18 Experimental Modal Analysis Clarence W. de Silva

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The University of British Columbia

18.1 Introduction ........................................................................ 18-1

18.2 Frequency-Domain Formulation ....................................... 18-2

Transfer-Function Matrix † Principle of Reciprocity

18.3 Experimental Model Development ................................... 18-8

Extraction of the Time-Domain Model

18.4 Curve Fitting of Transfer Functions .................................. 18-10

Problem Identification † Single- and Multi-Degree-of-Freedom

Techniques † Single-Degree-of-Freedom Parameter Extraction

in the Frequency Domain † Multi-Degree of Freedom Curve

Fitting † A Comment on Static Modes and Rigid-Body

Modes † Residue Extraction

18.5 Laboratory Experiments ..................................................... 18-18

Lumped-Parameter System † Distributed-Parameter System

18.6 Commercial EMA Systems ................................................ 18-24

System Configuration

Summary

In experimental modal analysis (EMA), first the modal information (natural frequencies, modal damping ratios,

and mode shapes) of a test object is determined through experimentation, and this information is then used to

determine a model for the test object. Once an “experimental model” is obtained in this manner, it may be used in a

variety of practical uses including system analysis, fault detection and diagnosis, design, and control. This chapter

presents some standard techniques and procedures associated with EMA.

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