简介：Experimentalandnumericalstudieshaveshownsimilaritiesbetweenlocalizedturbulenceinchannelandpipeflows.Byscalinganalysisofadisturbed-flowmodel,thispaperproposesalocalReynoldsnumberReMtocharacterizethethresholdoftransitiontriggeredbyfinite-amplitudedisturbances.TheReMrepresentsthemaximumcontributionofthebasicflowtothemomentumratiobetweenthenonlinearconvectionandtheviscousdiffusion.ThelowercriticalReMobservedinexperimentsofplanePoiseuilleflow...

简介：为了加快全球定位系统（GPS）的捕获速度，提高系统的捕获灵敏度，对GPS系统捕获策略进行了深入地研究。在对其捕获的基本原理和传统的最大值捕获系统进行分析的基础上，提出了一种新颖的GPS多峰值捕获策略。该策略通过多峰值选择减少了系统搜索单元数目，通过增加进入唐检测器的峰值个数来提高捕获灵敏度。利用蒙特卡洛方法进行了仿真分析，仿真结果表明：该新颖策略的捕获时间更短，同时捕获灵敏度比传统的最大值捕获系统要高2.8dB。总体来说，该新颖策略算法更适用于对GPS弱信号的捕获，也可应用于其他卫星导航系统。

简介：Thispapercontinuesourrecentworkontherelationshipbetweendiscretecontactinteractionsatthemicroscopicscaleandcontinuumcontactinteractionsatthemacroscopicscale(Hulikaletal.,J.Mech.Phys.Solids76,144–161,2015).Thefocusofthisworkisonadhesion.Weshowthatacollectionofalargenumberofdiscreteelementsgovernedbyathreshold-forcebasedmodelatthemicroscopicscalecollectivelygivesrisetocontinuumfracturemechanicsatthemacroscopicscale.Akeystepistheintroductionofanefficientnumericalmethodthatenablesthecomputationofalargenumberofdiscretecontacts.Finally,whilethisworkfocusesonscalinglaws,themethodologyintroducedinthispapercanalsobeusedtostudyroughsurfaceadhesion.

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简介：Thewave-seabedinteractionissueisofgreatimportanceforthedesignoffoundationaroundmarineinfrastructures.Mostpreviousinvestigationsforsuchaproblemhavebeenlimitedtouncoupledoronewaycoupledmethodsconnectingtwoseparatedwaveandseabedsubmodelswiththecontinuityofpressuresattheseabedsurface.Inthisstudy,astronglycoupledmodelwasproposedtorealizebothwaveandseabedprocessesinasameprogramandtocalculatethewavefieldsandseabedresponsesimultaneously.Theinformationbetweenwavefieldsandseabedfieldswerestronglysharedandthusresultsinamoreprofoundinvestigationofthemechanismofthewave-seabedinteraction.Inthisletter,thewaveandseabedmodelswerevalidatedwithpreviousexperimentaltests.Then,asetofapplicationofpresentmodelwerediscussedinpredictionofthewave-inducedseabedresponse.Numericalresultsshowthewave-inducedliquefactionareaofcoupledmodelissmallerthanthatofuncoupledmodel.

简介：Inapreviouspaper,amethodhasbeendevelopedtostudythestabilitycharacteristicsoflaminarboundarylayersovercompliantwalls.Inthispaper,theeffectofdoublelayeredcompliantwallandKramertypecompliantwallondelayingthetransitionisinvestigated,anditisshownthattheredoesexistthepossibilitytode-laythetransitionbyapplyingsuchcompliantwalls.

简介：Thestabilitycharacteristicsoflaminarboundarylayersovercompliantwallswasstudiedbythelineartheory.Unlikethepreviousauthors,thecoupledmotionofthefluidandsolidwasrequiredtosat-isfythecontinuityconditionsofboththevelocityandstressattheinterface.Resultsofcalculationsshowthatasthespeedratioordensityratioexceedsacertainthresholdvalue,thetwotypesofunstablewaveswillnolongerbedistinguishable,andthetangentialcomponentofthedisturbancestressisnolongernegligi-ble.Sotheneglectofit,asthepreviousauthorsdid,isunjustified.

简介：Oscillatoryturbulentflowoveraflatplateisstudiedusinglargeeddysimulation(LES)andReynolds-averageNavier-Stokes(RANS)methods.Adynamicsubgrid-scalemodelisemployedinLESandSaffman’sturbulencemodelisusedinRANS.Theflowbehaviorsarediscussedfortheacceleratinganddeceleratingphasesduringtheoscillatingcycle.ThefrictionforceonthewallanditsphaseshiftfromlaminartoturbulentregimearealsoinvestigatedfordifferentReynoldsnumbers.

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简介：Thisletterdescribesnumericalsimulationoftheunsteadyflowoveraslow-flyingbatbyusingtheimmersedboundarymethodbasedonthemeasuredbatwinggeometryandkinematics.Themainvorticalstructuresaroundthebatflappingwingsareidentified,illuminatingthelift-generatingroleoftheleadingedgevorticesgeneratedmainlyinthedownstroke.Furthermore,theliftdecompositionindicatesthatthevortexlifthasthedominantcontributiontothetime-averagedliftandtheliftassociatedwiththefluidaccelerationhastherelativelymoderateeffect.

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简介：Theflowstructuresinaseparatedshearlayeractuatedbyasyntheticjetactuatorwerestudiedusingexperimentalmethods.Whenforcedatafrequencymuchlowerthanthenaturalsheddingfrequency(fH/U=0.042orfX_r/U=0.24),theverticalflappingmotionoftheshearlayerdownstreamoftheseparationpointbecameprominent.Thesizeofthepeakinthepressurespectraattheforcingfrequency(St_A=f_AH/U)measuredneartheseparationpoint(x/H=1)increasedlinearlywiththeforcingamplitude(u′/U)suggestingalinearresponseofthepressurefluctuationstotheforcingbythesyntheticjet.ThelinearresponsedidnotholdforthepressurefluctuationsawayfromthejetexitasthemagnitudeofthepeakforSt_Ameasuredatx/H=3soonsaturatedwhentheforcingamplitudebecamelargerthan0.3.

简介：Asawidelyusedfloodenergydissipator,thesteppedspillwaycansignificantlydissipatethekineticorhydraulicenergyduetotheair-entrainmentinskimmingflowoverthesteps.Thefree-surfaceaerationinvolvesthesharpdeformationofthefreesurfaceandthecomplexturbulentshearflows.Inthisstudy,thevolumeoffluid(VOF),mixture,andEulerianmethodsareutilizedtosimulatetheair-entrainmentbycouplingwiththeReynolds-averagedNavier–Stokes/largeeddysimulation(RANS/LES)turbulencemodels.Thefreesurfacedeformation,airvolumefraction,pressure,andvelocityarecomparedforthethreedifferentnumericalmethods.OnlytheEulerian+RANSmethodfailstocapturethefree-surfaceaeration.TheairvolumefractionpredictedbytheVOF+LESmethodbestmatchestheexperimentalmeasurement,whilethemixture+LESmethodpredictstheinceptionpointoftheairentrainmentmoreaccurately.

简介：Basedonthemultiplescatteringmethod,thispaperinvestigatesabenchmarkproblemofthepropagationofliquidsurfacewavesoverfinitegraphene(orhoneycomb)structuredarraysofcylinders.Comparingthegraphenestructuredarraywiththesquarestructuredandwithtrianglestructuredarrays,itfindsthatthefinitegraphenestructurecanproducemorecompletebandgapsthantheotherfinitestructures,andthefinitegraphenestructurehaslesslocalizedabilitythantheotherfinitestructures.

简介：这研究的目的是描绘元素的碳和器官的碳(EC和OC，分别地)喷雾器粒子(PM2.5)的内容在Tongliao收集了，在东北中国的HorqinSandland的一个地点。在春天2005期间，PM2.5集体集中是126±71μg·m?3，与更高的灰尘集中，在五期间，灰尘比在非尘封的天下暴雨(255±77对106±44μg·m?3)。在一个热/光的反射方法决定的PM2.5的平均OC和EC集中是15.7±7.3μg·m?3和3.3±1.7μg·m?3，分别地并且碳的喷雾器在正常的天与21.7%相比在灰尘暴风雨期间说明了9.9%PM2.5质量。到EC的OC的平均比率在灰尘暴风雨期间类似于在非尘封的天的那些，并且在OC和EC之间的关联系数高，0.86。高OC/EC比率，八碳部分的分布，和在有OC和EC的K之间的强壮的关系显示农村生物资源烧是到地区性的碳的喷雾器的主导的贡献者。

简介：Thisletterpresentsananalyticalsolutiontothehydrodynamiclubricationofacircularpointcontactslidingoveraflatsurfacewithcavitation.ThesolutionisfoundbysolvingtheReynoldsequationwithReynoldsboundaryconditionforcavitation.Thecavitationboundaryisshowntobestraightlinesdirected108.4°againsttheslidingdirection.Theresultisexperimentallyverifiedinthelimitoflargevaluesofviscosity,slidingvelocityandradiusofasphericalball.Thesolutionraisesquestionsaboutthecouplingbetweencavitationandfilmruptureandcanbeusedasanindependentcheckonthevalidityofnumericalsolutions.

简介：Environmentalpollutionanddecliningresourcesoffossilfuelsinrecentyears,haveincreaseddemandforbetterfueleconomyandlesspollutionforgroundtransportation.Amongthealternativesolutionsprovidedbyresearchersinrecentdecades,hybridelectricvehiclesconsistedofaninternalcombustionengineandanelectricmotorhavebeenconsideredasapromisingsolutionintheshort-term.Inthepresentstudy,fueleconomycharacteristicsofaparallelhybridelectricvehicleareinvestigatedbyusing...

简介：Thisstudyaimsatthemechanismofdragreductioninturbulentboundarylayer(TBL)withsuperhydrophobicsurface.Comparingthetime-resolvedparticleimagevelocimetry(TRPIV)measurementresultswiththatofhydrophilicsurface,thedragreductionrateoverasuperhydrophobicsurfaceisapproximately10%.Toinvestigatethecharacteristicsofcoherentstructureinadrag-reducedTBLwithsuperhydrophobicsurface,amodifiedmulti-scalespatiallocally-averagedstructurefunctionisproposedfordetectingcoherentstructure.Theconditionalsamplingandspatialphase-lockaveragemethodsareemployedtoobtainthetopologyofphysicalquantitieslikethevelocityfluctuation,spanwisevorticity,andReynoldsstressduringejectandsweepprocess.Theresultsindicatethatthesuppressionofcoherentstructureburstinthenear-wallregionisthekeymechanisminreducingtheskinfrictiondragforTBLoversuperhydrophobicsurface.

简介：Themechanicalbackgroundofthebivariatesplinespaceofdegree2andsmoothness1onrectangularpartitionispresentedconstructively.Makinguseofmechan-icalanalysismethod,byactingcouplesalongtheinterioredgeswithsuitableevaluations,thedeflectionsurfaceisdividedintopiecewiseform,therefore,therelationbetweenaclassofbivariatesplinesonrectangularpartitionandthepurebendingofthinplateisestablished.Inaddition,theinterpretationofsmoothingcofactorandconformalitycon-ditionfromthemechanicalpointofviewisgiven.Furthermore,byintroducingtwistingmoments,themechanicalbackgroundofanysplinebelongtotheabovespaceissetup.

简介：Non-equilibriumturbulencephenomenahaveraisedgreatinterestsinrecentyears.Significanteffortshavebeendevotedtonon-equilibriumturbulencepropertiesincanonicalflows,e.g.,gridturbulence,turbulentwakes,andhomogeneousisotropicturbulence(HIT).Thenon-equilibriumturbulenceinnon-canonicalflows,however,hasrarelybeenstudiedduetothecomplexityoftheflows.Inthepresentcontribution,adirectnumericalsimulation(DNS)databaseofaturbulentflowisanalyzedoverabackwardfacingramp,theflowneartheboundaryisdemonstrated,andthenon-equilibriumturbulentpropertiesoftheflowinthewakeoftheramparepresentedbyusingthecharacteristicparameterssuchasthedissipationcoefficientCεandtheskewnessoflongitudinalvelocitygradientSk,butwithoppositeunderlyingturbulentenergytransferproperties.TheequationofLagrangianvelocitygradientcorrelationisexamined,andtheresultsshowthatnon-equilibriumturbulenceistheresultofphasede-coherencephenomena,whichisnottakenintoaccountinthemodelingofnon-equilibriumturbulence.Thesefindingsareexpectedtoinspiredeeperinvestigationofdifferentnon-equilibriumturbulencephenomenaindifferentflowconditionsandtheimprovementofturbulencemodeling.