A Feasibility Study of Using Inverse Finite Element Methods for Structural Health Monitoring of Offshore Access Systems

Abstract

Over the past decade, the offshore industry, particularly the wind energy sector, has exhibited continuous growth, emphasizing the escalating significance of sustainability within this domain. The current work seeks to enhance this aspect by exploring offshore access systems featuring composite gangways.

Composite offshore structures however pose challenges due to the involved complex damage mechanisms and the need for novel maintenance procedures, introducing uncertainties concerning their operation. A Structural Health Monitoring (SHM) system is proposed for increasing confidence in the safe operation of the new composite gangway.

The suggested SHM system relies on inverse Finite Element Methods (iFEM) deflection reconstruction using Fiber Optics (FO) strain data. The gangway design is simplified to a U-shaped beam geometry under bending load, modeled using IQS4 elements. Its performance was assessed using mock strain data generated numerically through FEM software.

Deflection reconstruction using both tri-axial and uni-axial strain measurements was investigated, revealing that uni-axial measurements can be sufficient for the current application. The sensing network was streamlined by focusing on line configurations along the length of the beam, leveraging the capabilities of FO sensors.

The introduction of strainless inverse elements highlighted the limitations of strain pre-extrapolation with Smoothed Element Analysis (SEA) for such a geometry. Modeling guidelines and their effect on improving the robustness of SEA are explored. A strain sensing network using four uni-axial sensing lines is found to offer a sufficiently accurate deflection reconstruction for the application.