Ansys Car Cavity Acoustic 253

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ANSYS, Inc. Proprietary Car Cavity Acoustics using ANSYS Car Cavity Acoustics using ANSYS Muthukrishnan A Assistant Consultant TATA Consultancy Services 185,Lloyds Road, Chennai- 600 086 INDIA

Transcript of Ansys Car Cavity Acoustic 253

Page 1: Ansys Car Cavity Acoustic 253

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Car Cavity Acoustics using ANSYSCar Cavity Acoustics using ANSYS

Muthukrishnan AAssistant ConsultantTATA Consultancy Services185,Lloyds Road, Chennai- 600 086INDIA

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Introduction

• The study of vehicle interior acoustics in the automotive industry has gained importance due to

– Legal restrictions – Growing demand for comfort– To reduce the number of prototypes– High performance of modern computers

• The objectives of efficient automobile design are– Safety– Fuel consumption– Interior comfort

• The challenges are– Lower weight improves the fuel efficiency but

increases the vibrational sensitivity– Increase in weight generally improves the safety

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Objectives

• To predict the individual effect of low frequency noise (50-200Hz) on the car cavity due to sound absorption of

– Floor carpet– Roof lining – Seat– Front window open– Combined effect of all the above

• In all the above cases the front wall is excited with constant displacement of 1mm

• Location of interest– Drivers right ear (DRE) located at (1.50, 0.8, 1.25)

metre in the global X, Y, Z directions respectively – Passengers right ear (PRE) at the back of the driver

located at (0.6, 0.8, 1.25) in the global X, Y, Z directions respectively.

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Classification of Noise inside the Vehicle

Major source of low frequency noiseRoad excited vibrationMay be noticeableFan noiseNot importantEngine inletNot importantEngine exhaust

Major source of high frequency noiseEngine airborne noise and itstransmission

Major source of low frequency noiseEngine vibration

Noise inside the vehicleOrigin of noise

Noise based on frequency:Low frequency noise (50-200Hz)High frequency noise(200-4000Hz)

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Flow Chart for Finite Element Analysis

DIMENSIONAL MEASUREMENT OF ACTUAL CAR

FE MODEL

MODAL ANALYSIS

HARMONIC ANALYSIS

SOUND PRESSURE LEVEL

BOUNDARY CONDITIONS

EXCITATION FORCES

FREQUENCY RANGE

MATERIAL PROPERTIES

NATURAL FREQUENCY

END

ENDTIME HISTORY POST PROCESSING

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Case Studies

• The following five cases were analysed for a typical Indian car (Ambassador Mark IV)

– Car cavity with no absorption– Car cavity with roof absorption– Car cavity with seat absorption– Car cavity with full absorption– Car cavity with full absorption and window open

condition

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Element Specification

MATERIAL PROPERTIES (AIR)1.2 Kg/m3Density343 m/sVelocity of sound in air

Sound pressure Level in dBSound pressure Level Average pressurePressure

ELEMENT OUTPUTS

• Fluid structure interface• Impedance

Surface loads

#4 (Ux,Uy,Uz,PRES)-if Fluid structure interaction is present#1 PRES – if no structure at the interface

Degrees of freedom (D.O.F)8Number of nodesFluid 30 (3D volume element)ELEMENT NAME

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Ambassador Car Cavity - Dimensions

1.98 0.210.32

0.30

0.50

0.30

0.30 1.58 0.52 0.11

0.42

0.23

0.06

0.39

Overall dimensions of cavityLength = 2.51mWidth = 1.40mHeight = 1.10m

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Different Finite Element Views Of Car Cavity

Isometric view of interior elements

Isometric view of car cavity

Interior rear view of outer elements

Interior side view of outer elements

Hexagonal MappedMesh typeFluid 30 (Volume element)Element type 27411Number of nodes24570Number of elements

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Modal Analysis Of Car Cavity

• Modal analysis is done for the car cavity and the natural frequencies are obtained using theoretical calculation and ANSYS.

• The frequency range of interest is 0-200 Hz.

• Theoretical calculation is made considering a rectangular box with the overall dimensions. This enables a quick verification of computed frequencies.

f = (c/2)Where, c is the speed of sound in air, L is the length of the car cavity, W is the width of the car cavity, H is the height of the car cavity

• In ANSYS, the equation of motion for an undamped system, expressed in matrix notation as [M]{ } + [K] {u} = {0} .For harmonic vibration {u} = {Φ}i COS ωi t and the solution is given by [K] - ωi

2[M]= 0

/H)(r /W)(q/L)(p ooo ++

u••

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Ambassador Car Cavity-Mode Shape

At 74.99Hz At 122.69Hz

At 137.20Hz At 145.65Hz

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Ambassador Car Cavity-Mode Shape

At 162.10Hz

At 188.73Hz

At 175.02Hz

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Comparison-Modal Frequencies

198.36NA(0,1,1)

183.6188.73(2,1,0)

170.29175.02(1,0,1)

155.97162.1(0,0,1)

140.32145.65(1,1,0)

136.71137.2(2,0,0)

122.55122.69(0,1,0)

68.3574.99(1,0,0)

THEORITICAL RESULTS

ANSYS RESULTSMODESMODAL FREQUENCY

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Harmonic Analysis-Solver Options

SteppedStepped or Ramped Boundary condition

Sub-steps of 5HzFrequency sub-steps

50Hz to 200HzHarmonic frequency range

Time/FrequencyLoad step options

Real + ImaginaryDOF Print out format

FullAnalysis type-Solution Method

HarmonicAnalysis options

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Pressure Plot-No Absorption

No impedance-Pressure plot

At 75 Hz At 125 Hz

At 135 Hz At 145 Hz

No impedance-Pressure plot

At 175 HzAt 165 Hz

At 190 Hz

NO IMPEDANCE SOUND PRESSURE LEVEL

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50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220

Frequency in Hz

Soun

d pr

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re le

vel i

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NO impedance DRE NO impedance PRE

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Roof Absorption

Impedance value is set to 1 on all the six faces of the element.

Surface load

0.13 (50 Hz -125 Hz)0.53 (130Hz –200Hz)

Sound absorption coefficient (MU)

2400 m/sVelocity of sound (SONC)

1100 Kg/m3Density (DENS)

Material properties

3D-Model

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Roof Absorption – Pressure plot

Roof impedance only-Pressure plot

At 125 Hz

At 75 Hz

At 135 HzRoof impedance only-Pressure plot

At 145 Hz At 165 Hz

At 190 HzAt 175 Hz

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No Absorption and Roof Absorption: SPL at DRE and PRE

Roof Impedance comparison chart

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50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220

Frequency in Hz

Soun

d pr

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re le

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NO impedance DRE NO impedance PRERoof Absorption coeff 0.13/0.53 DRE Roof Absorption coeff 0.13/0.53 PRE

98.6095.06Minimum SPL133.31132.95Maximum SPL

PRE in dBDRE in dBDescription

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Floor Absorption

Impedance value is set to 1 on all the six faces of the element.

Surface load

0.2 (50 Hz -125 Hz)0.55 (130Hz – 200Hz)

Sound absorption coefficient (MU)

343 m/sVelocity of sound (SONC)

55 Kg/m3Density (DENS)

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Floor Absorption – Pressure plot

Floor impedance only-Pressure plot

At 135 HzAt 125 Hz

At 75 Hz

Floor impedance only-Pressure plot

At 145 Hz

At 175 Hz At 190 Hz

At 165 Hz

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No Absorption and Floor Carpet Absorption: SPL at DRE and PRE

Floor carpet impedance comparison chart

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50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220Frequency in Hz

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NO impedance DRE NO impedance PREFloor impedance 0.2/0.55 DRE Floor impedance 0.2/0.55 PRE

107.78104.18Minimum SPL125.91125.45Maximum SPL

PRE in dBDRE in dBDescription

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Seat Absorption

Impedance value is set to 1 on all the six faces of the seat element.

Surface load

0.1/0.5 (50Hz –200Hz)

Sound absorption coefficient (MU)

343 m/sVelocity of sound (SONC)

80Kg/m3Density (DENS)

Material properties

3D Model

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Seat Absorption – Pressure Plot

Seat impedance only-Pressure plot

At 75 Hz

At 135 Hz At 145 Hz

At 125 Hz

Seat impedance only-Pressure plot

At 190 HzAt 175 Hz

At 165 Hz

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No Absorption and Seat Absorption: SPL at DRE and PRE

Seat impedance comparison chart

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Frequency in Hz

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NO impedance DRE NO impedance PRE Seat impedance 0.1 DRE

Seat impedance 0.1 PRE Seat impedance 0.5 DRE Seat impedance 0.5 PRE

93.10102.8772.2592.88Minimum SPL124.32130.71118.40135.53Maximum SPL

PRE in dBDRE in dBPRE in dBDRE in dB

0.5 absorption0.1 absorptionDescription

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Full Absorption

3D Model

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Full Absorption – Pressure plot

Full impedance -Pressure plot

At 75 Hz

At 135 Hz At 145 Hz

At 125 Hz

Full impedance -Pressure plot

At 190 HzAt 175 Hz

At 165 Hz

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No Absorption and Full Absorption: SPL at DRE and PRE

Full impedance comparison chart

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Frequency in Hz

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NO impedance DRE NO impedance PRE FULL impedance DRE FULL impedance PRE

70.5091.32Minimum SPL101.66122.89Maximum SPLPRE in dBDRE in dBDescription

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Full Absorption with window open

3D Model

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Full Absorption with window open –Pressure plot

Full impedance –Window open-Pressure plot

At 75 Hz

At 135 Hz At 145 Hz

At 125 Hz

Full impedance –Window open-Pressure plot

At 190 HzAt 175 Hz

At 165 Hz

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No Absorption and Full Absorption Window Open: SPL at DRE and PRE

Full impedance window open comparison chart

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50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220

Frequency in Hz

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NO impedance DRE NO impedance PREFULL impedance DRE FULL impedance PREFULL impedance-window open-Impedance=1 DRE FULL impedance-window open-Impedance=1 PREFULL impedance-window open-Pressure=0 DRE FULL impedance-window open-Pressure=0 PRE

MinimumMaximum

Description

54.8173.4363.0083.3997.40114.3296.38114.14PRE in dBDRE in dBPRE in dBDRE in dB

Pressure =0Absorption Coefficient =1

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Conclusions

• In each case, the SPL was compared with that of no absorption and found to decrease considerably.

• The major individual contributors were found to be seat and window open condition.

• It has been found that the reduction in SPL predominantly occurs at modal frequency.

• Interior acoustics can be improved by having seat with more sound absorption coefficient suitably placed.

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References

• Kopuz et al(1995).Analysis of interior acoustic fields using the finite element method and the boundary element method. Applied acoustics 45 pp 193-210.

• T.Priede (1971) Origins of automotive vehicle noise. Journal of sound and vibration 15, pp 61-73

• Utsuno, et al., Analysis of the sound field in an automobile cabin by using the boundary element method. SAE Paper No. 891153, 1990, pp. 1147-52

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Acknowledgement

• I sincerely acknowledge the valuable guidance given by Prof.Chandramouli, IITM, Chennai in completing this project.

• I acknowledge the support and sponsorship given by my organization TCS for encouraging me to present this paper