Bend stiffeners are critical components for flexible risers and umbilical cables employed to ensure a safe transition at the riser-vessel interface, avoiding overbending and accumulation of high cyclic fatigue damage. The analysis and design of bend stiffeners usually consider the system as a unique beam, in which the pipe bending response is linear. However, the structural mechanics of these complex layered structures is governed by internal friction mechanisms that yield non-linear moment versus curvature relationship. In fact, the pipe structure exhibits an approximately bi-linear hysteretic bending moment against curvature relationship arising from the progressive activation of friction and consequential slipping between adjacent layers. The flexible pipe bending stiffness substantially reduces after a given critical curvature (i.e., after slip between adjacent layers) is reached. In this paper, the effect of this flexible pipe non-linear response on the bend stiffener design is evaluated. The mathematical formulation and the solution methodology are presented. A set of four non-linear ordinary differential equations is obtained from geometrical compatibility, equilibrium of forces and moments and constitutive equations and a numerical solution is obtained using the shooting method. A finite element analysis is developed to validate the analytical model and to assess the effect of the radial clearance between the structures on the bend stiffener response. A case study is presented for some static loading conditions and it is observed that the bending stiffness bi-linear behavior may not affect the bend stiffener extreme load design results, but it may significantly influence the fatigue analysis.
- Ocean, Offshore and Arctic Engineering Division
The Effect of Flexible Pipe Non-Linear Bending Stiffness Behavior on Bend Stiffener Analysis
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Caire, M, & Vaz, MA. "The Effect of Flexible Pipe Non-Linear Bending Stiffness Behavior on Bend Stiffener Analysis." Proceedings of the ASME 2007 26th International Conference on Offshore Mechanics and Arctic Engineering. Volume 3: Pipeline and Riser Technology; CFD and VIV. San Diego, California, USA. June 10–15, 2007. pp. 103-109. ASME. https://doi.org/10.1115/OMAE2007-29108
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