Structural integrity analysis of marine dynamic cables

Report, 2024

Over the last two decades, there has been a global emphasis on renewable energy due to the climate change crisis. This has been a catalyst for tapping into offshore renewable energy sources such as wave energy convertors and offshore wind farms. This has resulted in the need for durable marine dynamic power cables, with long fatigue life, to utilise theses sources. Offshore power cables are typically designed to have a service life of around twenty-five years however, a pattern is emerging where these cables are only lasting ten years or even as low as two. The main consensus as to why the fatigue life is so short is due a combination of global and local fatigue, and a phenomenon called water treeing. The global fatigue is due to the harsh oceanic sea states that the cables will endure, fretting and wear are the main contributors to local fatigue of the cables. Water treeing is the development of a crack in the insulating material of the cable, these cracks grow due to the mechanical and Maxwell stresses acting on the crack whilst the cable is in operation. The purpose of this paper is to develop numerical simulation methods to analyse the structural integrity of marine dynamic power cables and estimate their fatigue life. To perform a comprehensive global analysis of the cable, SIMA and MATLAB are used to identify critical regions along the cable’s length. This serves as a basis for subsequent local models where Abaqus and Python can be implemented to calculate the maximum wear depth and accumulated damage due to fretting. To conduct analysis of water tree crack propagation COMSOL and MATLAB will be implemented to analyse the effects of both mechanical and Maxwell stresses on the water tree crack, leading to an estimate of the overall fatigue life.