Quasi-static Analyses of Slender Structures with Complex Cross-Sections using Explicit FEM Codes
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It has previously been done analyses to find global stiffness values of an umbilical cable, with mixed results or no results at all when subjected to bending. There have also been difficulties in finding a distinct stick-slip point during bending. In this thesis, several models have been examined to get a step closer to resolve these particular issues. To begin with, a very simple flexible cable has been tested to see if the program ANSYS LS-Dyna can provide good global stiffness values, then of course with the use of an explicit scheme. When this first analysis gave good results, it was possible to conclude that the program could handle analyzing long slender structures with good accuracy. Further it was also developed a model with the aim of predicting the stick-slip phenomenon during bending. Results from this model could imply that there existed a stick-slip point, only a short time after the bending started. Finally, a last model was developed, including two armour layers wound around a cover of polyethylene. Other analyses have had problems with the behavior of the tendons during bending, that is they have been spreading, and not been following a loxodromic curve. Different cable lengths were tested, showing relative good results for the axial- and bending stiffness, but not so good results for the torsional stiffness. In addition to be able to develop models that could give realistic global stiffness values, focus have been on reducing the CPU time as much as possible. Therefore, much time has been spent on modeling the models right, and choosing the right path and length of loading.