Investigation into ultrasonic wave propagation and defect detection in wind turbine main shaft based on COMSOL

To address the limitations of conventional manual inspection of wind turbine main shafts, including missed detection of small or deeply embedded defects, low inspection efficiency, and high maintenance cost, this study investigates an ultrasonic nondestructive testing method based on numerical simulation. A simplified local finite element model of a wind turbine main shaft was established in COMSOL Multiphysics to analyze ultrasonic wave propagation and defect-echo characteristics in 42CrMo4 steel. Excitation frequencies within the range of 1-10 MHz were compared under identical model settings. The results indicate that, for the model geometry, material parameters, defect size, mesh strategy, and boundary conditions considered in this study, the 4 MHz excitation case produces relatively distinct defect echoes and provides a favorable compromise between detection sensitivity and penetration capability. Additional simulations of idealized rectangular, triangular, and circular defects suggest that distinguishable echo responses can be obtained for the modeled defect configurations. All conclusions are based solely on numerical simulations under predefined modeling assumptions and are therefore limited to the simplified local model and preset defect geometries. Experimental validation and further parametric studies are required before the results can be extended to field inspection of wind turbine main shafts. This work provides a numerical reference for excitation-frequency selection in ultrasonic testing and a basis for subsequent experimental verification.