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AnApproachtoFailureModesandEffectsAnalysisusingMultipleModelsP.G.Hawkins,R.M.Atkinson,D.R.Bull,Prof.K.A.Edge,Prof.D.J.Woollons,Prof.C.R.BurrowsUniversityofExeter,UniversityofBath,SchoolofEngineering,FluidPowerCentre,NorthParkRd,ClavertonDown,Exeter.EX44QFBath.BA27AYUK.UK.E-mail:P.G.Hawkins@ex.ac.uk://’smethodsofmodellingfunctionsandgoalscanbeappliedtoareliabilityprocedureknownasFailureModesandEffects.Theuseoffunctionalmodelslinksstructuretopurposeandthecentralthemeofthispaperistoshowhowthedesignobjectivesofasystemcanbelinkedtothestructureusingfunctionalmodelsasanintermediary.ThemodelsaredemonstratedusingtheagreedexampleofaWaterSupplyProcessControlSystem.1.IntroductionReliabilityassessmentisbecomingestablishedasanintegralpartofthedesignprocessofcomplexsystemsinhighcapitalcostandhighriskapplications,suchasaircraftsubsystems.Thepurposeistoprovideinsightintothekeyareasofasystemandtohighlightpotentialproblemareassothattheycanbedealtwithatthedesignstageoftheproject.Thistypeofassessmentallowscomparisonstobemadebetweencompetingsystemdesignsandprovidesadeeperunderstandingoftheirconstructionandoperation,allofwhichhelpstoimprovesystemsafety.Thisinformationcanbeutilisedtoformulatedetailedoperationalandmaintenancemanualsandprocedures,aswellasbeingfed-forwardtoimprovethesafetyandreliabilityofsubsequentdesigns.FailureModesandEffectsAnalysis(FMEA)isoneofthemostcommonlyusedtechniquesforassessingthereliabilityofengineeringdesigns.Theanalysisinvolvesidentifyingpotentialcomponentfailuremodesandevaluatingtheconsequencesoftheseonasystem'sperformance.Theeffectsofthecomponentfailureareanalysedbyconsideringtheconsequenteffectsofthatfailureonneighbouringcomponentsandthenpropagatingthemuptothesystemlevel.Thecriticalityofcomponentsandcertaincomponentfailuremodescanthereforebeassessedandstepstakentoamendthedesignsothatcriticalfailuremodesbecomesufficientlyimprobable.AnanalysisofcurrentFMEApracticehasshownthatthegreatestcriticismistheinabilityofFMEAtoinfluencedesignbecausethetime-scaleoftheanalysisoftenexceedsthedesign/developmentphase.ItisthereforeoftenthecasethatFMEAisseennotasadesigntoolbutsolelyasadeliverabletothecustomer.ToreducethetotaltimeforanFMEA,anautomatedapproachissought.Engineeringsystemsaredesignedtoachievesetsofgoalsand,althoughanFMEAwillinvolveacomparisonbetweenasystem'snormalandfaultybehaviour,itisonlywhenthisbehaviouralchangeaffectsoneofthesystemgoalsthatafailureeffectisdeemedtohaveoccurred.Theeffectisthendescribedintermsofthegoalsthathavenotbeenachieved.Also,acomplexsystemcanbeanalysedatdifferentlevelsofresolutionand,ateachlevel,sub-systemgoalscanbedefined.Thetoplevelisthesystemlevelwherethecustomerspecificationisdefinedandthelowestisthepartlevelwhereeachnut,boltandspringhasaroletoplayinthefunctionofthesystem.Atanystageinthedesignprocessboththehardwareandthesystemlevelgoalswillbegivenattheoppositeextremesofresolution.AnFMEAthenconsistsofacombinedtop-downandbottom-upanalysis.Fromthetop,thesystemgoalsaredecomposedintosub-systemgoalsand,fromthebottom,thecomponentbehavioursaretranslatedintothefunctionsrequiredforthesub-systemgoalstobemet.Failuremodesaretheninsertedandtheresultingbehaviouralchangespropagatedthroughfunctionalchangestoeffectsongoalachievement.ThispaperdescribesasetofmodellingformalismswhichprovidethetoolsforthisapproachtotheFMEAofdynamicengineeringsystems.Section2isanoverviewofthemultiplemodelapproach.Section3definesfunctionalandteleologicalmodels.Section4discusseshowthemodelscanbeusedtoproduceafailuremodesandeffectsanalysisandSection5illustratestheprocessusingtheagreedexampleofawatersupplyprocesscontrolsystem(WSPC).2.TheUseofMultipleModelsWhendesigningoranalysingasystem,aconceptisneededofhowthevariablesareinter-related.Usuallymultiplemodelsarerequiredinordertoprovidedifferentformulationsofthecoreconceptofasysteminordertomatchthemodellingperspectivetotheparticulartaskinhand,forexample;phasesofdesign,FMEA,simulation,controlorfaultdiagnosis.Theparticularmodelformalismsthatareuseddependontheobjectivesofthemodellingexerciseandthemodellingtechniquesused.Intheengineeringdomaintheformalismscommonlyusedarefunctional(whatasystemcando),behavioural(describesorpredictsthesystem'sdynamicresponse)andschematicorstructural(aniconicmodelofthesystem'sstructureandconnectivity)[6].Aparticularlyimportantfactorwhichspansallthreeformalismsistheresolutionofamodel,describingitsgranularityorlevelofdetail.Duringengineeringanalysisitiscommontofindhierarchicalmodelsusedsothatdifferentresolutionscanbeusedforperforminganalyseswithdifferentlevelsofdetailinordertoensureboththecorrectnessandtheefficiencyoftheprocess.3.FunctionalandTeleologicalModelsThefunctionofasystemisdefinedastherelationbetweenitsbehaviourandthegoalsassignedtoitbythedesigner(Chittaro[3][4]).AfunctionalmodelinChittaro'sworkutilisesahierarchyofmodelsconsistingof:•thefunctionalrolemodel(thesystembehaviourinterpretedintermsofnetworksofoperatorsact
本文标题:An Approach to Failure Modes and Effects Analysis
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