简介:在与喉咙直径的一张超声的嘴相结合的一个低动力的弧气体加热器的流动不到1mm相当复杂、困难在量的详细描述。单原子的气体氩和氦的加热弧的超声的喷气推进器的实验被执行了,他们的表演测量了。流动特征在数字模拟的帮助下被分析。结果证明粘滞效果是引起理想、真实的性能之间的大差别的最重要的因素。出口流动的大外部节是慢吞吞的。这在氦是特别显著的,在嘴的70%出口区域可能在亚声的流动的地方。磨擦力量能比网推进的大得多,在氦更高若干次到达,导致很低的效率。引起理想、真实的流动之间的差别的另外的因素包括:在喉咙区域,延长到嘴扩大节的电的弧,到入口气体并且从热血浆的热转移,和在真空房间的环境压力的复杂流动。当处理如此的复杂状况时,超声的嘴流动的平常的概念必须极大地被修改,这被认出当处理如此的复杂状况时。在这份报纸介绍的一般概念能在指导这台设备的设计和操作是有用的。
简介:Bacterialflagellarfilamentcanundergoastress-inducedpolymorphicphasetransitioninbothvitroandvivoenvironments.Thefilamenthas12differenthelicalforms(phases)characterizedbydifferentpitchlengthsandhelixradii.Whensubjectedtothefrictionalforceofflowingfluid,thefilamentchangesbetweenaleft-handednormalphaseandaright-handedsemi-coiledphaseviaphasenucleationandgrowth.Thispaperdevelopsnon-localfiniteelementmethod(FEM)tosimulatethephasetransitionunderad...
简介:Abriefaccountisprovidedoncrack-tipsolutionsthathaverecentlybeenpublishedintheliteraturebyemployingtheso-calledGRADELAmodelanditsvariants.TheGRADELAmodelisasimplegradientelasticitytheoryinvolvingoneinternallengthinadditiontothetwoLame'constants,inanefforttoeliminateelasticsingularitiesanddiscontinuitiesandtointerpretelasticsizeeffects.Thenon-singularstrainsandnon-singular(butsometimessingularorevenhypersingular)stressesderivedthiswayunderdifferentboundaryconditionsdifferfromeachotherandtheirphysicalmeaninginnotclear.Thisisdiscussedwhichfocusontheformandphysicalmeaningofnon-singularsolutionsforcrack-tipstressesandstrainsthatarepossibletoobtainwithintheGRADELAmodelanditsextensions.
简介:Aerodynamicforcesandpowerrequirementsinforwardflightinabumblebee(Bombusterrestris)werestudiedusingthemethodofcomputationalfluiddynamics.Actualwingkinematicdataoffreeflightwereusedinthestudy(thespeedrangesfrom0m/sto4.5m/s;advanceratiorangesfrom0-0.66).Thebumblebeeemploysthedelayedstallmechanismandthefastpitching-uprotationmechanismtoproduceverticalforceandthrust.Theleading-edgevortexdoesnotshedinthetranslatoryphaseofthehalf-strokesandismuchmoreconcentratedthanthatofthefruitflyinapreviousstudy.Athoveringandlow-speedflight,theverticalforceisproducedbyboththehalf-strokesandiscontributedbywinglift;atmediumandhighspeeds,theverticalforceismainlyproducedduringthedownstrokeandiscontributedbybothwingliftandwingdrag.Atallspeedsthethrustismainlyproducedintheupstrokeandiscontributedbywingdrag.Thepowerrequirementatlowtomediumspeedsisnotverydifferentfromthatofhoveringandisrelativelylargeatthehighestspeed(advanceratio0.66),i.e.thepowercurveisJshaped.Exceptatthehighestflightspeed,storingenergyelasticallycansavepowerupto20%-30%.Atthehighestspeed,becauseofthelargeincreaseofaerodynamictorqueandtheslightdecreaseofinertialtorque(duetothesmallerstrokeamplitudeandstrokefrequencyused),thepowerrequirementisdominatedbyaerodynamicpowerandtheeffectofelasticstorageofenergyonpowerrequirementislimited.
简介:Anewalgorithmforsolvingthethree-dimensionalelasticcontactproblemwithfrictionispresented.Thealgorithmisanon-interiorsmoothingalgorithmbasedonanNCPfunction.Theparametricvariationalprincipleandparametricquadraticprogrammingmethodwereappliedtotheanalysisofthree-dimensionalfrictionalcontactproblem.Thesolutionofthecontactproblemwasfinallyreducedtoalinearcomplementarityproblem,whichwasreformulatedasasystemofnonsmoothequationsviaanNCP-function.Asmoothingapproximationtothenonsmoothequationswasgivenbytheaggregatefunction.ANewtonmethodwasusedtosolvetheresultingsmoothingnonlinearequations.Thealgorithmpresentediseasytounderstandandimplement.ThereliabilityandefficiencyofthisalgorithmaredemonstratedbothbythenumericalexperimentsofLCPinmathematicalwayandtheexamplesofcontactproblemsinmechanics.
简介:Non-transferreddcarcplasmageneratorsarewidelyusedinmaterialsprocessing.Theyaregenerallyconsideredsteadily-operatingdevises.However,unsteadyphenomenadoexistinthem,andmaycausenon-idealeffectsinprocesseswhichrequirehighcontrollabilityandreproducibility.Theseunsteadyphenomenacancauseparameterfluctuationsinthearcandtheplasmajet,someofwhichhavebeenstudiedinrecentyears.Severaltypesandmechanismsofthesephenomenahavebeenidentified.Thispaperreviewst...
简介:Researchonparticulatecharacteristicshasbeenanimportantfrontierinphysicsandchemistryduringthepastdecades.Ithashoweverbeenmostlyfocusedongranularmaterialswithshort-rangeinteractions.Inthiswork,itwasfoundthatthepowerlawofparticlesizedistributionappliedtothelong-rangeinteractingsystemoffloatingdustinair,fromwhichwededucedthatself-organizedcriticalitymightholdforfloatingdustjustasgranularmaterialswithshort-rangeinteractions.Thisfeaturemayrevealunderlyingkineticmechanisms,importantindispersedparticlesystems.Inindustry,powerlawofsizedistributionofdispersedparticlescanbeusedtoinvestigatethechangeofdustsize,andthepowerlawparametercouldbetakenasanimportantindexfordustseparation.
简介:Aninvestigationisdescribedforinstabilityproblemofflowthroughapipeofcircularcross-section.Asadisturbancemotion,weconsiderageneralnon-axisymmetricmode.Anassociatedamplitudeormodulationequationhasbeenderivedforthisdisturbancemotion.Thisequationbelongstoadiffusiontype.ThecoefficientofitcanbenegativewhileReynoldsnumberincreases,becauseofthecomplexinteractionbetweenmoleculardiffusionandconvection.Thenegativediffusivity,whenitoccurs,causesaconcentrationandfocussingofenergywithindecayingslugs,actingasaroleofreversingnaturaldecays
简介:NON-SYMMETRICALLARGEDEFORMATIONOFASHALLOWTHINSPHERICALSHELLWangXinzhi(王新志)RenDongyun(任冬云)WangLinxiang(王林祥)YehKaiyuan(叶开沅)(Gan...
简介:Inthispaperathreedegreesoffreedomautoparametricsystemwithlimitedpowersupplyisinvestigatednumerically.Thesystemconsistsofthebody,whichishungonaspringandadamper,andtwopendulumsconnectedbyshapememoryalloy(SMA)spring.Shapememoryalloyshaveabilitytochangetheirmaterialpropertieswithtemperature.ApolynomialconstitutivemodelisassumedtodescribethebehavioroftheSMAspring.Thenon-idealsourceofpoweraddsonedegreeoffreedom,sothesystemhasfourdegreesoffreedom.Theequationsofmotionhavebeensolvednumericallyandpseudoelasticeffectsassociatedwiththemartensiticphasetransformationarestudied.Itisshownthatinthistypesystemonemodeofvibrationsmightexciteordampanothermode,andthatexceptdifferentkindsofperiodicvibrationstheremayalsoappearchaoticvibrations.Fortheidentificationoftheresponsesofthesystem’svarioustechniques,includingchaostechniquessuchasbifurcationdiagramsandtimehistories,powerspectraldensities,Poincar`emapsandexponentsofLyapunovmaybeused.
简介:Bothclinicalandpostmortemstudiesindicatethat,inhumans,thecarotidsinusofthecarotidarterybifur-cationisoneofthefavoredsitesforthegenesisanddevelop-mentofatheroscleroticlesions.Hemodynamicfactorshavebeensuggestedtobeimportantinatherogenesis.Tounderstandthecorrelationbetweenatherogenesisandfluiddynamicsinthecarotidsinus,thebloodflowinarterywassimulatednumerically.Inthosestudies,thepropertyofbloodwastreatedasanincompressible,Newtonianfluid.Infact,however,thebloodisacomplicatednon-Newtonianfluidwithshearthinningandviscoelasticproperties,especiallywhentheshearrateislow.Avarietyofnon-Newtonianmod-elshavebeenappliedinthenumericalstudies.Amongthem,theCassonequationwaswidelyused.However,theCas-sonequationagreeswellonlywhentheshearrateislessthan10s~(-1).Theflowfieldofthecarotidbifurcationusuallycoversawiderangeofshearrate.WethereforebelievethatitmaynotbesufficienttodescribethepropertyofbloodonlyusingtheCassonequationinthewholeflowfieldofthecarotidbifurcation.Inthepresentstudy,threedifferentbloodconstitutivemodels,namely,theNewtonian,theCas-sonandthehybridfluidconstitutivemodelswereusedintheflowsimulationofthehumancarotidbifurcation.Theresultswerecomparedamongthethreemodels.TheresultsshowedthattheNewtonianmodelandthehybridmodelhadverysimilardistributionsoftheaxialvelocity,secondaryflowandwallshearstress,buttheCassonmodelresultedinsignificantdifferencesinthesedistributionsfromtheothertwomod-els.ThisstudysuggeststhatitisnotappropriatetoonlyusetheCassonequationtosimulatethewholeflowfieldofthecarotidbifurcation,andontheotherhand,Newtonianfluidisagoodapproximationtobloodforflowsimulationsinthecarotidarterybifurcation.
简介:Non-sphericalmicronandnano-sizedparticlesandtheircompositeshavebecomeessentialinselectapplicationareasofoptics,wearresistance,personnelprotection,chemicalmechanicalpolishing,andbiomedicine.Inthispaper,thesynthesisofcompositeandceramicnon-sphericalparticlesusingstopflowlithographyisreported.Precursorsuspensionsofpoly(ethyleneglycol)diacrylate,2-hydroxy-2-methylpropiophenoneandSiO2orAl2O3areprepared.Theprecursorsuspensionflowsthroughamicrofluidicdevicemountedonanuprightmicroscopeandispolymerizedinanautomatedprocess.Aphotomaskpatternedwithtransparentgeometricfeatures,whichdefinethecross-sectionalshapesoftheparticles,maskstheUVlighttosynthesizemicronsizedparticles.Particleswithaxialdimensionsrangingfrom35to167μmweresynthesized.Controlofdevicechanneldepthandobjectivelensmagnificationenablesthemanipulationoftheparticlesize.Compositeparticlesintriangular,square,pentagonal,hexagonal,andcircularcrosssectionsweresynthesized.Subsequently,thetransformationofthecompositeparticlesintothecorrespondingmetaloxideparticleswasachievedthroughpolymerburn-offandsintering.
简介:ThereareNdomainsDj.(j=0,1,……,N-1)ofdifferentphysicalparametersinthewholespaceandtheirinterfaces.Sjj+1arenon-horizontallysmoothcurvedsurfaces.ThefollowingboundaryproblemiscalledHelmholtzboundaryproblem:Theanalyticalsolutionoftheaboveproblemisgiveninthispaper.
简介:NON-LINEARELASTICTHEORYOFRECTANGULARRETICULATEDSHALLOWSHELLSTRUCTURESNieGuo-hua(聂国华)(DepartmentofEngineeringMechanics,TongjiU...
简介:Inoffshoreengineeringdesign,itisconsiderablysignificanttohaveanadequatelyaccurateestimationofmarineenvironmentalparameters,inparticular,theextremewindspeedoftropicalcyclone(TC)withdifferentreturnperiodstoguaranteethesafetyinprojectedoperatinglifeperiod.Basedonthe71-year(1945–2015)TCdataintheNorthwestPacific(NWP)bytheJointTyphoonWarningCenter(JTWC)ofUS,anotablegrowthoftheTCintensityisobservedinthecontextofclimatechange.Thefactimpliesthatthetraditionalstationarymodelmightbeincapableofpredictingparametersintheextremeevents.Therefore,anon-stationarymodelisproposedinthisstudytoestimateextremewindspeedintheSouthChinaSea(SCS)andNWP.Wefindthattheextremewindspeedsofdifferentreturnperiodsexhibitanevidentenhancementtrend,forinstance,theextremewindspeedswithdifferentreturnperiodsbynonstationarymodelare4.1%–4.4%higherthanstationaryonesinSCS.Also,thespatialdistributionofextremewindspeedinNWPhasbeenexaminedwiththesamemethodologybydividingthewestseaareasoftheNWP0°–45°N,105°E–130°Einto45subareasof5°×5°,whereoilandgasresourcesareabundant.Similarly,remarkablespacialin-homogeneityintheextremewindspeedisseeninthisarea:theextremewindspeedwith50-yearreturnperiodinthesubarea(15°N–20°N,115°E–120°E)ofZhongshaandDongshaIslandsis73.8m/s,whilethatinthesubareaofYellowSea(30°N–35°N,120°E–125°E)isonly47.1m/s.Asaresult,thepresentstudydemonstratesthatnon-stationaryandin-homogeneouseffectsshouldbetakenintoconsiderationintheestimationofextremewindspeed.
简介:Thispaperpresentsasimpleapproachforimprovingtheperformanceoftheweightedessentiallynonoscillatory(WENO)finitevolumeschemeonnon-uniformgrids.ThistechniquereliesonthereformulationofthefifthorderWENO-JS(WENOschemepresentedbyJiangandShuinJ.Comput.Phys.126:202–228,1995)schemedesignedonuniformgridsintermsofonecell-averagedvalueanditsleftand/orrightinterfacialvaluesofthedependentvariable.Theeffectofgridnon-uniformityistakenintoconsiderationbyaproperinterpolationoftheinterfacialvalues.Onnonuniformgrids,theproposedschemeismuchmoreaccuratethantheoriginalWENO-JSscheme,whichwasdesignedforuniformgrids.Whenthegridisuniform,theresultingschemereducestotheoriginalWENO-JSscheme.Inthemeantime,theproposedschemeiscomputationallymuchmoreefficientthanthefifth-orderWENOschemedesignedspecificallyforthenon-uniformgrids.Anumberofnumericaltestcasesaresimulatedtoverifytheperformanceofthepresentscheme.