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. 2024 Feb 22;24(5):1421.
doi: 10.3390/s24051421.

Phased Array Ultrasonic Method for Robotic Preload Measurement in Offshore Wind Turbine Bolted Connections

Yashar Javadi  1   2 , Brandon Mills  1 , Charles MacLeod  1 , David Lines  1 , Farhad Abad  3 , Saeid Lotfian  3 , Ali Mehmanparast  3 , Gareth Pierce  1 , Feargal Brennan  3 , Anthony Gachagan  1 , Carmelo Mineo  4
Affiliations

Phased Array Ultrasonic Method for Robotic Preload Measurement in Offshore Wind Turbine Bolted Connections

Yashar Javadi et al. Sensors (Basel). .

Abstract

This paper presents a novel approach for preload measurement of bolted connections, specifically tailored for offshore wind applications. The proposed method combines robotics, Phased Array Ultrasonic Testing (PAUT), nonlinear acoustoelasticity, and Finite Element Analysis (FEA). Acceptable defects, below a pre-defined size, are shown to have an impact on preload measurement, and therefore conducting simultaneous defect detection and preload measurement is discussed in this paper. The study demonstrates that even slight changes in the orientation of the ultrasonic transducer, the non-automated approach, can introduce a significant error of up to 140 MPa in bolt stress measurement and therefore a robotic approach is employed to achieve consistent and accurate measurements. Additionally, the study emphasises the significance of considering average preload for comparison with ultrasonic data, which is achieved through FEA simulations. The advantages of the proposed robotic PAUT method over single-element approaches are discussed, including the incorporation of nonlinearity, simultaneous defect detection and stress measurement, hardware and software adaptability, and notably, a substantial improvement in measurement accuracy. Based on the findings, the paper strongly recommends the adoption of the robotic PAUT approach for preload measurement, whilst acknowledging the required investment in hardware, software, and skilled personnel.

Keywords: non-destructive testing (NDT); offshore wind turbines (OWT); phased array ultrasonic testing (PAUT); robotics; total focusing method (TFM); ultrasonic stress measurement.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Methodology of the robotic PAUT of the bolt.
Figure 2
Figure 2
Definition of healthy A-scans in the application of PAUT (instead of the single-element approach) for the bolt preload measurement.
Figure 3
Figure 3
The effect of small defects on the stress.
Figure 4
Figure 4
Experimental setup for the robotic PAUT of the bolt.
Figure 5
Figure 5
The influence of small defects on the stress: (a–c) Test#1 and (d–f) Test#2. The only difference between (a), (b), and (c) is the zoom scale, which allows for the display of all A-Scans (each A-Scan is specified by a different color individually) produced by all elements of the array. Similarly, for (d), (e), and (f).
Figure 6
Figure 6
The 1st and 2nd backwall echo.
Figure 7
Figure 7
Orientation change for bolt testing.
Figure 8
Figure 8
Sector scan of the bolt: θz = 0° (a) and θz = 90° (b).
Figure 9
Figure 9
TFM image used to find the defect ((a): no defect detected, (b): SDH was detected).
Figure 10
Figure 10
Software adjustment—(a) Acoustic Path 1, which excludes the defect, (b) Acoustic Path 2, which passes through the centre of the defect and (c) Acoustic Path 3, which passes along the edge of the defect.
Figure 11
Figure 11
FEA Details: (a) Mesh model including the simulated stress concentration defect (SDH), (b) the centre path of interest within the model and (c) an example of the FEA results for a load of 30 KN.
Figure 12
Figure 12
Average stress calculated by FEA to be comparable with the ultrasonic results.
Figure 13
Figure 13
Example of applying a numerical method to solve the acoustoelastic equation using the direct PAUT approach.
Figure 14
Figure 14
Loadcell measurement and FEA (a), PAUT stress measurement (b) and comparison between PAUT and FEA results (c). * T1R1 stands for the acoustic path, which includes the wave generated by transmitting element 1 and received by receiving element 1.
Figure 15
Figure 15
The connection of AI and robotic PAUT for offshore wind applications.
See this image and copyright information in PMC

References

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