A New Analytical Expression to Estimate the Bending Stiffness of Flexible Risers

Abstract

Flexible risers are complex structures used in offshore oil exploitation activities. Such structures are composed of several concentric polymeric and steel armour layers which withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. Determining the equivalent flexural stiffness of such structures is an important task for the global structural analysis, since it provides a probable value that can be used in this analysis to predict the load distribution along the line (that is important in critical regions such as the TDP and the top). Besides that, estimates for the flexural stiffness are also important for predicting instabilities in the line (loop formation). However, the complexity imposed mainly by geometry and contact conditions renders a finite element analysis of these structures practically unfeasible, even considering that all the materials obey a linear elastic behaviour. So, in order to achieve this task, analytical methods have been proved to be, till now, a better choice. The aim of this work is to present the basis of a new analytical equation to estimate the flexural structural behaviour of flexible risers. Emphasis is given on the geometrical analysis of armour layers.