Response of Flexible Risers in Bend Stiffener Area

Abstract

Flexible risers is a vital part of a floating production system (FPS). In order to predict the riser life time, many procedure may be applied.

In this thesis it is assumed that the pipe could be represented with help of performing two sets of global anlayis. Where in the first set it is assumed that the bending stiffness of the pipe is similar to the stick region of the flexible pipe and in the second part the bending stiffness it is assumed a bending stiffness similar to the slip regime of the flexible pipe. The dynamic analysis for these two sets is performed in SIMLA, which is mainly a special purpose tool for pipe laying, but robust enough for to perform most of pipeline engineering problems. The analysis is set to be from a semi submersible in typical North Sea loading conditions. The nodal displacement time series obtained from these analysis is then stored into blocks with constant amplitude loading for the upper part of the riser configuration.

The results obtained from the global analysis is then used as inputs for a local analysis performed in BFLEX2010, which is a special purpose FEM software for stress analysis of flexible pipes. The local analysis is mostly focused on the fatigue of the flexible riser and it is performed an investigation from the effect of introducing different gaps between the pipe and the bend stiffener. The data obtained from these analysis, results in more distributed stress concentration within the bends stiffener region, especially for the largest sea states. There is also performed analysis where it is assumed no contact interference with the bend stiffener and the pipe, where it results in a much larger stress concentration at the hang of region, and a more even stress distribution along the riser.