ABSTRACT
Experimental modal analysis (EMA) is basically a procedure of “experimental modeling.” The primary
purpose here is to develop a dynamic model for a mechanical system, using experimental data. In this
sense, EMA is similar to “model identification” in control system practice, and may utilize somewhat
related techniques of “parameter estimation.” It is the nature of the developed model, which may
distinguish EMA from other conventional procedures of model identification. Specifically, EMA
produces a modal model as the primary result, which consists of:
1. Natural frequencies
2. Modal damping ratios
3. Mode shape vectors
Once amodalmodel is known, standard results ofmodal analysismaybeused to extract an inertia (mass)
matrix, a damping matrix, and a stiffness matrix, which constitute a complete dynamic model for the
experimental system, in the time domain. Since EMA produces a modal model (and in some cases a
complete time-domaindynamicmodel) for amechanical system fromtest data of the system, its uses canbe
extensive. In particular, EMA is useful in mechanical systems, primarily with regard to vibration, in:
1. Design
2. Diagnosis
3. Control
In the area of design, the following three approaches that utilize EMA should be mentioned:
1. Component modification
2. Modal response specification
3. Substructuring
In component modification, we modify (i.e., add, remove, or vary) inertia (mass), stiffness, and
damping parameters in a mechanical system and determine the resulting effect on the modal
response (natural frequencies, damping ratios, and mode shapes) of the system. In modal response
specification, we establish the best changes, from the design point of view, in system parameters (inertia,
stiffness, and damping values and their degrees of freedom (DoF), in order to give a “specified”
(prescribed) change in the modal response. In substructuring, two or more subsystem models
are combined using dynamic interfacing components, and the overall model is determined. Some of the
subsystem models used in this manner can be of analytical origin (e.g., finite element models).
