Identification of the dynamic characteristics of nonlinear structures

APPENDIX
 III]
DETAILS OF EXPERIMENTAL WORK
1. THE BEAM/ABSORBER STRUCTURE (USED IN CHAPTER 2)
The Beam/Absorber test rig, as referred in Chapter 2, is an existing apparatus used for
standard projects for many years and was not specially designed for research. A
photograph of the rig and its main components are shown Fig. 
and Fig. 
The physical dimension of the main beam and the centre mass are shown in Fig. A3.1.3
and Fig. 
Fig. A3.1.1 Photograph of the Test Rig
Fig. 
Main Components of the Beam/Absorber Rig

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Details of Experimental Work
284
Fig. A3.1.3 Dimension of Component No. 1 (Main Beam)
Fig. A3.1.4 Dimension of Component No. 2 (Centre Mass)
Component No. 3 is a uniform beam with dimension (length x width x height) being
(all dimensions are in mm) and Component No. 4 is a rigid mass with
dimension 
as shown in 
2. 
DETAILS OF CONSTANT FORCE CONTROL
In some modal tests, such as for the measurement of structural nonlinearity, it is required
that the amplitude of the excitation force should be kept constant. In cases where the
damping of the structure to be tested is not very light (i.e., if the damping ratio is of the
order of 1% or more), the amplitude of the excitation force can be controlled to be
constant based on a feed-back control loop as shown in 
Amplifier
Shaker
Unit 
If 
If F=F*
If 
Force Gauge
increase the generator output V
next frequency point
decrease the generator output V
V
Frequency
Response 
Computer
Analyser
Fig.3.2.1 Excitation Force Amplitude Control
F
F = Actual Force
F* = Target Force

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Appendix 
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Details of Experimental Work