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外文翻译--在液压系统中测量压力波传播速度 英文版【优秀】.pdf

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外文翻译--在液压系统中测量压力波传播速度 英文版【优秀】.pdf

AbstractPressurewavevelocityinahydraulicsystemwasdeterminedusingpiezopressuresensorswithoutremovingfluidfromthesystem.Themeasurementswerecarriedoutinalowpressurerange0.2–6barandtheresultswerecomparedwiththeresultsofotherstudies.Thismethodisnotasaccurateasmeasurementwithseparatemeasurementequipment,butthefluidisintheactualmachinethewholetimeandtheeffectofairistakenintoconsiderationifairispresentinthesystem.Theamountofairisestimatedbycalculationsandcomparisonsbetweenotherstudies.Thismeasurementequipmentcanalsobeinstalledinanexistingmachineanditcanbeprogrammedsothatitmeasuresinrealtime.Thus,itcouldbeusede.g.tocontroldampers.KeywordsBulkmodulus,pressurewave,soundvelocity.I.INTRODUCTIONRESSUREwavevelocitysoundvelocityisanimportantfactorwhenhydraulicsystemsareanalyzedanddevised.Itisaparameterinmanyequationsthatmodelthedynamicsofhydraulicsystemsanditisalsoanimportantparameterwhendampersofhydraulicsystemsaredimensioned.Withthehelpofpressurewavevelocitythebulkmodulusofahydraulicsystemcanbedefined,orviceversa.Differentmeansformeasuringpressurewavevelocityarepresentedinmanystudies.Normallythesemeasurementsarecarriedoutinseparatemeasurementequipment,sothatthemeasuredfluidisremovedfromtheoriginalmachine.Thisaffectscertaincharacteristicsofthefluid,suchastheamountofairormoistureconcentration,andtheresultsofpressurewavevelocitymeasurementsmaydifferfromtheoriginalsituation.Separatewavevelocitymeasurementinstrumentationisveryoftendesignedinsuchawaythatatleastentrainedaircanberemovedfromthemeasuredfluid.Thus,theresultsofmeasurementdonottaketheeffectofairintoconsideration,oronlydissolvedairisnoticed.Thisdoesnotcorrespondtorealsystems,becauseairispresentinfluids,especiallyatlowpressures.Separatepressurewavemeasurementequipmentusuallycannotbeconnectedtothemachine,sorealtimemeasurementofwavevelocityisimpossible.Inmanyearlierstudiespressurewavevelocityhasbeenmeasuredwithultrasonictransducers.Theultrasoundtechniquemaybebasedon,e.g.timeofflightorpulseechoprinciples.Thismethodisveryaccurateanaccuracyofeven±0.005m/scanbeachieved,1althoughlargererrorshavealsobeenpresentedintheliterature24.Benefitsoftheultrasoundtechniqueare,e.g.longtermstability,precision,sensitivity,capabilityofapplyingtoopticallyopaque,concentratedandelectricallynonconductingsystemsandthepossibilitytoautomatethemeasurement.However,instrumentationdesignandthesamplestudiedmayaffecttheaccuracyofthemethod.5.Anothermethodfordefiningpressurewavevelocityistomeasurethebulkmodulusofafluidusingamethodbasedondeterminationofthevolumechangeofthesampleundercompressionorexpansion.69.Useofthistechniquepreventsunwantedpressuregradientsbetweenthesampleandthesurroundingsystem.Theusefulpressurerangeofthemethodiswide0.1350MPa.Theamountofentrainedaircanalsobetakenintoconsideration.Drawbacksofthemethodaretheneedtofirstdeterminethespecificvolumeofthesampleunderatmosphericpressureandtheobviousrequirementofmeasuringthedensityofthesampleunderallthepressuresused.Thus,thismethodcannotbeusedforcontinuousrealtimemeasurements.Calculationofthebulkmodulusandfurthermorethepressurewavevelocitysoundvelocityisshownin1and2inchapterII.Someresearchershaveusedpressuretransducerstodetectpressurewavevelocitiesinoils.HarmsandPrinke10presentedamethodbasedonphasedifference.Inthismethodexcitationshouldbeconstant,e.g.pumprippling,becausethesignaliscomparedattwopointsandthevalueofthewavevelocityiscalculatedfromthetimedifferenceofthesesignals10.Choetal.11andYuetal.12measuredthewavepropagationtimeandcalculatedacrosscorrelationfunctionofthepressuresignals.Methodsbasedonpressuremeasurementsmakerealtimemeasurementspossibleandtheinfluenceofaircanbetakenintoconsideration.YetanothermethodfordeterminingpressurewavevelocitywaspresentedbyApfel13.Thismethodisatechniquethatmeasurestheadiabaticcompressibilityanddensityofafluidwhenthesampleamountsareextremelysmall,4nl4μl.Pressurewavevelocitiescanbecalculatedfromthesedata.Thismethodisapplicable,e.g.forsupercooledorsuperheatedsamples,biologicalorhazardoussamplesorineverycasewhenthebulkpropertiesoffluidshavetobedeterminedfromsmallsampleamounts.Thefluidstudiedisacousticallylevitatedonanimmisciblehostliquidatacertainspotofthetestequipment.Areferencemeasurementofafluidwhosepropertiesarewellknownismadeattheexactsamespot.Theresultsarerelativelyaccuratewithina2margincomparedwiththesamevaluesdeterminedbytraditionalmethods.Inordertocalculatepressurewavevelocities,thedensityoftheMeasuringPressureWaveVelocityinaHydraulicSystemLariKela,andPekkaVähäojaPWorldAcademyofScience,EngineeringandTechnology492009610samplehastobemeasuredusingdifferentequipment.Obviously,thismethodissuitableforlaboratoryexperimentsonly.1314.Pressurewavevelocitysoundvelocitycanbeusedtoevaluatevariousimportantcharacteristicpropertiesoffluids.Forinstance,ithasbeenusedtodeterminetheconcentrationofsolventsinoils4,tocalculatethephysicalpropertiesofhydraulicandotherlubricatingfluids,aswellasfueloils7,1517,toestimatethestructuralandmechanicalpropertiesoffats18andthephysicalpropertiesofpetroleumfractionsandpetroleumreservoirfluids3,5andtodeterminethecompositionofoilwatermixturesandemulsions2ortomeasurethepropertiesofmagnetorheologicalMRfluids19.Themostimportantaimofthisstudywastodevelopamethodformeasuringpressurewavevelocitythatenablesrealtimemeasurements,whicharenecessaryif,e.g.realtimecontrolsystemsforhydraulicsareconstructed.AnotheraimwastocollectdataforfutureresearchwithaHelmholtzresonatorattachedtothissystem.II.THEORETICALASPECTSOFPRESSUREWAVEVELOCITYDETERMINATIONSThebulkmodulusofelasticmaterialBisdefinedasthequotientofpressurevariationandrelativevolumevariationaffectedbypressurevariationBVdVdP−1wherePispressureandVisvolume20.Pressurewavesconsideredinthispaperaresimilartowavesthatproduceaudiblesound.Thus,pressurewavesarehandledaslongitudinalvibration–moleculesmovingbackandforthinthedirectionofpropagationofthewave,producingsuccessivecondensationsandexpansionsinthemedium.Thesealterationsofdensitiesaresimilartothoseproducedbylongitudinalwavesinabar.Asseeninmanystudies,mentionedalsointhispaper,thedifficultyofthemathematicsissidesteppedbyrestrictingthewavesunderconsiderationtoonedimension.21.Itisworthnotingthatatravellingwavedoesnotcarrymaterial,justthewaveanditsenergymove.Choetal.11havepresentedthreedefinitionsforbulkmodulus,whicharewidelyusedinmanytextbooks.Thesedefinitionsareonlyapplicabletotheirownspecificconditions,andinthispaperthesonicbulkmodulus2isused,whichhasthesamevalueastheadiabaticbulkmodulus.ThesonicbulkmodulusBisderivedfromthesonicvelocityinthefluidandfluiddensity11,20Bρa22whereρisdensityandaiswavevelocitysoundvelocity.Equation2canbesolvedforthebulkmodulusorwavevelocity,dependingonwhichoneistheknownfactor.Inthispaperdensityisknownandwavevelocityismeasured,sothebulkmoduluscanbecalculated.Butas2presents,thesameparametersthataffectthevalueofwavevelocityalsoaffectthebulkmodulusandthisistakenintoconsiderationinthetheoryreview.Themainfactorsthataffectthevalueoftheeffectivebulkmodulusofahydraulicsystemarefluidpressureandtemperature.TheireffectsarepresentedinFig.1.Otherfactorsthataffectthevalueoftheeffectivebulkmodulusare,e.g.theaircontentofthefluid,piperigidityandinterfaceconditionsbetweenthefluidandtheair12.Fig.1Effectoftemperatureandpressureonwavevelocityinanoilsample●335.1K,■370.7K,▲402.1K5Partoftheaircontentdissolvesinamolecularformandtherestofit,entrainedair,existsintheformofsmallbubbles.Dissolvedairhasonlyalittleeffectonthebulkmodulus11,butthevolumetricpercentofentrainedairwithinafluidisoneofthemostinfluentialvariableswhenthebulkmodulusisevaluated.Ithasbeenprovedthatonepercententrainedaircanreducetheeffectivebulkmodulusofafluidbyasmuchas1085MPa,whichcorrespondstoa75percentdecreaseinthefluidmanufacturersvalue22.Itshouldbenotedthatalsoothergases,notonlyair,affectthebulkmodulusandsonicwavevelocity,andthetypeofgashasagreatereffectthandoesthequantityofthegas23.Thelowerthemolecularweightofthegas,thegreatertheeffectonthesonicwavevelocity23.Fluidpressurehasaneffectonthevalueofthebulkmodulus,particularlyinthelowerrangeofpressure.Onereasonfortheeffectofpressureonthebulkmodulusistherelationshipbetweenentrainedaircontentanddissolvedaircontentinafluid.Someentrainedairbecomesdissolvedairwhenpressureincreases.12.Theinfluenceofpressurecanbediscussedatthemolecularlevel,also.Ifthepressureofthefluidunderstudyislow,thefluidmoleculesfitamongeachothereasilyandasignificantamountoffreespaceisstillavailable.Whenthefluidiscompressed,thefreespacedecreasesquicklyatlowerpressures.Whenthepressureofthesystemishigh,thefreespaceisalmostnegligible.Atthispointafurtherdecreaseinvolumeisconnectedwithinteractionsbetweenfluidmoleculesandtheirneighbouringmolecules.24.IfahydraulicsystemspressureismorethanWorldAcademyofScience,EngineeringandTechnology49200961150bar,theeffectoffreeairisonlyminor9.Fluidtemperatureaffectsthedensityoftheaircontent,thesizeofairbubblesinthefluidandthereforetheequivalentcompressibilityofthefluid.Anincrementoftemperaturealsocauseschangesinthemolecularlevelofthefluid.Morevigorouscollisionsbetweenmoleculesareobserved,whichmayeventuallycausechangesinmolecularstructures,andadecreaseintheireffectivevolumeisprobable.24.Therebytemperaturehasanimportantinfluenceonthebulkmodulusandsonicwavevelocity,especiallyindynamicsituations.Theinfluenceoftemperaturehasbeenstudied,e.g.by23.Theirstudiesincludedatemperaturerangebetween30°Cand130°C,andtheeffectoftemperatureonsonicwavevelocityseemedtobesignificant23.However,theeffectoffluidtemperaturecanbeignoredifthefluidtemperatureisapproximatelyconstant12,andinmanystudiesthishasbeendone.Inaddition,thebulkmodulusoflubricatingoilsatlowpressurescanbealmostindependentofthetemperature25.Thedensityandbulkmodulusofsolidpartse.g.pipeswillnotvaryasmuchasthedensityofafluidwhentemperatureandpressurevary10.Thus,theeffectofpiperigidityonthebulkmoduluscanbeignoredifrigidpipesareassumedinahydraulicsystem12.Themoisturecontentofthefluidmayalsoplayaroleifpressurewavevelocitiesaredetermineditslightlyreducesthevalueofthepressurewavevelocity23.Theviscosityofthefluidalsoaffectsthepressurewavevelocity26,butofcoursetheviscosityofafluiddependsonitsmolecularstructureinthefirstplace,hencetheeffectofviscosityonthepressurewavevelocityvarieswithdifferentfluids.III.TESTEQUIPMENTThetestequipmentandtheprincipleofmeasurementaredepictedinFigs.2and3,respectively.Themeasurementswerecarriedoutbyidentifyingapressurepulseattwopoints,P1andP2,usingpiezosensors.ThedistancebetweenpointsP1andP2variableLinFig.3isknownandtwodifferentdistanceswereusedinthetests.Theshorterdistancewas2.75mandthelongerwas4.26m.DistancesL1andL2werealways1.03mand0.11m,respectively.Apressurewavewasexcitedbymeansofapistoninsideapipe.Thisexcitationsystemenablesexcitationofapurepressurewave,becauseunnecessaryelbowsandinterfacesareavoided,sothatreflectionsandtransmissionsofthewaveareminimized.Thepistonwasmovedlightlybutrapidlywithahammer.Asphericalplugvalveandanadjustablevalvewereinstalledinthetestequipmentsothatflowandpressurecouldbecontrolledduringthemeasurements.Thispropertywasusedinthemeasurementssothattwomeasurementserieswerecarriedout.Thefirstonewasdoneunderconstantpressurewithoutflowwiththebothvalvesclosed.Thesecondonewasdonewithflow,sothatflowandpressurewascontrolledwiththeadjustablevalve.Theeffectofflowonwavevelocityisinsignificant,asseenlaterinthetext.Themeasurementswerecarriedoutovertwodayssothattemperaturecouldbeassumedtobeconstant.Thetestequipmentdidnotincludeatemperaturesensor,butthetestequipmentwasinsidealaboratorysothatthefluidtemperaturecouldbeassumedtobethesameasthesurroundingtemperature.Thelowestpressureusedwas0.2barandthehighestwas6.1bar,and545measurementswereexecutedbetweentheselimits.ExamplesofthemeasurementresultsaredepictedinFigs.4and5.ThemeasurementsystemincludedoneKyowaPG20KUpressuresensorforreferencepressure,twoKuliteHKM375M7barVGpressuresensorsforrecognizingapressurewaveattwopoints,aKyowaStrainAmplifierDPM6HfortheKyowapressuresensor,aThandar30V2AprecisionpowersupplyfortheKulitepressuresensors,aNationalInstrumentsUSB621116input16bit250kS/sDAQcard,aHPCompaqnx9010laptopcomputerwithMicrosoftWindowsXP,DasyLabv.8.00.004measurementsoftwareandMeasurementAutomationExplorerv.4.1.0.3001.Themeasurementfrequencywas25kHz0.04msandtheblocksizewas1024bit.Fig.2TestequipmentFig.3PrincipleofthemeasurementsFig.4Responseofthepressurewaveatdetectionpointoneupper,dottedlineandtwolower,dashedline.NotethepressuredifferencebetweenthedetectionpointsbecauseofflowWorldAcademyofScience,EngineeringandTechnology492009612Fig.5Samecaseasabove.Thetimedifferencebetweenthedetectionpointscanbereadfromthesurveybox.NotethatthelinesaremodifiedforpublishingbydecreasingtheirresolutionsnotablyfromtheoriginalThevolumeflowofthetestequipmentQcanbeestimatedwiththeHagenPoiseulleequation327Q128214ppld−ηπ3wheredispipediameter,ηisdynamicviscosity,lispipelength,p1ispressureatpoint1andp2ispressureatpoint2.Duringthemeasurementspressurewillvaryfromzeroto0.5barpipelength2.75mortoalmostonebarpipelength4.26m.Thismeansthattheabsolutemaximumflow,whichisevenoverestimatedhereonpurpose,isconstantlylessthan1.2l/min0.4m/satatemperatureof18˚Canditseffectontheresultsisimpossibletonoticeinthisarrangement.FluidviscositywasmeasuredwithaBrookfieldDVIIrotationviscometeranddensitybyusingthespecificweightmethodweighinganaccuratevolumeofthefluidatthedesiredtemperature.Fluiddensitywas874kg/m3atatemperatureof18˚Cand864kg/m3atatemperatureof40˚C.Thedynamicfluidviscositiesatthecorrespondingtemperatureswere121cPand42cP.Thefluidwasacommercialmineraloilbasedhydraulicoil.IV.RESULTSOFMEASUREMENTSAltogether545measurementswereanalyzed.Theaveragepressureofthemeasurementswas2.9barandthemeasuredaveragepressurewavevelocitysoundvelocity,1377m/s.TheresultsofallthemeasurementsarepresentedinFig.6,whichindicatesthemagnitudeofthewavevelocityinthepressurerangebetween0.2barand6bar.InFig.6themeasuredresultsoftheflowsituationandnonflowsituationareseparated,butascalculatedearlier,thismeasurementarrangementisnotaccurateenoughtorecognizetheeffectofflow.Thus,alltheresultsarehandledtogetherfromhereon.100011001200130014001500160017001800190020000123456PressurebarVelocitym/sFig.6Allthemeasuredresults,545measurements.●weremeasuredwithoutflowand■weremeasuredwithflowAlltheresultsarepresentedtogetherinTableIsothatthemeasuredpressureisroundedtoanaccuracyof0.1barandtheaveragewavevelocityofallthemeasurementsintheroundedpressureareaiscalculated.NotethatthedeclaredvalueofpressureisalwaysmeasuredbyareferencepressuresensorseePrefinFig.3.Thus,inTableIpressureisinthefirstcolumnp,thenumberofmeasurementsinthepressurerange0.05≤pi≤0.14barisincolumn2nandtheaveragewavevelocityofmeasurementsatthedeclaredpressureareincolumn3a.TheresultsofTableIareillustratedinFig.7.TABLEIPRESSUREWAVEVELOCITIESATDIFFERENTPRESSURES.PPRESSUREOFTHESYSTEMBAR,NNUMBEROFMEASUREMENTSANDATHEDETERMINEDPRESSUREWAVEVELOCITYM/Spnapnapna0.2213132.3913834.4213750.3413662.4313314.52313770.41512952.52013834.6613870.51413262.6414114.71713880.6913682.71313594.8713650.7913602.81413904.9713880.81213482.9314055.01713830.9313903.01713845.1513891.02013573.1613715.2513931.1313603.21013935.3413971.2914003.31313735.4313891.31913793.4514235.51013931.4313903.51913935.6114471.51713603.6313905.701.6514073.71613965.8113651.71513713.81013845.9213741.8913913.9313906.0213741.9513504.02013916.1413742.02013774.1513842.1514034.2171387averagesumaverage2.21313824.3813972.95451377WorldAcademyofScience,EngineeringandTechnology492009613

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