Structural health monitoring of wind towers: remote damage detection using strain sensors

Abstract

Exploiting wind energy in complex sites like mountain terrains implies the necessity for remote structural health monitoring of the wind towers. In fact, such slender vertical structures exposed to wind may experience large vibrations and repeated stress cycles leading to fatigue cracking. Possible strategies for remote fatigue damage detection are investigated. Specifically, this paper is focused on the use of suitable strain sensors for crack detection in critical sites of the structure, suggesting several strategies taking into account the possibility of wind direction changes and/or wind calm phases. They are based on a radial arrangement of strain sensors around the tower periphery in the vicinity of the base weld joint. The most promising strategy uses the strain difference between adjacent strain sensors as an index of the presence of a crack. The number of sensors to be installed is dictated by the minimum crack size to be detected, which in turn depends on the expected extreme wind conditions and programmed inspection/repair schedule for the structure.

A survey of health monitoring systems for wind turbines

“…Benedetti et al [115] proposed using perturbations in the local strain field as a damage indicator and validated the method on an FEM of a turbine tower. While straightforward, this method does not provide the convenient global damage detection of VBDD, requiring strain sensors in the area immediately surrounding the damage.…”

Fatigue and Fracture Resistance of Heavy-Section Ferritic Ductile Cast Iron

“…Damage tolerant design and structural health monitoring approaches have been then proposed to overcome these limitations. They were originally developed in the aeronautic context and have now been extended to the wind energy branch, especially in offshore and hardly-accessible installations [48,49]. According to these approaches, the fatigue life is exclusively thought of as the propagation of cracks up to a critical size leading to structural collapse or functionality loss.…”

Bi-axial neutral axis tracking for damage detection in wind-turbine towers

“…Strain sensors are local level sensors and hence more sensitive to smaller levels of damage . Many strain‐based damage detection techniques have been proposed in literature, and their performance has even been compared with displacement‐based methods …”