting point
                                                                                             was to model a 2D cross-section of a
                                                                                             cable, including material specifications.
                                                                                             What was of concern was that the cable
                                                                                             cross-section had a double armor layered
                                                                                             structure with 50-60 armor wires in each
                                                                                             layer, where each layer twisted along
                                                                                             the length in the opposite direction to
                                                                                             the other layer. Building the model to
                                                                                             reflect bend and axial load conditions
                                                                                             with contact for the internal structures
                                                                                             was done, but also included adding in the
                                                                                             contact for these counter-rotating armor
                                                                                             wires. This resulted in well over 3,000
                                                                                             localized regions of high contact pressure
                                                                                             along a unit length of cable, creating high

OIL GAS&                                     Kevlar® is a registered trademark of E.I. du Pont de Nemours and Company.
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