R. V. COLLEGE OF ENGINEERING

(Autonomous Institution Affiliated to VTU, Belgaum)

Technical Seminar on

“VIBRO-ACOUSTIC ANALYSIS PROCEDURES FOR THE EVALUATION OF THE SOUND INSULATION

CHARACTERISTICS OF AGRICULTURAL MACHINERY CABINS”

Presented by

SUDESHKUMAR C A 1RV11ME109

Under the guidance of

Dr. Ramesh Sharma

Dept. of Mechanical Engineering

Contents

1. Introduction…………………………………………………….1

2. Literature review……………………………………………….2

3. Concept of Sound insulation procedures……………………...5

4. Insertion loss……………………………………………………6

5. Numerical Prediction Tools……………………………………8

6. Numerical Modelling approaches……………………..............9

7. Conclusions………………………………………………........13

8. Applications………………………………………...................14

9. Scope for future………………….............................................15

10. References………………………………………………..........16

1

INTRODUCTION

• Over the last few years, customer demands regarding acoustic performance, along with the tightening of legal regulations on noise emission levels and human exposure to noise, have made the noise and vibration properties into important design criteria for agricultural machinery cabins.

• Vibration + Acoustics = Vibro-acoustic

• Research

*University of Salford Manchester (developing and implementing novel measurement methods for vibro-acoustics)

* Gaus (GAUS researchers develop vibro acoustic modelling tools with the aim to minimize noise radiation and transmission from structures, such as car chassis)

2

Literature review

1. W. Desmet, B. Pluymers, P. Sas have analysed procedures for sound insulation using the Insertion loss concept and Numerical prediction tools.

2. W. Desmet, B. Pluymers, P. Sas have made use of Harvester driver’s cabin and scale model for the analysis of experimental tool.

3. GAUS has developed many Sound insulation modelling tools which helped to know the latest developments in Vibro-acoustic field.

Harvester driver’s cabin and scale model

3Harvester driver’s cabin Cabin scale model

Modelling tools developed by GAUS

644

Concept of Sound insulation procedures

• There are mainly three concepts 1. Insertion loss

2. Numerical prediction tools

3. Numerical modelling approaches

5

Insertion loss

6

W source, sound power radiated by an acoustic source in a certain Environment.

W cabin, sound power radiated in that environment by the considered cabin when the same acoustic source is placed in the cabin interior.

Insertion loss of the cabin scale model

7**Insertion loss should be maximum to have a good insulation system.Insertion loss should be maximum to have a good insulation system.

Numerical prediction tools

• The main numerical prediction tools for solving low-frequency (vibro-)acoustic problems are based on

1. The Finite Element (FE) method and

2. The Boundary Element (BE) method

1. The finite element method is a commonly used method for predicting the steady-state pressure field in a closed cavity volume.

1. The boundary element method is a commonly used alternative method for solving acoustic problems, especially for predicting the steady-state pressure field in unbounded fluid domains. 8

Numerical modelling approaches

1. Fully coupled approach

2. Semi-coupled approach

3. Uncoupled approach

9

Fully coupled approach

10

IL of the cabin scale model calculated with the fully coupled approach using a pulsating panel

Semi-coupled approach

11

IL of the cabin scale model calculated with the semi coupled approach using a pulsating panel

IL of the cabin scale model calculated with the semi coupled approach using a free-field source strength characterization

Uncoupled approach

12

IL of the cabin scale model calculated with the uncoupled approach using a pulsating panel

Conclusions

• In all three approaches, the pulsating panel source modelling method performs better than the free-field source strength method at low frequency.

• Honeycomb structures help to minimize the noise in a harsh environment, such as a turbo engine used in agricultural machines.

• It is concluded from validations on a cabin scale model that the semi-coupled approach provides a good balance between prediction accuracy and computational load.

13

14

Applications

1. Fully Coupled approach Ex: Petrol banks, Volvo buses etc.

2. Semi-Coupled approach Ex: corporate office

3. Uncoupled approach Ex: Grass cutting machine

Scope For Future

• Many researches are going on to maximize the insertion loss.

• GAUS is developing advanced level of Sound insulation modelling tools.

15

References

[1] Direct Journal of Sound and Vibration 266 (2003) 407–441.

[2] F. Fahy, Sound intensity (Elsevier Applied Science, London, 1989).

[3] http://gaus.recherche.usherbrooke.ca/?portfolio=vibroacoustic

[4] ISO 140-3: Acoustics – Measurement of sound insulation in buildings and of building elements - Part 3: laboratory measurements of airborne sound insulation of building elements (1995).

[5] S. Amini, P.J. Harris, A comparison between various boundary integral formulations of the exterior acoustic problem, Comput. Methods Appl. Mech. Eng., Vol. 84 (1990), 59-75.

[6] F. Jacobsen, Random errors in sound intensity estimation, J. Sound Vib., Vol. 128 (1989), 247-257. W. Desmet, B. Pluymers, P. Sas, “Vibro-acoustic analysis procedures for the evaluation of the sound insulation characteristic of agricultural machinery cabins”, Science

16

Thank You…!!!