Digital Twin-like Model Updating of a Laboratory Offshore Wind Turbine with Few-Parameters Soil-Structure Interaction Model

Being structures that are highly sensitive to dynamic loads, Offshore Wind Turbines (OWTs) are designed to preclude any sort of resonance. However, during operation, OWTs have been known to experience modal property changes, especially, fundamental natural frequencies, which, once close to the forcing frequencies, can lead to resonance. To avoid this, these structures need to be constantly monitored to assess these modal property changes before they lead to failure. In this study, a digital twin-like model updating is carried out on a laboratory OWT (LOWT) to detect the change(s) in its soil stiffness, occasioned by the application of cyclic loads. To reduce the number of updating parameters, a few-parameters soil-structure interaction (SSI) model is incorporated into the finite element (FE) model of the LOWT, which is created in the commercial software, ANSYS. Two sets of sensing data which are acquired from the prototype LOWT are used for the model updating of the FE model in two respective stages: first, calibration in the original state; and second, update after the application of cyclic loading. For the two updates, the FE model mirrored the conditions of the prototype, based on the modal properties comparison from both, thereby, enabling successful monitoring of the soil stiffness conditions of the LOWT. The results show that soil stiffness increase with the increase in the application of cyclic loading and that the few-parameters SSI model has a high sensitivity to soil stiffness changes. The proposed methodology holds great potential as a model updating system, which draws closer to achieving the digital twin (DT) technology deployment in the monitoring of OWT foundations, and demonstrates the usefulness of a reduced-order SSI model for OWT model updating.