| As a composite structure, offshore flexible pipe has lower bending stiffness, lower weight, better chemical and fatigue resistance compared with steel pipe. So flexible pipes have been widely researched and used. But for the complexities in the design and manufacture of flexible pipes, only a few companies in the world have this technique. In China, basic research and technical development about it is little in this field.Offshore flexible pipes are classified into two categories:bonded flexible pipe and non-bonded flexible pipe which is the main type of offshore flexible pipe. Local analysis which is very important in the design of offshore flexible pipes is to predict the mechanical properties, the distribution of stress in the structure, failure model and so on. But the frictions and contacts between layers will cause great nonlinear response of flexible pipes which will also increase the difficulties in the analysis. In the past 20 years, lots of papers were released about the local analysis, but all of them neglected the friction effects which cause highly nonlinear behavior of un-bonded flexible among the hypotheses. Because of the great limitations of these analytical solutions in the practical applications, the local analysis seems more necessary nowdays.So this paper will try to do the cross-section analysis of non-bonded flexible pipes using finite element method. We will include the friction and contact effect in the analysis. In the FE analysis, explicit algorithm is used to do the quasi-static analysis avoiding the convergence problems in implicit algorithm. Accordiong to a detail reasearch, a detail local FE model is built. Basic an analysis about how to ensure the accuracy of quasi-static analysis, the equal axial stiffness, equal tensional stiffness and equal bending stiffness of flexible pipes is calculated and compared with the exisiting experiment results which will give some guide and experience about this kind of reasearch. |
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