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Mass Normalized Mode Shapes Using Impact Excitation and Continuous-Scan Laser Doppler Vibrometry

Summary: Mass Normalized Mode Shapes Using Impact Excitation and Continuous-
Scan Laser Doppler Vibrometry
Matthew S. Allen1
and Michael W. Sracic
Department of Engineering Physics, University of Wisconsin-Madison
535 Engineering Research Building, 1500 Engineering Drive, Madison, WI 53706
Email: msallen@engr.wisc.edu
Conventional scanning laser Doppler vibrometer (LDV) systems cannot be effectively employed with impact excitation
because they typically measure a structure's response at only one point at a time. This necessitates exciting the structure at
multiple points to create a multi-input-single-output modal test data base, which is not only tedious, but prone to errors due to
variations in the impact characteristics from one point to the next. Previous works [1, 2] have demonstrated that an LDV can
be used to measure the mode shapes of a structure over a surface by scanning the laser spot continuously as the structure's
response decays. The author recently presented a procedure [3] that allows one to post-process continuous-scan LDV
(CSLDV) measurements of the free decay of a structure using standard modal parameter identification techniques. Using this
approach, one can find the natural frequencies, damping ratios and mode shapes of a structure at hundreds of points
simultaneously from a few free responses. The procedure employs a novel resampling approach to transform the continuous-
scan measurements into pseudo-frequency response functions, fits a complex mode model, and then accounts for the time
delay between samples to obtain the mode shapes. This paper extends the previous work by presenting an algorithm that uses


Source: Allen, Matthew S. - Department of Engineering Physics, University of Wisconsin at Madison


Collections: Engineering