Using SCADA in updating failure probability of a monopile support structure

Assessment of existing offshore wind turbine support structures is crucial for a condition-based inspection planning and life extension decision. This paper aims at utilizing SCADA as new information to update failure probability of monopile support structures in fatigue failure mode.
The SCADA was collected from a Belgian offshore wind farm. It is assumed that fatigue loading of the monopile support structure comes mainly from wind action. One-year data of measured strain is used together with the concurrently measured 10-minute wind speed to built the limit state function. Fatigue-critical strain history is derived from the data at three measuring locations on the same circumference. The 10-minute mean wind speed is considered as a random variable and used to calculate the fatigue damage. Fatigue damage is calculated using Miner's rule. The year-to-year variation of the 10-minute mean wind speed, the unrepresentativeness of the measured strain, and the measurement uncertainty are considered together with uncertainties in Miner's rule and the S-N curve. The Bayesian approach is used to update the 10-minute mean wind speed distribution considering measurement data. Consequently, the failure probability of the support structure can be updated.
The results show that after three years of measurement, there is no significant differences in the calculated failure probability between cases where the updated 10-minute mean wind speed distribution and the design distribution are used. The load factor applied to the measured stress (e.g. stress concentration factor, corrosion effects, or interpolation factor for unmeasured locations) significantly affects the calculated failure probabilities.
In conclusion, the wind measurement data can be used to predict failure probability of the monopile support structure given that a limited concurrently measured strain data is available. Further research is needed to combine the SCADA with inspection data (crack, corrosion) for optimising the inspection plan or a life extension purpose.