Anomaly Detection in Offshore Wind Turbine Structures using Hierarchical Bayesian Modelling

Abstract

Population-based structural health monitoring (PBSHM), aims to share information between members of a population. An offshore wind (OW) farm could be considered as a population of nominally-identical wind-turbine structures. However, benign variations exist among members, such as geometry, sea-bed conditions and temperature differences. These factors could influence structural properties and therefore the dynamic response, making it more difficult to detect structural problems via traditional SHM techniques. This paper explores the use of a hierarchical Bayesian model to infer expected soil stiffness distributions at both population and local levels, as a basis to perform anomaly detection, in the form of scour, for new and existing turbines. To do this, observations of natural frequency will be generated as though they are from a small population of wind turbines. Differences between individual observations will be introduced by postulating distributions over the soil stiffness and measurement noise, as well as reducing soil depth (to represent scour), in the case of anomaly detection.

Figures (5)

• Figure 1: FE model construction in relation to the offshore environment.
• Figure 2: A graphical model representing the hierarchical model with partial pooling.
• Figure 3: Generated natural frequency observations for five turbine structures.
• Figure 4: Density plots showing the posterior samples for each chain, for the learned parameters. Vertical dashed lines indicate the expected values used in generating the data. Black lines indicate population-level parameter posteriors while the coloured lines (for $s_k$) represent each turbine $k$ in $1:K$.
• Figure 5: Average natural frequency of five samples for increasing levels of scour depth, in comparison to the posterior distribution of natural frequency for the third structure.