On the Small Scale Nonlinear Finite Element Analysis of Flexible Risers

In this paper an efficient small-scale, detailed finite-element modelling method for flexible risers is presented. The method can be effectively implemented in a fully-nested (FE2 ) multiscale analysis based on computational homogenization. To reduce the computational cost only a small fraction of a flexible pipe is used for a detailed nonlinear finite-element analysis at the small scale by exploiting the cyclic symmetry of the model and applying periodic boundary conditions. In this model, using three-dimensional elements, all layer components are individually modelled and a surface-to-surface frictional contact model is used to simulate their interaction. The approach is applied on a 5-layered pipe made of inner, outer and intermediate polymer layers and two intermediate armour layers, each made of 40 steel tendons. The capability of the method in capturing the detailed nonlinear effects and the great advantage in terms of significant CPU time saving are demonstrated by comparing the results obtained on elements of pipe of different lengths.