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