Nexans Norway is, together with Marintek, currently developing a software for detailed analysis of complex umbilical cross-section designs. The software development project combines numerical methods with small-scale testing of involved materials, as well as full-scale testing of a wide variety of umbilical designs, essential for calibration and verification purposes. Each umbilical design is modelled and comparisons are made with respect to global behaviour in terms of: 1. Axial strain versus axial force 2. Axial strain versus torsion 3. Torsion versus torsion moment for various axial force levels 4. Moment versus curvature for different tension levels. The applied theory is based on curved beam and curved axisymmetric thin shell theories. The problem is formulated in terms of finite elements applying the Principle of Virtual Displacements. Each body of the cross-section interacts with the other bodies by contact elements which are formulated by a penalty formulation. The contact elements operate in the local surface coordinate system and include eccentricity, surface stiffness and friction effects. The software is designed to include the following functionality: 1. Arbitrary geometry modelling including helical elements wound into arbitrary order 2. The helical elements may include both tubes and filled bodies 3. Elastic, hyper-elastic, and elastic-plastic material models 4. Initial strain 5. Contact elements, including friction 6. Tension, torsion, internal pressure, external pressure, bending and external contact loading (caterpillars, tensioners, etc.). The paper focuses on the motivation behind the development program including a description of the different activities. The theory is described in terms of kinematics, material models and finite element formulation. A test example is further presented comparing predicted behaviour with respect to full-scale test results.
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