Table Of ContentINTERNATIONAL CENTRE FOR MECHANICAL SCIENCES
COURSES AND LECTURES - No. 276
NOISE GENERATION AND CONTROL
IN MECHANICAL ENGINEERING
P.O.A.L. DAVIES
UNIVERSITY OF SOUTHAMPTON
M.HECKL
TECHNICAL UNIVERSITY OF BERLIN
G.L. KOOPMAN
UNIVERSITY OF HOUSTON, TEXAS
EDITED BY
G. BIANCHI
POLITECNICO DI MILANO
SPRINGER-VERLAG WIEN GMBH
Per Ia stampa di questo volume il CNR ha assegnato il contributo n. 206072/07/67078.
This work is subject to copyright.
All rights are reserved,
whether the whole or part of the material is concerned
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© 1982 by Springer-Verlag Wien
Originally published by Springer-Verlag Wien New York in 1982
ISBN 978-3-211-81710-0 ISBN 978-3-7091-2894-7 (eBook)
DOI 10.1007/978-3-7091-2894-7
Tire ackrwu•led,lled iiiiJl<>r!ullcc· of the da11ger.~ of rwi.'l" pollutio11 clellltlllcl• tlrclt the
('ltgilwer, aiUI ill particulur tlr~· mccha11ical ellgill<'<'r. be able 110t only. a11d 110t so r11uc/r, to
jl~~el remedi< s to tire problem as it presellts itself ill ecrclr cusc·, but tlrat lw be, ubor•e all.
"se11sitive" to tlw problem of noise ill all stages of machine desig11 ullll i11stallutio11. Tlri.<
"sensitivity" ca11 gil•c· useful fruit> only if it is based upo11 a11 illfrmate lmvwlec~~e of tlw
plw11omc:11a of rwise prvductio11 cmd prvpagatio11 ill muchi11e unci plu11ts irrstal!atum.
This book is a col/ectio11 of lectures ,11ive11 011 these themes i11 Vllc' of tire ucll'allced
courses we have orga11i.:ecl at the hrtematio11al Celltre for Aleclrallical Scic•11cc•.< .
.-1 view of the basic clejt11itio11s of acoustic cJU<llltities a11d the tecluriques for tlreir
represerrtati01r and meclsurc'lll<'llt i.~ gi1•e11 by C. L 1\.ovpmurr, wlro tlw11 tm·sellt.~ the mc1i11
body of pertinent acoustic tlreory: wut>c· acoustics, ray acvu.~tics. ejji·cts of bo111rdaries.
acoustic sources. The theory i~ tln·n applied to a typical, CVIIt'c'llliollcll source of 110i.~e. tlw
motor l'ehicle, wlriclr is tlwrou,l/lrly a11aly.:ecl with <ldflclllced t<·clllllcJm·s fin till' sllul\' o/
body i11teractio11.
P.0. . 4.L Dal'ies treats tire question of flou• c.K~ociatecl norse·. with Ofll'licatioll.< to
common problems in industrial c'll,llilleerillg, such as l'alt•c·s, fulls, blowers. comprc·ssor.~.
/'articular attention is ,1/it•err to tlw problems of .wrmd .~e11c·ratio11 a11d propagaticm in flo,.
ducts and tv that of aircraft noise.
M. Heck/ considers tlw problem of the tra1m11is.~ion cllld prvpa}lation of sOJmd i11
structures. The ejji·cts ojfvrm anclmateric.rl.< 011 the tra11smissio11 of l'ibratvry c·ne~I!.Y ancltlre
possibilities of damping are studied. The mecha11isms of tire rc.u/iatio11 of .~owrd from
structures, the loss of tra11smissio11 i11 walls. the possibilities of cl<.~mpill,l!, so111HI U'itlt
oppvrttmdy selected materials are also examinc:cl.
The l'olume, for its very origilr as a collectil'c' lc·cture series. Cc.IIIIIOt prc·suiiiC' to gil•c• a11
exhaustil•c· ami lwmo,~~em•ous treatment of all noise problem.< irr uwclruwc.rl c'll,l!,illcerirrg. It
does i11dicate a correct tlJIJlTOclch to the rigorous c·xc.llllillativrr of jillldc.wrulfc.rl !'rob/ems .r.<
expaierrced by actil•c· researcltc·rs ill the field.
Ciul'atnll llru11clri
Secret.rry (,cllc rt~l of CIS. II
CONTENTS
page
I) G.L. Koopman
Sound, Vibration and Shock I. Measuring Systems . . . . . . . . . . . . . . . . . . . 1
1. Sensing Transducer and Signal Conditioner . . . . . . . 1
1.1 Pressure Sensing Transducers . . . . . . . . . . . . . . 4
1.2 Mechanical Vibration (and Force) Sensing Transducers . 8
2. Data Storage. Magnetic Tape Recorder 12
3. Signal Processing . 16
3.1 Sound Level Meter . 16
3.2 Analysers ..... . 17
3.3 Real Time Analysers 19
4. Readout and Display 21
4.1 Meters ...... . 21
4.2 Graphic Level Recorders ... 21
4.3 Oscilloscopes . . . . . . . . 22
Sound, Vibration and Shock II. Spectra . . . . . . . . . . . . . . . . . . . . . . . . 25
1. Deterministic Wave Forms . . . . . . . . . . . . 27
1.1 Periodic Functions . . . . . . . . . . . . . . . . 27
1.2 Aperiodic Functions (Fourier Transform Analysis) 29
1.3 Aperiodic Functions (Shock Spectrum Analysis) 30
2. Non-Deterministic Wave Forms 36
2.1 Random Processes 36
2.2 Auto-correlation Function . . . . 37
Theory of Acoustics I. Waves, Rays and Statistical Fields .. 43
1. Introduction to Wave Motion .... . 43
1.1 Wave Acoustics . . . . . . . . . . . .46
1.1.1 Plane Wave Propagation in Air .. . . .48
1.1.2 Spherical Wave Propagation in Air .. 50
1.1.3 Propagation Losses .. . 52
1.2 Ray Acoustics ... . . 54
1.3 Energy Acoustics .. . . 60
G.L. Koopman cont. 'd page
Theory of Acousticsll. Propagation and the Effects of Boundaries ....... . .. 65
1. Reflection of Sound from Passive Boundaries . . . . . . . . . . . . . . . . 65
1.1 The Rigid Plane Boundary: Plane-Wave Reflection and Interference ... . 66
1.2 The Rigid Plane Boundary: Spherical Wave Reflection and Interference . . 67
1.3 Screening of Spherical Waves by a Barrier . . . . . . . . . . . . . . . . .68
1.4 Plane Boundary of Finite Impedance: Plane-Wave Reflection and Interference . 70
1.5 The Impedance Tube ................... . . 73
1.6 Physical Realization of Acoustically Absorbing Boundaries . . . . . . . . . . 74
Acoustic Sources I. Elementary Source Characteristics . . . . . . . . . . . . . . . . 79
1. Source Characteristics . 81
1.1 Acoustic Power Radiation . 81
1.2 Radiation Impedance . 82
2. Field Characteristics . . . . 84
3. Examples of Spherical Sources . . . . 85
3.1 Pulsating Sphere (Monopole) . . . . . 85
3.1.1 The Monopole as a Point Source . . . . 89
3.2 Oscillating Sphere (Dipole) . . . . . . . 90
3.2.1 The Dipole as an Elementary Solution. . . . 91
Acoustic Sources II. Extended Sources . . . . . . 93
Acoustic Sources Ill. Sources Due to Mechanical Impact 107
Interior Noue in Transportation Vehicles ....... . 121
II) P.O.A.L. Davies
Flow Noue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . · 141
1.1 Specification of Source Strength and Source Characteristics . . . . . . 142
1.2 Characteristics of Point Aerodynamic Sources . . . . . . . . . . . . . 146
1.3 Aerodynamic or Flow Associated Sources in the Industrial Environment 148
1.4 Valve and Blow-off or Discharge Noise . . . . . 149
1.5 Fans and Blowers (rotating machinery) Noise . . 151
1.6 Sources Associated with Cyclic Flow . . . . . . . 153
2.0 Aircraft Noise Mechanism ... 154
2.1 Propulsion Noise . . . . . . 155
2.1.1 Jet Mixing Noise . . . . . . . 156
2.1.2 Shock Associated Noise .... 159
2.1.3 Fan or Compressor Noise . . .. 160
2.2 Airframe Noise . . . . . . . . . 164
P.O.A.L. Davies cont.'d page
2.2.1 Boundary Layer and Flight Noise . 165
2.2.2 Landing Configuration Noise . . . 166
3.0 Sound Generation and Propagation in Flow Ducts . . . 167
3.1 Plane Wave Propagation in Ducts, Zero Flow ... 168
3.2 Sound Propagation in Ducts Carrying Flow . . . . 173
3.3 Sound Generation by Flow Acoustic Coupling ... 179
3.4 Source Identification and Characterization . . . . . 185
3.5 Duct Propagation of High Amplitude Pressure Waves 188
· 3.6 The Radiation of Sound from Duct Walls . . . . . . 191
3.6.1 Prediction of Valve Noise . . ........... . 192
Appendix A. Acoustic Analogies for Sources of Aerodynamic Sound . . . . . . . 195
Al.O Lighthill's Acoustic Analogy ............ . 195
Al.l Wave Models of Distributed Sources . . . . . . . . . . 198
A1.2 Classical Models of Acoustic Sources (after Lighthill) 199
A1.3 Aerodynamic Sound Radiation to a Remote Observer 202
Al.4 Sources in Motion . . . . . . . . . . 203
Al.5 Turbulence as a Source of Sound. . ... 204
A1.5.1 Correlation length and Time Scales 205
A1.5.2 Intensity of Turbulence Generated Sound 207
III) M. Heckl
Structure Borne Sound . . . . . . . . . . . . . . . . . . . . . . . • • . • . . . 209
1. Basic Equations . . . . . . . . . . . . . . . . 210
2. Bending Wave Field on Beams and Plates . . . . 212
3. Energy Considerations . . . . . . . . . . . . . 214
4. Energy Considerations for Coupled Structures 217
5. General Laws of Vibration Damping . . . . 220
6. Damping Layers . . . . . . . . . . . . . . 228
7. Vibration Damping by Sandwich Plates . . 232
8. Damping by Localized Absorbers . . . . . 234
9. Attenuation of Structure Borne Sound by Discontinuities . . . 236
9.1 Elastic Interlayers . . . . . . . . . . . . . . . . 236
9.2 Changes in Cross-section, Corners, Junctions, etc. · 243
10. Radiation of Structure Borne Sound . . . 245
10.1 The Basic Mechanism . . . . . . . . . . 245
10.2 Examples of Radiation Efficiencies . . 249
10.3 Special Cases . . . . . . . . . . . . . . 251
M. Heck! cont.'d page
Transmission Lou of WaUs and Enclosures . . . . . . . . . . . . . 255
1. Transmission Loss of Single Walls ....... . 256
2. Double Walls . . . . . . . . . . . . . . . . . . . 262
3. Partitions Made Out of Sound Absorbing Material 264
4. Pipes ... 267
5. Enclosures ................... . 271
Noise Reduction by Sound Absorbing Materials ..... ·. . . . . . . . . . . . . 276
1. Basic Mechanisms and Empirical Data . 280
2. Noise Reduction by Sound Absorption 280
3. Dissipative Mufflers . . . . . . . . . . 281
SOUND, VIBRATION AND SHOCK I
Measuring Systems
When converting the wave motion of sound and vibration into a
measurable quantity for the purpose of analysis, it is necessary to use
combinations of several instruments which together make up the overall
measurement system. A typical layout of possible combinations is shown
in figure 1.
1. Sensing Transducer and Signal Conditioner
The transducer, as the name implies, is a device which converts one
form of energy into another. In sound and vibration analysis, sensing
transducers are used for the conversion of acoustic or vibratory motion
into electrical energy, the most convenient form for measurement, re
cording, and analysis. Basically, sensing transducers fall into the
following two electrical classifications:
2 G.L. Koopman
TYPE OF 1. SENSING SIGNAL
SAVE MOTION ~ TRANSDUCEJl. ----~ CONDITIONER
sound pressure, microphone, amplifier,
displacement, capacitance guage, attenuator,
velocity, vibroll'eter, impedance
acceleration, accelerometer, transformer
strain strain gauge, bridge
'
2. DATA 3. SIGNAL ~ 4.READOUT
STORAGE PROCESSOR AND DISPLAY
magnetic r.m.s. meter, meter,
tape filter, asci lloscope,
recorder probability graphic level
density recorder.
analyzer,
auto-correlation
Figure 1.
(a) Non-generating devices which require a supply voltage. The
mechanical response of this device causes a change in capaci-
tance, inductance, or resistance in its electrical network and
an output signal is produced.
V IN·----IIJo~~- ,.-___.t----1.-~V OUT
·'-----MECHANICAL DISTURBANCE
(b) Generating devices which do not require a separate supply
voltage. These devices contain an element which generates a
voltage proportional to the relative velocity or a charge
proportional to the strain in the element.
