REAL-TIME IDENTIFICATION OF STRUCTURAL MODES

THE GOAL OF THE PROPOSED RESEARCH IS TO REFINE AN IMPROVED METHOD OF ESTIMATING, IN A NEAR-REAL-TIME MANNER, MODAL FREQUENCIES AND DAMPING RATIOS OF RANDOMLY EXCITED AEROELASTIC VIBRATIONS FROM FLIGHT TEST MEASUREMENTS. THE ESTIMATION METHOD OPERATES WITHOUT KNOWLEDGE OF THE RANDOM EXCITATION, AS WELL AS WITH KNOWLEDGE OF A DETERMINISTIC FORCING FUNCTION APPLIED TO THE AIRCRAFT THROUGH AN EXCITATION SYSTEM. THE METHOD IS DESIGNED TO ACCOMMODATE CLOSELY-COUPLED AEROELASTIC MODES AND MODAL FREQUENCIES FROM1 TO 128 HZ WITH LIMITED DATA SAMPLING TIME. THE METHOD EMPLOYS SAMPLED DATA CORRELATION USING A SET OF MOVING "WINDOWS" OF VARYING LENGTH IN TIME AND A RUNNING LEAST SQUARES ESTIMATION OF THE COEFFICIENTS OF A DIFFERENCE EQUATION MODEL IN THE TIME DOMAIN FOLLOWED BY CONVERSION TO THE FREQUENCY DOMAIN FOR INTERPRETATION OF MODAL FREQUENCIESAND DAMPING RATIOS. THIS METHOD IS BASED ON AN ADAPTATION OF THE REAL-TIME NON-INTRUSIVE PARAMETER IDENTIFICATION PROCEDURE DEVELOPED BY SYSTEMS TECHNOLOGY, INC., FOR THE NASA AMES RESEARCH CENTER/DRYDEN FLIGHT RESEARCH FACILITY.