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.

To facilitate the transition to liquid hydrogen (LH2) as an alternative aircraft fuel, the stor
age tanks need to be closely monitored to allow for safe operation. This research explores
the feasibility of using an acoustic emission-based structural health monitoring method to
detect and localise simulated damage on a metal double-walled vacuum insulated tank. The
complicated inner and outer tank geometry makes it a novel application of an established
method.

To be able to perform experiments, a metal double-walled vacuum insulated tank with a fixed
and flexible support was cut in half to make the inner tank accessible. Pencil lead break tests
were performed on the inner and outer tank and recorded by lead zirconate titanate (PZT)
sensors to assess localisation accuracy. It was found that a pencil lead break (PLB) performed
on the inner tank could be detected by a sensor placed on the outer tank. Subsequently, an
accuracy of 80% was achieved in making the distinction whether the PLB was located on the
inner or outer tank. For the PLBs placed on the inner tank a 1D localisation accuracy of
17 [mm] and 21 [mm] was achievable for the flexible and fixed support respectively. For the
outer tank a 1D localisation accuracy of 46 [mm] was achievable, while for 2D localisation
this was 41 [mm].

It is concluded that with sensors placed solely on the outer tank, both the inner and outer
tank can be monitored. Additionally, simulated damage on the inner and outer tank could
be localised with an accuracy below 10% of the tank’s dimension. Therefore, based on the
feasibility study performed, acoustic emission-based structural health monitoring is deemed a
viable method to enhance the reliability and safety of metal double-walled vacuum insulated
LH2 tanks.