Laser Covariance Vibrometry for Unsymmetrical Mode Detection

摘要

Simulated cross-spectral covariance (CSC) from optical return from simulated surface vibration indicates CW phase modulation may be an appropriate phenomenology for adequate classification of vehicles by structural mode. The nonlinear structural to optical relationship is close to unity, avoiding nulls and high values; optical return contains sufficient spectral ID information necessary for data clustering. The FE model has contact between the homogeneous rolled armor and vehicle hull, a simple multi-layer skin model typical of most vehicles. Most of the high frequency energy moved to lower frequencies. This nonlinearity segments contact vibration modes into two classes: symmetrical modes that do not vary with minor structural changes, and those that do. The fundamental mode symmetry created features that were insensitive to slight structural load path changes. Structural aging simulation affected spectral and CSC fine structure generated by non-symmetrical modes. Structural vibration spectral analysis related to the nonlinear contact uses methods from Maj Winthrop's December 2004 AFIT PhD dissertation. Analysis of the propagated optical field confirms the spectral reduction results of Fl Lt Pepela's December 2003 AFIT thesis.