Dynamic Wind Turbine Blade Inspection Using Micro-Polarisation Spatial Phase Shift Digital Shearography
2.1. System Principle and Setup
2.2. Carrier Mask Modulation and Window Selection Phase Map Retrieval
2.3. Filtering Algorithms and Phase Sequence Retrieval
2.4. Steps of the Proposed Method
- Set up the proposed SPS-DS system described in Section 2.1 and use a heating gun to heat up the area of the WTB surface where there is known defect at the subsurface.
- Record a sequence of the speckle patterns at the heated area. Decompose the recorded video into frame-by-frame images.
- From the initial frame at time to time , generate carrier masks at four phase values in different pixels and form a large mask to modulate the whole image, as expressed in Equation (2).
- Transform the modulated speckle patterns from time to time into 2D in the frequency domain and select the central speckle rings in each speckle pattern as described above with denoting the lower frequency in Equation (4). Transform the derived frequency domain patterns into the original domain using inverse 2D Fourier transform to form the complex terms from to .
- Multiply the derived at time with conjugates of that at time , as described in Equation (7), and calculate the phase map at time , as in Equation (8).
- In each of the initial phase maps derived at , adopt the WFF algorithm in their complex domain and obtain a new filtered phase .
- Form the sequence from time to time , as described in Equation (9), produce the dynamic phase map series, and develop the defect variation along with the temperature change due to the dynamic thermal loading as a video sequence.
3. Experiments and Discussion
3.1. Pre-Test Using a Composite Sample
3.2. Test on the WTB with Known Defects
3.3. Phase Maps
Conflicts of Interest
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Li, Z.; Tokhi, M.O.; Marks, R.; Zheng, H.; Zhao, Z. Dynamic Wind Turbine Blade Inspection Using Micro-Polarisation Spatial Phase Shift Digital Shearography. Appl. Sci. 2021, 11, 10700. https://doi.org/10.3390/app112210700
Li Z, Tokhi MO, Marks R, Zheng H, Zhao Z. Dynamic Wind Turbine Blade Inspection Using Micro-Polarisation Spatial Phase Shift Digital Shearography. Applied Sciences. 2021; 11(22):10700. https://doi.org/10.3390/app112210700Chicago/Turabian Style
Li, Zhiyao, Mohammad Osman Tokhi, Ryan Marks, Haitao Zheng, and Zhanfang Zhao. 2021. "Dynamic Wind Turbine Blade Inspection Using Micro-Polarisation Spatial Phase Shift Digital Shearography" Applied Sciences 11, no. 22: 10700. https://doi.org/10.3390/app112210700