Final project for my vibrations class was to preform modal analysis of an object of our choosing as well as compare our results using FEA software simulations.

1. Vibration Study of a OCDC Bracket
EM 406 – Mechanical Vibrations

2. So what is an OCDC bracket?
OCDC (Operator Controlled Discharge Chute)

3. Overview of Presentation
Testing • Test Setup
• RT Pro Settings
Results
• Reciprocity
• Sample Data and Plots
• Mode Shapes
Analysis
• Comparison of Modes
• Lessons Learned
• Discussion & Conclusion

4. Modal analysis was performed on the OCDC
bracket and data was collected.
OCDC Bracket with two accelerometers
Placed in separate locations
Modal Data Collection Setup and Equiptment:
Hammer, data acquisition unit, and
computer running RT Pro

5. Details of Test Setup (RT Pro Settings)
Test Setup Details
Analysis Settings
Measurement
Points
2048
Frequency Range 1000
Lines 800
Frames Multiple
Windowing Force/Exponential
Averages 5
Trigger Level 2%
Physical Test Settings
Hammer Tip Nylon
Test Points 91
Settings were changed
until proper coherence
was achieved throughout
frequency range.
Accelerometer data tapered off
properly with Force/Exponential
window
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
8
6
4
2
-2
-4
-6
-8
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
Acceleration Response
Time [sec]
Acceleration [g's]
0 200 400 600 800 1000 1200
0
Coherence
Frequency [HZ]

6. The layout of the points on bracket
0
1
79
72
2
3
57
4
5
0
28
24
19
12
1
2
16
9
2
32
3
30
39
4
37
46
5
44
53
6
51
84
77
7
3
2.5
2
1.5
1
0.5
0
x
78
71
64
65
89
85
80
73
66
90
86
81
58
74
67
91
87
50
82
88
83
59
75
68
76
69
70
60
43
52
61
6362
36
45
54
5655
29
38
y
47
48
49
15
8
1
31
40
41
42
26
22
17
10
3
33
3534
27
23
18
11
4
5
25
20
21
13
14
6
7
z

7. Sample plots from data collection
12
10
8
6
4
2
-2
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
Hammer Impact Force
Hammer Impact Force [lbf]
Time [sec]
8
6
4
2
0
-2
-4
-6
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0 200 400 600 800 1000 1200
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Coherence
Frequency [HZ]
-8
Acceleration Response
Time [sec]
Acceleration [g's]

8. Confirmation of linearity in the bracket through a
reciprocity test
0 200 400 600 800 1000 1200
3
10
2
10
1
10
0
10
-1
10
-2
10
-3
10
Frequency (Hz)
Magnitude (gn/lbf)
Reciprocity
FRF 1
FRF 2

9. CMIF Used to Identify Mode Shapes

10. Mode shapes and Natural Frequencies
Mode Description Frequency (Hz)
Bending 163.8
Twisting 216.3
Bending 371.3
Bending/Twisting 491.3
Bending/Twisting 536.3

11. Mode 1: f = 163.8 Hz & ζ = 0.0084

12. Mode 2: f = 216.3 Hz & ζ = 0.0064

13. Mode 3: f = 371.3 Hz & ζ = 0.0038

14. Mode 4: f = 491.3 Hz & ζ = 0.0040

15. Mode 5: f = 536.3 Hz & ζ = 0.0038

16. ANSYS Mode 1: f = 163.46 Hz
% 퐷푖푓푓푒푟푒푛푐푒 =
퐹퐸퐴 −퐸푥푝푒푟푖푚푒푛푡푎푙
퐸푥푝푒푟푖푚푒푛푡푎푙
∙ 100 =
163.46−163.80
163.80
∙ 100 = .21%

17. SolidWorks Mode 2: f = 212.98 Hz
% 퐷푖푓푓푒푟푒푛푐푒 =
퐹퐸퐴 −퐸푥푝푒푟푖푚푒푛푡푎푙
퐸푥푝푒푟푖푚푒푛푡푎푙
∙ 100 =
212.98−216.30
216.30
∙ 100 = 1.53%

18. SolidWorks Mode 3: f = 387.34 Hz
% 퐷푖푓푓푒푟푒푛푐푒 =
퐹퐸퐴 −퐸푥푝푒푟푖푚푒푛푡푎푙
퐸푥푝푒푟푖푚푒푛푡푎푙
∙ 100 =
387.34 −371.30
371.30
∙ 100 = 4.32%

19. SolidWorks Mode 4: f = 504.57 Hz
% 퐷푖푓푓푒푟푒푛푐푒 =
퐹퐸퐴 −퐸푥푝푒푟푖푚푒푛푡푎푙
퐸푥푝푒푟푖푚푒푛푡푎푙
∙ 100 =
504.57 −491.30
491.30
∙ 100 = 2.70%

20. SolidWorks Mode 5: f = 560.41 Hz
% 퐷푖푓푓푒푟푒푛푐푒 =
퐹퐸퐴 −퐸푥푝푒푟푖푚푒푛푡푎푙
퐸푥푝푒푟푖푚푒푛푡푎푙
∙ 100 =
560.41 −536.30
536.30
∙ 100 = 4.50%

21. Lessons learned from analyzing the OCDC bracket
• Place grid lines on outside of object if dealing with complex
geometries for more accessibility for hammer strikes.
• Hammer strikes near edges and corners requires precise strikes and
careful technique.
• When doing FEA simulation in ANSYS material thickness makes a
HUGE difference in the results.
• Complicated part geometry is difficult to recreate in Excel

22. What makes this project special
• Relatively complex geometry allows for unique mode shapes.
• The bracket is a key component in a multi-component system
• Could apply constraints in simulation testing to obtain useful design
data.