A Numerical Model Research For Structural Analysis Of The Unbounded Flexible Riser

The unbounded flexible riser is suitable for rough deep-sea conditions due to its structural features, i.e. small rigidity, light in mass, strong corrosion resistance and anti-fatigue performance. The design process of unbounded flexible pipe is very complicated because of its complex structure. One of the problems associated with the complex design of unbounded flexible risers is the difficulty in its analysis. To capture the many important aspects of their structural response, including the energy dissipation due to frictional slip between layers, the hysteretic response and the fatigue damage, efficient and accurate tools are required. However, the numerical simulation analysis of the unbounded flexible riser are confronted with a number of challenges resulted from its strong nonlinear characteristics in the friction and contact between different layers of the unbounded flexible riser. The aim of the present project is to develop a detailed numerical model for unbounded flexible pipe to predict the structural response under complex loading.There two typical methods in previous studies on the FEM for the flexible pipe. One model is presented with its emphasis on modeling the polymer layer and helical tension armor layer. The carcass and pressure armor layers are not including, so the model can be only used to analysis the response under simplex loading. And because of the uncomplicated modeling, the analysis results can be only verified by analytical results instead of experiment measured results. The other model used shell element to simulate polymer layer and beam element to simulate helical tendon. This method is very effective and efficient when used to predict response under radial loading. It cannot be used to analysis structural response under complex loading because of its neglecting frictional effect among layers. However, the idea of using orientation shell element to model carcass and press armor layers is worth considering.This paper presents a detailed finite-element analysis of unbounded flexible risers. In the finite-element model, all layers are modeled separately with contact inter faces between each layer. The finite-element model includes the main features of the riser geometry with very little simplifying assumptions made. The numerical results are compared to the analytical solutions and experiment measured results for tensile and torsion loading. The very good agreement found from numerical and experimental comparisons validates the use of our numerical model to provide benchmark solutions against which further detailed investigation will be made.