A Simplified Wind Turbine Blade Crack Identification Using Experimental Modal Analysis (EMA)

Khalid Fatihi Abdulraheem, Ghassan Al-Kindi


Abstract: Wind turbines blades rotate and flutter in extreme weather and fatigue loading conditions while subjected to random wind speeds. Furthermore, the wind turbines are usually located in remote areas with elevated heights thus difficult to be reached, examined, and assessed. Therefore, performing maintenance and repair is very challenging process due to the difficult and limited machine accessibility. The wind turbine blades conditions have significant contribution to turbine durability, reliability and performance issues, practically for offshore and megawatt-class wind turbines. Hence, to ensure their proper functioning, a robust condition monitoring system (CMS) for early detection of blade deterioration to be developed and implemented. Experimental modal analysis investigates the effect of structure dynamics variations, which may result from the presence and propagation of cracks, on the behavior of the vibrational modal parameters including modal frequencies, modal shapes and damping. To enable the emulation of wind turbine blades, a stepped beam is used in this paper to examine the application of experimental Modal Analysis technique in identification of blade fault. The aim is to assess the applicability of using the experimental modal analysis as a structural health monitoring (SHM) approach for wind turbine blades. An impact hammer test has been performed for the stepped beam with different crack sizeslocated at predetermined places. The Frequency Response Function (FRF) has been obtained experimentally as the frequency response ratio of the structure output to the input excitation force, H (ω) = X (ω)/F (ω). The stepped beam FRF has been calculated at different impact location and 3D plots are generated to define the structure modal shape. The results proved that the use of modal parameters allow for the detection and estimation of crack size in the stepped beam, hence motivate and provide a reference to investigate its implementation to wind turbine blades.


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Experimental Modal Analysis; Impact hammer test; Wind turbine blade fault identification; Vibration based modal Analysis; Frequency Response Function (FRF).

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