Design and analytical validation of automotive silencer to reduce vibration in it.

1. A Project Seminar
On
Performance Enhancement of Automotive
Silencer using Experimental & Finite Element
Analysis.
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2.  Vibration in exhaust system is known to be a predominant
component of the automobile noise generation. Fortunately, over the
last few decades, it has been possible to reduce it the level of the
other components (the engine body noise, cooling system noise,
etc.) by means of a Silencer.
UNDESIRABLE EFFECTS OF VIBRATIONS:
 Vibration causes undesirable noise which is unwanted. This noise
affects the workability of the workers & increases mental stress level
which might result in reduced efficiency of workers.
 Vibration is responsible for loosening of the machines parts or the
components of any assembly.
 Excessive stresses induced in the system. These excessive
stresses may cause failure of the system.
 Vibration creates rapid wear of machine parts such as bearings,
gears, nuts & bolts & other vital components.
 Due to heavy vibrations it is difficult to get exact & correct readings
from the instruments.

3. •Structural vibrations may collapse the structures such as
buildings, bridges etc; if the natural frequency of the
excitation coincides with natural frequency of that structure.
•Excessive vibration is harmful for human beings. Effects of
very low frequency vibrations (1-2 Hz) that cause kinetosis,
also known as motion sickness. Symptoms include
asthenia, dizziness, cold sweat and nausea.
• Vibration induced in the machinery/equipment proves
detrimental to normal performance when present in
excessive levels.
•Vibration disturbances cause resolution problems in
electronic microscopes, optical systems, and surface finish
problems on precision grinders and jig borers, and also
hamper delicate work on micro circuitry.

4. Purpose of Silencer
 Automotive silencer should sustain vibration
generated due to high pressure exhaust gas.
 An automotive requires a silencer to reduce the
amount of noise emitted by a vehicle.
 Silencers use neat technology to cancel out the
noise.
 Silencers are installed along the exhaust pipe as a
part of the exhaust system of an I.C. engine to reduce
its exhaust noise.
 The silencer reduces exhaust noise by dampening
the pulsations in the exhaust gases and allowing
them to expand slowly.

5. Objective
 The specimen silencer belongs to one of reputed
company and possess problem of high vibration
and hence damage because of the it.
 According to JIS D 1601 Vibration Testing for
Automobile Silencer the damageable frequencies
are 33Hz and 67Hz so the basic objective of the
study is attenuate the design in order withstand
stresses generated at this frequency.

6. Experimental Analysis
Equipments Used In Experimentation-
 FFT Analyzer
 Piezoelectric accelerometer
 Postprocessor (RT ProPhoton)
 Existing model of silencer.
Experiment is performed on a `live' 4-wheeler for the given
model of the silencer.

7. Block diagram for experimental setup.

8. FPGA based 3-axis
simultaneous vibration analyzer
Silencer under test

9. Position of Accelerometer Actual Set up

10. FFT TEST ANALYSIS REPORT

11.  The graph obtained from
the experimentation
shows the natural
frequency of the existing
silencer lies at about
34Hz followed by 49Hz
and 68Hz.
 JIS D 1601 Vibration
Testing for Automobile
Silencer the damageable
frequencies are 33Hz
and 67Hz

12. Analytical Analysis

13. CAD model of Existing silencer.

14. Element Size 10mm
Material Steel
Young’s Modulus 2e5 Mpa
Density 7850 kg/m3
Passions Ratio 0.3
Thickness of plate 2 mm
Details of existing silencer

15. Meshing of the existing Silencer

16. Mesh Details
Material Endurance limit 170 N/mm2
Mesh type Solid mesh
Number of nodes 7120
Number of elements 7180

17. Modal Analysis
 Modal analysis is the study of the dynamic
properties of structures
under Vibrational excitation. Modal analysis is the
field of measuring and analyzing the dynamic
response of structures during excitation.
 It is done with SIMO(Single Input, Multiple output)
approach one point of excitation and then response
is measured at many other pts.

18. 1st mode of frequency for 35Hz 2nd mode of frequency 43Hz

19. 3rd Mode of frequency 52Hz
4th Mode of Existing Silencer 100Hz

20. Natural frequencies of first 4 modes of existing
model of silencer
Mode 1st 2nd 3rd 4th
Frequency
(Hz)
35 43 52 100
From above table we can conclude that 1st mode, 2nd
mode and third mode lies between 33Hz and 67Hz
which causes excess vibration and hence damage.
Frequencies obtained and the behavior of the
existing silencer under the free excitation is
damageable hence it is necessary to modify the
model in order to reduce the effect of vibration.

21. •By structural design
•By added damping
•By vibration isolation

22. By structural design
 This involves structural modification. The modification can be
in terms of changing mass or stiffness or both. Reduction in
stiffness is not desirable as this can have implication for static
design, durability.
 Hence stiffener can be added.
 Beam like structures one can use beam stiffener or in circular
shell like structure one can use bead structure.
 To reduce the vibration and to shift the frequency the stiffener
is added in a bead pattern.

24. Dimensions of the
bead-

25. 1st mode of modified Silencer

26. 2nd mode of modified Silencer

27. 3rd mode of modified

28. Natural frequencies of first 3 modes of
modified model of silencer-
Mode 1st 2nd 3rd
Frequency
(Hz)
103 140 380
First 3 modes of Natural frequencies for the
existing silencer was 35Hz,43Hz & 53Hz. The
modified design shifts it to 103Hz,140Hz &
380Hz.

29. Frequency Response
Analysis
 The first category is one of which is most preferred, which is
implementable at design stage if one of aware of possible
vibration hot spot and point of stress concentration.
 Frequency response analysis is a method used to compute
structural response to steady-state oscillatory excitation & the
excitation is explicitly defined in the frequency domain.

30. Existing Silencer FRA X- Direction

31. Modified Silencer FRA X- Direction

32. Existing Silencer FRA Y- Direction

33. Modified Silencer FRA Y-
Direction

34. Existing Silencer FRA Z- Direction

35. Modified Silencer FRA Z-Direction

36. •The maximum allowable stress on silencer is 170
N/mm 2.
At 33 Hz Stress in
N/mm2
At 67 Hz Stress in
N/mm2
377.73 11.07
57.29 18.93
62.87 19.03
The stresses in existing Silencer
At 33Hz Stress in
N/mm2
At 67 Hz Stress in
N/mm2
1.97 2.12
7.53 11.98
2.29 2.47
The stresses in modified Silencer

37. RESULTS AND DISCUSSIONS
Mode No Existing Frq(Hz) Modified Freq(Hz)
1 35 103
2 43 140
3 52 340
Comparison of frequencies of modal analysis

38. RESULTS AND DISCUSSIONS
Comparison of FRA
At 33 Hz Stress in
N/mm2
At 67 Hz Stress in
N/mm2
377.73 11.07
57.29 18.93
62.87 19.03
The stresses in existing Silencer
At 33Hz Stress in
N/mm2
At 67 Hz Stress in
N/mm2
1.97 2.12
7.53 11.98
2.29 2.47
The stresses in modified Silencer

39. CONCLUSIONS
 The difference between results of experimental and analytical
method is about 2.94%.
 The dynamic performance is increased by changing design i.e. by
adding stiffener in the form of bead in the modified silencer.
 The stresses induced in the modified silencer are less than
permissible yield strength of material i.e. 170 N/mm2.
 As in the modified silencer we are adding the bead as stiffener the
design becomes more reliable than existing model in order to reduce
vibration.
 The strength of the silencer can be increased by changing the
material or the thickness of the plate.

40. Completion Certificate

41. Thank You