Numerical study on the displacement reconstruction of subsea pipelines using the improved inverse finite element method

Abstract

The structural health monitoring (SHM) and integrity management of subsea pipelines are essential in the offshore oil and gas industry. Previous studies have achieved strain and thermal monitoring using distributed fiber optic sensors (DFOS). However, assessing the in situ displacement of subsea pipelines is still challenging. This study put forward a displacement reconstruction approach based on limited strain data using the inverse finite element method (iFEM). First, we developed a new inverse beam element with a 2nd order shape function for axial deformation to extend the application scope of the standard iFEM to subsea pipelines undergoing complex axial forces. Then, a model truncation procedure and a continuous displacement reconstruction algorithm were proposed to rebuild high accuracy and smooth displacement field. Besides, the strain sensing scheme for iFEM was adapted to DFOS system and made easier to implement in engineering applications. Finally, the proposed method was verified through a series of numerical studies. It showed that the improved iFEM offers superior accuracy and better noise robustness than the standard iFEM, especially with coarse meshes and low spatial resolution strain data. Thus, it reveals a promising prospect in the online displacement monitoring and SHM for subsea pipelines.