Bluewater has partnered with DNV to pilot the hybrid twin solution on the Aoka Mizu FPSO, using data from that sensor system to monitor the fatigue damage in the hulland then update the RBI inspection plan accordingly (if needed).

In this paper, the hybrid twin method is presented which combines strain gauges’ data with 3D Finite Elements analysis of the hull structure, allowing the complete reconstruction of the structural response everywhere in the structure, based on the measurements from only a few sensors.

The method is validated using one full year of actual strain gauges’ measurements on the hull. The responses at main deck level are cross validated using some sensors as references and predicting their responses from the other sensors. The FPSO heading is also predicted from the deck strains and compared to direct heading measurements to validate the implicit calculation of the environment from the response. By combining the deck sensor readings with the 3D Finite Element model the fatigue damage at selected hot spots in the hull is calculated.

Those damage values are then used in the RBI calculation to replace the design damage values so that the RBI is updated based on measurements.

The key benefit for such approach to operators is the possibility for operators to keep track of the remaining life of the structure and being able to demonstrate it, which is crucial when it comes to optimizing inspection plans, selling, or redeploying an asset.

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