PSI - Issue 80

Francisco J.G. de Oliveira et al. / Procedia Structural Integrity 80 (2026) 1–10

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Author name / Structural Integrity Procedia 00 (2023) 000–000

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von Ka´rma´n vortices are strongest (Porteous et al., 2014) and where the largest bending moments develop. Because the strain measured at the root reflects the net e ff ect of all spanwise load contributions, the instrumented root section e ff ectively records an integrated bending-moment response.

1 a

b)

a)

4

y / D

6

8 6 4 2 0 2 4 6

2 a

4

y / D

6

8 6 4 2 0 2 4 6

x / D

0.0

0.2

0.4

0.6

0.8

U [m/s]

Fig. 3. a) : PIV flow snapshots captured in FOV C 1 and C 2, for FST cases 1 a and 2 a . b) : Longitudinal distribution of the PDF of ε across the data retrieved by θ − 45 ◦ f and θ − 135 ◦ f . The PDF contours are overlayed with the mean, standard deviation and maximum and minimum limits of strain experienced by the cylinder. Adapted from (de Oliveira et al., 2024).

Previous studies have shown that free-stream turbulence (FST) can amplify the vibration levels of cantilevered blu ff bodies (Wang et al., 2019). By employing distributed fibre-optic sensing, it becomes possible to track how the structural response develops along the span when exposed to such turbulent inflows. The simultaneous acquisition of strain and flow data further enables the identification of the flow structures that directly influence the body’s dynamics. To separate the mean and fluctuating components of the strain response, a Reynolds decomposition is applied:

f ) + ε ′ ( y / D , t ,θ α f )

ε ( y / D , t ,θ α

f ) = ε ( y / D ,θ α

(1)

where ε denotes the mean strain field and ε ′ the fluctuations, measured along the sensing lines θ α f ,α = [ − 45 ◦ , − 135 ◦ ]. Figure 3 b) shows the spanwise evolution of the probability density function (PDF) of the recorded signals, together with the mean, standard deviation, and maximum-minimum ranges of strain for FST cases 1 a and 2 a . Introducing turbulence (case 2 a ) widens the maximum-minimum envelope of ε ′ , while also increasing the standard deviation, with the strongest changes occurring near the root. Moreover, the PDF of ε ′ exhibits higher kurtosis towards the root, indicating the presence of intermittent stresses consistent with enhanced structural vibration. The influence of FST on the time-averaged loads is further assessed by analysing the mean tip deflection recon structed from the fibre-optic measurements. Earlier work by Bearman and Morel (1983b) demonstrated that higher turbulence intensities in the inflow tend to increase mean loading on a cylinder, linked to a shortening of both the re circulation bubble and the vortex-formation length. Here, the structural deflection is recovered using a shape-sensing approach following Xu and Sharif-Khodaei (2020); de Oliveira et al. (2025):