Advancing Marine Riser Simulations: A Python-based Approach using Cosserat Rod Theory

Abstract

Marine risers, critical components in offshore drilling operations, are subject to complex forces that can lead to material fatigue and reduced service life of subsea wellheads. This master’s thesis presents the development of a novel finite element program using Python and Cosserat rod elements for dynamic analysis of marine risers, to aid the ongoing developments in increase measurement accuracy to prolong the service life of subsea wellheads.

The program models the forces acting on the riser, including hydrodynamic forces from waves and current, and provides detailed data for input to neural networks. The aim of the neural networks is to enhance understanding of the behavior of the Reactive Flex Joint (RFJ), a flexible joint designed to reduce fatigue life on wellheads by counter-acting bending moments. The program has been validated against OrcaFlex, demonstrating high accuracy and acceptable efficiency. The program is built to be continuously improved, and has a robust and modular programming foundation. Although the current version has some limitations, like the assumption of linear wave theory, it can easily be improved in future iterations.

This work has potential real-world applications, including its original purpose of generating input to ongoing research on the RFJ, and modeling softer slender structures like subsea umbilicals and flexible marine risers. This work contributes to the ongoing effort to increase the service life of subsea wellheads, and to the novel approach of modeling slender subsea structures with Cosserat rods.