Classification society DNV GL has developed a methodology for hull condition monitoring that incorporates the use of the ship’s digital twin, a virtual model prepared during the design stage. Combined with wave, position and sensor monitoring, it vastly enhances the value of predictive and preventive maintenance.
"Design models, which are also sometimes referred to as digital twins, die at birth. It is our ambition to bring these models back to life during the operational phase of an asset," said Dr Gaute Storhaug, Principal Specialist at DNV GL Maritime Advisory.
In its Nerves of Steel Extraordinary Innovation Project, DNV GL - Maritime has been investigating new ways of calculating the wave-induced damage risk for ship hulls. Designers and yards invest significant amounts of time and money in preparing analytical models to document the design of ships and offshore structures and to perform simulations. The continued use of such a virtual model as a digital twin during operation is a great means to visualise all key components, perform analyses and calculations, and improve the understanding and control of the long-term effects of operation on the ship’s structural and functional components. This adds significant value to the asset.
In addition, a digital twin can be very useful for inspection and maintenance planning, while extending the ship's lifetime through preventive actions to avoid hull damages. The increased transparency and control that the digital twin provides can even result in a competitive advantage by improving predictability. This makes the vessel more attractive to cargo owners, banks, insurance companies, class societies, vetting companies, investors, buyers and other stakeholders.
"Using sensor technology to determine the response of a vessel or offshore structure to specific wave conditions, as well as to monitor structural and functional components, is common practice in the industry today," says Ørjan Fredriksen, Senior Engineer, Technical Advisory Structures, who was the project manager for the Nerves of Steel Extraordinary Innovation Project. "Sensors can capture physical effects such as deformation, vibration or temperature under real-life conditions that cannot always be easily described by numerical models," he adds. "But the number of sensors installed on board limits the number of data points available to monitoring. Considering the complexity of modern ships and the interdependencies between all their components, comprehensive instrumentation can provide crucial insights."
Combining the data provided by these sensors with the ship's digital twin makes sensor-based hull condition predictions much more meaningful and accurate. It does this by extending the range of structural details accessible to monitoring. This may include any element considered during the design that may be critical during operation. Examples of typical fatigue-critical details on ships are the stiffener end connections of frames and transverse bulkheads, stringer toes and heels, or terminations of hatch coamings.
A hybrid monitoring approach as described above can also be helpful in determining the best sensor positions to ensure cost-effective instrumentation. This concept has been applied successfully on assets of various types, including container ships, FPSOs, semi-submersibles, flare towers, pipelines, and fixed platforms.