ACO 3_Acoustic Reflections Off a Water-Sediment Interface

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1、SolvedwithCOMSOLMultiphysics5.2AcousticReflectionsOffaWater-SedimentInterfaceIntroductionThisvalidationmodelcomputesthereflectioncoefficientofacousticwavesoffawater-sedimentinterface.Homogeneouswavesareincidentfromafluid(water)domainandarereflectedandtransmittedatawater-sedimentinterface.Thesedimen

2、tdomainismodeledusingBiot’stheorywiththeuseofthePoroelasticWavesinterface.Itincludesthedetailedinteractionbetweenthepressurewavesinthesaturatingfluidandtheelasticwavesintheporousmatrix(thesediment).ThemodelresultsarecomparedwiththoseobtainedbyStollandKan(Ref.1).Avisualcomparisonoftheresultswiththos

3、epresentedinRef.1showsgoodagreement.PMLλ/3Waterkθ0H=2λFloquetperiodicityW=λSedimentPMLλ/3Figure1:Sketchofthewater-sedimentsystem.ThecomputationalunitcellhasthewidthWandtheheightHwithperfectlymatchedlayersatthetopandbottom.λistheacousticwavelengthinwater.Anacousticwavewithwavevectorkisincidentatanan

4、gleθ0onthewater-sedimentinterface.1

5、ACOUSTICREFLECTIONSOFFAWATER-SEDIMENTINTERFACESolvedwithCOMSOLMultiphysics5.2Knowledgeabouttheplanewavereflectionandrefractioncoefficientsareimportantwheninterpretingacousticdatatakenfrommarineseismology.Thekindofmodelstudiedherecanprovideinsightintothedifferentp

6、henomenaatplay.ThesedimentismodeledusingBiot’stheorywiththeadditionoftheporousmatrixskeletonhavingviscoelasticproperties.Thisisachievedbysimplyallowingthebulkmodulusandtheshearmodulustohaveasmallimaginarycomponent(aconstantattenuationfactor).Insidetheporousmaterialthreetypesofwavescanpropagate,afas

7、tandaslowlyattenuatingpressurewave,andashearwave.Theinterplaybetweenthesewavesandtheincominghomogeneouspressurewaveinthefluidresultsinnontrivialbehaviorofthereflectioncoefficient.SeeRef.1forfurtherdiscussion.ModelDefinitionAsketchofthemodeledsystemisshowninFigure1.Anacousticwaveisincidentonthewater

8、-sedimentinterfaceatanangleθ0,definingthewavevectorωk=k()sin()θ,–cos()θk=----0000cwhereωistheangularfrequency2πf.ThewavevectorisusedtodefineanincidentplanewaveoftheformP()x=1Pa⋅exp()–i()kx⋅inwherex=(x,y).Th