Affiliations: Dynamics Laboratory, Mechanical Engineering
Department, School of Engineering of Sao Carlos, University of Sao Paulo,
Brazil
Note: [] Corresponding author: Paulo Sergio Varoto, Dynamics Laboratory,
Mechanical Engineering Department, School of Engineering of Sao Carlos,
University of Sao Paulo, Av. do Trabalhador São-Carlense, 400 São
Carlos -- S.P. CEP:13566-590, Brazil. Tel.: +55 16 273 9423 / 273 9399; Fax:
+55 16 273 9402; E-mail: varoto@sc.usp.br
Abstract: The Electrodynamic Vibration Exciter (shakers) has been one of the
most employed excitation sources in modal tests. The shaker is an
electromechanical device that provides a mechanical motion due to the input
signal sent to its coil. Despite being widely used, it is well known that the
shaker interacts with the structure under test. In particular, when the
structure passes through a given resonance, the force delivered by the shaker
abruptly decreases, causing the so called drop off phenomenon. This paper aims
to study this force drop off phenomenon in the single shaker modal testing.
Analytical models are developed to help in understanding the physical
principles involved in the interaction between the shaker and the structure
under test. Experimental analyses are performed using different shakers as well
as excitation signals, in order to evaluate the effects of the input signal, as
well as the power amplifier operational modes, on the structure dynamics.
Preliminary tests revealed that significant distortions might occur during
vibration tests using shakers and these distortions significantly affect the
determination of the structure response.
Keywords: modal testing, mechanical vibration, shaker, force drop off
