简介:Anumericalstudybasedonawakeoscillatormodelwasconductedtodeterminetheresponseperformanceofvortex-inducedvibration(VIV)onalongflexiblecylinderwithpinned-pinnedboundaryconditionssubjectedtolinearandexponentialshearflows.Thecouplingequationsofastructuralvibrationmodelandwakeoscillatormodelweresolvedusingastandardcentralfinitedifferencemethodofthesecondorder.TheVIVresponsecharacteristicsincludingthestructuraldisplacement,structuralfrequency,structuralwavenumber,standingwavebehavior,travellingwavebehavior,structuralvelocity,liftforcecoefficientandtransferredenergyfromthefluidtothestructurewithdifferentflowprofileswerecompared.ThenumericalresultsshowthattheVIVdisplacementisacombinationofstandingwavesandtravellingwaves.Forlinearshearflow,standingwavesandtravellingwavesdominatetheVIVresponsewithinthelow-velocityandhigh-velocityzones,respectively.Thenegativevaluesofthetransferredenergyonlyoccurwithinthelow-velocityzone.However,forexponentialshearflow,travellingwavesdominatetheVIVresponseandthenegativeenergyoccursalongtheentirelengthofthecylinder.
简介:Amodelbasedonthedatafromforcedvibrationexperimentsisdevelopedforpredictingthevortex-inducedvibrations(VIV)ofelasticallymountedcircularcylindersinflow.Theassumptionsforfreeandforcedvibrationtestsareexploredbriefly.Energyequilibriumistakenintoaccounttosetuptherelationshipbetweenthedynamicresponseofself-excitedoscillationsandtheforcecoefficientsfromforcedvibrationexperiments.Thegapbetweenthesetwocasesisbridgedstraightforwardlywithcarefultreatmentofkeyparameters.Givenreducedmassmandmaterialdampingratioζofanelasticallymountedcircularcylinderinflow,theresponsecharacteristicssuchasamplitude,frequency,lock-inrange,addedmasscoefficient,cross-flowfluidforceandthecorrespondingphaseanglecanbepredictedallatonce.InstanceswithdifferentcombinationofreducedmassandmaterialdampingratioarecomparedtoinvestigatetheireffectsonVIV.Thehysteresisphenomenoncanbeinterpretedreasonably.ThepredictionsandtheresultsfromrecentexperimentscarriedoutbyWilliamson'sgroupareinrathergoodagreement.
简介:AmethodofcoupledBEM-FEManalysisfortheelasticspatialstructuresystemispresented.Itcanbeappliedtothecalculationofthestressanddeformationofthelarge-diamatercylinderstructuresystemanditissuitableforsymmetricornon-symmetricstructuresunderthedistributedorconcentratedload.NumericalexamplesshowthattheproposedmethodandcomputerprogramBEFEMarequiteefficientintheanalysisofthelarge-diametercylinderstructureproblemsinoceanengineering.
简介:Thispapergivesthedirectivityfunctionofasectoralmul-ti-elementcylinderarray,analyzeitsphasefactor,explainindetailthesideloberejectionbyselectingthenumberofelements,bafflingandamplitudeweighting.Theyareparticularlyusefulfordirectionaltrackingofacousticalsignalandtargetlocating.
简介:在这份报纸,我们在旋涡流的控制上做了数字研究并且由依附薄splitter盘子拖柱体的减小。有依附的splitter盘子的方形的剖面图的柱体的wake结构为雷纳兹数字的一个范围被分析,基于事件溪流和柱体的高度,在laminar范围。管理流动的海军司烧方程被控制体积方法在蹒跚的格子安排上解决。我们为连接压力的方程使用了半含蓄的方法(简单)为计算的算法。我们的结果证明柱体在上游的一个splitter盘子的存在减少drag,但是它在当板长度在1.5次以后是柱体的高度时,流频率的旋涡上有小影响。一个下游的splitter盘子的存在阻抑流频率的旋涡。进内部方面的液体的乘火车分开砍层被下游的splitter板妨碍。我们的结果建议由依附柱体在上游、下游的同轴的splitter盘子,流的旋涡能被压制,以及减小在拖被获得。我们做了参量的研究决定这些splitter盘子的最佳的长度以便完成低拖并且低旋涡流频率。
简介:TheseparatedturbulentflowaroundacircularcylinderisinvestigatedusingLarge-EddySimulation(LES),Detached-EddySimulation(DES,orhybridRANS/LESmethods),andUnsteadyReynolds-AveragedNavier-Stokes(URANS).Thepurposeofthisstudyistoexaminesometypicalsimulationapproachesforthepredictionofcomplexseparatedturbulentflowandtoclarifythecapabilityofapplyingtheseapproachestoatypicalcaseoftheseparatedturbulentflowaroundacircularcylinder.Severalturbulencemodels,i.e.dynamicSub-gridScale(SGS)modelinLES,theDES-basedSpalart-Allmaras(S-A)andk?ωShear-Stress-Transport(SST)modelsinDES,andtheS-AandSSTmodelsinURANS,areusedinthecalculations.Sometypicalresults,e.g.,themeanpressureanddragcoefficients,velocityprofiles,Strouhalnumber,andReynoldsstresses,areobtainedandcomparedwithpreviouscomputationalandexperimentaldata.Basedonourextensivecalculations,weassessthecapabilityandperformanceofthesesimulationapproachescoupledwiththerelevantturbulencemodelstopredicttheseparatedturbulentflow.
简介:
简介:Inthispaper,thefocusedwavegroupswithdifferentparametersandtheiractionsonaverticalcylinderareexperimentallystudied.Theharmonicwavecharacteristicsofthefocusingwavesareanalyzedbytheadditionandsubtractionofthecrestandtroughfocusingwaves.Theanalyzedresultsshowthathigherorderharmonicscanbegeneratedbecauseoftheinteractionofcomponentwaves.Nonlinearityincreaseswiththeinputtedwaveamplitudeandthefrequencywidthincrement.Further,thewaverun-uparoundtheverticalcircularcylinderisexperimentallystudied.Itincreaseswiththewavesteepnessandtherelativecylinderdiameterincrease.However,thevariationsofwaverun-uparoundthecircularcylinderaredifferent.Theresearchesprovideareferenceforfurthernumericalstudies.
简介:Inthispaper,theprincipleofmirrorimageisusedtotransformtheproblemofwavediffractionfromacircularcylinderinfrontoforthogonalverticalwallsintotheproblemofdiffractionoffoursymmetricincidentwavesfromfoursymmetricallyarrangedcircularcylinders,andthentheeigenfunctionexpansionofvelocitypotentialandGrafsadditiontheoremareusedtogivetheanalyticalsolutiontothewavediffractionproblem.Therelationofthetotalwaveforceoncylindertothedistancebetweenthecylinderandorthogonalverticalwallsandtheincidenceangleofwaveisalsostudiedbynumericalcomputation.
简介:WestudyamodifiedversionoftheLane-Emdenequationofthesecondkindmodellingathermalexplosioninaninfinitecylinderandasphere.Wefirstshowthatthesolutiontotherelevantboundaryvalueproblemisboundedandthatthesolutionsaremonotonedecreasing.Theupperbound,thevalueofthesolutionatzero,canbeapproximatedanalyticallyintermsofthephysicalparameters.Weobtainsolutionstotheboundaryvalueproblem,usingboththeTaylorseries(whichworkwellforweaknonlinearity)andthe(5-expansionmethod(validforstrongnonlinearity).Fromhere,weareabletodeducethequalitativebehaviorofthesolutionprofileswithachangeinanyoneofthephysicalparameters.
简介:Thehydrodynamicanalysisofmulti-floatingbodiesisimportantandwidelyusedinmarineengineering.Inthisstudy,wesystematicallysimulatedthewavediffractionproblemofafixedverticalfour-cylinderstructureinregularwavesinthetimedomaininaviscousnumericalwavetank.Thehydrodynamicinteractionofwaveswithabottom-mountedstructureconsistingoffourverticalcylindersarrangedatthecornersofasquareshowsacomplicatedinterferencephenomenon.Inthispaper,weillustrateandanalyzetherun-uparoundthestructureandthecorrespondingwaveforces.Toinvestigatetheviscouseffectonthenear-trappingphenomenon,wepayparticularattentiontoinvestigatingthewavesnear-trappedinsidethefour-cylinderstructure,andmakeacomparativestudyoftheviscous-andinviscid-flowsolutionswiththeexperimentalmeasurements.Theresultsshowthatthemaximumwaveelevationoccursontheinnersideoftheleesidecylinder,andthatthewaveelevationsontheoutersideofthecylindersarelowerthanthoseontheinnerside.Wecanconcludethatviscosityhasanobviousdampingeffectonwaveelevationsinsidethestructure.Thecylindersshowatendencytodriftapartfromeachotherwhenthenear-trappingphenomenonoccurs.
简介:Thispaperdiscussesnumericalresultsfromthree-dimensionallargeeddysimulationsofanoscillatingcylinderunderprescribedmovementsinuniformflow.Sixcases,namelypurein-line,purecross-flowandtwogroupsof'FigureofEight'oscillationpatternsareunderinvestigationatReynoldsnumberRe=24000.The'FigureofEight'patternineachgroupiswithidenticalshapebutoppositeorbitaldirections.Thenumericalresultsonhydrodynamicforces,higherorderforcecomponents,andvortexsheddingmodesareextensivelystudiedandcomparedwiththemeasuredexperimentaldata.Itisfoundthatthefluidforceinphasewiththevelocity,whichrepresentstheenergytransferbetweenthefluidandthecylinder,hasoppositesignanddifferentmagnitudeduetotheoppositeorbitaldirection.Higherorderforcecomponentsincross-flowdirectionarefoundtooccuratoddnumbertimesoftheoscillatingfrequency,whileevennumbersdominatethehigherorderforcecomponentsinin-linedirection.The2Cand2Tvortexsheddingmodesarewellreproducedduetotheoppositeorbitaldirectioneffect.Comparisonsbetweennumericalandexperimentalresultsindicatethatthepresentnumericalmodelcouldbearationaltoolfortheidentificationofhydrodynamiccoefficientswhicharenormallyappliedinempiricalmodelstopredictthevortex-inducedvibrationsofslendermarinestructures.
简介:Wakestructuresandvortexinducedvibration(VIV)ofaspring-supportedwide-D-sectioncylinderwereexperimentallyinvestigatedusinganX-wire,anovelphase-lockedparticleimagevelocimetry(PIV),andanaccelerationsensoratalowspeedwindtunnel.Comparedwiththefixedcase,the2P(twopair)vortexmodeasdefinedbyGovardhanandWilliamson(2000)ratherthanS(singlevortex)modeexistsinthewake.Thevelocitydeficitbehindthecylinderismuchlargerthanthatoffixedcase.Themeandragcoefficientincreasesfrom1.42forthefixedcaseto1.64forthevibratingcase.TheReynoldsstresspresentsevendistributionandsmallwithincreaseddistanceofX/D=-2toX/D=-10.Thepowerspectradensitybasedonacceleratorandhotwiredatapresentsahighlightidentical.Itshowsthatafterastronginteractionthecylindervibrationandthevortexsheddingcometoastablestate.Thevortexsheddingistotallylockedonandcontrolledbythecylindervibration.
简介:Thelargedesignfreedomofvariable-stiffness(VS)compositematerialpresupposesitspotentialforwideengineeringapplication.PreviousresearchindicatesthatthedesignofVScylindricalstructureshelpstoincreasethebucklingloadascomparedtoquasi-isotropic(QI)cylindricalstructures.Thispaperfocusesontheanti-bucklingperformanceofVScylindricalstructuresundercombinedloadsandtheefficientoptimizationdesignmethod.Twokindsofconditions,bendingmomentandinternalpressure,andbendingmomentandtorqueareconsidered.Influencesofthegeometricaldefects,ovality,onthecylinder'sperformancesarealsoinvestigated.Toincreasethecomputationalefficiency,anadaptiveKrigingmeta-modelisproposedtoapproximatethestructuralresponseofthecylinders.InthisimprovedKrigingmodel,amixedupdatingruleisusedinconstructingthemeta-model.Ageneticalgorithm(GA)isimplementedintheoptimizationdesign.TheoptimalresultsshowthatthebucklingloadofVScylindersinallcasesisgreatlyincreasedascomparedwithaQIcylinder.
简介:Ananalysisisperformedtostudytransientfreeconvectiveboundarylayerflowofacouplestressfluidoveraverticalcylinder,intheabsenceofbodycouples.Thesolutionofthetime-dependentnon-linearandcoupledgoverningequationsiscarriedoutwiththeaidofanunconditionallystableCrank–Nicolsontypeofnumericalscheme.Numericalresultsforthesteady-statevelocity,temperatureaswellasthetimehistoriesoftheskin-frictioncoefcientandNusseltnumberarepresentedgraphicallyanddiscussed.Itisseenthatforallflowvariablesasthecouplestresscontrolparameter,Co,isamplified,thetimerequiredforreachingthetemporalmaximumincreasesbutthesteady-statedecreases.