精品机械工程及自动化专业毕业设计翻译.docx

精品机械工程及自动化专业毕业设计翻译.docx

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精品机械工程及自动化专业毕业设计翻译

Studiesindynamicdesignofdrillingmachineusingupdatedfiniteelementmodels

Abstract

TheaimofthepresentworkistodevelopupdatedFEmodelsofadrillingmachineusinganalyticalandexperimentalresults.TheseupdatedFEmodelshavebeenusedtopredicttheeffectofstructuraldynamicmodificationsonvibrationcharacteristicsofthedrillingmachine.Twostudieshavebeencarriedoutonthemachine.Inthefirststudy,modaltestshavebeencarriedoutonadrillingmachineusinginstrumentedimpacthammer.Modalidentificationhasbeendoneusingglobalmethodofmodalidentification.ForanalyticalFEmodelingofthemachine,acomputerprogramhasbeendeveloped.TheresultsobtainedusingFEM,havebeencorrelatedwiththeexperimentalonesusingmodeshapecomparisonandMACvalues.AnalyticalFEmodelhasbeenupdated,withthehelpofaprogram,whichhasbeendevelopedusingdirectmethodsofmodelupdating.Inthesecondstudy,modaltestinghasbeencarriedoutusingrandomnoisegeneratorandmodalexciter.Globalmethodhasbeenusedformodalidentification.AnalyticalFEmodelinghasbeendoneusingI-DEASsoftware.CorrelationofFEresultswiththeexperimentaloneshasbeencarriedoutusingFEMtoolssoftware.UpdatingoftheanalyticalFEmodelhasalsobeendoneusingtheabovesoftware,basedonanindirecttechniqueviz.sensitivitybasedparameterestimationtechnique.TheupdatedFEmodels,obtainedfromboththestudieshavebeenusedforstructuraldynamicmodifications（SDM）,forthepurposeofdynamicdesignandtheresultsofSDMpredictionsareseentobereasonablysatisfactory.

ArticleOutline

1.Introduction

2.Modaltestingandidentification

3.Finiteelementformulationofdrillingmachine

4.ComparisonofanalyticalFEandexperimentalresults（modelcorrelation）

5.Finiteelementmodelupdating

6.SDMstudiesusingupdatedmodelsfordynamicdesign

7.Conclusions

References

1.Introduction

Dynamicdesignaimsatobtainingdesireddynamiccharacteristicsinmachinesandstructures,whichmayincludeshiftingofnaturalfrequencies,desiredmodeshapesandvibratoryresponse.Theultimateobjectivesaretohaveaquieterandmorecomfortableenvironment,higherreliabilityandbetterqualityofproduct.Theconventionaldynamicdesignisbasicallyhitandtrialmethodinwhichwetrytoachievedesireddynamiccharacteristicsbymakingseveralprototypes.Thedisadvantageofthistechniqueisthatactualdesigncycletakesalotoftimeandthereforeitisnotcosteffective.However,modelupdatingbaseddynamicdesignsavesdesigncycletimeaswellasreducesthecostinvolved.Varioustoolsusedforupdatingbaseddynamicdesignare:

experimentalmodalanalysis（EMA）includingmodaltestingandmodalidentification,modelupdatingandstructuraldynamicmodification.

Ewins[1]andMaiaandSilva[2]haveexplainedthebasicconceptsofmodaltesting,whichisanexperimentalapproachtoobtainmathematicalmodelofastructure.Inamodaltest,thestructureundertestisexcitedeitherbyanimpacthammerorbyamodalexciter,andtheresponseofthestructureisrecordedatseveralexperimentalpoints,intheformoffrequencyresponsefunctions（FRFs）,usingadualchannelFFTanalyzer.Theexperimentalmodalmodelgivesinformationaboutthenaturalfrequencies,correspondingmodeshapesandmodaldampingfactorandisusefulformodelupdating.Themodelupdatingtechniqueshelpsustobringanalyticalfiniteelementmodelsclosertorealsystems.InmodelupdatinganinitialanalyticalFEmodelconstructedforanalyzingthedynamicsofastructureisrefinedorupdatedusingtestdatameasuredonactualstructuresuchthattheupdatedmodeldescribesthedynamicpropertiesofthestructuremorecorrectly.TheinaccuraciesinFEM,whenappliedtodynamicproblemsareduetouncertaintiesinboundaryconditionsandstructuraldampingetc.

FriswellandMottershead[3]havediscussedthefiniteelementmodelupdatinginstructuraldynamics.BaruchandBar-ItzhackandBaruch[4]and[5]consideredanalyticalmassmatrixtobeexactanddevelopedadirectmethodforupdatingusingtestdata.BermanandNagy[6]developedamethodofmodelupdating,whichusesmeasuredmodesandnaturalfrequenciestoimproveanalyticalmassandstiffnessmatrices.Structuraldynamicmodification（SDM）techniques[7]and[8]arethemethodsbywhichdynamicbehaviourofthestructureisimprovedbypredictingthemodifiedbehaviourbroughtaboutbyaddingmodificationslikethoseoflumpedmasses,rigidlinks,dampersetc.Thusthedynamicdesignusingupdatedmodelisexpectedtobehelpfulinordertopredictaccuratelyandquickly,theeffectofpossiblemodificationsonthedynamiccharacteristicsofthestructureatcomputerlevelitself,thussavingtimeandcost.

Sestieri[7]hasdiscussedSDMapplicationtomachinetoolsandengines.Kundra[8]gavethemethodofstructuraldynamicmodificationviamodels.Modak[9]hasdiscussedSDMpredictionsusingupdatedFEmodelforanF-structure.Heusedconstrainednonlinearoptimizationmethodforupdatingofamachinetoolusingstiffnessparametersattheboundary[10].ThepresentpaperdealswiththeFEmodelupdatingusingdirectaswellasindirectmethod,andtousethisupdatedFEmodelfordynamicdesignbasedonSDMpredictionsofamachinetoolviz.adrillingmachine.Twodifferentstudiesarereportedusingdifferenttechniquesforanalyticalandexperimentalanalysisandforupdating.Variousobjectiveswithwhichthepresentresearchworkhasbeencarriedoutare

•TodevelopupdatedFEmodelsofacomplexstructurelikethatofadrillingmachineandtousetheseupdatedmodelstopredicttheeffectofvariousmodificationsonmodalpropertiesofthemachine.

•Toseewhetherhammerexcitationyieldsgoodresultsforfairlycomplexstructureslikedrillingmachineornot,andtocomparetheseresultswiththoseobtainedfrommodalexciter.

•ToanalyzetheresultsofSDMpredictionsobtainedusingtheupdatedmodelsderivedinthestudies.

2.Modaltestingandidentification

Inthetwostudiesmentionedearlier,differenttechniqueshavebeenused,formodaltestingandidentification.Inthefirststudy,impacthammerisusedtoexcitethedrillingmachinestructure,atvariouspointsasshowninFig.1andFig.2.Responseistakenatafixedpointwiththehelpofanaccelerometer.

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Fig.1. Experimentalsetup（Study1）.

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Fig.2. Hammerexcitationlocations.

Inthepresentstudy,thedrillingmachineisexcitedat30locationsandtherefore,30FRFsareobtained.TheseFRFsarerecordedintheformofinertance.TheexperimentalFRFs,thusobtainedaretransferredtocomputer.ModalidentificationormodalparameterextractionconsistsofcurvefittingatheoreticalexpressionforanindividualFRFtotheactualmeasureddataobtained.TheexperimentalFRFsareanalyzedbyGRF-MmethodusingmodalanalysissoftwareICATS[11]toobtainmodalparametersofthedrillingmachine.Inthesecondstudy,themachinetoolstructurehasbeenexcitedatthebaseatpoint28,referringtoFig.2,usingmodalexciterandresponsehasbeenmeasuredatvariouspointsusingpiezoelectricaccelerometers.ThemodalidentificationoftheFRFs,thusmeasuredhasbeencarriedoutusingglobalmethodGRF-MmethodinICATSsoftware.

Table1comparestheexperimentalnaturalfrequenciesobtainedfromboththemethods,whichshowsminordifferencesinthetwomodalfrequencies

Table1.

Mode1

10.29Hz

8.67HZ

0.953

11.20Hz

8.79Hz

0.946

Mode2

65.14Hz

47.34HZ

0.901

63.37Hz

44.40Hz

0.906

3.Finiteelementformulationofdrillingmachine

Severalbookshavegiventhebasicconceptsoffiniteelementanalysis,someofthemare:

Zienkiewicz[12]andBathe[13].

Thedrillingmachinestructureisverycomplicatedwithdifferentmountingsandaccessories.Thereforeexactmodelingandanalysisoftheactualstructureisdifficultandittakesmorecomputationaleffort.HoweverforanalyticalFEanalysis,simplifiedmodelofdrillingmachineshasbeenconsidered.Instudy1,thefiniteelementmodellinghasbeendoneusingaprogramdevelopedinMATLAB.Beamelementshavebeenusedfortheanalysis.Thejointsandboundaryconditionsareconsideredtoberigidandinfluenceofstructuraldampingonmodalmodelparameters,isignored.Therelevantdatausedforthedrillingmachineisgivenbelow:

25mmpillartype,height = 1.655 m,massdensity = 7800 kg/m3,Young’smodulus = 200 Gpa,numberofnodes = 30,numberofelements = 29,numberofnodesperelement = 2,degreesoffreedompernode = 3.

Fig.3showsthestructureofthedrillingmachinewiththenodenumbersgivenforstudy1.

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Fig.3. DrillingmachinestructureforFEanalysis.

Theeigenvaluesandeigenvectorshavebeencalculated.TheanalyticalFEmodelofthestructureconsistsof90 × 90-sizemassandstiffnessmatrices（30 × 3,30nodesand3d.o.f.pernode）.Butbyexperimentonly30coordinatescanbemeasured.ThereforeFEmodelhasbeenreducedusingGuyan[14]reductionmethodwiththehelpofaprogramdevelopedinMATLAB.

Instudy2,thefiniteelementmodellinghasbeendoneusingI-DEASsoftware.Themodelhasbeenmadeusingbeammesh.AlthoughtheFEmodelhasbeensimplifiedbutthebeamelementshasrotationaldegreeoffreedom,whichcannotbemeasuredexperimentally.ThereforetheFEmodelneedstobereduced.TheFEmodelhasbeenreducedusingmodelreductionutilityinFEMtoolssoftware.Fig.4andFig.5showsthemodeshapeanimationforthefirstandsecondmoderespectively,usingI-DEASsoftware.

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Fig.4. Modeshapeanimation（firstmode）.

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Fig.5. Modeshapeanim