Installation manual

Echosoundertheory
Severalextraordinaryphysicalphenomenaareassociatedwithacousticcavitation.
Chemicalreactionscanbeinitiatedorincreasedinactivity;livingcellsand
macromoleculescanberuptured;violentlyoscillatingbubblesclosetoasolid
surfacecanerodethetoughestofmetalsorplastics;lightmaybeproduced
bycavitation(sonoluminescence).Thehighpressuresandhightemperatures
(calculatedtobe30,000°Kelvin)attheinteiorduringthecollapsingphaseof
cavitatingsinglebubblescancauseemissionofareproduciblepulseoflightof
durationlessthan50picoseconds.
Ofdirectimportancetotheuseofsoundsourcesatseaisthefactthat,asthesound
pressureamplitudeincreases,ambientbubblesbegintooscillatenonlinearly,and
harmonicsaregenerated.Atsealevel,theamplitudeofthesecondharmonicis
lessthan1percentofthefundamentalaslongasthepressureamplitudeofthe
fundamentalofaCWwaveislessthanabout0.01atmrms(lkPa)(Rusby1970).
Thisincreasestoabout5percentharmonicdistortionwhenthesignalisabout10
kPa.
Whenthepeakpressureamplitudeissomewhatgreaterthan1atm,theabsolute
pressureforasoundsourceatsealevelwillbelessthanzeroduringtherarefaction
partofthecycle.InusingCWbelow10kHz,thisnegativepressure,ortension,is
thetriggerforasharplyincreasedlevelofharmonicdistortionandtheissuanceof
broadbandnoise.Anyattempttoincreasethesoundpressureamplitudeappreciably
beyondtheambientpressurewillcausenotonlytotaldistortionbutalsothe
generationofalargecloudofbubbleswhichwillactuallydecreasethefar-eld
acousticpressure.
Thedetailedbubbleactivitiesduringcavitationhavebeenstudiedinseveral
laboratories.Acousticianshaveidentiedgaseouscavitationresultinginstreamers
ofhissingbubblesthatjetawayfromregionsofhighacousticpressureswings,and
vaporouscavitation,whichradiatesshockwavesofbroadbandnoise.
—HermanMedwin&ClarenceS.Clay(1998)
[5]
InordertocontrolthepoweroutputontheSimradES70,usetheNormalOperation
functionontheOperationmenu.
Relatedtopics
•Howtochoosepassivemodeonpage97
•Howtochangetheoutputpoweronpage98
•Howtoadjustthepulsedurationonpage98
Aboutpulseduration
Theechosounder’spulsedurationisameasurementforh
o w l o n g theacousticpulselasts.
5.from“FundamentalsofAcousticalOceanography”,AcademicPress,SanDiego,1998
343539/B
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