简介:Thenatureofthethree-dimensionaltransitionarisingintheflowpastacylinderisinvestigatedbyapplyingtheLifschitz-HameiritheoryalongspecialLagrangiantrajectoriesexistinginitswake.ResultsshowthatthevonKarmanstreetisunstablewithregardtoshort-wavelengthperturbations.Theasymptoticanalysispredictsthepossibleexistenceofbothsynchronous(asmodesAandB)andasynchronous(asmodeC)instabilities,eachassociatedtospecificLagrangianorbits.Theproposedstudyprovidesusefulqualitativeinformationontheoriginofthedifferentmodesbutnoquantitativeagreementbetweenthegrowthratespredictedbytheasymptoticanalysisandbyaglobalstabilityanalysisisobserved.Thereasonsforsuchmismatcharebrieflydiscussedandpossibleimprovementstothepresentanalysisaresuggested.
简介:Theanalysisofthedataofmodeltestsoftwolargedeepwharvesandmonographicexperimentalstudiesshowthattwoaspectsaretobeimprovedsoastopredictthewaveupliftforcesonthebottomofacircularcylinder.Thefirstaspectistheupliftpressuredistributiononthebottom,andthesecondisthecorrectdeterminationofthephaseformaximumhorizontalwaveforces.Thesecondproblemhasbeensolved.Synthesizingtheresultsoftheoreticalanalysisandexperiments,wesuggestadiagramforthedeterminationofthephasewhenthemaximumhorizontalwaveforceappears.Onthebasis-efthediagramthesimultaneouswaveupliftforcescanbeobtainedforthestructuralstabilityanalysis.
简介:Thephysicalmechanismforgenerationofstreamwisevortices(orribvortices)inthecylinderwakeisnumericallyinvestigatedwithafinite-differencescheme.Rayleigh’stheoryofcentrifugalinstabilityforinviscidaxisymmetricflowisextendedtoanalyzethe2-Dprimaryflows.Accordingly,ananalyticaldimensionlessgroupRay=-(r/vθ)■vθ/■r-1isderived,wherevθrepresentsthevelocityofafluidelementrelativetotheoncomingflow,risthelocalcurvatureradiusoftheelementpathline.CentrifugalinstabilityoccurswhenRay>0.StabilityanalysesarecarriedoutwiththisdiscriminantforprimaryflowsatdifferenttimelevelsinahalfsheddingperiodofthevonKarman(orvK)vortices.UnstableareasareidentifiedandthelocationsofribvorticesarecoincidentwellwiththeunstableareaswithinthefirstwavelengthofvKvorticesbehindthecylinder.Thenumericalresultsalsoshowthatribvorticesexperienceamplificationinthisregion.Itisapparentthatcentrifugalinstabilityplaysanimportantroleinthegenerationofribvorticesinthecylinderwake.
简介:Wepresentthesimulationofthedynamicsoffluid-cylinderinteractionsinanarrowthree-dimensionalchannelfilledwithaNewtonianfluid,usingaLagrangemultiplierbasedfictitiousdomainmethodologycombinedwithafiniteelementmethodandanoperatorsplittingtechnique.Asexpected,asettlingtruncatedcylinderturnsitsbroadsideperpendiculartothemainstreamdirectionandthecenterofmassmovestothecentralaxisofthechannel.Inthecaseoftwotruncatedcylinders,theyfirstmovearoundeachotherforawhileandthenstaytogetherina"T"shape.Afterthe"T"shapehasbeenformedforalongenoughtime,wefoundnovortexsheddingbehindthecylinders.Whensimulatingthefluidizationof60truncatedcylinders,wecapturedthefeaturesofinteractionsamongfluidizedcylindersasobservedinexperiments.
简介:Throughaseriesofmodeltests,thewaveforcesonhorizontalandinclinedcircularcylindersaremeasuredandanalyzed.BasedonMorisonEquationandStokessecondorderwavetheory,therelationshipbetweenthehydrodynamicforcecoefficientswithKCnumberandsub-mergedwaterdepthaswellforhorizontalcylindersareanalyzed,alsotherelationshipbetweenthehydrodynamicforcecoefficientswithKCnumber,inclinedangleandtheeffectofwaterfreesurfaceaswellfortheinclinedcylindersareinvestigated.
简介:Theelectric-staticbodyforcemodelisobtainedbysolvingMaxwell’selectromagneticequations.Basedontheelectro-staticmodel,numericalmodelingofflowaroundacylinderwithadielectricbarrierdischarge(DBD)plasmaeffectisalsopresented.Theflowstreamlinesbetweenthenumericalsimulationandtheparticleimagevelocimetry(PIV)experimentareconsistent.Accordingtothenumericalsimulation,DBDplasmacanreducethedragcoefficientandchangethevortexsheddingfrequenciesofflowaroundthecylinder.
简介:FlowfieldsaroundarotatingcircularcylinderinauniformstreamarecomputedusingalowdimensionalGalerkinmethod.ResultsshowthattheformationofaFopplevortexpairbehindastationarycircularcylinderiscausedbythestructuralinstabilityinthevicinityofthesaddlelocatedattherearofthecylinder.Forrotatingcylinderabifurcationdiagramwiththeconsiderationoftwoparameters,ReynoldsnumberReandrotationparameterα,isbuiltbyakinematicanalysisofthesteadyflowfields.
简介:Basedonthe1stordercnoidalwavetheory,thenonlinearwavediffractionaroundacircularcylinderinshallowwaterisstudiedinthispaper.Theequationofthewavesurfacearoundthecylinderisformulatedandbyusingthisformulathewavesurfaceelevationonthecylindersurfacecanbeobtained.Inthispaper,theformulaforcalculatingthecnoidalwaveforceonacircularcylinderisalsoderived.Forthewaveconditionswhichareoftenencounteredinpracticalengineeringdesigns,theratiosofthenonlinearwaveforcestothelinearwaveforcesarecalculated,andtheresultsareplottedinthispaperfordesignpurposes.Inordertoverifythetheoreticalresults,modeltestsareconducted.Aftercomparingthetestresultswiththetheoreticalones,itisconcludedthat,inshallowwater,forthecaseofTg/d1/2>8-10andH/d>0.3,thecnoidalwavetheoryshouldbeusedtocalculatethewaveactiononacylindricalpier.
简介:Theinertiasofthefluidandtheinnercylinderincoaxialcylinderrheometer(CACR)havegreatinfluenceontheunsteadyflowofnon-Newtonianfluid.EvenfortheNewtonianfluidthereexistthesocalled'stressovershoot'phenomenon.Inthepresentarticlethisphenomenonwasstudiedindetailandamethodcorrectingthemeasuredresultsforanunsteadyflowintherheometerwasproposed.Itisfoundthattheinertiaeffectofthefluidcanbeignoredwhenthegapbetweencylindersissmall.
简介:灵活圆形的柱体的导致流动的颤动(FIV)上的集体比率的效果试验性地在一辆拖引的坦克被调查。分别地,有7.9公里和4.8公里的外部、内部的直径的一个Tygon试管为学习被采用。试管被连接到一辆马车并且从休息拖引到一稳定在慢下来在1.6m的距离上再休息在前加快m/s到1.6仍然流水。雷纳兹数字基于柱体,外部直径是80013,000,并且减少的速度(柱体天赋频率使正常化的速度和外部直径)从2~25跨越了。当连接时,柱体在11N的轴的虚荣下面从420公里被伸长到460公里。把伸长的长度基于柱体,方面比率(到外部直径的柱体长度的比率)作为58被计算。三集体比率(柱体的比率结构的质量到代替的液体质量,m*)被分别地用空气,水,和合金粉末(nickel-chromium-boron矩阵合金)填满柱体内部0.7,1.0,和3.4决定。一个光方法为反应大小被采用。多频率颤动在两个被观察同轴(IL)并且跨流动(CF)回答;在高级雷纳兹数字,颤动模式直到3rd在CF反应被识别。模式转变被发现为最高测试的集体比率在更低的减少的速度发生。颤动振幅和频率关于减少的速度被确定并且表示。一个重要减少的颤动振幅与增加集体比率在IL反应被发现,并且仅仅起始、上面的分支在IL和CF反应振幅存在。规范的反应频率被揭示线性地关于减少的速度增加,并且为线性关系的斜坡被发现为测试的三格相同。
简介:Corioliseffectisconsideredintheanalysisofarotatingpiezoelectrichollowcylinder.AninhomogeneousBesselequationgoverningtheradialmechanicaldisplacementisderived,whichcanbeapproximatedasanEulertypedifferentialequationwhenthecylinderisverythin.NumericalexamplesshowthattheCorioliseffectcanbesignificantundercertainconditions.
简介:Thelarge-diametercylinderstructure,whichismadeoflargesuccessivebottomlesscylindersplacedonfoundationbedorpartlydrivenintosoil,isarecentlydevelopedretainingstructureinChina.Itcanbeusedinport,coastalandoff-shoreworks.Themethodforstabilityanalysisofthelarge-diametercylinderstructure,especiallyforstabilityanalysisoftheembeddedlarge-diametercylinderstructure,isanimportantissue.Inthispaper,anideaispresentedthatis,em-beddedlarge-diametercylinderquayscanbedividedintotwotypes,i.e.thegravitywalltypeandthecylinderpilewalltype.Amethodforstabilityanalysisofthelarge-diametercylinderquayofthecylinderpilewalltypeisdevelopedandamethodforstabilityanalysisofthelarge-diametercylinderquayofthegravitywalltypeisalsoproposed.Theeffectofsig-nificantparametersonthestabilityofthelarge-dianetercylinderquayofthecylinderpilewalltypeisinvestigatedthroughnumericalcalculation.