Mono-laser scanning measurement of radial operating deflection shapes for cylindrical shells: validation by 3D Digital Image Correlation

Abstract

Cylindrical shells, such as gas pipes and wind turbine towers, are common structural components. Ensuring the stability of these structures necessitates accurate measurement of their three-dimensional (3D) operating deflection shapes (ODSs). Laser Doppler Vibrometry (LDV) and Digital Image Correlation (DIC) are two prevalent optical measurement techniques. Measuring radial vibrations of a cylindrical shell only using a 1D scanning laser Doppler vibrometer (1D-SLDV) poses a challenging yet practical problem, as the cost of a 1D-SLDV is significantly lower than that of a 3D-SLDV. Addressing this issue, the authors previously proposed a scheme for measuring radial ODSs of a cylinder via mono-laser scanning. By leveraging the geometric relationship, the displacements measured by the laser at each point are transformed to obtain radial displacements. Although it was proven through numerical simulation using the finite element (FE) method, experimental validation via 3D measurements is critical and still pending. To ensure the reliability of this scheme, it is experimentally validated in this study through comparison with the actual radial ODSs captured by 3D DIC. To validate the accuracy of the corrected radial ODSs, the cosine similarity (CS) values across the radial ODSs obtained through the FE method, LDV, and DIC are calculated, demonstrating a high degree of similarity. Particularly, the LDV and DIC yield consistent radial ODSs, with their CSs exceeding 95% for each excitation frequency.