tutorial fundamentals acoustics 1 structural part - asmefiles.asme.org/divisions/ncad/21411.pdf ·...
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-
StructuralAcousticsTutorial
Part1Fund
amentals
Dr.Step
henA.H
ambric
ASM
EIM
ECE2009
Orlando
,Florida
-
Overview
Instructor
StructuralVibratio
nsMod
esin
beamsandplates
Mob
ility
Soun
dradiated
bystructuralwaves
Ra
diationefficiency
Structuralwavesgen
erated
byim
pingingsoun
dTransm
ission
loss
Briefintrodu
ctiontonum
ericalm
etho
dsFE,B
E,SEA
-
Instructor
Dr.Step
henA.H
ambric
App
liedRe
searchLab,Pen
nStateUniversity
AlsoProfessorinPen
nStatesG
radu
ateProgramin
Acoustics
AssociateDire
ctor,Pen
nStateCe
nterfo
rAcoustics
andVibration(CAV
)
Accom
panyingmaterials:
StructuralAcousticsTutorials,Parts1and
2,from
AcousticsToda
ymagazine
Dow
nloadatwww.ham
bricacou
stics.com
http://www.hambricacoustics.com/
-
Motivation
Structurescan
amplify
(and
atten
uate)sou
nd
sourcessubstantially
Soun
dSource
TransferFun
ction
Soun
datReceiver
dBdB
dB
-
StructuralAcoustic
TransferF
unctions
Definetransferfu
nctio
n:
How
isitdefined
?
2rad
P F
2 22
2
=
rad
oo
ao
rd
oPcAv
F
v Fc
PA
Soun
dpo
wer
radiation
efficiency
Soun
dpo
wer
App
liedforce2
Surface
averaged
mob
ility
Fluid
impe
dance
-
SurfaceAveraged
Mob
ility
Averaged
surfacevibratio
nam
plitu
descaused
byknow
nforces(m
obilitie
s)
2 2
v F
Peaksinth
emob
ility
functio
narecaused
by
mod
esofreson
ance
-
Mod
esofR
eson
ance
Supe
rposition
offorwardandbackwardtravelingwaves
Exam
pleforfle
xureofsim
plysupp
ortedbe
am:
Foro
therbou
ndarycond
ition
s,waven
umbe
rschange,
e.g.,forfree
bou
ndaries:
22
22
=
=m
mEI
mEI
kA
aA
22
2
(21)
4
mm
EIa
A
-
Mod
esofR
eson
ance
Canalsobecompu
tedwith
Finite
Element(FE)
mod
elsorm
easured
Measuredandsimulated
resonancefreq
uenciesseldom
matchexactly
Glassplates
with
free
bo
undary
cond
ition
s
-
Mob
ilityasaSummationofM
odes
Astructuresm
obilityfu
nctio
nisasim
ple
seriessum
mationofm
odalre
spon
sestoa
drivingforce
Exam
ple:sim
plysupp
ortedrectangularp
late
()
02
11
02
,sin
sin
4
1sin
sin
,(
)
==
=
mo
mo
nn
mx
ny
xy
ab
hab
xy
mx
ni
yv
aF
b
Mod
alm
ass
(fractionof
staticm
ass)
Differen
ce
betw
eendrive
andresonance
freq
uencies
Mod
eshapeat
respon
selocatio
n
Mod
eshapeat
drivelocatio
n
-
Mod
alRespo
nsePeaks
Whyisntm
odalre
spon
seinfin
iteat
resonancefreq
uencies?
Be
cause
mniscom
plex,due
todam
ping
Forlightlydam
pedsystem
s:
whe
re
isth
elossfa
ctor
()
22
1, ,
()
oo
mn
vxy
Fxy
12
+
mn
mn
i
-
Dam
ping
Mechanism
s
Thinshe
etsofrub
beradhe
red
toth
esurface,orsand
wiche
dbe
tweenstructures
Adjoining
structures
Co
uplinglosses
Jointlosses(friction)
Soun
dradiation
-
EffectsofDam
ping
on
Mod
alRespo
nsePeaks
Peak(and
antip
eak)amplitu
desde
creasewith
increasing
dam
ping
Mob
ilityapp
roache
sthemeanlevelsofaninfin
iteplate
How
can
mob
ility
ofaninfin
iteplate
becom
puted?
-
Infin
iteStructureM
obilitie
s
Astructureiseffectivelyinfin
itewhe
nwavesre
flected
from
bou
ndariesare
veryweakwith
respecttotheoriginal
wavesemanatingfrom
asou
rce
Forplates:
Usefulfor:
scalingmob
ilitie
s
pe
rformingen
gine
eringestim
atesof
prop
osed
materialchanges
Ch
ecking
mob
ilitym
easuremen
taccuracy
()
inf
inf
1/
8
==
YvF
Dh
-
Infin
iteStructureM
obility
ScalingExam
ple
Tw
opane
lswith
identicalgeo
metriesand
differentm
aterials
Lexan(plastic)and
Aluminum
-
Infin
iteStructureM
obility
ScalingExam
ple
Measuredmob
ilitie
sofbothpane
ls
-
Infin
iteStructureM
obility
ScalingExam
ple
Aluminum
panelm
obilityscaledtoth
atofLexan / /
==
AlAl
AlAl
Lexan
Lexan
Lexan
Lexan
Ef
cf
cE
-
RadiationEfficiency
2
rad
ooP cAv
ff c
1.0 (f)
CriticalFrequ
ency,w
here
bend
ingandacou
stic
wavespe
edsmatch
Structureradiates
poorly
Peakra
diation
=1
-
Coincide
nce
Bend
ingwavesare
dispersive,slowerth
an
acou
sticwavesatlow
freq
uencies(sub
sonic),
andfasterath
igh
freq
uencies(sup
ersonic)
-
RadiatingFlatBaffle
dPane
lBe
lowCoinciden
ce
Pressures
Odd
/Odd
>Odd
/Even>
Even
/Even
-
RadiatingFlatBaffle
dPane
lIncreasing
Frequ
ency
Intensities
(propo
rtional
tosqu
areof
pressure)
-
RadiationEfficiencyEffectsof
Coincide
nceFreq
uencyShifts
ff c
1.0 (f)
f c
Stiffer,lighter
structurewith
fasterwaves
Highe
r
-
f c
RadiationEfficiencyEffectsof
Coincide
nceFreq
uencyShifts
ff c
1.0 (f)
Flim
sier,heavier
structurewith
slow
erwaves
Lower
-
Soun
dPo
werTransferFunctio
ns
Co
mbining
surfaceaveragedmob
ilitywith
radiationefficiencytellsusho
wwella
structureradiatessou
ndwhe
ndriven
bya
know
nforce
-
(1,1)m
ode>
loud
speakerm
ode
-
Acoustic
WavesIm
pingingon
Structures
-
Soun
dTransm
ission
Loss
ofanInfin
itePanel [
](
)(
)
()(
)
20
0
4
4
2
0
0
2
00
si
2sin
s
2s
n
ni
i
n
=
++
Dk
h
c
Dk
c
Dam
ping
im
portanta
tcoincide
nce
Massim
portant
below
coincide
nce
(masslaw)
Stiffne
ss
impo
rtanta
bove
coincide
nce
Dipsoccurwhe
nmassan
dstiffne
ss
term
scancel
=0
=90
-
Soun
dTransm
ission
nearC
oinciden
ce
-
FiniteElement(FE)A
nalysis
Usedgene
rallyto
mod
el
structures
Plates,beams,and
solids
Alsosometim
esusedto
mod
elacoustic
region
s,
usuallyinside
anob
ject
Manycommercial
softwarepackages
available
-
Boun
daryElement(BE
)Analysis
Usedtom
odelth
ebo
unda
riesofacoustic
region
sInside
oro
utside
avibratin
gsurface
Oncesurfacepressuresand
velocitie
sareknow
n,th
eacou
sticfieldanyw
herem
ay
becom
puted
Somecommercialsoftw
are
packagesareavailable(not
asm
anyasFEpackages)
-
Coup
ledFE/BEAnalyses
Im
pedancematricesofstructures(fromFE)and
acou
sticre
gion
s(fromBE)m
aybecoup
led
Enforcecontinuityofn
ormalfluctuatingvelocityalong
bo
undary
-
StatisticalEne
rgyAnalysis(SEA
)
SEAm
odelstheen
ergyexchangebe
tweenlarge
grou
psofreson
ancesinintercon
nected
structuresand
acoustic
region
sUsuallyusedathighfreq
uencies,whe
rem
odecoun
ts
areveryhigh
Exchangeofe
nergyism
odeled
statistically
Getcalculatio
nsaveragedoverlargeregion
s,and
overw
ide
freq
uency(usuallyone
thirdoctave)bands
Fastcom
putatio
ns,ind
epen
dentofincreasing
freq
uency
Va
One
softw
are
Structural-Acoustics TutorialPart 1 - FundamentalsOverviewInstructorMotivationStructural Acoustic Transfer FunctionsSurface Averaged MobilityModes of ResonanceModes of ResonanceMobility as a Summation of ModesModal Response PeaksDamping MechanismsEffects of Damping on Modal Response PeaksInfinite Structure MobilitiesInfinite Structure Mobility Scaling ExampleInfinite Structure Mobility Scaling ExampleInfinite Structure Mobility Scaling ExampleRadiation EfficiencyCoincidenceRadiating Flat Baffled PanelBelow CoincidenceRadiating Flat Baffled Panel Increasing FrequencyRadiation Efficiency Effects of Coincidence Frequency ShiftsRadiation Efficiency Effects of Coincidence Frequency ShiftsSound Power Transfer FunctionsSlide Number 24Acoustic Waves Impinging on StructuresSound Transmission Loss of an Infinite PanelSound Transmission near CoincidenceFinite Element (FE) AnalysisBoundary Element (BE) AnalysisCoupled FE/BE AnalysesStatistical Energy Analysis (SEA)
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