|
|
||
|
|
|
|
Floating offshore structures consist of 3 parts; topside process module, floating platform and subsea modules. Flexible pipes play a role of connecting the platform to flowlines. They are usually used for dynamic applications that receive various loads cyclically. With respect to mechanical behaviors, they have high axial tensile stiffness and low bending stiffness. The bending stiffness of flexible pipes is known to be about 1/25 of that of steel catenary risers with same diameter. This feature is due to the complex un-bonded multi-layers. The flexible pipes consist of metal and polymer layers. The model used in this paper is composed of eight layers. From the inside, carcass, pressure sheath, pressure armor, a pair of anti-friction tapes, a pair of tensile armor layers and fabric tape are laid as shown here
This and the next 2 images are from:
Dong-Hyun Yoo, Beom-Seon Jang and Ran-Hui Yun, “A simplified multi-layered finite element model for flexible pipes”, Marine Structures, Vol. 63, pp 117-137, January 2019, https://doi.org/10.1016/j.marstruc.2018.08.006
ABSTRACT: A flexible pipe connects offshore platforms to the flowlines and transport gas and oil. It may experience axial compression due to the reversed end cap effect during installation. This can trigger radial buckling or lateral buckling of tensile armor layers. The ultimate strength assessment of the flexible pipe is complicated and time-consuming due to material nonlinearity, large deformation, and nonlinear contact mechanism. These difficulties make the nonlinear analyses difficult to converge. This paper proposes a simplified 5-layered model which can improve the convergence without deteriorating the accuracy. Analytical methods are suggested to determine an equivalent layer to replace inner four layers. In addition, the factor of penetration tolerance (FTOL) of shell element layers needs to reflect the thinning of polymer layers, which makes the axial stiffness equal to the solid element model. Analytical methods are used to determine the factor and a stepwise increasing approach is applied in a numerical analysis.
The 5-layered model with the stepwise FTOL application is verified by comparing with 8-layered model, analytical model and experiment results with respect to axial and bending stiffness. The model is used for an ultimate strength assessment, the failure mechanism and the interaction between layers are investigated in detail with incremental loading.
Page 350 / 444