Development of a Structural Monitoring System for the Digital Twin of the Hull Structure of an Ore Carrier

Ship structures are constantly subjected to wave loads and the excessive loads or repetitive loads increase a risk of failure. To avoid economic and environmental losses caused by the failure of ship structures, ship manoeuvring, maintenance, and design decisions are made so that the stress due to loads acting on the hull does not exceed the strength of the structure. However, because there is uncertainty in both the stress and the strength, there is the potential for safety and economics to be compromised. One solution to reduce the uncertainty is a digital twin that provides stress information at areas of interest in the ship structure in cyber space. In general, a digital twin is an integrated model that accurately reconstructs the state of a physical object based on sensing data measured in physical space and digital models that simulate the behavior of physical objects. Stress monitoring of the ship structure, including unmeasured parts, using the digital twin helps crews, shipping companies, and other stakeholders make rational decisions based on the situation. In this study, we developed a structural monitoring system for digital twins of ship structures with the aim of improving the safety and economic efficiency of ships. This system reconstructs and show the stress due to wave loads in a whole area of the hull structure. We developed a measurement module to obtain strain data from an interrogator of fiber optic sensors, an analysis module to calculate the stress at areas of interest based on the strain data and the Kalman filter, and a visualizing module with the graphical user interface (GUI) to show the stress of the hull structure, including the unmeasured parts. The analysis module also counts stress continuously and estimates the cumulative fatigue damage. These modules were integrated to form into the structural monitoring system for a digital twin. The structural monitoring system was implemented on an ore carrier in February 2023 and has been continuously operated without any serious troubles. In this paper, we introduce the modules with related technologies and the structural monitoring system with monitoring and operating data. This works is expected to provide valuable insights for building a digital twin for ship structures.