72 4. MEASURED DATA ANALYSIS
Figure 4.4: ISPE test article broad band random excitation (left) and response (right).
4.1.11 ILLUSTRATIVE EXAMPLE: WIRE ROPE TEST ARTICLE
In 2006, during the conducting of U.S. Army sponsored research at Measurement Analysis
Corporation, time history data was measured on a test article consisting of a “rigid mass” sup-
ported by four wire-rope isolators, which was subjected to random excitation delivered by a
vertically oriented electrodynamic shaker. Time histories of acceleration of the rigid mass and
the shaker applied load were recorded. Employing a series of mathematical operations on the
measured data records, time history records of (a) isolator deflection and (b) isolator internal
force were estimated. In one particular test, broadband random excitation was delivered by the
shaker. Preliminary data analysis of the estimated isolator deflection and isolator internal force
probability density functions is summarized, along with a photograph of the test configuration,
in Figure 4.5.
e distortion in isolator internal force probability density with respect to ideal Gaussian
probability density indicates the presence of nonlinear behavior [2].
4.1.12 ILLUSTRATIVE EXAMPLE: ISS P5 MODAL TEST
During conduct of the ISS P5 modal test in 2001, nonlinear behavior of the test article was
suspected. In particular, modal frequencies and mode shapes associated with successive data
records were inconsistent with one another. As a result, a series of data records were acquired
and subjected to in-depth preliminary data analysis. e source of anomalous dynamic behavior
was quickly localized to a left-side trunnion that connected the ISS P5 test article to the test
fixture; left- and right-side trunnion locations are illustrated in Figure 4.6.
e preliminary data analysis strategy employed to evaluate and locate suspected nonlinear
behavior was based on the theoretical premise that:
a. response of a linear system to sinusoidal excitation at one frequency will also occur at the
excitation frequency;
4.1. PART 1: PRELIMINARY MEASURED DATA ANALYSIS 73
Enidine WR2-200-10B
Wire-Rope Isolators
Isolator Deflection Isolator Internal Force
X
Z
Y
Figure 4.5: Wire rope isolators subjected to broadband random excitation.
Left Trunnion
Right Trunnion
Figure 4.6: ISS P5 test article trunnion locations.
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