ic測(cè)量不確定度分析中的模型加工誤差分析

ic測(cè)量不確定度分析中的模型加工誤差分析

1u3000rack形式u50表面分析與標(biāo)準(zhǔn)模擬測(cè)試基于高度集中的1992年事實(shí)。第一階段的u50表面分析被推遲到1999年和lat，但仍有不完整的表面分析。Suchsituationisnotcuriousatall;thepointisjustassaidinreference:“experimentaluncertaintyhaslongbeenatopicofdiscussionandcontroversy…….Theproblemisnotthelackofgoodmethodology……;referencesonthesubjectexistandarereadilyavailable.Thedifficultyhasbeenintheapplicationofthemethodologywithconsistencyandregularity.Forthenovice,oreventheexperiencedresearcher,themassofequationspresentedinthereferencescanbeintimidating.Further,althoughsomeexamplesillustratingtheapplicationoftheuncertaintyanalysismethodologyarepresentedinthereferences,itissometimesdifficultforthereadertograsphowtheexamplesapplytotheirparticulartestingrequirements.”O(jiān)nekindofconfusionisabouttheuncertaintyanalysisingeometricparameters.Themeasurandsofhydrodynamictestofshipmodelaretheforcesandmomentsandusually,themeasurementresultsareexpressedinnon-dimensionalformulaesothatmanydimensionalorgeometricparametersareinvolvedintheseformulae.Fromviewpointofmathematicalconsideration,thereisnodoubtaboutsuchuncertaintyanalysismethodsgivenintheITTC-recommendedUAprocedures.Butfromviewpointofphysics,itisnotquiterational.Severalexampleswereshowninthispapertoraisethequestiontobediscussed,toillustratewhatsuchconfusionislike.Somerecommendationwasputforwardtoperformsuchuncertaintyanalysis.2內(nèi)省試驗(yàn)2.1u3000et/which-pch-案例見(jiàn)表1Usually,skinfrictionresistancecoefficientistheoreticallycalculatedthroughtheITTC-1957frictionalcorrelationlinewhereListhelengthofshipmodel,Vthetowingspeedand!thekinematicviscosity.Oneofquestionsis:whetherisLthelengthbetweenperpendiculars,thelengthonwaterline,or,thelengthoverallsubmerged?Foraspecificshipmodel(foranexample,seeTab.1),theabovethreekindsoflengtharequitedifferent,which,ofcourse,willleadtodifferentskinfrictionresistancecoefficientsand,confusedlyandevenveryslightly,leadtodifferentskinfrictionresistancethroughthefollowingequation,whereSwetisthewettedsurfaceareaofshipmodel.Obviously,forthefrictionresistanceofshipmodelitself,thisdifferenceismoresignificantthantheuncertaintyofaspecificlengthifequation(1)isused.Asamatteroffact,thefrictionalcorrelationlineisbasedonengineeringmethodologyand,thelengthinequation(1)isacharacteristiclength,whichrepresentsthegeometricscaleandismainlyusedtoperformextrapolationofthemodel-scalemeasurementtothatoffullscale.Inanotherword,weareactuallyinterestedinpredictionofthefullscaleresistance.Theoretically,wecanadoptanykindoflengththatcanrepresentthecharacteristicsoftheshipgeometry.Itisanoptionbutnotanuncertainty.Ofcourse,thesamekindoflengthshouldbeadoptedfortheshipmodelandthefullscaleship.Thenextquestionis:whenweperformtheuncertaintyanalysisofCF,howtodeterminetheuncertaintyofL,thecharacteristiclength?Inreference,biasuncertaintyinskinfrictioncalculationwastracedbacktouncertaintyinmodellength,speedandviscosityasfollows,Notethatthebiaslimitinmodellengthduetomanufacturingerrorinthemodelgeometrycannotonlybebasedonthemeasurementofthelengthonwaterlineoranyotherspecifickindoflength,butshouldbeontheconceptionofthecharacteristiclengthinstead.Asinreference,suchanuncertaintycanbeadoptedfromthemodelaccuracyof±1mminallco-ordinatesasassumedinITTCProcedure7.5-01-01-01Rev01‘ShipModels.’HencethebiaslimitinmodellengthwillbeBL=2mm.Thisisacceptable,asitissaidinreferencethat,“Theuseofsomeappropriateuncertaintyanalysisisindispensableinexperimentationandanyappropriateorapproximateanalysisisfarbetterthannoanalysis,aslongastheprocessisexplainedfortheuser.”Thefinalquestionis:sinceitisacharacteristiclength,whetheristhevalueofthelengthinequation(1)assignedasitsnominalvalueoritspracticalmeasurementvalue?Asamatteroffact,thefrictionresistanceisnotdirectlyrelatedwithanyspecificlengthoftheshipmodelasaninfiniteplate.Itisrecommendedbytheauthorthatitisbettertoadoptthenominalvalueoflengthinequations(1)and(2),andtherewillbenouncertaintyinlengthtobeconsidered.Thisisphysicalbutnotmathematicalconsiderationandmoreimportant,forsakeofsimplicity.2.2u3000使用u3000unizaceifichitching聯(lián)合,sitace.uss.sitate.u2004和sitacepoles3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.3.Forsakeofsimplicitytodiscussinthispaper,itissupposedthatthetotalresistanceiscomposedoftwocomponents,residualresistanceandfrictionresistance,asinequations(4)and(5),where,thetotalandresidualresistancecoefficients,CTandCR,willbeobtainedfrommodeltestandthen,CRisdirectlyusedtopredicttheresistanceoffullscaleshipaccordingtotheFroudelaw.Itisshowninequations(2),(4)and(5)thattheresidualresistanceanditscoefficientarethefunctionofthegeometricparameterSwet,thewettedsurfaceareaofshipmodel.Ideally,Swetshouldbemeasuredforaspecificshipmodel,butactually,itisimpractical.Forinstead,Swetiscalculatedfromthedataofhullformdesign,i.e.,itistheoreticalandnominal.Ontheotherhand,thewaterlineordraftischeckedandtheweightordisplacementofshipmodelismeasuredbeforeandaftermodeltest.AmethodforuncertaintyanalysisinSwetisgiveninreference,inwhichsomerelationshipisassumedbetweentheuncertaintyofSwetandthedisplacementofshipmodel.Theerrorofwettedsurfaceareaismainlyresultedfromthedeformation,theerrorofmodelscaleanddraftofhullmodel.Itisimpossibletoestimatetheuncertaintyofthesurfaceareacausedbythemodelhulldeformationwithoutanykindofdetailedmeasurementandpropercalculation.Whethertheshipmodelisweightierorlighterafterthewaterlinehasbeencheckedwilldependmainlyontwotypesofsituation:oneisthatthe(scaleof)shipmodelislargerorsmaller,theotheristhatthedraftofshipmodelislargerorsmaller.However,itisdefinitethattheshipmodeliseitherweightierorlighterafteritswaterlinehasbeenchecked,i.e.,thereexistadefiniteerrorofshipmodelweight.Iftheerrorofshipmodelweightiswithinthelimitofuncertaintycausedbydraftchecking,itcannotbejudgedwhetherthemodelislargerorsmallerwithoutanymeasurementofthemodelgeometry.Itisrecommendedbytheauthorthatifpossible,somemeasurementorestimationofthemodelgeometrycanbeperformedtojudgewhetherthemodelislargerorsmallerandtoestimateuncertaintyofthewettedsurfacearea.Ifnogeometrymeasurementisavailable,thebiaslimitineachdimension(longitudinal,lateralandvertical)canbeusedtoestimatethebiaslimitofwettedarea,whilethedraftissupposedaccuratewherethegeometricparametersLandBarethecharacteristicparametersrepresentingthelengthandwidthofshipmodel,respectively.Theuncertaintycausedbytheerrorofdraftcheckingcanbecalculatedasfollows,whereBmeansthebiasuncertaintywhileitssubscriptsindicateindividualcomponent.Thisuncertaintyisnotrelatedtothe“size”ofshipmodel.Sothesumofuncertaintyisobtained,Inanaddition,thetrimandsinkageofthemodelandthewaveprofilealongtheshipmodelsurfacewillvarywiththetowingspeed,sothattheactualwettedsurfaceareawillbequitedifferentfromthetheoretically-calculatedornominalvalueand,therewillbemoresignificantuncertaintyintheactualwettedareathaninnominalwettedarea.Theuncertaintyoftheactualwettedareacannotbeestimatedseparately,butitwillbeincludedintotheprecisionuncertaintyofthetotalresistanceandtheresidualresistancethroughrepetitivetest.Itisnotedagainthatthewettedareainequations(2),(4)and(5)isanominalgeometricparameterbasedonengineeringconsiderationbutnotthepracticalwettedsurfaceareaintowingtest.3as法律政策Obliquetowingtestistakenasanexampleinthispaper.Foraspecificmodel,thehydrodynamicforcesandmomentsactingonthismodelarethefunctionofthetowingspeedV,anddriftangleβ.Forexamples,LateralforceYawingmomentThemeasurementresultsofthehydrodynamicforcesandmomentswillbeexpressedinnon-dimensionalformulainordertopredictthefullscaleperformancealthoughitisstillabigchallengetoestablishthecorrelationbetweenthemodelscaleandthefullscaleformanoeuvrability.Usually,thenon-dimensionalformulaeforaship/submarinemodelareasfollows,LateralforcecoefficientYawingmomentcoefficientwhereListhelengthofshipmodelasinequation(1).Foratorpedomodel,thefollowingexpressionsareusuallyadoptedalternatively,LateralforcecoefficientYawingmomentcoefficientForuncertaintyanalysisinthesehydrodynamiccoefficients,howtodealwiththegeometricparametersintheaboveformulae?Willtherebeanydifferenceresultedinuncertaintyanalysisbetweenequations(10)and(11)?Istheuncertaintyofthesegeometricparameterspropagatedintotheuncertaintyofthemeasuredhydrodynamiccoefficientsthroughtheaboveformulae?Arethesegeometricparametersintheaboveequationsmoresignificantthanothersinuncertaintyanalysis?Similarly,thesegeometricparametersareofcharacteristicdimensionsandtheoretically,anykindofgeometricparameterthatcanrepresentthedimensionofthemodelcanbeadoptedintheaboveformulaeandtherewillnotexistanydifferenceinpredictionofmaneuverabilityoffullscaleship.Forstateofthearts,thereisnoanalyticalmethodtoshowtherelationbetweenthegeometryandthehydrodynamicforces/momentsofshipmodel.Astheshiphullisusuallyconsideredasathickwingwithsmallaspectratio,thelateralforceofshipmodelwillbehighlyrelatedtothelateralprojectedarea(theareaoflongitudinalsection)andtheratioofdrafttolength.So,theparameterL2inequation(10a)shouldbetakenasawholetorepresentthe“size”ofthelateralprojectareaanditsrelativeuncertaintywillestimatedbythatofthelateralprojectareaorthatofthecombinationparameteroflengthanddraft,L×TOtherwise,theparameterL3inequation(10b)canbeconsideredascomposedoftwoparameters,L2andL,wheretheparameterL2representsthelateralprojectedareaastheabove.Takeatorpedomodeltestforanexampleagain.Therewillbenodifferencewhenanyoneofthefollowingthreeexpressionstopredictthelateralforceoffullscaletorpedo,buttherewillbedifferenceinuncertaintyanalysisifitisbasedfromthesemathematicalformulae.LetL=4500mm,Dmax=355mm,thebiaslimitofLis2mmandthebiaslimitofDmaxis1mmduetomodelmanufactureerrors.Therelativebiasuncertaintyofthelateralforceresultedfromthemanufactureerrorwillbe0.089%,whichiscalculatedthroughequation(10a),or0.56%,whichiscalculatedthroughequation(13a),or0.28%,whichiscalculatedthroughequation(13b)Whichoftheabovethreevaluesisproper?Accordingtotheabovediscussion,itisclearthatthebiasuncertaintyresultedfromthegeometryis0.28%,whateverkindofnon-dimensionalequationsisadopted.4u3000來(lái)源Itiswell-knownthatthethrustcoefficientofaspecificpropellermodelisexpressedinthefollowingequation,whereDisthediameterofpropeller,ntherotatingspeedofpropeller,VAthespeedofadvanceofpropeller.ThereappearsonlyonegeometricparameterDintheaboveequation.Istheuncertaintyofthediameterreallypropagatedintotheuncertaintyofthrustthroughequation(14)?Ofcourse,itisnot.Itcanbearguedthatitissometimes,whenpropelleris“heavier”,to“cut”shortthediameteroftheprototypepropellertomakeadjustmentofhydrodynamicmatching.Itisnotmeantthatthediameteristhemostsignificantgeometricparameter,buttheveryreasonisthatitisthemostfeasibleandpracticaladjustmentinengineeringandfurthermore,thefactisthatitisthepitchofpropellerthatischangedbysuchcutting,i.e.,aftercutting,thepropellerisactuallyofanotherdesign.Fromphysicalviewpoint,wecanadoptanalternativeequationasfollows,whereAeistheexpandedareaofpropelleranditsuncertaintyisnotmerelyrelatedtothatofthediameter.Insomesense,Aecanrepresenttheerrorofpropellermanufactureevenbetterthanthediameter.WecanalsoexpressthethrustcoefficientinthefollowingformulaLet’sgobacktotheequation(14).IfthethrustcoefficientisassumedphysicallyrelatedtothecharacteristicareaparameterD2andthen,thesensitivitycoefficientwillbeOntheotherhand,thebiasuncertaintyofKTiscontributedbyalotofparticularsofpropellermodel,suchasdiameter,area,pitch,thickness,camber,chord,etc,andthereisqualitativebutnoanalyticalrelationbetweenKTandtheseparticulars.Forthethrustcoefficientofaspecificpropellermodelinopenwatertest,theuncertaintycanbeanalyzedthroughthefollowingequations,wheretheKTvsJcurvewillbeobtainedfrommodeltest.whereU(X)meanstheuncertaintyofthevariableX,theD-relateduncertaintymeanstheuncertaintyresultedfromthecharacteristicareaofpropeller.Inopinionoftheauthor,itisdifficulttofindoutaproperparametertobetakenassuchanareaparameter,andsoitisdifficulttoestimatesuchanuncertainty.Maybeitisbettertoneglectthiskindofuncertaintyasinthefollowing,WithdevelopingofCFD,thebiasuncertaintyduetothemanufactureerrorsofpropellercanbeestimatedandthenincludedintheuncertaintyofthethrust.5u3000y.國(guó)際通用規(guī)則Inuncertaintyanalysisofmeasurement,itisnecessarytolistandassessallthesourcesofuncertaintyforaspecificmodeltest.Itismoreimportanttoidentifyandestimatethesignificantsourcesofuncertaintybeforetest,soastomakesomeimprovement,ifpossible,toreducetheuncertaintyofmeasurement.ItwillalsobebenefitedfromthepretestUAestimationtoneglectsomeminorsourcesofuncertaintyinthepost-testanalysisandreportofuncertainty,whic