Unconventional Boundary Conditions

When performing a modal test, a number of mechanisms are available to approximate free-free boundary conditions. Some test setups may be more difficult to implement than others, but ultimately the effects of the boundary conditions on the actual modes of the system are of concern. An expensive setup...

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Bibliographic Details
Published in:Sound and Vibration 2015-08, Vol.49 (8), p.13
Main Authors: Dardeno, Tina, Logan, Patrick, Avitabile, Peter
Format: Magazinearticle
Language:English
Subjects:
Aluminum
Boundary conditions
Finite element analysis
Software
Online Access:Get full text
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Summary:When performing a modal test, a number of mechanisms are available to approximate free-free boundary conditions. Some test setups may be more difficult to implement than others, but ultimately the effects of the boundary conditions on the actual modes of the system are of concern. An expensive setup may not be any better than an equivalent, inexpensive "Rube Goldberg" approach. In lieu of an expensive setup, a low-cost, easily deployed configuration may be improvised from common objects not native to the test lab. In this article, several different boundary conditions are employed, with two being very, very unconventional. The effects of the supports on the flexible modes are explored through testing with multiple support configurations. Natural frequencies and mode shapes of the modes (flexible and rigid-body modes) are presented. Drive-point frequency response functions for the different support configurations are compared. Some other considerations are discussed relative to the general items of concern when performing these types of free-free modal tests.
ISSN:1541-0161