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An Efficient 1st Order Stress Hysteresis Model for Helically Laid Rectangular Elements in Power Cables and Umbilicals


 It is essential to calculate the mechanical stress efficiently in power cables, umbilicals and hybrids to reduce the risk of failure and halts during production, transportation, installation and operation phases. The global analysis, where these conditions are simulated, can under certain circumstances produce a very large volume of data, which often needs to be processed into a specific format or transformed into a result.
 This paper describes a model for helically laid rectangular elements, that efficiently process large data volumes into 1st order stress. The hysteresis model applies the results from the global analysis as input, together with stress parameters from local FEA, element dimensions and material properties. As it is positioned as a link between the global and local analysis, it calculates the stress in time domain, which can either be used directly or processed further.
 A case study is also being presented in this paper where time domain results from the 1st order stress model are first run through a rainflow counting algorithm, which extracts all the ranges and their associated cycles. These ranges are afterward measured against the element’s SN curve, followed by a Palmgren-Miner summation to give an estimate of the local fatigue damage. The model has through this study shown to give an improved fatigue life compared to an alternative 1st order technique used in the past and is found highly efficient compared to its complexity.