Non-Linear Stress Analysis of Complex Umbilical Cross-Sections

Abstract

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: • Axial strain versus axial force; • Axial strain versus torsion; • Torsion versus torsion moment for various axial force levels; • 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: • Arbitrary geometry modelling including helical elements wound into arbitrary order; • The helical elements may include both tubes and filled bodies; • Elastic, hyper-elastic, and elastic-plastic material models; • Initial strain; • Contact elements, including friction; • 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.

An Overview of Structural Design, Analysis and Common Monitoring Technologies for Floating Platform and Flexible Cable and Riser

“…Numerical studies have been performed to analyze the bending behavior of the unbonded flexible pipes. Saevik and Ekeberg (2009) developed specialized software by combining the numerical method with model tests, material tests, and full-scale experiments to analyze stresses in the armor wire section based on curved beam and thin shell theory. Zhang and Qiu (2007) proposed a simple model to simulate the behavior of tensile armored steel wire during unbonded flexible pipe bending and analyzed the displacement field of the wire, stress-strain in the wire cross-section, armored wire extrusion with other layers, and bending hysteresis.…”

Friction, Contact Pressure, and Nonlinear Behavior of Steel Tubes in Subsea Umbilicals

“…Hence, there are more uncertainties related to prediction of frictional stresses due to larger pitch length and the elastic energy stored in an element during bending, which has encouraged many researchers to develop methodologies to accurately calculate fatigue life of umbilicals by considering nonlinear effects and frictional stresses. Among these efforts are works by Witz and Tan [9], Saevik and Ekeberg [10], Sodahl et al [11], and Qing-zhen et al [12].…”

Friction models for evaluating dynamic stresses in non-bonded flexible risers

“…More importantly, static and dynamic friction coefficients and the corresponding smooth transition between these two friction coefficients were observed by Rabinowicz [8] in some tests. Several works have been reported in the literature, see [3,9,10,11,12,13], concerning the hysteric bending behavior of helix elements versus full scale tests. Most of the work demonstrated that good correlation in terms of axial stress of helix elements and hysteresis bending moment-curvature relationship.…”