Flexible Riser Bending Hysteresis Influence on Bend Stiffener Response

Abstract

The bending stiffness response is an important parameter in the lifetime assessment of unbounded flexible risers. Its behavior is governed by interlayer friction mechanisms leading to a non-linear moment x curvature relationship that is highly dependent on the internal pressure. In order to investigate its influence on the critical bend stiffener hang-off region response, a detailed finite element analysis is carried out using a specialized tool for a short segment length of a selected 2.5″ ID riser cross section. Different internal pressures are numerically analyzed and the resulting local hysteretic bending response is then adjusted and directly incorporated into a global dynamic analysis tool that uses an equivalent elasto-plastic formulation with a hardening parameter that controls the behavior of the slippage mechanism. A fully coupled irregular wave dynamic analysis is then carried out and the flexible riser curvature distribution response in the bend stiffener region compared for different bending hysteresis models adopted.

Improving the Mathematical Formulas for Identification of Bitumen's Viscoelastic Properties at Large Shear Strains

“…Proceedings of the 56 th SIMS October 07-09, 2015, Linköping, Sweden For many structures, for example steel tubes, the bending moment and the bending curvature are related through a real (non-complex) coefficient of proportionality, which is referred to as the structure's bending stiffness. However, for cables and umbilicals the bending characteristics may be nonlinear due to nonlinear materials, such as lead sheaths on power phases, and due to stick / slip behavior of helical elements as explained in Féret and Bournazel (1987) and in Caire (2014). Further, the bending characteristics may include dynamic behaviors due to viscoelastic materials, which is the case for cables and umbilicals with bitumen-coated armor wires.…”

Proceedings of the 56th Conference on Simulation and Modelling (SIMS 56), October, 7-9, 2015, Linköping University, Sweden

“…Proceedings of the 56 th SIMS October 07-09, 2015, Linköping, Sweden For many structures, for example steel tubes, the bending moment and the bending curvature are related through a real (non-complex) coefficient of proportionality, which is referred to as the structure's bending stiffness. However, for cables and umbilicals the bending characteristics may be nonlinear due to nonlinear materials, such as lead sheaths on power phases, and due to stick / slip behavior of helical elements as explained in and in Caire (2014). Further, the bending characteristics may include dynamic behaviors due to viscoelastic materials, which is the case for cables and umbilicals with bitumen-coated armor wires.…”