简介：Anewquantitativeconceptisintroducedinthispaper,whichmaybeusedtofacilitatethemeasurementofthecontrollabilityofasubspace～subspacecontrollabilitydegree.Thentheconcreteformofthesubspacecontrollabilitydegreeofaflexiblestructureisderived,andtheerrorsofsubspacecontrollabilitydegreeanddynamicalresponsecausedbythesubstitutionofarepeatedmodesubspaceforacloselyspacedmodesubspacearediscussed.Alltheresultsshowthatthissubstitutionisrationalundersomeconditions.

简介：Byusingthemethodofstressfunctions,theproblemofmode-ⅡGriffithcrackindecagonalquasicrystalswassolved.First,thecrackproblemoftwo-dimensionalquasicrystalswasdecomposedintoaplanestrainstateproblemsuperposedonanti-planestateproblemandsecondly,byintroducingstressfunctions,the18basicelasticityequationsoncouplingphonon-phasonfieldofdecagonalquasicrystalswerereducedtoasinglehigherorderpartialdifferentialequations.Thesolutionofthisequationundermixedboundaryconditionsofmode-ⅡGriffithcrackwasobtainedintermsofFouriertransformanddualintegralequationsmethods.Allcomponentsofstressesanddisplacementscanbeexpressedbyelementalfunctionsandthestressintensityfactorandthestrainenergyreleaserateweredetermined.

简介：Thepresentworkusesdynamicmodedecomposition(DMD)toanalyzewakeflowofNACA0015airfoilwithGurneyflap.ThephysicsofDMDisfirstintroduced.ThenthePIV-measuredwakeflowvelocityfieldisdecomposedintodynamicalmodes.Thevortexsheddingpatternbehindthetrailingedgeanditshigh-orderharmonicshavebeencapturedwithabundantinformationsuchasfrequency,wavelengthandconvectionspeed.Itisobservedthathigh-orderdynamicmodesconvectfasterthanlow-ordermodes;moreoverthewavel...

简介：Thepresentstudydevelopsthefracturetheoryforatwo-dimensionaloctagonalquasicrystals.TheexactanalyticsolutionofaModeⅡGriffithcrackinthematerialwasobtainedbyusingtheFouriertransformanddualintegralequationstheory,thenthedisplacementandstressfields,stressintensityfactorandstrainenergyreleaserateweredetermined,thephysicalsenseoftheresultsrelativetophasonandthedifferencebetweenmechanicalbehaviorsofthecrackproblemincrystalandquasicrystalwerefiguredout.Theseprovideimportantinformationforstudyingthedeformationandfractureofthenewsolidphase.

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简介：FlowstructuresofaMach6transitionalboundarylayerovera260mmlongflaredconeareinvestigatedbytheparticleimagevelocimetry(PIV).Particleimagesnearthecurvedwallareinitiallytransformedintosurface-fittedorthogonalcoordinatesandsplicedwiththeir180°-symmetricimagestosatisfyano-slipconditionatthewall.Theresultsarethenreverselytransformedtothephysicaldomain.Directnumericalsimulation(DNS)isalsoperformedtovalidatetheexperimentalresults.Theexperimentalandnumericalresultsareinagreement,indicatingastrongdilatationprocesswithinthesecond-modeinstability.

简介：Aninvestigationisdescribedforinstabilityproblemofflowthroughapipeofcircularcross-section.Asadisturbancemotion,weconsiderageneralnon-axisymmetricmode.Anassociatedamplitudeormodulationequationhasbeenderivedforthisdisturbancemotion.Thisequationbelongstoadiffusiontype.ThecoefficientofitcanbenegativewhileReynoldsnumberincreases,becauseofthecomplexinteractionbetweenmoleculardiffusionandconvection.Thenegativediffusivity,whenitoccurs,causesaconcentrationandfocussingofenergywithindecayingslugs,actingasaroleofreversingnaturaldecays

简介：Experimentswereconductedinawatertunnelbytomographictime-resolvedparticleimagevelocimetry(Tomo-TRPIV).TheReynoldsnumberReθis2460onthebaseofmomentumthickness.Accordingtothephysicalmechanismofthestretchandcompressionofmulti-scalevortexstructuresinthewall-boundedturbulence,thetopologicalcharacteristicsofturbulencestatisticsinlogarithmiclayerwereillustratedbylocal-averagedvelocitystructurefunction.Duringcoherentstructuresbursting,resultsrevealthatthetopologicalstructuresofvelocitygradients,velocitystrainratesandvorticitiesbehaveasantisymmetricquadrupolemodes.Athree-layerantisymmetricquadrupolevortexpacketconfrmsthatthereisatightrelationshipbetweentheouterlayerandthenear-walllayer.

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简介：AnewlydevelopedZfracturecriterionforthecompositematerialswasintroduced,thenewconceptsofin-planeaveragestrain,in-planedilatationalstrainenergydensityfactorandreciprocalcharacteristicfunctionwerepresented.ManyexperimentalresultsshowthattheZfracturecriterioncanbewellusedtopredictthecrackpropagatingdirectionformodeⅠcrackincarbon-fiberreinforcedcompositelaminates.

简介：Nonlinearinteractionsofthetwo-dimensional(2D)secondmodewithobliquemodesarestudiednumericallyinaMach6.0flat-plateboundarylayer,focusingonitsselectiveenhancementeffectonamplificationofdifferentobliquewaves.Evolutionofobliquemodeswithvariousfrequenciesandspanwisewavenumbersinthepresenceof2Dsecondmodeissimulatedsuccessively,usingamodifiedparabolizedstabilityequation(PSE)method,whichisabletosimulateinteractionoftwomodeswithdifferentfrequenciesefficiently.Numericalresultsshowthatobliquemodesinabroadbandoffrequenciesandspanwisewavenumberscanbeenhancedbythefiniteamplitude2Dsecondmodeinstabilitywave.Theenhancementeffectisaccomplishedbyinteractionofthe2Dsecondmode,theobliquemode,andaforcedmodewithdifferencefrequency.Twotypesofobliquemodesarefoundtobemoreamplified,i.e.,obliquemodeswithfrequencyclosetothatofthe2Dsecondmodeandlow-frequencyfirstmodeobliquewaves.Eachofthemmaycorrespondtoonetypeoftransitionroutesfoundintransitionexperiments.Thespanwisewavenumberoftheobliquewavepreferredbythenonlinearinteractionisalsodeterminedbynumericalsimulations.

简介：BasedontheZufiriatheoreticalmodel,anewmodelregardingtheasymptoticbubblevelocityfortheRayleigh-Taylor(RT)instabilityispresentedbyuseofthecomplexvelocitypotentialproposedbySohn.TheproposedmodelisanextensionoftheordinaryZufiriamodelandcandealwithnon-idealfluids.Withthecontrolvariablemethod,theeffectoftheviscosityandsurfacetensiononthebubblegrowthrateoftheRTinstabilityisstudied.TheresultisconsistentwithCao’sresultifweonlyconsidertheviscouseffectandwithXia’sresultifweonlyconsiderthesurfacetensioneffect.TheasymptoticbubblevelocitypredictedbytheZufiriamodelissmallerthanthatpredictedbytheLayzermodel,andtheresultfromtheZufiriamodelismuchclosertoWhite’sexperimentaldata.

简介：Theefficiencyandaccuracyaretwomostconcernedissuesinthemodelingandsimulationofmulti-bodysystemsinvolvingcontactandimpact.Thispaperproposedaformulationbasedonthecomponentmodesynthesismethodforplanarcontactproblemsofflexiblemulti-bodysystems.Aflexiblebodyisdividedintotwoparts:acontactzoneandanun-contactzone.Fortheun-contactzone,byusingthefixed-interfacesubstructuremethodasreference,afewlow-ordermodalcoordinatesareusedtoreplacethenodalcoordinatesofthenodes,andmeanwhile,thenodalcoordinatesofthelocalimpactregionarekeptunchanged,thereforethetotaldegreesoffreedom(DOFs)aregreatlycutdownandthecomputationalcostofthesimulationissignificantlyreduced.Byusingadditionalconstraintmethod,theimpactconstraintequationsandkinematicconstraintequationsarederived,andtheLagrangeequationsofthefirstkindofflexiblemulti-bodysystemareobtained.Theimpactofanelasticbeamwithafixedhalfdiskissimulatedtoverifytheefficiencyandaccuracyofthismethod.

简介：Ahigherorderasymptoticsolutionofnear-tipfieldisstudiedforplane-atrainMode-Ⅰquasi-staticsteadycrackgrowthintheincompressible(v=1/2)elasticperfectly-plasticmedia.Theresultsshowthatthenear-tipstressandstrainarefullycontinuous,andthestrainpossessesIn(A/r)singularityatthecracktip.Theexpressionsofthestress,strainandvelocityineachregionarealsogiven.

简介：Foracompression-shearmixedmodeinterfacecrack,itisdifficulttosolvethestressandstrainfieldsconsideringthematerialviscosity,thecrack-tipsingularity,thefrictionaleffect,andthemixedloadinglevel.Inthispaper,amechanicalmodelofthedynamicpropagationinterfacecrackforthecompression-shearmixedmodeisproposedusinganelastic-viscoplasticconstitutivemodel.Thegoverningequationsofpropagationcrackinterfaceatthecrack-tiparegiven.Thenumericalanalysisisperformedfortheinterfacecrackofthecompression-shearmixedmodebyintroducingadisplacementfunctionandsomeboundaryconditions.Thedistributedregularitiesofstressfieldoftheinterfacecrack-tiparediscussedwithseveralspecialparameters.Thefinalresultsshowthattheviscosityeffectandthefrictionalcontacteffectonthecracksurfaceandthemixed-loadparameterareimportantfactorsinstudyingthemixedmodeinterfacecracktipfields.Thesefieldsarecontrolledbytheviscositycoefficient,theMachnumber,andthesingularityexponent.

简介：TheSchmidtmethodisadoptedtoinvestigatethefractureproblemofmultipleparallelsymmetricandpermeablefinitelengthmode-IIIcracksinafunctionallygradedpiezoelectric/piezomagneticmaterialplane.Thisproblemisformulatedintodualintegralequations,inwhichtheunknownvariablesarethedisplacementjumpsacrossthecracksurfaces.Inordertoobtainthedualintegralequations,thedisplacementjumpsacrossthecracksurfacesaredirectlyexpandedasaseriesofJacobipolynomials.Theresultsshowthatthestress,theelectricdisplacement,andthemagneticfluxintensityfactorsofcracksdependonthecracklength,thefunctionallygradedparameter,andthedistanceamongthemultipleparallelcracks.Thecrackshieldingefectisalsoobviouslypresentedinafunctionallygradedpiezoelectric/piezomagneticmaterialplanewithmultipleparallelsymmetricmode-IIIcracks.

简介：Westudythedynamicbehaviorofaquartzcrystalresonator(QCR)inthickness-shearvibrationswiththeuppersurfacecoveredbyanarrayofmicro-beams(MBs)underlargedeflection.ThroughtakingintoaccountthecontinuousconditionsofshearforceandbendingmomentattheinterfaceofMBs/resonator,dependencesoffrequencyshiftofthecompoundQCRsystemversusmaterialparameterandgeometricalparameterareillustratedindetailfornonlinearandlinearvibrations.Itisfoundthatthefrequencyshiftproducesalittleright(left)translationforincreasingelasticmodulus(length/radiusratio)ofMBs.Moreover,thefrequencyright(left)translationdistancecausedbynonlineardeformationbecomesmoreseriousinthesecond-ordermodethaninthefirst-orderone.