UNIVERSITI PUTRA MALAYSIA

SAMIRA MOHAMADY

FK 2010 45

NUMERICAL MODELING AND MINIMIZATION OF ENCLOSURE INTERIOR NOISE USING LOCAL ACTIVE SOUND CONTROL

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Numerical Modeling and Minimization of Enclosure

Interior Noise using Local Active Sound Control

By

SAMIRA MOHAMADY

Thesis Submitted to the School of Graduate Studies, University Putra Malaysia, in

Fulfilment of the Requirements for the Degree of Master of Science

August 2010

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Dedicated

To

My dearest parents

For their extensively love

and

Their endless care

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Abstract of thesis presented to the senate of University Putra Malaysia in fulfillment

of the requirement of the degree of Master Science

NUMERICAL MODELING AND MINIMIZATION OF ENCLOSURE

INTERIOR NOISE USING LOCAL ACTIVE SOUND CONTROL

By

SAMIRA MOHAMADY

August 2010

ABSTRACT

Chairman: Raja Mohd Kamil b. Raja Ahmad, PhD

Faculty: Engineering

Low frequency noise has detrimental effects on human’s physiology and

psychology. To reduce low frequency noise, active control of sound is more effective

compared to passive sound absorbers. Reduction of low frequency noise in structures

like vehicle cabin and room in a house is therefore important. These structures can

be modeled as a three dimensional (3D) enclosure with a flexible boundary structure

on one of its side. In this thesis minimization of sound pressure in an enclosure with

five rigid walls and a flexible plate on its top side using local active noise control

technique was investigated. The acoustic environment of the enclosure was modeled

using the finite element method. COMSOL© MULTIPHYSICS software which

provides structural and acoustical modules was used to create finite element model

of the enclosure. Modal analysis of this system was performed and the

eigenfrequencies were compared against those obtained in related analytical and

experimental works. In order to verify the finite element modeling procedure,

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convergence analysis of the system was performed. The eigenfrequencies of the

finite element model were compared with the ones obtained for analytical and

experimental models and the mean absolute error of 5.8 % and 4.3 % were achieved

respectively. Local control method has been used to design the controller in reducing

the interior sound pressure field at two observer locations. The estimated noise

reduction was assessed by calculating the estimated sound potential energy in the

enclosure with and without controller. An average of 140.4 dB reduction in estimate

potential energy in low frequency range has been obtained. Reduction of sound

pressure at each observer position is around 60 dB. This implies that local active

control of sound can be used in reducing sound pressure level at desired observer

locations within the enclosure.

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Sari tesis dipersembahkan kepada senat bagi University Putra Malaysia dalam

perlaksanaan syarat-syarat darjah bagi Master Sains

PEMODELAN BERANGKA DAN PENGURANGAN HINGAR DI DALAM

MEDAN TERTUTUP MENGGUNAKAN KAWALAN BUNGI AKTIF

SETEMPAT

Oleh

SAMIRA MOHAMADY

Ogos 2010

ABSTRAK

Pengerusi: Raja Mohd Kamil b. Raja Ahmad, PhD

Fakulti: Kejuruteraan

Hingar berfrekuensi rendah mempunyai kesan yang akan menjejaskan fisiologi dan

psikologi manusia. Di dalam pengurangan hingar frekuensi rendah, kawalan aktif

bunyi adalah lebih berkesan berbanding dengan penyerap bunyi yang pasif.

Pengurangan hingar frekuensi rendah dalam struktur-struktur seperti kabin

kenderaan dan bilik dalam sebuah rumah adalah penting. Struktur-struktur ini boleh

dimodelkan untuk dijadikan sebagai satu ruang tertutup tiga dimensi (3D) dengan

sempadan struktur yang fleksibel pada salah satu sisinya. Dalam tesis ini kajian

mengenai keberkesanan mengawal bunyi dalam sesebuah kawasan dengan lima

dinding tegar dan satu plat boleh lentur pada sisi atas menggunakan teknik kawalan

hingar aktif setempat telah dijalankan. Persekitaran akustik kawalan dimodelkan

dengan menggunakan kaedah unsur terhingga. Perisian COMSOL©

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MULTIPHYSICS yang menyediakan modul-modul struktur dan akustik digunakan

bagi mencipta model elemen terhingga bagi ruang tertutup tersebut. Analisis modal

sistem ini dijalankan dan frekuensi eigen dibandingkan dengan nilai yang diperolehi

daripada kerja eksperimen dan analisis yang sedia ada. Dalam mengesahkan model

elemen terhingga, prosedur analisis penumpuan mesh bagi sistem telah dijalankan

bagi mendapatkan bilangan elemen yang terbaik bagi model tersebut.. Dalam

membandingkan frekuensi eigen antara model elemen terhingga dan analitikal,

begitu juga dengan model elemen terhingga dengan eksperimen. Min ralat mutlak

5.8 % dan 4.3 % telah diperolehi secara langsung. Kaedah kawalan setempat telah

digunakan untuk mengurankan tekanan bunyi pedalaman di kedua-dua lokasi

pemerhati. Pengurangan hingar telah ditaksirkan dengan pengiraan tenaga keupayaan

bunyi dianggarkan dalam kawalan dan tanpa kawalan. Purata 140.4 pengurangan dB

Penurunan tekanan suara pada setiap posisi pemerhati adalah sekitar 60 dB.dalam

tenaga keupayaan dianggarkan di dua lokasi-lokasi pemerhati telah diperolehi. Ini

menandakan kawalan aktif setempat itu boleh digunakan untuk mengurangkan

tekanan bunyi di mana-mana lokasi pemerhati yang berada di dalam ruang tertutup.

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ACKNOWLEDGEMENT

First of all, I would like to express my sincere thanks to my supervisor, Dr Raja

Kamil who has given the knowledge and the ability to observe, think and develop.

I wish also to thanks very much my co-supervisor, Dr Montazeri for his valuable

guide and advice and encouragement.

I am grateful to my co-supervisors, Dr Rizal and Dr Nawal, for their insightful

suggestion, comments and support.

Most of all, I am deeply indebted to my parents. Their love, dedication and help were

always the foundation of my work and patient during this long course of learning. I

also want to express my thanks to my greatest sister, brothers and brother in low and

whole family for their unconditional care, patient and help.

I am also expressing my thanks to my colleagues who have shared their experience

of work and life.

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I certify that an Examination Committee has met on to conduct the

final examination of Samira Mohamady on her Master of Science thesis entitled

"Modeling and control of interior noise in an enclosure using local active control of

sound” in accordance with Universiti Pertanian Malaysia (Higher Degree) Act 1980

and Universiti Pertanian Malaysia (Higher Degree) Regulations 1981. The

Committee recommends that the candidate be awarded the relevant degree. Members

of the Examination Committee are as follows:

Chairman, PhD

Professor

Faculty of Graduate Studies

Universiti Putra Malaysia

(Chairman)

Examiner 1:

Professor

Faculty of Graduate Studies

Universiti Putra Malaysia

(Internal Examiner)

Examiner 2:

Professor

Faculty of Graduate Studies

Universiti Putra Malaysia

(Internal Examiner)

Examiner 3:

Professor

Faculty of Graduate Studies

Universiti Putra Malaysia

(External Examiner)

___________________

Bujang Kim Huat, PhD

Professor/Deputy Dean

School of Graduate Studies

Universiti Putra Malaysia

Date:

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This thesis was submitted to the Senate of Universiti Putra Malaysia and has been

accepted as fulfilment of the requirement for the degree of Master of Science. The

members of the Supervisory Committee were as follows:

Raja Mohd Kamil bin Raja Ahmad, PhD

Lecturer

Faculty of Engineering

University Putra Malaysia

(Chairman)

Rizal bin Zahari , PhD

Lecturer

Faculty of Engineering

University Putra Malaysia

(Internal Member)

Nawal Aswan bin Abdul Jalil , PhD

Lecturer

Faculty of Engineering

University Putra Malaysia

(Internal Member)

Allahyar Montazeri, PhD

Lecturer

Faculty of Electrical Engineering

Iran University of Science and Techlonogy

(External Member)

________________________________

HASANAH MOHD GHAZALI, PhD

Professor and Dean

School of Graduate Studies

Universiti Putra Malaysia

Date: December 2010

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DECLARATION

I declare that the thesis is my original work except for quotations and citations,

which have been duly acknowledged. I also declare that it has not been previously,

and is not concurrently submitted for any other degree at University Putra Malaysia

or other institutions.

_______________________

SAMIRA MOHAMADY

Date: August 2010

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TABLE OF CONTENTS

Page

DEDICATED ........................................................................................................... i

ABSTRACT ............................................................................................................ ii

ABSTRAK ............................................................................................................. iv

ACKNOWLEDGEMENT ...................................................................................... vi

LIST OF TABLES ................................................................................................ xiii

LIST OF FIGURES ............................................................................................... xv

CHAPTERS:

1 INTRODUCTION ........................................................................................ 1

1.1 Problem Statement ................................................................................. 3

1.2 Objectives .............................................................................................. 4

1.3 Methodology .......................................................................................... 4

1.4 Scope of Work ....................................................................................... 5

1.5 Chapter Layout ....................................................................................... 5

2 LITERATURE REVIEW ............................................................................. 8

2.1 Sound Wave and its Types ..................................................................... 8

2.2 Noise and its Types .............................................................................. 10

2.3 Vibration Induced Sound ...................................................................... 11

2.4 Sound Induced vibration ....................................................................... 11

2.5 Modal Analysis .................................................................................... 12

2.6 Sound Field in Closed Spaces ............................................................... 12

2.7 Numerical Acoustic Modeling .............................................................. 13

2.8 Vibro-Acoustic Modeling ..................................................................... 16

2.9 Acoustic Modeling of an Enclosure with all solid boundaries ............... 16

2.9.1 Analytical Modeling of a fully Rigid Enclosure .................. 17

2.9.2 Experimental Modeling of a Fully Rigid Enclosure ............ 18

2.9.3 Finite Element Modeling of Enclosure ............................... 19

2.10 Modeling of Plate ........................................................................... 20

2.10.1 Analytical Modeling of plate ............................................ 21

2.10.2 Experimental Modeling of Plate ...................................... 22

2.10.3 Finite Element Modeling of Plate ..................................... 25

2.11 Vibro-Acoustic Modeling of Enclosure-Plate System...................... 26

2.11.1 Analytical model of Vibro-Acoustic Model of Enclosure-

Plate ............................................................................................... 26

2.11.2 Experimental Vibro-Acoustic Model of Enclosure-Plate .. 28

2.11.3 Finite Element Vibro-Acoustic Model of Enclosure-Plate 30

2.12 COMSOL Multiphysics®

................................................................ 33

2.13 Export Data from COMSOL to MATLAB ...................................... 35

2.14 Noise Control Methods in an Enclosure .......................................... 35

2.14.1 Passive Control of Sound ..................................................... 35

2.14.2 Active Control of Sound ....................................................... 36

2.14.3 Control source and sensor placement ............................... 41

2.15 Concluding Remark ........................................................................ 42

3 MODELLING OF ENCLOSURE .............................................................. 43

3.1 Analytical Model .................................................................................. 43

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3.1.1 Analytical Model of the Enclosure ......................................... 43

3.1.2 Analytical Model of Plate ....................................................... 52

3.1.3 Model of Coupled System (Plate-Enclosure) .......................... 57

3.2 Experimental Arrangement ................................................................... 71

3.3 Finite Element Modeling ...................................................................... 74

3.3.1 Modeling Method in COMSOL Multiphysics Software .......... 75

3.3.2 Model of the uncoupled Enclosure ......................................... 77

3.3.3 Model of Plate ........................................................................ 86

3.3.4 Model of Coupled system ....................................................... 92

3.3.5 Vibro-Acoustic Model Excited with Point Source .................. 96

3.4 Concluding Remark .............................................................................. 99

4 LOCAL SOUND PRESSURE CONTROL METHOD ............................. 100

4.1 Active Control of Sound in an Enclosure ............................................ 100

4.2 Modal Interaction Model .................................................................... 101

4.3 Global Control Strategy ...................................................................... 106

4.4 Local Control Strategy ........................................................................ 108

4.5 Simulation of active sound control system ......................................... 112

4.5.1 Location of Secondary sources ............................................. 113

4.5.2 Local Sound Pressure Minimization Process ........................ 114

4.6 Control Source Calculation ................................................................. 119

4.7 Concluding Remark ............................................................................ 120

5 RESULT AND DISCUSSION ................................................................. 121

5.1 Vibro-Acoustic Model ........................................................................ 121

5.2 Uncoupled FE Modeling ..................................................................... 122

5.2.1 FE Model of Uncoupled Enclosure ....................................... 122

5.2.2 Convergence Analysis of Uncoupled Enclosure ................... 125

5.2.3 FE Model of Uncoupled Plate .............................................. 127

5.2.4 Convergence Analysis of Uncoupled Plate ........................... 130

5.2.5 FE Model of coupled Plate-Enclosure system ....................... 132

5.2.6 Convergence Analysis of Coupled Plate - Enclosure ............ 135

5.3 Comparison of Modeling Results ........................................................ 136

5.3.1 Validation of Uncoupled FE Model of Plate - Enclosure ...... 137

5.3.2 Validation of Coupled FE Model of Plate - Enclosure .......... 138

5.4 Result of Vibro-Acoustic Model Response when Excited by a Point

Source .......................................................................................... 140

5.5 Result of noise reduction process using local active control method .... 142

5.6.1 Computation of pressure Level at observers due to Primary

Source .......................................................................................... 143

5.6.2 Pressure Computation due to S1 Source ............................... 145

5.6.3 Pressure Computation due to S2 Source ............................... 146

5.7 Estimated Potential Energy ................................................................. 147

5.8 Discussion of Results .......................................................................... 152

5.9 Concluding Remark ............................................................................ 154

6 CONCLUSION AND FUTURE WORKS ................................................ 155

6.1 Conclusion ......................................................................................... 155

6.2 Contribution of Study ......................................................................... 156

6.3 Limitation of Study ............................................................................. 157

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6.4 Future Studies ..................................................................................... 157

REFRENCES ...................................................................................................... 158

APPENDIX A.1 ................................................................................................... 163

APPENDIX A.2 ................................................................................................... 164

APPENDIX A.3 ................................................................................................... 165

APPENDIX A.4 ................................................................................................... 166

APPENDIX B ...................................................................................................... 167

BIODATA OF STUDENT................................................................................... 172

LIST OF PUBLICATIONS ................................................................................. 173