COBEM99

S21 Vibrações e Análise Modal

Title:

IDENTIFICATION OF DYNAMIC LOADS: A COMPARATIVE ANALYSIS OF TIME AND FREQUENCY DOMAIN TECHNIQUES

Summary :

ABSTRACT. FORCE IDENTIFICATION HAS BECOME A TOPIC OF INTEREST IN THE MODAL AND VIBRATION TESTING COMMUNITY SINCE EARLY 1980’S. SIMILARLY TO MOST IDENTIFICATION TECHNIQUES, THE KNOWLEDGE OF INPUT FORCES ( AND POSSIBLY MOMENTS ) ACTING ON A GIVEN STRUCTURE FROM RESPONSE MEASUREMENTS REPRESENTS NA INVERSE PROBLEM IN MECHANICS. INVERSE PROBLEMS ARE NOTORIOUSLY KNOWN FOR THEIR INHEIRENT NUMERICAL ILL CONDITIONING SINCE THEY REPRESENT A DECONVOLUTION OPERATION IN THE TIME DOMAIN. TWO METHODS HAVE BEEN USED TO ESTIMATE THE FORCE FROM MEASURED MOTIONS, THE PSEUDO-INVERSE TECHNIQUE AND THE SWAT METHOD. THE PSEUDO-INVERSE TECHNIQUE IS A FREQUENCY DOMAIN BASED DORCE IDENTIFICATION METHOD THAT REQUIRES THE KNOWLEDGE OF THE MEASURED STRUCTURE’S RESPONSES (USUALLY ACCELERATIONS ) AS WELL AS THE STRUCTURE’S FREQUENCY FUNCTION ( FRF ) MODEL. IT REQUIRES NA INVERSION OF THE SYSTEM’S FRF MATRIX FOR ALL SPECTRAL LINES IN THE FREQUENCY RANGE OF INTEREST. THIS INVERSION PROCESS USUALLY OFFERS NUMERICAL DIFFICULTIES AT SOME FREQUENCIES. THE SWAT ( SUM OF THE WEIGHTED ACCELERATIONS TECHNIQUE ) IS A TIME DOMAIN TECHNIQUE BASEAD ON THE PRINCIPLE OF MOTION OF THE MASS CENTER. IT EMPLOYS THE MEASURED TIME DOMAIN ACCELERATION SIGNALS IN THE IDENTIFICATION PROCESS AND REQUIRES THAT SUITABLE WEIGHTING FACTORS BE DEFINED IN ORDER TO GIVE GOODS ESTIMATES OD THE RESULTING FORCE ACTING ON THE STRUCTURE ( AND POSSIBLY ITS LINE OF ACTION ). THE MAIN OBJECTIVE OF THIS PAPER IS TO COMPARE THESE TWO FORCE IDENTIFICATION TECHNIQUES, DESCRIBE THEIR MAIN ADVANTAGES AS WELL AS MAIN PITFALLS IN THE IDENTIFICATION OF SOME SPECIAL TYPES OF EXCITATION SIGNALS COMMONLY EMPLOYED IN MODAL AND VIBRATION TESTING. KEYWORDS: PSEUDO-INVERSE, SWAT, MODAL TESTING, FORCE IDENTIFICAITON.

Author :

Santos, Marcelo Alves
Varoto, Paulo Sergio

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