AUTONOMOUS MODAL IDENTIFICATION OF THE SPACE-SHUTTLE TAIL RUDDER

Autonomous modal identification automates the calculation from experim ental data of natural vibration frequencies, damping, and mode shapes of a structure. This technology complements damage detection technique s that use continuous or periodic monitoring of vibration characterist ics. The approach incorporates the Eigensystem Realization Algorithm a s a data analysis engine and an autonomous supervisor to condense mult iple estimates of modal parameters using the consistent-mode indicator and correlation of mode shapes. The procedure was applied to free-dec ay responses of a Space Shuttle tail rudder and successfully identifie d the first seven vibration modes of the structure. The final modal pa rameters are a condensed set of results for 87 individual cases requir ing approximately 5 min of computer time on a Unix workstation.