3.3. PART 3: RESPONSE DOF SELECTION FOR MAPPING EXPERIMENTAL MODES 63
3.3.4 ALLOCATION OF MODAL EXCITATION RESOURCES
Planning of excitation resources for a modal test involves placement and orientation of shakers
based on
1. accessibility and structural integrity of candidate test article locations; and
2. ability to adequately excite all target modes (using modal gains, see Equation (3.48)).
Employing the above criteria, diagonally oriented shakers (and in-line accelerometer
channels intended for measurement of drive point frequency response functions, to be discussed
in Chapter 4) were allocated as depicted in Figure 3.18.
38
25
1
X
Z
Y
Location (Coordinates)
TAM Node
1
25
38
Description
Lower-Center-Front
Lower-Left-Rear
Grapple Fixture
X (in)
776.38
890.33
820.24
Y (in)
0
-54.5
0
Z (in)
380.31
380.31
466.16
Fx/Ftot
0.58
0.58
0.58
Fy/Ftot
0.58
0.58
0.58
Fz/Ftot
0.58
0.58
-0.58
Direction Cosines (Radians)
Figure 3.18: ISS P5 excitation allocation.
e anticipated adequacy of excitation resources was evaluated on the basis of predicted
modal gains associated with the test article finite element model, as summarized in Table 3.6.
Note that the most prominent shaker location for each individual mode is designated in bold
print and modes with non-negligible test fixture kinetic energy are shaded.
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