PSI - Issue 45

Mark Mogeke et al. / Procedia Structural Integrity 45 (2023) 36–43 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

38

3

Root mean square of stress Circular wave frequency

[MPa] [rad/s] [rad/s] [rad/s]

 RMS



Circular wave encounter frequency Circular modal peak frequency

 e  p  

Wave amplitude

[m]

Virtual hull monitoring (VHM) is a digital structural health monitoring approach that can be used to calculate the fatigue damage accumulated in a ship’s hull. Ship -board data – such as speed, position, and bearing – is enriched with available wave data. The development of digital structural health monitoring approaches is being actively pursued. Hulkkonen et al. (2019) re-constructed the time history of a ship’s operations by fusing nowcast wave data with Automatic Identification System messages. This information was connected to structural analysis to provide a sound basis for estimating the existing and future service needs of the ship. Hageman et al. (2020) assessed the accuracy of calculated fatigue accumulation on FPSO (Floating Production Storage and Offloading) hulls, operating in the West Africa region, when using wave hindcasts. Data from deployed wave buoys provided a full wave spectrum, and three different wave models were considered. In general, the wave models provided reasonable results. Schirmann et al. (2020) found that knowledge on the differences between wave models to resultant ship response predictions and fatigue damage estimates are limited. Thus, different wave hindcasts and wave buoy datasets as well as the resultant heave, pitch, and vertical bending moment responses and fatigue damage for a destroyer-sized combatant were compared. The results showed that differences between the wave data sources promulgated to the vessel response predictions. These differences were amplified in the calculation of fatigue damage. Thompson (2020) assessed a VHM approach against full-scale measurements from a naval ship trial. It was concluded that accurate hull monitoring without additional instrumentation is possible but further work is required. Validation and convergence studies on multiple ships are required to validate VHM. Thompson (2020) reported VHM for a naval combatant of displacement hullform. Another class of ship for which an IHM dataset is available is a naval High Speed Light Craft (HSLC). The objective of the work presented in the present paper is to improve understanding of the resolution of the operational profiles and the influence of different data sources required in VHM. To meet this objective, the following activities are carried out: Sourcing and analysis of wave hindcasts of varying spatial-temporal resolution to enable the wave environment to be coupled to ship operational parameters (speed and bearing); calculation of the short-term stress spectral responses using the speed, heading, and wave data, and; comparison of the calculated stress spectra and the stress spectra derived from strain measurements. The work contributes to the naval architecture and structural integrity community, as attention is paid to ocean areas that are relatively less-trafficked and less studied than ocean areas such as the North Atlantic (long-term wave buoy and satellite measurements are often limited at locations of interest (Durrant et al., 2014), and utilisation of IHM data collected during sea trials and a long-term campaign. 2. Materials and method 2.1. Study Platform The study platform is the Armidale class patrol boat HMAS Maryborough (II) , shown in Fig. 1a, operated by the Royal Australian Navy. These ships feature a semi-planing hullform and were constructed from marine-grade aluminium alloys. 2.2. Instrumented Hull Monitoring A hull monitoring system was commissioned on-board Maryborough in 2015. The sensors included foil-based strain gauges, pressure transducers, a Global Positioning System (GPS) receiver, and a motion reference unit.