Modal-based damage localization on wind turbine blades under environmental variability

Abstract

With wind power establishing itself as a widely effective form of renewable energy source, a diverse range of maintenance schemes is being investigated towards life-time extension of existing wind farms. Among the numerous structural and mechanical parts of a Wind Turbine (WT), blades are the most critical and costly components. Exposed to a number of degradation mechanisms, such as cracks and fatigue, they may be well rendered structurally ineffective and unsafe. Detecting and localizing thus the existence of damage on WT blades is a crucial and essential task for planning optimal maintenance and assuring operational reliability of WTs. One of the main challenges for deploying Structural Health Monitoring (SHM) methodologies on in-service WT blades lies in the operational and environmental variability. It is widely reported that fluctuations in ambient temperature exert a strong impact on the vibration features of WTs, insinuating the damage induced structural changes may often be masked by changes due to temperature influences. With WTs operating in highly-varying climate conditions, it becomes thus imperative that temperature effects be properly taken into account within the context of damage detection and localisation. In this contribution, the most common vibration-based criteria for damage localization are examined and compared through a numerical application on a small- scale WT blade. The study is built around a 3-dimensional finite element model of the blade, which comprises an exterior laminate composite surface, modelled with shell elements, and interior foam represented by solid elements. The efficacy of localization is evaluated under varying environmental conditions and a critical assessment on the accessibility of sensing information and the severity of damage is presented.