Experimental Modal Analysis of a Half-Scale Model Rear Twin-Engine Mounted Aircraft Fuselage Section

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Chamberlain, Diego
Modal Analysis , Aircraft , Noise , Vibration
Experimental modal testing using an impact hammer is a commonly used method for obtaining the modal parameters of any structure for which the vibrational behavior is of interest. Natural frequencies and associated mode shapes of the structure can be extracted directly from measured FRFs (Frequency Response Functions) through various curve fitting procedures. This thesis provides an overview of the modal testing conducted on various scaled aerospace components. These components are part of a half-scale model rear twin-engine mounted aircraft fuselage tail section which is being constructed in order to provide relevant vibrational and dynamic trends to a leading Canadian aerospace manufacturer. The experimental modal results were used to validate the associated computational modal data. It is this initial validation step which forms the foundation of the research project presented herein and which will allow for future modal testing work to be conducted on the half-scale assembly once completed. Testing set-up, experimental equipment and the methodology employed are all described in detail. Furthermore, a series of validity checks were done by ensuring that the experimental results satisfy the requirements inherent to linear modal analysis including repeatability, reciprocity and linearity. This provided confidence in the employed testing procedure. Recorded natural frequencies (eigenvalues), mode shapes (eigenvectors), coherence plots and other important experimental data are presented along with notable trends. Finally, key literature has been referenced where appropriate and important concepts to modal analysis are expanded upon. This thesis, then, demonstrates that experimental modal analysis can be successfully implemented into a testing methodology that helps establish vibrational trends and, thus, better understand and help resolve vibro-acoustic issues on aircraft.
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