简介:Amethodofobtainingbottombackscatteringstrengthbyemployinganomnidirectionalprojectorandomnidirectionalhydrophoneisproposed.Thebackscatteringstrengthisextractedfrommonostaticbackscatteringdata.ThemethodwasadoptedinanexperimentconductedintheSouthYellowSeaofChina.Theseafloorsurfacewasrelativelysmoothandcoveredbyasmallquantityofshellfragments,asobservedthroughadigitalcamerasystem.Samplingdatashowedthatthemaincomponentofthesedimentatthisexperimentalsitewasfinesand.Inthispaper,wedetailthecalculationmethod.Preliminaryresultsofbackscatteringstrengthasafunctionofgrazingangle(20°–70°)inthefrequencyrangeof6–24kHzarepresented.Themeasuredbackscatteringstrengthincreasedwiththegrazingangleandchangedmorerapidlyatlargegrazingangles(60°–70°).Acomparisonofthedataatdifferentfrequenciesrevealsthatthemeasuredbackscatteringstrengthsubstantiallyriseswiththeincreaseofacousticfrequency.AfittingcurveofLambert’slawagainstthemeasureddatashowsthatthebackscatteringstrengthdeviatesfromLambert’slawatlargegrazingangles.
简介:AnovelmodelingtechniquebasedonthecoupledEulerian-Lagrangian(CEL)methodisprovidedtosolvethegeotechnicalproblemswithlargedeformations.Thetechniqueisintendedtosolvetheupdateproblemofsoilmechanicalpropertiesduringspudcanpenetrationinnormallyconsolidatedclaysoil.IntheCELmodel,thenormalmethodofassigninganincreasingshearstrengthprofilewithdepth(NA)isdefectiveduetoitsEulerianframework.Inthispaper,anewtechniqueisproposedtoupdatesoilmaterialpropertiesbyintroducingthermo-mechanicalcoupledanalysis(TMCA)totheCELmodels.DuringestablishmentoftheCELmodels,theoptimalpenetrationvelocityandminimummeshsizearedeterminedthroughparametricstudies.Reasonabilityandaccuracyarethenverifiedthroughcomparisonofthepreliminaryresultswiththesoilflowconfigurationandpenetrationresistance(Fv)ofacentrifugetest,andtheresultsoftheproposedmethodarecomparedwiththoseoftheremeshingandinterpolationtechniquewithsmallstrain(RITSS)method.ToachieveaCELmodelwithsatisfactoryaccuracy,theNAandTMCAmethodsimplementedintheCELmodelsandtheRITSSmethodarefirstadoptedinweightlesssoil.ComparisonofthefindingswiththoseobtainedinpreviousstudiesshowsthattheTMCAmethodcanupdatematerialpropertiesandpredictFv.TheTMCAmethodisthenappliedtosoilswithself-weightanddifferentshearstrengthprofiles.Resultsshowthattheproposedmethodiscapableofaccuratelymodelingthelargedeformationproblemofspudcanpenetrationinnon-homogeneousclay.