简介：Glowdischargeisintroducedasanartificialdisturbancetoinvestigatetheevolutionoffirst-andsecond-modeinstabilitiesinahypersonicflatplateboundarylayer.ExperimentsareconductedinaMach6.5quietwindtunnelusingRayleighscatteringvisualizationandparticleimagevelocimetry(PIV).Detailedanalysisoftheexperimentalobservationsisprovided.Itisfoundthattheartificiallyintroduced17kHzdisturbance,whichbelongstothefirst-modefrequencyband,caneffectivelyenhancefirst-modewaves.Moreover,itcanenhancesecond-modewavesevenmoreintensely.Possiblemechanismstoexplainthisphenomenonarediscussed.

简介：AnartificialdisturbanceisintroducedintotheboundarylayeroveraflatplatetoinvestigatetheeffectonthetransitionprocessintheMach6.5windtunnelatPekingUniversity.Alinearstabilitytheory(LST)isutilizedtopredicttheevolutionoftheeigenmodes,andthefrequencyoftheartificialdisturbanceischosenaccordingtotheLSTresults.Theartificialdisturbanceisgeneratedbyglowingdischargeonthesurfaceoftheplateclosetotheleadingedge.TheRayleigh-scatteringvisualizationandparticleimagevelocimetry(PIV)measurementsareperformed.Bycomparingtheexperimentalresultswithartificialdisturbanceswiththoseunderthenaturalcondition(withoutartificialdisturbances),thepresentpapershowsthatthesecond-modeinstabilitywavesaresignificantlystimulatedbytheartificialdisturbances,andtheboundarylayertransitioniseffectivelytriggered.

简介：ItisdifficulttodesignaplatewithwideattenuationzonesinlowfrequencyregionbasedonBraggscatteringmechanism.Aplatewithperiodicrhombusholesisoptimizedanddesigned.Basedonthefiniteelementmethodunderperiodicboundaryconditions,thein-planedispersioncurvesofperiodicallyperforatedplatearecalculatedviaCOMSOL.ThefrequencyresponsesofperiodicallyperforatedplateareinvestigatedviaANSYSsimulation.Theplateswithperiodicholesaresuspendedanddynamicallytestedundersinusoidalexcitations.Theresultsshowthataperiodicallyperforatedplatewithrhombusholeshaswiderattenuationzonesthanplateswithcircularandhexagonalholes.Materialpropertieshaveagreatinfluenceonattenuationzones:nitrile-butadienerubberandsiliconrubbercaneasilyobtainlow-frequencyzones,whileincreasingporositycreateslowerandwiderzones.Thewidthofattenuationzoneincreasesasthehorizontalangleoftherhombusholesincreases.Ananalysisoftheattenuationzones'generationmechanismshowsthattheplatewithperiodicholesexhibitscharacteristicsofBraggscatteringandlocalresonantphononiccrystal,indicatinganinherentrelationshipbetweentwotypesofmechanisms.Theoptimizedplatehasacompleteattenuationzonerangingfrom5281.76-8824.30Hz.Thevibrationsaresignificantlyreducedwhenthenumberofperiodsisnolessthantwo.Theattenuationrangeobtainedviathenumericalmethodisgenerallyconsistentwiththeexperiment.Theresearchshedslightonthenoiseinsulationplateandhasthepotentialtoimprovethesoundenvironmentinvariousapplicationsduetoitssimplemanufacturing.

简介：Platestructuresareemployedasimportantstructuralcomponentsinmanyengineeringapplications.Hence,assessingthestructuralconditionsofin-serviceplatestructuresiscriticaltomonitoringglobalstructuralhealth.Modalcurvature-baseddamagedetectiontechniqueshaverecentlygarneredconsiderableattentionfromtheresearchcommunity,andhavebecomeapromisingvibration-basedstructuralhealthmonitoringsolution.However,computingerrorsarisewhencalculatingmodalcurvaturesfromlateralmodeshapes,whichresultfromunavoidablemeasurementerrorsinthemodeshapesasidentifiedfromlateralvibrationsignals;thismakescurvature-basedalgorithmsthatusealateralmeasurementonlytheoreticallyfeasible,butpracticallyinfeasible.Therefore,inthisstudy,long-gaugefiberBragggratingstrainsensorsareemployedtoobtainamodalcurvaturewithoutanumericaldifferentiationprocedureinordertocircumventthecomputingerrors.Severaldamageindicesbasedonmodalcurvaturesthatweredevelopedtolocatebeamdamageareemployed.Bothnumericalandexperimentalstudiesareperformedtovalidatetheproposedapproach.However,althoughpreviousstudieshavereportedrelativesuccesswiththeapplicationofthesedamageindicesonasimplebeam,onlyonedamageindexdemonstratedthecapabilitytolocatedamagewhenthestiffnessofthelocalregionchangednearthesensor.

简介：TheTibetanPlateau,knownas“theroofoftheworld”and“thethirdpoleoftheearth”,isaproductofthecollisionbetweenIndiaandAsiaduringthelast~50Ma.Theregionaltectonics–inparticular,growthandexpansionoftheplateau–hasbeenattributedprimarilytodeformationwithinthelithosphere.Theroleandpatternoftheunderlyingasthenosphericflow,however,remainmostlyunaddressed.Inlightofrecentseismictomographicimagesandpublishedseismicanisotropicdescriptionsoftheuppermantle,hereweproposethatanentrainedmantleflowislikelytoexistunderTibet,inducedbythenorthwardadvancingIndianplate.ThedirectionofmantleflowischaracterizedbyagradualrotationfromnorthwardinthesouthtoeastwardinthenorthasaresultofdeflectionbythedeeprootoftheTarimblock.Thepresenceofanunderlyingmantleflowisnotonlyabletoaccountforthewest-eastorientedfast-axisofseismicanisotropyinnorthernTibet,butcanalsoadequatelyexplainthesporadicnullsplittinginsouthernTibet.Specifically,thenullsplittingresults,atleastinpart,fromupwellingsofasthenosphericflowthroughtearsoftheunderthrustingIndianplatethathavebeenrevealedbyvariousseismicobservations.ThemantleflowmayinturnpromotetheblockextrusionunderTibetthathasbeenobservedinGPSmeasurements;hotasthenosphericupwellingsmayalsoleadtowidespreadpost-collisionalmagmatisminsouthernTibet.

简介：AlthoughtheIndus-TsangpoSuture(ITS)isthemostspectacularthrustsystemofcontinent-continentcollisionintheworld,fundamentalquestionsaboutitsstrengthevolutionanddeformationbehaviortransitionremainunanswered.Herewereported,forthefirsttime,frictionalmelting-inducedpseudotachylytesintheintensivelydeformedfelsicrocksalongtheITSzoneinsouthernTibet.ThisstudyrevealsthatpseudotachylytesinducedprofoundweaknessoftheboundaryfaultbetweenIndianandAsianplates.Theintrinsicallylowstrengthofthefoliatedmicrolitescrystallizedfromfrictionalmeltorglass(i.e.,pseudotachylyte)atseismogenicdepthscomparedwiththesurroundingcoarse-grainedquartzofeldspathicrocksinthebrittleandsemi-brittleregimeissufficienttoexplainthelocalizationofshearstrain,thedevelopmentofductileshearzonesembeddedinstrongwallrocks,andthetransitionfromthestrongtoweakfaultbehaviorswithoutinvokingthepresenceofhighfluidpressureorlowfrictioncoefficientmetasomaticmaterials(e.g.,smectiteorlizardite)withinthefaults.