by performance enhancement of automotive silencer using experimental & finite element analysis

A Project Seminar On

Performance Enhancement of Automotive Silencer using Experimental & Finite Element Analysis.

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Introduction 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.

•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.

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.

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.

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 givenmodel of the silencer.

Block diagram for experimental setup.

FPGA based 3-axis simultaneous vibration analyzer

Silencer under test

Position of Accelerometer

Actual Set up

FFT TEST ANALYSIS REPORT

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

Analytical Analysis

CAD model of Existing silencer.

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

Meshing of the existing Silencer

Mesh Details

Material Endurance limit 170 N/mm2

Mesh type Solid mesh

Number of nodes 7120

Number of elements 7180

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.

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

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

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.

THE VIBRATION RESPONSE CONTROL CAN BE ACHIEVED IN FOUR WAYS-

•By structural design

•By added damping

•By vibration isolation

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.

Modified Silencer

Dimensions of the bead-

Modal Analysis of Modified Silencer

1st mode of modified Silencer

2nd mode of modified Silencer

3rd mode of modified

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.

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.

Existing Silencer FRA X- Direction

Modified Silencer FRA X- Direction

Existing Silencer FRA Y- Direction

Modified Silencer FRA Y-Direction

Existing Silencer FRA Z- Direction

Modified Silencer FRA Z-Direction

• 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

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

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

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.

Completion Certificate

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