Pierre Blusseau looks at the use of finite element analysis (FEA) in the development, design, and review of cabling systems.
Finite element method (FEM), previously limited to the aeronautical and civil industries, has been adopted by a number of other industries, including the offshore energy sector, with the rapid decline in computer cost and increase in computer resource. The FEM methodology solves complex problems by creating multiple discrete problems that can be solved in relation to each other.
BPP-Cables has been using finite element analysis (FEA) packages for more than a decade for a large variety of physics problems, such as linear and non-linear structural analysis, vibration analysis and heat transfer analysis. Its engineers routinely perform local FEA in the development, design and review of cabling systems.
The use of FEA in research and development projects provides a powerful analysis tool to rapidly assess and verify novel engineering solutions. It can reduce and sometimes eliminate expensive and time-consuming physical testing.[Page Break]
BPP-Cables assessed the mechanical performance of corrugated layers as part of a feasibility study on screen sheath options for high voltage subsea cables using Abaqus, a recognised industry standard software package. Predicting the stresses in corrugated sheaths when subjected to tension and bending using classic mechanics hand calculations is difficult and time consuming.
However, by modelling the corrugated layers in FEA software it allowed BPP-Cables to study hundreds of different corrugated profiles (ie, various corrugation height and pitch values.) Results were used to select optimum sheath configurations for different cable loading conditions. The use of Python scripts for the automatic creation, submission and post-processing of the analysis tasks reduced the overall duration of this study.
Cable design also benefits from the use of FEA. Thermal analyses can be performed on cable cross-sections to estimate heat dissipation from electrical conductors into the external environment.[Page Break]
Outputs predict thermal stress levels as well as temperature distributions (which can be compared for validation against hand calculations described in IEC standards), in all cable components. FEA is particularly valuable when investigating the suitability of cable designs for complex or onerous operating conditions. It can be used to predict the change in outer diameter of a downhole cable under high tensile load from the suspended equipment.
FEA is a valuable tool for review and verification of cable ancillary components. These include cable protections systems, such as bend stiffeners and bend restrictors. The analysis determines the system's stiffness curves and the component stresses under loading ensuring the cabling system's integrity.
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Pierre Blusseau is a Senior Engineer, BPP-Cables, London. UK. www.bpp-cables.com