Vibration study of a OCDC bracket

Vibration Study of a OCDC Bracket

EM 406 – Mechanical Vibrations

So what is an OCDC bracket?

OCDC (Operator Controlled Discharge Chute)

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

Modal analysis was performed on the OCDC bracket and data was collected.

OCDC Bracket with two accelerometersPlaced in separate locations

Modal Data Collection Setup and Equiptment:Hammer, data acquisition unit, and computer running RT Pro

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

Accelerometer data tapered off properly with Force/Exponential window

Settings were changed until proper coherence was achieved throughoutfrequency range.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-8

-6

-4

-2

0

2

4

6

8Acceleration Response

Time [sec]

Acc

ele

rati

on

[g's

]

0 200 400 600 800 1000 12000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Coherence

Frequency [HZ]

The layout of the points on bracket

0

1

2

3

4

5

01

23

45

67

0

0.5

1

1.5

2

2.5

3

x

64

71

78

65

72

79

66

73

80

85

89

57

67

74

81

86

90

58

68

75

82

87

91

50

59

69

76

83

88

70

77

84

51

60

43

52

61

44

6263

53

36

45

54

37

5556

46

y

29

38

47

30

4849

39

31

40

1

8

15

4142

32

2

9

16

33

3

10

17

22

26

3435

4

11

18

23

27

5

12

19

24

28

6

13

20

25

7

14

21

z

Sample plots from data collection

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-2

0

2

4

6

8

10

12Hammer Impact Force

Ham

me

r Im

pact

Forc

e [

lbf]

Time [sec]

0 200 400 600 800 1000 12000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1Coherence

Frequency [HZ]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-8

-6

-4

-2

0

2

4

6

8Acceleration Response

Time [sec]

Acc

ele

rati

on

[g's

]

Confirmation of linearity in the bracket through a reciprocity test

0 200 400 600 800 1000 120010

-3

10-2

10-1

100

101

102

103

Frequency (Hz)

Mag

nitu

de (

gn/l

bf)

Reciprocity

FRF 1

FRF 2

CMIF Used to Identify Mode Shapes

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

Mode 1: f = 163.8 Hz & ζ = 0.0084

Mode 2: f = 216.3 Hz & ζ = 0.0064

Mode 3: f = 371.3 Hz & ζ = 0.0038

Mode 4: f = 491.3 Hz & ζ = 0.0040

Mode 5: f = 536.3 Hz & ζ = 0.0038

ANSYS Mode 1: f = 163.46 Hz

%𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 =𝐹𝐸𝐴 −𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙

𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙∙ 100 =

163.46−163.80

163.80∙ 100 = .21%



212.98−216.30

216.30∙ 100 = 1.53%

SolidWorks Mode 2: f = 212.98 Hz



387.34 −371.30

371.30∙ 100 = 4.32%




504.57 −491.30

491.30∙ 100 = 2.70%




560.41 −536.30

536.30∙ 100 = 4.50%


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

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.

Engineering

Vibration study of a OCDC bracket