模态测试分析介绍.ppt

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1、ExperimentalModalAnalysism+pSmartOfficeSeminarOverviewWhytest?SDoF/MDoFTheExperimentalModalAnalysis(EMA)ProcessEMA/FEAGettingStartedCreateaModeloftheStructureDoFrequencyResponseFunction(FRF)MeasurementsEstimatetheModalParametersVisualizeandValidatetheModeShapes

2、WhyTest?StructuralanalysisInvestigatingvibration-relatedproblems–noise,fatigueValidation/refinementofmodelse.g.FEmodelsPredictingdynamiceffectsofstructuralmodificationPredictingdynamicresponsetoappliedloads“Whilemodalanalysistheoryhasnotchangedoverthelastcentur

3、y,theapplicationofthetheorytoexperimentallymeasureddatahaschangedsignificantly.”RJAllemangSDoFSystemsSingleDegreeofFreedomSDOFThesingledegreeoffreedom(SDOF)modelenablesustounderstandthefundamentalconceptsoffreeandforcedvibration,naturalfrequency,resonanceanddam

4、ping.Singledegreeoffreedomsystemshaveonlyoneresonantfrequencywithuniformamplitudeofvibration.MDoFSystemsMultipleDegreeofFreedomMDOFFormultipledegreesoffreedom,resonancemayoccuratanumberofdifferentfrequencies,eachofwhichcorrespondstoadifferentpatternorshapeofthe

5、system’smotion.Theseareknownasthenaturalornormalmodesofvibration,ormodeshapesMDoFSystemsInameasurement,eachdegreeoffreedomisameasurementataphysicalpointinagivendirectionMeasurementpointsare‘connected’toformarepresentativegeometryMDoFsystemshavemorethanonenatura

6、lfrequencyand‘modeshapes’TheExperimentalModalAnalysisProcessModalanalysisistheprocesstodeterminethemodalparametersofalinear,timeinvariantmechanicalstructure.Modalparameters:ModalFrequenciesModalDampingModeShapes/ModalVectorsFEM/FEA(FiniteElementMethod/Analysis)

7、isanalternativewaytofindmodalparameters.EMAversusFEAFEA:BasedonacomputermodelofthestructureandmaterialpropertiesNodampingLessrealEasytostudychangesEMA:RequiresthephysicalstructureGivesdampingvaluesExactrealvaluesstudychangeswithoptionalSDMsoftwareCombiningbothi

8、sbest!FEA/EMACorrelationandUpdatingTargetModeSelectionSensorPlacementMethodsSensorEliminationMethodsPretestAnalysisTESTApplications:findingoptimallocationsforsensors,actuat